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Journal Cover Journal of Geophysical Research : Space Physics
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   ISSN (Online) 2169-9402
   Published by AGU Homepage  [17 journals]
  • Lower-hybrid drift waves and electromagnetic electron space-phase holes
           associated with dipolarization fronts and field-aligned currents observed
           by the Magnetospheric Multiscale mission during a substorm
    • Authors: O. Le Contel; R. Nakamura, H. Breuillard, M. R. Argall, D. B. Graham, D. Fischer, A. Retinò, M. Berthomier, R. Pottelette, L. Mirioni, T. Chust, F. D. Wilder, D. J. Gershman, A. Varsani, P.-A. Lindqvist, Yu. V. Khotyaintsev, C. Norgren, R. E. Ergun, K. A. Goodrich, J. L. Burch, R. B. Torbert, J. Needell, M. Chutter, D. Rau, I. Dors, C. T. Russell, W. Magnes, R. J. Strangeway, K. R. Bromund, H. Y. Wei, F. Plaschke, B. J. Anderson, G. Le, T. E. Moore, B. L. Giles, W. R. Paterson, C. J. Pollock, J. C. Dorelli, L. A. Avanov, Y. Saito, B. Lavraud, S. A. Fuselier, B. H. Mauk, I. J. Cohen, D. L. Turner, J. F. Fennell, T. Leonard, A. N. Jaynes
      Abstract: We analyse two ion scale dipolarization fronts associated with field-aligned currents detected by the Magnetospheric Multiscale mission during a large substorm on August 10, 2016. The first event corresponds to a fast dawnward flow with an anti-parallel current and could be generated by the wake of a previous fast earthward flow. It is associated with intense lower-hybrid drift waves detected at the front and propagating dawnward with a perpendicular phase speed close to the electric drift and the ion thermal velocity. The second event corresponds to a flow reversal: from southwward/dawnward to northward/duskward associated with a parallel current consistent with a brief expansion of the plasma sheet before the front crossing, and with a smaller lower-hybrid drift wave activity. Electromagnetic electron phase-space holes are detected near these low-frequency drift waves during both events. The drift waves could accelerate electrons parallel to the magnetic field and produce the parallel electron drift needed to generate the electron holes. Yet, we cannot rule out the possibility that the drift waves are produced by the anti-parallel current associated with the fast flows, leaving the source for the electron holes unexplained.
      PubDate: 2017-10-16T16:30:53.105102-05:
      DOI: 10.1002/2017JA024550
       
  • Classification of Solar Wind with Machine Learning
    • Authors: Enrico Camporeale; Algo Carè, Joseph E. Borovsky
      Abstract: We present a four-category classification algorithm for the solar wind, based on Gaussian Process. The four categories are the ones previously adopted in Xu and Borovsky [2015]: ejecta, coronal hole origin plasma, streamer belt origin plasma, and sector reversal origin plasma. The algorithm is trained and tested on a labeled portion of the OMNI dataset. It uses seven inputs: the solar wind speed Vsw, the temperature standard deviation σT, the sunspot number R, the f10.7 index, the Alfven speed vA, the proton specific entropy Sp and the proton temperature Tp compared to a velocity-dependent expected temperature. The output of the Gaussian Process classifier is a four element vector containing the probabilities that an event (one reading from the hourly-averaged OMNI database) belongs to each category. The probabilistic nature of the prediction allows for a more informative and flexible interpretation of the results, for instance being able to classify events as 'undecided'. The new method has a median accuracy larger than 90% for all categories, even using a small set of data for training. The Receiver Operating Characteristic curve and the reliability diagram also demonstrate the excellent quality of this new method. Finally, we use the algorithm to classify a large portion of the OMNI dataset, and we present for the first time transition probabilities between different solar wind categories. Such probabilities represent the 'climatological' statistics that determine the solar wind baseline.
      PubDate: 2017-10-16T16:30:50.075918-05:
      DOI: 10.1002/2017JA024383
       
  • An empirical model of Titan's magnetic environment during the Cassini era:
           evidence for seasonal variability
    • Authors: Slawa Kabanovic; Sven Simon, Fritz M. Neubauer, Zachary Meeks
      Abstract: Based on the magnetic field data collected during the Cassini era, we construct an empirical model of the ambient magnetospheric field conditions along the orbit of Saturn's largest moon Titan. Observations from Cassini's close Titan flybys as well as 191 non-targeted crossings of Titan's orbit are taken into account. For each of these events we apply the classification technique of Simon et al. [2010a] to categorize the ambient magnetospheric field as current sheet, lobe-like, magnetosheath, or an admixture of these regimes. Independent of Saturnian season, Titan's magnetic environment around noon Saturn local time is dominated by the perturbed fields of Saturn's broad magnetodisk current sheet. Only observations from the nightside magnetosphere reveal a slow, but steady change of the background field from southern lobe-type to northern lobe-type on a time scale of several years. This behavior is consistent with a continuous change in the curvature of the bowl-shaped magnetodisk current sheet over the course of the Saturnian year. We determine the occurrence rate of each magnetic environment category along Titan's orbit as a function of Saturnian season and local time.
      PubDate: 2017-10-16T16:30:46.114232-05:
      DOI: 10.1002/2017JA024402
       
  • On the Dawn-Dusk Asymmetry of the Kelvin-Helmholtz Instability Between
           2007-2013
    • Authors: Z. W. Henry; K. Nykyri, T. W. Moore, A. P. Dimmock, X. Ma
      Abstract: Using data from Time History of Events and Macroscale Interactions during Substorms (THEMIS), a statistical study was performed to determine whether a dawn-dusk asymmetry exists in the occurrence rates of the Kelvin-Helmholtz (KH) instability during Parker-Spiral (PS) and Ortho-Parker-Spiral (OPS) orientations of the interplanetary magnetic field (IMF). It is determined from the data that there is a strong preference toward the dawn side during PS orientation, and although a preference to the dusk side during OPS is suggested, this requires further study for an unambiguous confirmation. The uncertainty in the OPS result is due to a low number of events which satisfied our selection criteria. Because IMF is statistically in PS orientation, the KHI preference for the dawn-flank during this orientation may help explain the origin of the plasma sheet asymmetry of cold-component ions because it has been shown that KHI can drive kinetic-scale wave activity capable of ion heating.
      PubDate: 2017-10-16T16:30:44.081471-05:
      DOI: 10.1002/2017JA024548
       
  • The Variability of Atmospheric Deuterium Brightness at Mars: Evidence for
           Seasonal Dependence
    • Authors: Majd Mayyasi; John Clarke, Dolon Bhattacharyya, Justin Deighan, Sonal Jain, Michael Chaffin, Edward Thiemann, Nick Schneider, Bruce Jakosky
      Abstract: The enhanced ratio of deuterium to hydrogen on Mars has been widely interpreted as indicating the loss of a large column of water into space, and the hydrogen content of the upper atmosphere is now known to be highly variable. The variation in the properties of both deuterium and hydrogen in the upper atmosphere of Mars is indicative of the dynamical processes that produce these species and propagate them to altitudes where they can escape the planet. Understanding the seasonal variability of D is key to understanding the variability of the escape rate of water from Mars. Data from a 15-month observing campaign, made by the MAVEN Imaging Ultraviolet Spectrograph high-resolution echelle channel are used to determine the brightness of deuterium as observed at the limb of Mars. The D emission is highly variable, with a peak in brightness just after southern summer solstice. The trends of D brightness are examined against extrinsic as well as intrinsic sources. It is found that the fluctuations in deuterium brightness in the upper atmosphere of Mars (up to 400 km), corrected for periodic solar variations, vary on timescales that are similar to those of water vapor fluctuations lower in the atmosphere (20-80 km). The observed variability in deuterium may be attributed to seasonal factors such as regional dust storm activity and subsequent circulation lower in the atmosphere.
      PubDate: 2017-10-16T16:30:42.132565-05:
      DOI: 10.1002/2017JA024666
       
  • Ionospheric response to 22-23 June 2015 storm as investigated using ground
           based ionosondes and GPS receivers over India
    • Authors: Ram Singh; S. Sripathi
      Abstract: In this paper, we present response of equatorial and low latitude ionosphere to 22/23 June 2015 geomagnetic storm using chain of ground based ionosondes located at Tirunelveli (8.73°N,77.70°E; geom: 0.32°N), Hyderabad (17.36°N, 78.47°E; geom 8.76°N), and Allahabad (25.45°N, 81.85°E; geom 16.5°N) along with chain of GPS receivers. Uniqueness of this storm is that in contrast to the equatorial plasma bubbles that were detected in the European sector, we see suppression of plasma bubbles in the Indian sector. The observations suggest that westward penetration during local midnight caused abrupt decrease of virtual height (h’F (km)) to ~200 km and suppressed plasma bubbles due to undershielding. Later, the layer increased to 500 km simultaneously due to overshielding effect. On 23rd, we observed negative storm in the northern hemisphere while positive storm in the southern hemisphere. In addition, absence of equatorial Es layers at Tirunelveli and presence of F3 layer at Tirunelveli/Hyderabad seem to be associated with EEJ/CEJ variations. However, on 24th, we observed strong negative storm effects at Allahabad/Hyderabad, while positive storm effect at Tirunelveli. Simultaneous enhancement of h’F (km) at all three ionosonde stations at 20:30 UT on 23rd during recovery phase suggest eastward DD Electric field that caused pre-sunrise spread F at Hyderabad/Allahabad but void of spread F at Tirunelveli suggesting its mid-latitude origin. Periodogram analysis of foF2 and h’F (km) in the present analysis suggest the presence of shorter periods (~2 hours) associated with PP Electric Fields while larger periods (>2 hours) associated with DD Electric field/winds.
      PubDate: 2017-10-16T16:30:40.006387-05:
      DOI: 10.1002/2017JA024460
       
  • Is the Dst Index Sufficient to Define All Geospace Storms'
    • Authors: Joseph E. Borovsky; Yuri Shprits
      Abstract: The purpose of this commentary is (1) to raise awareness about some shortcomings of the use of the Dst index to identify storms, to gauge storm intensity, and to represent stormtime space-weather phenomena and (2) to initiate discussions about different types of storms and about improved identifiers for different types of storms.
      PubDate: 2017-10-16T16:30:37.187623-05:
      DOI: 10.1002/2017JA024679
       
  • Two-Dimensional Vlasov Simulations of Fast Stochastic Electron Heating in
           Ionospheric Modification Experiments
    • Authors: David Carruthers Speirs; Bengt Eliasson, Lars K. S. Daldorff
      Abstract: Ionospheric heating experiments using high-frequency ordinary (O)-mode electromagnetic waves have shown the induced formation of magnetic field-aligned density striations in the ionospheric F region, in association with lower hybrid (LH) and upper hybrid (UH) turbulence. In recent experiments using high-power transmitters, the creation of new plasma regions and the formation of descending artificial ionospheric layers (DAILs) have been observed. These are attributed to suprathermal electrons ionizing the neutral gas, so that the O-mode reflection point and associated turbulence is moving to a progressively lower altitude. We present the results of two-dimensional (2-D) Vlasov simulations used to study the mode conversion of an O-mode pump wave to trapped UH waves in a small-scale density striation of circular cross section. Subsequent multiwave parametric decays lead to UH and LH turbulence and to the excitation of electron Bernstein (EB) waves. Large-amplitude EB waves result in rapid stochastic electron heating when the wave amplitude exceeds a threshold value. For typical experimental parameters, the electron temperature is observed to rise from 1,500 K to about 8,000 K in a fraction of a millisecond, much faster than Ohmic heating due to collisions which occurs on a timescale of an order of a second. This initial heating could then lead to further acceleration due to Langmuir turbulence near the critical layer. Stochastic electron heating therefore represents an important potential mechanism for the formation of DAILs.
      PubDate: 2017-10-16T14:56:12.015235-05:
      DOI: 10.1002/2017JA024665
       
  • Applying Nyquist's method for stability determination to solar wind
           observations
    • Authors: Kristopher G. Klein; Justin C. Kasper, K. E. Korreck, Michael L. Stevens
      Abstract: The role instabilities play in governing the evolution of solar and astrophysical plasmas is a matter of considerable scientific interest. The large number of sources of free energy accessible to such nearly collisionless plasmas makes general modeling of unstable behavior, accounting for the temperatures, densities, anisotropies, and relative drifts of a large number of populations, analytically difficult. We therefore seek a general method of stability determination that may be automated for future analysis of solar wind observations. This work describes an efficient application of the Nyquist instability method to the Vlasov dispersion relation appropriate for hot, collisionless, magnetized plasmas, including the solar wind. The algorithm recovers the familiar proton temperature anisotropy instabilities, as well as instabilities that had been previously identified using fits extracted from in situ observations in Gary et al. (2016). Future proposed applications of this method are discussed.
      PubDate: 2017-10-16T14:55:29.667365-05:
      DOI: 10.1002/2017JA024486
       
  • Spacecraft and instrument photoelectrons measured by the Dual Electron
           Spectrometers on MMS
    • Authors: Daniel J. Gershman; Levon A. Avanov, Scott A. Boardsen, John C. Dorelli, Ulrik Gliese, Alexander C. Barrie, Conrad Schiff, William R. Paterson, Roy B. Torbert, Barbara L. Giles, Craig J. Pollock
      Abstract: Secondary electrons are continuously generated via photoemission from sunlit spacecraft and instrument surfaces. These particles can subsequently contaminate low energy channels of electron sensors. Spacecraft photoelectrons are measured at energies below that of a positive spacecraft potential and can be removed at the expense of energy resolution. However, fluxes of photoelectrons generated inside electron instruments are independent of spacecraft potential and must be fully characterized in order to correct electron data. Here we present observations of spacecraft and instrument photoelectron populations measured with the Dual Electron Spectrometers (DES) on NASA's Magnetospheric Multiscale (MMS) mission. We leverage observations from Earth's nightside plasma sheet taken during MMS commissioning and develop an empirical model of instrument photoelectrons. This model is used with DES velocity distribution functions to correct plasma moments, and has been made publicly available on the MMS science data center for use by the scientific community.
      PubDate: 2017-10-16T02:30:39.067298-05:
      DOI: 10.1002/2017JA024518
       
  • Systems science of the magnetosphere: Creating indices of substorm
           activity, of the substorm-injected electron population, and of the
           electron radiation belt
    • Authors: Joseph E. Borovsky; Kateryna Yakymenko
      Abstract: To more fully monitor the elements of the magnetosphere-ionosphere system and its activity, indices are created to quantify the rate of substorm onset occurrence, the rate of substorm activations, the intensity of the 130 keV substorm-injected electrons and the intensity of the 1.2 MeV radiation-belt electrons. The reactions of these various indices to the onset of isolated substorms are examined, and the behaviors of the indices are explored before and during high-speed-stream-driven storms and during solar wind rarefactions after high-speed streams. Autocorrelation functions of the indices are analyzed and compared with autocorrelation functions of solar wind parameters and geomagnetic indices. Lagged-time correlations between the indices and solar wind variables and geomagnetic indices are surveyed. These 1 h resolution indices are available to the research community.
      PubDate: 2017-10-14T12:16:45.495124-05:
      DOI: 10.1002/2017JA024250
       
  • Simultaneous FPI and TMA measurements of the lower-thermospheric wind in
           the vicinity of the poleward-expanding aurora after substorm onset
    • Authors: Shin-ichiro Oyama; Ken Kubota, Takatoshi Morinaga, Takuo T. Tsuda, Junichi Kurihara, Miguel F. Larsen, Masayuki Yamamoto, Lei Cai
      Abstract: Lower-thermospheric wind fluctuations in the vicinity of an auroral arc immediately before and after a substorm onset was examined by analyzing data from a ground-based green-line Fabry-Perot interferometer (FPI; optical wavelength of 557.7 nm) at Tromsø, Norway, and in-situ measurements from a trimethyl aluminum (TMA) trail released from a sounding rocket launched during the Dynamics and Energetics of the Lower Thermosphere in Aurora 2 (DELTA-2) campaign on 26 January 2009. Soon after the rocket launch but before disappearance of the TMA trail, a substorm onset occurred. The DELTA-2 TMA experiment appears to be the first case in which the substorm onset occurred during the TMA wind measurement. It is known that energy dissipation induced by the ionospheric closure current is compacted at the poleward side of the discrete arc in the ionospheric morning cell. Both FPI and TMA measurements were made at the poleward side, but the FPI measured winds nearer to the poleward edge of the arc than the TMA by 110-130 km. The FPI winds at distance of 53-74 km relative to the arc edge showed clear fluctuations immediately after the substorm onset, but there was no obvious similar fluctuation in the TMA-measured winds. The difference in the response at the two locations suggests that energy dissipation sufficient to be detected as the FPI/TMA wind perturbations was confined to the area from the poleward edge of the arc to a relative distance shorter than 163-203 km but longer than 53-74 km in this event.
      PubDate: 2017-10-13T13:35:29.021665-05:
      DOI: 10.1002/2017JA024613
       
  • Examining coherency scales, substructure, and propagation of whistler-mode
           chorus elements with Magnetospheric Multiscale (MMS)
    • Authors: D. L. Turner; J. H. Lee, S. G. Claudepierre, J. F. Fennell, J. B. Blake, A. N. Jaynes, T. Leonard, F. D. Wilder, R. E. Ergun, D. N. Baker, I. J. Cohen, B. H. Mauk, R. J. Strangeway, D. P. Hartley, C. A. Kletzing, H. Breuillard, O. Le Contel, Yu V. Khotyaintsev, R. B. Torbert, R. C. Allen, J. L. Burch, O. Santolik
      Abstract: Whistler-mode chorus waves are a naturally occurring electromagnetic emission observed in Earth's magnetosphere. Here, for the first time, data from NASA's Magnetospheric Multiscale (MMS) mission were used to analyze chorus waves in detail, including the calculation of chorus wave normal vectors, k. A case study was examined from a period of substorm activity around the time of a conjunction between the MMS constellation and NASA's Van Allen Probes mission on 07 April 2016. Chorus wave activity was simultaneously observed by all six spacecraft over a broad range of L-shells (5.5 < L < 8.5), magnetic local time (06:00 < MLT < 09:00), and magnetic latitude (-32° < MLat < -15°), implying a large chorus active region. Eight chorus elements and their substructure were analyzed in detail with MMS. These chorus elements were all lower band and rising tone emissions, right-handed and nearly circularly polarized, and propagating away from the magnetic equator when they were observed at MMS (MLat ~ -31°). Most of the elements had “hook” like signatures on their wave power spectra, characterized by enhanced wave power at flat or falling frequency following the peak, and all the elements exhibited complex and well organized substructure observed consistently at all four MMS spacecraft at separations up to 70 km (60 km perpendicular and 38 km parallel to the background magnetic field). The waveforms in field-aligned coordinates also demonstrated that these waves were all phase coherent allowing for the direct calculation of k. Error estimates on calculated k revealed that the plane wave approximation was valid for six of the eight elements and most of the subelements. The wave normal vectors were within 20-30° from the direction anti-parallel to the background field for all elements and changed from subelement to subelement through at least two of the eight elements. The azimuthal angle of k in the perpendicular plane was oriented earthward and was oblique to that of the Poynting vector, which has implications for the validity of cold plasma theory.
      PubDate: 2017-10-13T13:35:26.742971-05:
      DOI: 10.1002/2017JA024474
       
  • Substorm overshielding electric field at low latitude on the nightside as
           observed by the HF Doppler sounder and magnetometers
    • Authors: K. K. Hashimoto; T. Kikuchi, I. Tomizawa, T. Nagatsuma
      Abstract: The convection electric field increases during the growth phase of substorms, driving the DP2 ionospheric currents at high-to-equatorial latitudes, intensifying the eastward equatorial electrojet (EEJ) on the dayside. During the expansion phase, the electric field is often reversed, i.e., overshielding occurs at subauroral-to-equatorial latitudes where the EEJ turns to the westward counterelectrojet (CEJ). In this paper, we show that the HF Doppler sounders detected the eastward overshielding electric field at low latitudes on the nightside simultaneously with the CEJ on the dayside. We also show that the overshielding often occurs during the substorm recovery due to the convection reduction, resulting in a two-step form in both the dayside CEJ and nightside electric field. The opposite direction of the electric field on the day- and night-sides is consistent with the dusk-to-dawn potential electric field associated with the Region-2 field-aligned currents intensified by the substorm. The overshielding electric field was found to drive an eastward electrojet with appreciable magnitude in the nighttime equatorial ionosphere, which in turn causes an equatorial enhancement of the midnight positive bay.
      PubDate: 2017-10-13T13:35:22.6959-05:00
      DOI: 10.1002/2017JA024329
       
  • Lower Band Cascade of Whistler Waves Excited by Anisotropic Hot Electrons:
           One-dimensional PIC Simulations
    • Authors: Huayue Chen; Xinliang Gao, Quanming Lu, Yangguang Ke, Shui Wang
      Abstract: Based on THEMIS waveform data, Gao et al. [2016a] have reported two special multiband chorus events, where upper-band waves are located at harmonics of lower-band waves. And they proposed a new generation mechanism to explain this multiband chorus wave, named as lower band cascade. With a 1-D PIC simulation model, we have investigated the lower band cascade of whistler waves excited by anisotropic hot electrons. During each simulation, lower-band whistler-mode waves are firstly excited by the anisotropy of hot electrons. Later, upper-band harmonic waves are generated through the nonlinear coupling between the electromagnetic and electrostatic components of lower-band waves, which supports the scenario of lower band cascade. Moreover, the peak wave number (or frequency) of lower-band waves will continuously drift to smaller values due to the decline of the anisotropy of hot electrons. While, the peak wave number of upper-band harmonic waves will be kept nearly unchanged, but their amplitude continues to decrease after their saturation. We further find the magnetic amplitude of upper-band harmonic waves tends to increase with the increase of the wave normal angle of lower-band waves or the anisotropy of hot electrons. Besides, the amplitude ratio between upper-band and lower-band waves is positively correlated with the wave normal angle of lower-band waves, but is anti-correlated with the anisotropy of hot electrons. Our study has provided a more comprehensive understanding of the lower band cascade of whistler waves.
      PubDate: 2017-10-13T13:35:19.898228-05:
      DOI: 10.1002/2017JA024513
       
  • Storm and Substorm Causes and Effects at Midlatitude Location for the St.
           Patrick's 2013 and 2015 Events
    • Authors: A. Guerrero; J. Palacios, M. Rodríguez-Bouza, I. Rodríguez-Bilbao, A. Aran, C. Cid, M. Herraiz, E. Saiz, G. Rodríguez-Caderot, Y. Cerrato
      Abstract: Midlatitude locations are unique regions exposed to both geomagnetic storm and substorm effects, which may be superposed on specific events imposing an extra handicap for the analysis and identification of the sources and triggers. We study space weather effects at the midlatitude location of the Iberian Peninsula for the St. Patrick's day events in 2013 and 2015. We have been able to identify and separate storm and substorm effects on ground magnetometer data from San Pablo-Toledo observatory during storm time revealing important contributions of the Substorm Current Wedge on both events. The analysis of these substorm local signatures have shown to be related to the production of effective geomagnetically induced currents and ionospheric disturbances as measured from Global Navigation Satellite Systems data at MAD2 IGS permanent station and not directly related to the storm main phase. The whole Sun-to-Earth chain has been analyzed in order to identify the solar and interplanetary triggers. In both events a high-speed stream (HSS) and a coronal mass ejections (CME) are involved, though for 2015 event, the HSS has merged with the CME, increasing the storm geoeffectiveness. The enhancement of substorm geoeffectiveness is justified by the effects of the inclined magnetic axes of the Sun and of the Earth during equinox period.
      PubDate: 2017-10-13T11:31:06.969677-05:
      DOI: 10.1002/2017JA024224
       
  • Low-Energy (
    • Authors: Jie Ren; Q.-G. Zong, Y. Miyoshi, X. Z. Zhou, Y. F. Wang, R. Rankin, C. Yue, H. E. Spence, H. O. Funsten, J. R. Wygant, C. A. Kletzing
      Abstract: We report observational evidence of cold plasmaspheric electron (
      PubDate: 2017-10-13T11:26:26.222911-05:
      DOI: 10.1002/2017JA024316
       
  • Variabilities of low-latitude migrating and non-migrating tides in GPS-TEC
           and TIMED-SABER temperature during the sudden stratospheric warming event
           of 2013
    • Authors: S. Sridharan
      Abstract: The Global Positioning System (GPS) deduced total electron content (TEC) data at 15°N (geomagnetic), which is the crest region of equatorial ionization anomaly, are used to study tidal variabilities during the 2013 sudden stratospheric warming (SSW) event. The results from space-time spectral analysis reveal that the amplitudes of migrating diurnal (DW1) and semi-diurnal (SW2) tides are larger than those of non-migrating tides. After the SSW onset, the amplitudes of DW1, SW2, SW1, and DS0 increase. Moreover, they show 16-day variations similar to the periodicity of the high-latitude stratospheric planetary wave (PW) suggesting that the non-migrating tides (SW1 and DS0) are possibly generated due to non-linear interaction of migrating tides with PW. Similar spectral analysis on temperature at 10°N obtained from the Sounding of Atmosphere by Broadband Emission Radiometry (SABER) shows that the SW2 enhances at stratospheric heights and the SW2 is more dominant at 80-90 km, but its amplitude decreases around 100 km. The amplitudes of non-migrating tides become comparable to those of SW2 around 100 km and their contribution become increasingly important at higher heights. This suggests that the non-linear interaction between migrating tides and PW occur at low-latitude upper mesospheric heights, as SW2 exhibits 16-day periodicity in SABER temperature at 100 km as observed in TEC. Besides, it is observed that the eastward propagating tides are less dominant than westward propagating tides in both TEC and SABER temperature.
      PubDate: 2017-10-12T18:10:28.406896-05:
      DOI: 10.1002/2017JA024283
       
  • Characteristics of seasonal variation and solar activity dependence of the
           geomagnetic solar quiet daily variation
    • Authors: Atsuki Shinbori; Yukinobu Koyama, Masahito Nosé, Tomoaki Hori, Yuichi Otsuka
      Abstract: Characteristics of seasonal variation and solar activity dependence of the X- and Y-components of the geomagnetic solar quiet (Sq) daily variation at Memambetsu in mid-latitudes and Guam near the equator have been investigated using long-term geomagnetic field data with 1-h time resolution from 1957 to 2016. The monthly mean Sq variation in the X and Y components (Sq-X and Sq-Y) shows a clear seasonal variation and solar activity dependence. The amplitude of seasonal variation increases significantly during high solar activities, and is proportional to the solar F10.7 index. The pattern of the seasonal variation is quite different between Sq-X and Sq-Y. The result of the correlation analysis between the solar F10.7 index and Sq-X and Sq-Y shows almost the linear relationship, but the slope of the linear fitted line varies as function of local time and month. This implies that the sensitivity of Sq-X and Sq-Y to the solar activity is different for different local times and seasons. The pattern of the local time and seasonal variations of Sq-Y at Guam shows good agreement with that of a magnetic field produced by inter-hemispheric field-aligned currents (FACs), which flow from the summer to winter hemispheres in the dawn and dusk sectors and from the winter to summer hemispheres in the pre-noon to afternoon sectors. The direction of the inter-hemispheric FAC in the dusk sector is opposite to the concept of Fukushima's model.
      PubDate: 2017-10-12T18:10:24.977937-05:
      DOI: 10.1002/2017JA024342
       
  • Asymmetries in the magnetosheath field draping on Venus' night side
    • Authors: M. Delva; M. Volwerk, R. Jarvinen, C. Bertucci
      Abstract: Draping features of the interplanetary magnetic field around non-magnetic bodies, especially Venus, have been studied in detail in numerical simulations and also from observations. Existing analytical and numerical work for non-perpendicular IMF and solar wind velocity direction show a kink in the draped fieldlines in the near magnetosheath on the quasi-parallel side of the bow shock. Here, long-term magnetic field data from the Venus Express mission (2006-2014) are analyzed in the near night-side region of the magnetosheath, searching for differences in the draping pattern between the quasi-parallel- and quasi-perpendicular side of the shock. From these MAG data, the kink in the fieldlines occurring only on the quasi-parallel side is clearly identified from the change of sign in the field component parallel to the solar wind velocity. Furthermore, an asymmetry in the deflection of the out-of-plane field component due to the slipping of the fieldlines over the planetary obstacle is also found, which confirms predictions from numeral studies and from earlier work.
      PubDate: 2017-10-10T18:40:24.157847-05:
      DOI: 10.1002/2017JA024604
       
  • The effects of magnetospheric processes on relativistic electron dynamics
           in the Earth's outer radiation belt
    • Authors: C. L. Tang; Y. X. Wang, B. Ni, Z. P. Su, G. D. Reeves, J.-C. Zhang, D. N. Baker, H. E. Spence, H. O. Funsten, J. B. Blake
      Abstract: Using the electron phase space density (PSD) data measured by Van Allen Probe A from January 2013 to April 2015, we investigate the effects of magnetospheric processes on relativistic electron dynamics in the Earth's outer radiation belt during 50 geomagnetic storms. A statistical study shows that the maximum electron PSDs for various μ (μ = 630, 1096, 2290, and 3311 MeV/G) at L*~4.0 after the storm peak have good correlations with storm intensity (cc~0.70). This suggests that the occurrence and magnitude of geomagnetic storms are necessary for relativistic electron enhancements at the inner edge of the outer radiation belt (L* = 4.0). For moderate or weak storm events (SYM-Hmin > ~−100 nT) with weak substorm activity (AEmax  0.77). For storm events with intense substorms after the storm peak, relativistic electron enhancements at L* = 4.5 and 5.0 are observed. This shows that intense substorms during the storm recovery phase are crucial to relativistic electron enhancements in the heart of the outer radiation belt. Our statistics study suggests that magnetospheric processes during geomagnetic storms have a significant effect on relativistic electron dynamics.
      PubDate: 2017-10-10T11:20:55.008522-05:
      DOI: 10.1002/2017JA024407
       
  • Application of Manley-Rowe relation in analyzing nonlinear interactions
           between planetary waves and the solar semidiurnal tide during 2009 Sudden
           Stratospheric Warming event
    • Authors: Maosheng He; Jorge Luis Chau, Gunter Stober, Chris M. Hall, Masaki Tsutsumi, Peter Hoffmann
      Abstract: Upper mesospheric winds observed by the Svalbard specular meteor radar (16.01°E,78.16°N) are analyzed to study the tidal variabilities during the 2009 SSW. We report a textbook case of nonlinear interactions between planetary waves (PWs) and the SW2 tide (SWm denotes semidiurnal westward-propagating tidal mode with zonal wavenumber m). The Lomb-Scargle algorithm, bispectrum, wavelet spectra, and Manley-Rowe relations are combined to explore the frequency match, phase coherence, energy budget, and wavenumber relations among the interacting waves and their temporal evolution. Our results suggest that (1) 5-, 10-, 16-day PW normal modes interact with SW2 generating significant sidebands (S2Ss) at frequencies lower and higher than SW2, known as SW1 and SW3 enhancements, respectively, (2) SW2 is the main energy supplier for both SW1 and SW3, hence shrinks in the interactions, (3) whereas the PWs export relatively negligible energy to SW3 but accept energy from SW2 in generating SW1, therefore the PWs is not subject to the interactions but controlled by external dynamics, which might in turn act as a key in switching on/off the SW1 and SW3 interactions independently, (4) the SW1 enhancement could be explained as a byproduct of the planetary wave amplification by stimulated tidal decay (PASTIDE), (5) PASTIDE contributes energy to the secondary PW in the late SSW stage reported in previous studies, and (6) one SW1 component associated with the 16-day PW is very close to the semidiurnal lunar mode in frequency, which might contaminate the estimation of the lunar tidal amplification in previous studies.
      PubDate: 2017-10-09T19:40:51.763233-05:
      DOI: 10.1002/2017JA024630
       
  • Cold ion outflow modulated by the solar wind energy input and tilt of the
           geomagnetic dipole
    • Authors: Kun Li; Y. Wei, M. André, A. Eriksson, S. Haaland, E. A. Kronberg, H. Nilsson, L. Maes, Z. J. Rong, W. X. Wan
      Abstract: The solar wind energy input into the Earth's magnetosphere-ionosphere system drives ionospheric outflow, which plays an important role in both the magnetospheric dynamics and evolution of the atmosphere. However, little is known about the cold ion outflow with energies lower than a few tens of eV, as the direct measurement of cold ions is difficult because a spacecraft gains a positive electric charge due to the photoemission effect, which prevents cold ions from reaching the onboard detectors. A recent breakthrough in the measurement technique using Cluster spacecraft revealed that cold ions dominate the ion population in the magnetosphere. This new technique yields a comprehensive data set containing measurements of the velocities and densities of cold ions for the years 2001-2010. In this paper, this data set is used to analyze the cold ion outflow from the ionosphere. We found that about 0.1% of the solar wind energy input is transformed to the kinetic energy of cold ion outflow at the topside ionosphere. We also found that the geomagnetic dipole tilt can significantly affect the density of cold ion outflow, modulating the outflow rate of cold ion kinetic energy. These results give us clues to study the evolution of ionospheric outflow with changing global magnetic field and solar wind condition in the history.
      PubDate: 2017-10-09T19:40:49.245379-05:
      DOI: 10.1002/2017JA024642
       
  • Revisiting Ionosphere-Thermosphere Responses to Solar Wind Driving in
           Superstorms of November 2003 and 2004
    • Authors: O. P. Verkhoglyadova; A. Komjathy, A. J. Mannucci, M. Mlynczak, L. Hunt, L. J. Paxton
      Abstract: We revisit three complex superstorms of 19-20 November 2003, 7-8 November 2004 and 9-11 November 2004 to analyze ionosphere-thermosphere (IT) effects driven by different solar wind structures associated with complex Interplanetary Coronal Mass Ejections (ICMEs) and their upstream sheaths. The efficiency of the solar wind-magnetosphere connection throughout the storms is estimated by coupling functions. The daytime IT responses to the complex driving are characterized by combining and collocating (where possible) measurements of several physical parameters (total electron content or TEC, thermospheric infrared nitric oxide emission and composition ratio) from multiple satellite platforms and ground-based measurements. A variety of metrics are utilized to examine global IT phenomena at ~1 hour time scales. The role of direct driving of IT dynamics by solar wind structures and the role of IT pre-conditioning in these storms, which feature complex unusual TEC responses, are examined and contrasted. Furthermore, IT responses to ICME magnetic clouds and upstream sheaths are separately characterized. We identify IT feedback effects that can be important for long-lasting strong storms. The role of the IMF By component on ionospheric convection may not be well captured by existing coupling functions. Mechanisms of thermospheric overdamping and consequential ionospheric feedback need to be further studied.
      PubDate: 2017-10-09T19:40:46.869771-05:
      DOI: 10.1002/2017JA024542
       
  • Impact of oscillating IMF Bz during 17 March 2013 storm on the
           distribution of plasma over Indian low and mid latitude ionospheric
           regions
    • Authors: P. R. Shreedevi; R. K. Choudhary
      Abstract: We show evidence of a positive ionospheric storm occurring simultaneously at the equatorial, low and mid-latitude ionospheric regions in the Indian sector in response to an intense geomagnetic storm on 17 March 2013. The storm had its onset time coinciding with the local noon. An on-site Digisonde at Trivandrum (dip-equator) recorded a sharp decrease in the height of F-region peak in the afternoon, which is a signature of westward electric field associated with a CEJ. Coupled with it was a simultaneous increase in TEC in the entire Indian region. The magnitude of increase in TEC decreased slowly northward of the dip-equator and had almost no change near the anomaly crest. Further northward of the anomaly crest, the TEC started increasing again and at Shimla, a mid-latitude station, it had a value close to 2 times its monthly mean. We surmise that the westward electric field resulting from the CEJ pushed the F-layer at the dip-equator down to the altitude regions where recombination and diffusion played minimal roles. No loss of plasma due to diffusion while photo-production of ions was still taking place, led to an enhancement in the electron density near the equatorial / low-latitude region. The Joule heating of the thermosphere, on the other hand, gave rise to the TADs which pushed the plasma up in altitude at the equatorial anomaly region. It supplemented the loss of plasma at the anomaly crest region resulting in no change in the TEC and a marked increase in the TEC in the mid-latitude ionosphere.
      PubDate: 2017-10-09T19:40:42.04705-05:0
      DOI: 10.1002/2017JA023980
       
  • SC-associated electric field variations in the magnetosphere and
           ionospheric convective flows
    • Authors: S.-I. Kim; K.-H. Kim, H.-J. Kwon, H. Jin, E. Lee, G. Jee, N. Nishitani, T. Hori, M. Lester, J. R. Wygant
      Abstract: We examine magnetic and electric field perturbations associated with a sudden commencement (SC), caused by an interplanetary (IP) shock passing over the Earth's magnetosphere on 16 February 2013. The SC was identified in the magnetic and electric field data measured at THEMIS-E (THE-E: MLT = 12.4, L = 6.3), Van Allen Probe-A (VAP-A: MLT = 3.2, L = 5.1), and Van Allen Probe-B (VAP-B: MLT = 0.2. L= 4.9) in the magnetosphere. During the SC interval, THE-E observed a dawnward-then-duskward electric (E) field perturbation around noon, while VAP-B observed a duskward E-field perturbation around midnight. VAP-A observed a dawnward-then-duskward E-field perturbation in the postmidnight sector, but the duration and magnitude of the dawnward E-perturbation are much shorter and weaker than that at THE-E. That is, the E-field signature changes with local time during the SC interval. The SuperDARN radar data indicate that the ionospheric plasma motions during the SC are mainly due to the E-field variations observed in space. This indicates that the SC-associated E-field in space plays a significant role in determining the dynamic variations of the ionospheric convection flow. By comparing previous SC MHD simulations and our observations, we suggest that the E-field variations observed at the spacecraft are produced by magnetospheric convection flows due to deformation of the magnetosphere as the IP shock sweeps the magnetopause.
      PubDate: 2017-10-09T19:40:38.686833-05:
      DOI: 10.1002/2017JA024611
       
  • Coseismic Travelling Ionospheric Disturbances (CTIDs) during the Mw 7.8
           Gorkha, Nepal Earthquake on 25 April 2015 from ground and space borne
           observations
    • Authors: S. Tulasi Ram; P. S. Sunil, M. Ravi Kumar, S. -Y. Su, L. C. Tsai, C. H. Liu
      Abstract: Coseismic travelling ionospheric disturbances (CTIDs) and their propagation characteristics during Mw 7.8 Gorkha earthquake in Nepal on 25 April 2015 have been investigated using a suite of ground based GPS receivers and broad band seismometers along with the space borne Radio Occultation observations over the Indian subcontinent region. Depletion in vertical total electron content (VTEC), a so called ionospheric hole, is observed near the epicenter ~9 – 11 minutes after the onset of earthquake. A positive pulse preceding the depletion, similar to N-shaped perturbation, propagating with an apparent velocity of ~2.4 km/s is observed on the South. Further, the CTIDs in the southward direction are found to split in to fast (~2.4 – 1.7 km/s) and slow (~680 – 520 m/s) propagating modes at epicentral distances greater than ~800 km. However, the velocities of fast mode CTIDs are significantly smaller than the surface Rayleigh wave velocity (~3.7 km/s), indicating that they are not the true imprint of Rayleigh wave, instead, can probably be attributed to the superimposed wave front formed by the mixture of acoustic waves excited by main shock and propagating Rayleigh wave. The southward CTIDs are found to propagate at F2-region altitudes of ~300 – 440 km captured by COSMIC Radio Occultation observations. The CTIDs with periods of ~4 – 6 minutes are observed in all directions with significantly larger amplitudes and faster propagation velocities in South and East directions. The observed azimuthal asymmetry in the amplitudes and velocities of CTIDs are discussed in terms of the alignment with geomagnetic field and nature of surface crustal deformation during the earthquake.
      PubDate: 2017-10-09T19:40:33.434015-05:
      DOI: 10.1002/2017JA023860
       
  • Data Assimilation of Ground-based GPS and Radio Occultation Total Electron
           Content for Global Ionospheric Specification
    • Authors: C. Y. Lin; T. Matsuo, J. Y. Liu, C. H. Lin, J. D. Huba, H. F. Tsai, C. Y. Chen
      Abstract: This study presents an approach based on the Gauss-Markov Kalman filter to assimilate the total electron content (TEC) observed from ground-based GPS receivers and space-based radio occultation instrumentations (such as FORMOSAT-3/COSMIC (F3/C) and FORMOSAT-7/COSMIC-2 (F7/C2)) into the International Reference Ionosphere. Observing System Simulation Experiments (OSSEs) show that the data assimilation procedure consisting of the forecast and the measurement update steps can better improve the accuracy of the data assimilation analysis than the assimilation procedure using the measurement update alone. Compared with F3/C, the denser F7/C2 occultation observations can improve the analysis accuracy significantly as suggested by OSSEs. The real data assimilation results are further validated with Global Ionosphere Maps, the global ground-based GPS measurements, and the ionospheric F2-peak height and electron density sounded by ionosondes. Both the OSSEs and validation results confirm that a number of improvements to the data assimilation procedure presented in this paper can indeed be used to reconstruct the three-dimensional ionospheric electron density adequately.
      PubDate: 2017-10-09T19:40:30.12018-05:0
      DOI: 10.1002/2017JA024185
       
  • MMS observations and hybrid simulations of surface ripples at a marginally
           quasi-parallel shock
    • Authors: Imogen Gingell; Steven J. Schwartz, David Burgess, Andreas Johlander, Christopher T. Russell, James L. Burch, Robert E. Ergun, Stephen Fuselier, Daniel J. Gershman, Barbara L. Giles, Katherine A. Goodrich, Yuri V. Khotyaintsev, Benoit Lavraud, Per-Arne Lindqvist, Robert J. Strangeway, Karlheinz Trattner, Roy B. Torbert, Hanying Wei, Frederick Wilder
      Abstract: Simulations and observations of collisionless shocks have shown that deviations of the nominal local shock normal orientation, i.e. surface waves or ripples, are expected to propagate in the ramp and overshoot of quasi-perpendicular shocks. Here, we identify signatures of a surface ripple propagating during a crossing of Earth's marginally quasi-parallel (θBn∼45∘) or quasi-parallel bow shock shock on 2015-11-27 06:01:44 UTC by the Magnetspheric Multiscale (MMS) mission, and determine the ripple's properties using multi-spacecraft methods. Using two-dimensional hybrid simulations, we confirm that surface ripples are a feature of marginally quasi-parallel and quasi-parallel shocks under the observed solar wind conditions. In addition, since these marginally quasi-parallel and quasi-parallel shocks are expected to undergo a cyclic reformation of the shock front, we discuss the impact of multiple sources of non-stationarity on shock structure. Importantly, ripples are shown to be transient phenomena, developing faster than an ion gyroperiod and only during the period of the reformation cycle when a newly developed shock ramp is unaffected by turbulence in the foot. We conclude that the change in properties of the ripple observed by MMS is consistent with the reformation of the shock front over a timescale of an ion gyro-period.
      PubDate: 2017-10-06T17:40:49.10092-05:0
      DOI: 10.1002/2017JA024538
       
  • Thermal conductivity of the multicomponent neutral atmosphere
    • Authors: A. V. Pavlov
      Abstract: Approximate expressions for the thermal conductivity coefficient of the multicomponent neutral atmosphere consisting of N2, O2, O, He, and H are analyzed and evaluated for the atmospheric conditions by comparing them with that given by the rigorous hydrodynamic theory. The new approximations of the thermal conductivity coefficients of simple gases N2, O2, O, He, and H are derived and used. It is proved that the modified Mason and Saxena approximation of the atmospheric thermal conductivity coefficient is more accurate in reproducing the atmospheric values of the rigorous hydrodynamic thermal conductivity coefficient in comparison with those that are generally accepted in atmospheric studies. This approximation of the thermal conductivity coefficient is recommended to use in calculations of the neutral temperature of the atmosphere.
      PubDate: 2017-10-06T17:40:25.686866-05:
      DOI: 10.1002/2017JA024397
       
  • A Study on Sunward Propagating Alfvénic Fluctuations With a Power Law
           Spectrum Observed by the Wind Spacecraft
    • Authors: Honghong Wu; Xin Wang, Chuanyi Tu, Linghua Wang, Jiansen He, Hui Tian
      Abstract: Sunward propagating Alfvénic fluctuations with a power law spectrum (SAFP) have been recently observed in the upstream region of the Earth's bow shock. However, some physical properties of these fluctuations such as anisotropy remain unclear. Here we develop a new method for identifying SAFPs, and present for the first time the anisotropy of SAFPs power and spectral index. In this method, the propagation direction determination of SAFPs does not rely on a radial magnetic geometry but the pitch angle distribution of strahl electron outflow. Therefore, the SAFPs with any value of θRB (angle between the global mean magnetic field and the Sun-to-Earth radial direction) can be identified, so that enables the study of the spectral anisotropy. We find 508 SAFPs using the Wind spacecraft measurements from 1995 to 2014. We show that the SAFP has an averaged spectral index of −1.77 ± 0.28 and the index changes continuously from −2.18 ± 0.21 when θRB=0°–10° to −1.71 ± 0.03 when θRB=80°–90°. These SAFPs are observed more frequently in the slow solar wind especially at solar minimum. We also select antisunward propagating Alfvénic fluctuations with a power law spectrum using the same method for comparison. The results indicate that the power spectrum of SAFP is steeper, and the spectral intensity as well as the power anisotropy of SAFP is weaker. These new findings may provide information on the generation of turbulence in the upstream region.
      PubDate: 2017-10-06T14:46:07.996172-05:
      DOI: 10.1002/2017JA024422
       
  • Spontaneous hot flow anomalies at Mars and Venus
    • Authors: Glyn Collinson; David Sibeck, Nick Omidi, Joseph Grebowsky, Jasper Halekas, David Mitchell, Jared Espley, Tielong Zhang, Moa Persson, Yoshifumi Futaana, Bruce Jakosky
      Abstract: We report the first observations of Spontaneous Hot Flow Anomalies (SHFAs) at Venus and Mars, demonstrating their existence in the foreshocks of other planets beyond Earth. Using data from the ESA Venus Express and the NASA Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft, we present magnetic and plasma observations from events at both planets, exhibiting properties similar to “classical” Hot Flow Anomalies, with bounding shock-like compressive regions and a hot and diffuse core. However, these explosive foreshock transients were observed without any attendant interplanetary magnetic field discontinuity, consistent with SHFAs observed at Earth and our hybrid simulations.
      PubDate: 2017-10-06T13:11:03.920512-05:
      DOI: 10.1002/2017JA024196
       
  • Systematic evaluation of low frequency hiss and energetic electron
           injections
    • Authors: Run Shi; Wen Li, Qianli Ma, G. D. Reeves, C. A. Kletzing, W. S. Kurth, G. B. Hospodarsky, H. E. Spence, J. B. Blake, J. F. Fennell, S. G. Claudepierre
      Abstract: The excitation of low frequency (LF) plasmaspheric hiss, over the frequency range from 20 Hz to 100 Hz, is systematically investigated by comparing the hiss wave properties with electron injections at energies from tens of keV to several hundred keV. Both particle and wave data from the Van Allen Probes during the period from September 2012 to June 2016 are used in the present study. Our results demonstrate that the intensity of LF hiss has a clear day-night asymmetry, and increases with increasing geomagnetic activity, similar to the behavior of normal hiss (~100 Hz to several kHz). The occurrence rate of LF hiss in association with electron injections is up to 80% in the outer plasmasphere (L> 4) on the dayside, and the strong correlation extends to lower L shells for more active times. In contrast, at lower L shells (L < 3.5), LF hiss is seldom associated with electron injections. The LF hiss with Poynting flux directed away from the equator is dominant at higher magnetic latitudes and higher L shells, suggesting a local amplification of LF hiss in the outer plasmasphere. The averaged electron fluxes are larger at higher L shells where significant LF hiss wave events are observed. Our study suggests the importance of electron injections and their drift trajectories towards the dayside plasmasphere in locally amplifying the LF hiss waves detected by the Van Allen Probes.
      PubDate: 2017-10-05T13:40:31.502205-05:
      DOI: 10.1002/2017JA024571
       
  • Using the Coronal Evolution to Successfully Forward Model CMEs' In Situ
           Magnetic Profiles
    • Authors: C. Kay; N. Gopalswamy
      Abstract: Predicting the effects of a coronal mass ejection (CME) impact requires knowing if impact will occur, which part of the CME impacts, and its magnetic properties. We explore the relation between CME deflections and rotations, which change the position and orientation of a CME, and the resulting magnetic profiles at 1 AU. For 45 STEREO-era, Earth-impacting CMEs, we determine the solar source of each CME, reconstruct its coronal position and orientation, and perform a ForeCAT [Kay et al., 2015a] simulation of the coronal deflection and rotation. From the reconstructed and modeled CME deflections and rotations we determine the solar cycle variation and correlations with CME properties. We assume no evolution between the outer corona and 1 AU and use the ForeCAT results to drive the FIDO in situ magnetic field model [Kay et al., 2017a], allowing for comparisons with ACE and Wind observations. We do not attempt to reproduce the arrival time. On average FIDO reproduces the in situ magnetic field for each vector component with an error equivalent to 35% of the average total magnetic field strength when the total modeled magnetic field is scaled to match the average observed value. Random walk best fits distinguish between ForeCAT's ability to determine FIDO's input parameters and the limitations of the simple flux rope model. These best fits reduce the average error to 30%. The FIDO results are sensitive to changes of order a degree in the CME latitude, longitude, and tilt, suggesting that accurate space weather predictions require accurate measurements of a CME's position and orientation.
      PubDate: 2017-10-05T13:40:26.526437-05:
      DOI: 10.1002/2017JA024541
       
  • Low Altitude Emission of Energetic Neutral Atoms: Multiple Interactions
           and Energy Loss
    • Authors: K. LLera; J. Goldstein, D. J. McComas, P. W. Valek
      Abstract: Low Altitude Emissions (LAEs) are the energetic neutral atom (ENA) signature of ring current ions precipitating along the magnetic field to an altitude of 200-800 km. This altitude region is considered to be “optically thick” because ring current ions undergo multiple charge changing interactions (MCCIs) with Earth's dense oxygen exosphere. While each interaction involves an energy loss of ~36 eV, no prior study has determined the accumulated energy lost by 1-100 keV H+ emerging as LAEs. We have developed a 2-D model with a geomagnetic dipole that captures the net effects in energy loss and pitch angle evolution as a result of MCCIs without the computational requirements of a full Monte-Carlo simulation. Dependent on the amount of latitudinal migration, the energy loss is greater than 20% for ions below 60 keV for equatorward moving particles (30 keV for poleward). Since the ENA travels ballistically across a geomagnetic dipole, upon reionization, ion velocity along the local field increases (anti-parallel in the northern hemisphere). Redirecting the particle upward through MCCIs is most effective during poleward ENA motion. The net effect is to redirect precipitating ions (below 2,500 km) to eventually emerge from the optically thick region either as an ion or ENA. Precipitation is a joint ion-neutral process, affecting both the energy and pitch angle distribution through the transverse motion of ENA segments in a converging field. For particles that enter the MCCI regime, the energy loss and evolution of the pitch angle distribution must be considered within a realistic magnetic field.
      PubDate: 2017-10-04T17:06:48.829401-05:
      DOI: 10.1002/2017JA024016
       
  • Interpreting Observations of Large-Scale Traveling Ionospheric
           Disturbances by Ionospheric Sounders
    • Authors: L. H. Pederick; M. A. Cervera, T. J. Harris
      Abstract: From July to October 2015, the Australian Defence Science and Technology Group (DST Group) conducted an experiment during which a vertical incidence sounder (VIS) was set up at Alice Springs Airport. During September 2015 this VIS observed the passage of many large-scale traveling ionospheric disturbances (TIDs). By plotting the measured virtual heights across multiple frequencies as a function of time, the passage of the TID can be clearly displayed. Using this plotting method we show that all the TIDs observed during the campaign by the VIS at Alice Springs show an apparent downward phase progression of the crests and troughs. The passage of the TID can be more clearly interpreted by plotting the true height of iso-ionic contours across multiple plasma frequencies; the true heights can be obtained by inverting each ionogram to obtain an electron density profile. These plots can be used to measure the vertical phase speed of a TID, and also reveal a time lag between events seen in true height compared to virtual height. To the best of our knowledge this style of analysis has not previously been applied to other swept-frequency sounder observations. We develop a simple model to investigate the effect of the passage of a large-scale TID on a VIS. The model confirms that for a TID with a downward vertical phase progression, the crests and troughs will appear earlier in virtual height than in true height, and will have a smaller apparent speed in true height than in virtual height.
      PubDate: 2017-10-04T17:06:44.866185-05:
      DOI: 10.1002/2017JA024337
       
  • Shock-induced disappearance and subsequent recovery of plasmaspheric hiss:
           Coordinated observations of RBSP, THEMIS and POES satellites
    • Authors: Nigang Liu; Zhenpeng Su, Zhonglei Gao, G. D. Reeves, Huinan Zheng, Yuming Wang, Shui Wang
      Abstract: Plasmaspheric hiss is an extremely low frequency whistler-mode emission contributing significantly to the loss of radiation belt electrons. There are two main competing mechanisms for the generation of plasmaspheric hiss: excitation by local instability in the outer plasmasphere and origination from chorus outside the plasmasphere. Here, on the basis of the analysis of an event of shock-induced disappearance and subsequent recovery of plasmaspheric hiss observed by RBSP, THEMIS and POES missions, we attempt to identify its dominant generation mechanism. In the pre-shock plasmasphere, the local electron instability was relatively weak and the hiss waves with bidirectional Poynting fluxes mainly originated from the dayside chorus waves. On arrival of the shock, the removal of pre-existing dayside chorus and the insignificant variation of low-frequency wave instability caused the prompt disappearance of hiss waves. In the next few hours, the local instability in the plasmasphere was greatly enhanced due to the substorm injection of hot electrons. The enhancement of local instability likely played a dominant role in the temporary recovery of hiss with unidirectional Poynting fluxes. These temporarily recovered hiss waves were generated near the equator and then propagated toward higher latitudes. In contrast, both the enhancement of local instability and the recurrence of pre-noon chorus contributed to the substantial recovery of hiss with bidirectional Poynting fluxes.
      PubDate: 2017-10-04T17:06:35.82178-05:0
      DOI: 10.1002/2017JA024470
       
  • Solar cycle occurrence of Alfvénic fluctuations and related
           geo-efficiency
    • Authors: E. I. Tanskanen; K. Snekvik, J. A. Slavin, D. Pérez-Suárez, A. Viljanen, M. L. Goldstein, M. J. Käpylä, R. Hynönen, L. V. T. Häkkinen, K. Mursula
      Abstract: We examine solar wind intervals with Alfvénic fluctuations (ALFs) in 1995 - 2011. The annual number, the total annual duration and the average length of ALFs vary over the solar cycle, having a maximum in 2003 and a minimum in 2009. ALFs are most frequent in the declining phase of solar cycle, when the number of high-speed streams at the Earth´s vicinity is increased. There is a rapid transition after the maximum of solar cycle 23 from ALFs being mainly embedded in slow solar wind (< 400 km/s) until 2002 to ALFs being dominantly in fast solar wind (> 600 km/s) since 2003. Cross helicity increased by 30% from 2002 to 2003, and maximized typically 4-6 hours before solar wind speed maximum. Cross helicity remained elevated for several days for highly Alfvénic non-ICME streams, but only for a few hours for ICMEs. The number of substorms increased by about 40% from 2002 to 2003, and the annual number of substorms closely follows the annual cross helicity. This further emphasizes the role of Alfvénic fluctuations in modulating substorm activity. The predictability of substorm frequency and size would be greatly improved by monitoring solar wind Alfvénic fluctuations in addition to the mean values of the important solar wind parameters.
      PubDate: 2017-10-03T17:16:21.286042-05:
      DOI: 10.1002/2017JA024385
       
  • Quiet and Disturbed Time Characteristics of Blanketing Es (Esb) during
           Solar Cycle 23
    • Authors: V. Yadav; B. Kakad, A. Bhattacharyya, T. K. Pant
      Abstract: A sporadic E layer with dense ionization blocks the upper ionospheric layers in ionosonde observations and it is called, blanketing sporadic E (Esb). Although earlier studies have demonstrated that Esb occurrence is dependent on solar activity, seasons, local time and equatorial electrojet/counter electrojet (EEJ/CEEJ) strength, the physics behind this dependence is not well established particularly at the dip equatorial stations. Moreover, fewer comprehensive studies are available on Esb. Present work is a detailed statistical study of Esb occurrence and its characteristics during solar cycle 23 (1996-2006) at Indian dip equatorial station Trivandrum (dip latitude 0.5° N). In present study, solar flux dependence of Esb occurrence is clearly evident not only for magnetically quiet, but also for the disturbed periods with maximum during low solar activity. Known seasonal peak Esb occurrence during summer (May-Aug) is found to be dominated by larger percentage of total blanketing events (fbEs ≥ 8 MHz) on magnetically disturbed days as compared to quiet days. We noticed prevalent Esb occurrence in the post-midnight (00-06 IST) periods during low solar activity. Besides Esb characteristics, the present study aims to investigate effect of solar flux on association of Esb and CEEJ. Coexistence of Esb and CEEJ is emphasized in earlier observational studies. However, any dependence of their association on solar flux is not yet examined. We find that their association is weaker during low solar activity as compared to high solar activity in summer, indicating that Esb occurrence is highly likely on CEEJ days during high solar activity periods.
      PubDate: 2017-10-03T17:16:18.7822-05:00
      DOI: 10.1002/2017JA023911
       
  • Quantifying the Precipitation Loss of Radiation Belt Electrons during a
           Rapid Dropout Event
    • Authors: K. H. Pham; W. Tu, Z. Xiang
      Abstract: Relativistic electron flux in the radiation belt can drop by orders of magnitude within the timespan of hours. In this study, we used the drift-diffusion model that includes azimuthal drift and pitch angle diffusion of electrons to simulate low-altitude electron distribution observed by POES/MetOp satellites for rapid radiation belt electron dropout event occurring on May 1, 2013. The event shows fast dropout of MeV energy electrons at L>4 over a few hours, observed by the Van Allen Probes mission. By simulating the electron distributions observed by multiple POES satellites, we resolve the precipitation loss with both high spatial and temporal resolution and a range of energies. We estimate the pitch angle diffusion coefficients as a function of energy, pitch angle, and L-shell, and calculate corresponding electron lifetimes during the event. The simulation results show fast electron precipitation loss at L>4 during the electron dropout, with estimated electron lifetimes on the order of half an hour for MeV energies. The electron loss rate show strong energy dependence with faster loss at higher energies, which suggest that this dropout event is dominated by quick and localized scattering process that prefers higher energy electrons. The improved temporal and spatial resolution of electron precipitation rates provided by multiple low-altitude observations can resolve fast-varying electron loss during rapid electron dropouts (over a few hours), which occur too fast for a single low-altitude satellite. The capability of estimating the fast-varying electron lifetimes during rapid dropout events is an important step in improving radiation belt model accuracy.
      PubDate: 2017-10-03T17:16:12.571081-05:
      DOI: 10.1002/2017JA024519
       
  • Empirical Model of Precipitating Ion Oval
    • Authors: J. Goldstein
      Abstract: In this brief technical report published maps of ion integral flux are used to constrain an empirical model of the precipitating ion oval. The ion oval is modeled as a Gaussian function of ionospheric latitude that depends on local time and the Kp geomagnetic index. The three parameters defining this function are the centroid latitude, width, and amplitude. The local time dependences of these three parameters are approximated by Fourier series expansions whose coefficients are constrained by the published ion maps. The Kp dependence of each coefficient is modeled by a linear fit. Optimization of the number of terms in the expansion is achieved via minimization of the global standard deviation between the model and the published ion map at each Kp. The empirical model is valid near the peak flux of the auroral oval; inside its centroid region the model reproduces the published ion maps with standard deviations of less than 5% of the peak integral flux. On the subglobal scale, average local errors (measured as a fraction of the point-to-point integral flux) are below 30% in the centroid region. Outside its centroid region the model deviates significantly from the H89 integral flux maps. The model's performance is assessed by comparing it with both local and global data from a 17 April 2002 substorm event. The model can reproduce important features of the macroscale auroral region, but none of its subglobal structure, and not immediately following a substorm.
      PubDate: 2017-10-03T17:16:08.976858-05:
      DOI: 10.1002/2017JA024622
       
  • Structure and Properties of the Foreshock at Venus
    • Authors: N. Omidi; G. Collinson, D. Sibeck
      Abstract: The interaction of the solar wind with Venus is dominated by the planet's ionosphere which acts as an obstacle to the flow resulting in an induced magnetosphere and bow shock much smaller than their terrestrial counterparts. This study presents a 3-D electromagnetic hybrid (kinetic ions, fluid electrons) simulation of the solar wind interaction with an unmagnetized obstacle to examine the structure and properties of the Cytherean foreshock during periods of near radial IMF, i.e. when it lies upstream of the ionosphere. The interaction between the backstreaming ions and the solar wind results in the generation of two classes of ULF waves: (1) parallel propagating sinusoidal waves with periods ~20-30 seconds and (2) highly oblique fast magnetosonic waves. The joint nonlinear evolution of these waves result in the formation of structures called foreshock cavitons with dimensions comparable to the size of the planet. Foreshock cavitons are also present in the terrestrial foreshock. The excavation of plasma and magnetic field from their cores leads to lower average densities and magnetic field strengths in the foreshock. As in the case of Earth, this excavation results in the formation of a fast magnetosonic pulse/shock at the edge of the foreshock named the foreshock compressional boundary. Also similar to Earth, is the formation of spontaneous hot flow anomalies (SHFAs) as foreshock cavitons approach the bow shock. The size and properties of SHFAs at Venus are comparable to those at Earth and their existence has recently been established at Mars and Venus in a companion paper.
      PubDate: 2017-10-03T17:15:53.818966-05:
      DOI: 10.1002/2017JA024180
       
  • Magnetospheric ion evolution across the low-latitude boundary layer
           separatrix
    • Authors: S. K. Vines; S. A. Fuselier, K. J. Trattner, J. L. Burch, R. C. Allen, S. M. Petrinec, B. J. Anderson, J. M. Webster, R. E. Ergun, B. L. Giles, P.-A. Lindqvist, C. T. Russell
      Abstract: On 20 September 2015, the Magnetospheric Multiscale (MMS) spacecraft crossed the dusk magnetopause after a compression of the magnetosphere. Enhanced densities and fluxes of both colder (≤10 eV) and hotter (>1 keV) magnetospheric and magnetosheath heavy ion species were observed reaching the magnetopause. The evolution of the velocity distributions for H+, He+, and O+ measured by the Hot Plasma Composition Analyzer (HPCA) on MMS during this magnetopause crossing is presented. In particular, this study focuses on the changes in the species’ distribution functions as MMS passes from the magnetosphere through the electron edge of the low-latitude boundary layer (LLBL) separatrix and then into the LLBL. Two types of processes are suggested to play a role in the heating of colder magnetospheric ions across the LLBL separatrix in the region between the separatrix and the electron and ion edges of the LLBL. One mechanism leads to the formation and enhancement of ring distributions in this layer of the LLBL as the magnetospheric ions propagate across the separatrix. A second mechanism leading first to perpendicular heating and then to parallel heating of colder protons may arise from a possible two-stream instability as the magnetospheric ions first encounter the warmer magnetosheath electrons in the electron layer and then the warmer magnetosheath ions between the electron and ion edges of the LLBL separatrix. Perpendicular heating of He+ and O+ is seen more so in the main reconnection exhaust, due to non-adiabatic behavior of these ions as they are accelerated up to the bulk flow speed.
      PubDate: 2017-10-03T17:15:50.251083-05:
      DOI: 10.1002/2017JA024061
       
  • The Evolution of the Plasma Sheet Ion Composition: Storms and Recoveries
    • Authors: M. H. Denton; M. F. Thomsen, G. D. Reeves, B. A. Larsen, M. G. Henderson, V. K. Jordanova, P. A. Fernandes, R. H. W. Friedel, R. M. Skoug, H. O. Funsten, E. A. MacDonald, H. A. Spence
      Abstract: The ion plasma sheet (~few hundred eV to ~few 10s keV) is usually dominated by H+ ions. Here, changes in ion composition within the plasma sheet are explored both during individual events, and statistically during 54 calm-to-storm events and during 21 active-to-calm events. Ion composition data from the HOPE (Helium, Oxygen, Proton, Electron) instruments onboard Van Allen Probes satellites provide exceptional spatial and temporal resolution of the H+, O+, and He+ ion fluxes in the plasma sheet. H+ shown to be the dominant ion in the plasma sheet in the calm-to-storm transition. However, the energy-flux of each ion changes in a quasi-linear manner during extended calm intervals. Heavy ions (O+ and He+) become increasingly important during such periods as charge-exchange reactions result in faster loss for H+ than for O+ or He+. Results confirm previous investigations showing that the ion composition of the plasma sheet can be largely understood (and predicted) during calm intervals from knowledge of: (a) the composition of previously injected plasma at the onset of calm conditions, and (b) use of simple drift-physics models combined with calculations of charge-exchange losses.
      PubDate: 2017-10-03T17:15:45.259241-05:
      DOI: 10.1002/2017JA024475
       
  • Identifying ultra low frequency waves in the lunar plasma environment
           using trajectory analysis and resonance conditions
    • Authors: S. K. Howard; J. S. Halekas, W. M. Farrell, J. P. McFadden, K.-H. Glassmeier
      Abstract: Recent studies show that localized crustal magnetic fields on the lunar surface can reflect a significant portion of the incoming solar wind protons. These reflected ions can drive a wide range of plasma waves. It is difficult to determine the intrinsic properties of low frequency waves with single-spacecraft observations, which can be heavily Doppler-shifted. We describe a technique to combine trajectory analysis of reflected protons with the Doppler shift and resonance conditions to identify ultra low frequency waves at the Moon. On 31 January 2014 plasma waves were detected by one of the ARTEMIS probes as it approached the lunar wake; these waves were not detected by the second ARTEMIS probe located upstream in the undisturbed solar wind. The observed waves had a frequency below the local ion cyclotron frequency and had right-hand circular polarization in the reference frame of the Moon. By solving the Doppler shift and the cyclotron resonance equations we determined the conditions for reflected ions to excite the observed waves. Simulated trajectories of reflected ions correspond to ARTEMIS ion observations and support the hypothesis that reflected ions are the primary driver of the waves. By combining trajectory analysis with the resonance conditions, we identify scenarios where ions that satisfy the resonance conditions are present in the right location to generate the observed waves. Using this method we can uniquely identify the observed waves as upstream propagating right-hand polarized waves, subject to the assumption that they are generated by cyclotron resonance with ions.
      PubDate: 2017-10-03T10:07:56.819528-05:
      DOI: 10.1002/2017JA024018
       
  • Effect of intrinsic magnetic field decrease on the low- to middle-latitude
           upper atmosphere dynamics simulated by GAIA
    • Authors: Chihiro Tao; Hidekatsu Jin, Hiroyuki Shinagawa, Hitoshi Fujiwara, Yasunobu Miyoshi
      Abstract: The effects of decreasing the intrinsic magnetic field on the upper atmospheric dynamics at low to middle latitudes are investigated using the Ground-to-topside model of Atmosphere and Ionosphere for Aeronomy (GAIA). GAIA incorporates a meteorological reanalysis data set at low altitudes (
      PubDate: 2017-09-30T01:00:37.264439-05:
      DOI: 10.1002/2017JA024278
       
  • Diffusive transport of several hundred keV electrons in the Earth's slot
           region
    • Authors: Q. Ma; W. Li, R. M. Thorne, J. Bortnik, G. D. Reeves, H. E. Spence, D. L. Turner, J. B. Blake, J. F. Fennell, S. G. Claudepierre, C. A. Kletzing, W. S. Kurth, G. B. Hospodarsky, D. N. Baker
      Abstract: We investigate the gradual diffusion of energetic electrons from the inner edge of the outer radiation belt into the slot region. The Van Allen Probes observed slow inward diffusion and decay of ~200-600 keV electrons following the intense geomagnetic storm that occurred on 17 March 2013. During the 10-day non-disturbed period following the storm, the peak of electron fluxes gradually moved from L~2.7 to L~2.4, and the flux levels decreased by a factor of ~2-4 depending on the electron energy. We simulated the radial intrusion and decay of electrons using a 3-dimentional diffusion code, which reproduced the energy-dependent transport of electrons from ~100 keV to 1 MeV in the slot region. At energies of 100-200 keV, the electrons experience fast transport across the slot region due to the dominance of radial diffusion; at energies of 200-600 keV, the electrons gradually diffuse and decay in the slot region due to the comparable rate of radial diffusion and pitch angle scattering by plasmaspheric hiss; at energies of E> 700 keV, the electrons stopped diffusing near the inner edge of outer radiation belt due to the dominant pitch angle scattering loss. In addition to plasmaspheric hiss, magnetosonic waves and VLF transmitters can cause the loss of high pitch angle electrons, relaxing the sharp ‘top-hat' shaped pitch angle distributions created by plasmaspheric hiss. Our simulation indicates the importance of balance between radial diffusion and loss through pitch angle scattering in forming the diffusive intrusion of energetic electrons across the slot region.
      PubDate: 2017-09-29T18:55:55.297351-05:
      DOI: 10.1002/2017JA024452
       
  • Gravity wave-induced ionospheric irregularities in the postsunset
           equatorial valley region
    • Authors: D. L. Hysell; D. C. Fritts, B. Laughman, J. L. Chau
      Abstract: Plasma irregularities in the postsunset equatorial valley region ionosphere are investigated experimentally and through numerical simulation. Coherent radar backscatter observed at the Jicamarca Radio Observatory shows two classes of irregularities in different altitude bands – one mainly below about 125 km and the other mainly above. Irregularities in both bands are organized into wavefronts with wavelengths of a few km. However, only the irregularities in the high-altitude band exhibit consistent propagation speeds and directions. Some previous observations of irregularities in the nighttime electrojet suggest that gravity waves may sometimes influence their morphology. The possibility that the valley-region irregularities are also related to gravity waves (GWs) is therefore investigated numerically. A model of a GW packet propagating through a tidal wind field is used to drive another model which predicts the resulting ionospheric electrodynamics. The combined simulation shows that GWs can induce field-aligned currrents and excite resistive drift waves which could be responsible for the valley-region irregularities in the high-altitude band. The GWs also induce irregularities in the upper E region directly through simple dynamo action which subsequently deform under the influence of shear flow. This may explain the irregularities in the low-altitude band.
      PubDate: 2017-09-29T18:55:53.270649-05:
      DOI: 10.1002/2017JA024514
       
  • Seasonal variation of high-latitude geomagnetic activity in individual
           years
    • Authors: E. I. Tanskanen; R. Hynönen, K. Mursula
      Abstract: We study the seasonal variation of high-latitude geomagnetic activity in individual years in 1966 – 2014 (solar cycles 20 – 24) by identifying the most active and the second most active season based on westward electrojet indices AL (1966 - 2014) and IL (1995 - 2014). The annual maximum is found at either equinox in 2/3 and at either solstice in 1/3 of the years examined. The traditional two-equinox maximum pattern is found in roughly one fourth of the years. We found that the seasonal variation of high-latitude geomagnetic activity closely follows the solar wind speed. While the mechanisms leading to the two-equinox maxima pattern are in operation, the long-term change of solar wind speed tends to mask the effect of these mechanisms for individual years. Large cycle-to-cycle variation is found in the seasonal pattern: equinox maxima are more common during cycles 21 and 22 than in cycles 23 or 24. Exceptionally long winter dominance in high-latitude activity and solar wind speed is seen in the declining phase of cycle 23, after the appearance of the long-lasting low-latitude coronal hole.
      PubDate: 2017-09-29T18:55:33.135646-05:
      DOI: 10.1002/2017JA024276
       
  • Estimates of Ionospheric Transport and Ion Loss at Mars
    • Authors: T. E. Cravens; O. Hamil, S. Houston, S. Bougher, Y. Ma, D. Brain, S. Ledvina
      Abstract: Ion loss from the topside ionosphere of Mars associated with the solar wind interaction makes an important contribution to the loss of volatiles from this planet. Data from NASA's Mars Atmosphere and Volatile Evolution (MAVEN) mission combined with theoretical modeling are now helping us to understand the processes involved in the ion loss process. Given the complexity of the solar wind interaction, motivation exists for considering a simple approach to this problem and for understanding how the loss rates might scale with solar wind conditions and solar extreme ultraviolet irradiance. This paper reviews the processes involved in the ionospheric dynamics. Simple analytical and semi-empirical expressions for ion flow speeds and ion loss are derived. In agreement with more sophisticated models and with purely empirical studies, it is found that the oxygen loss rate from ion transport is about 5% (i.e., global O ion loss rate of Qion ≈ 4 x 1024 s-1) of the total oxygen loss rate. The ion loss is found to approximately scale as the square root of the solar ionizing photon flux and also as the square root of the solar wind dynamic pressure. Typical ion flow speeds are found to be about 1 km/s in the topside ionosphere near an altitude of 300 km on the dayside. Not surprisingly, the plasma flow speed is found to increase with altitude due to the decreasing ion-neutral collision frequency.
      PubDate: 2017-09-29T18:55:31.292446-05:
      DOI: 10.1002/2017JA024582
       
  • Swarm observation of field-aligned currents associated with multiple
           auroral arc systems
    • Authors: J. Wu; D. J. Knudsen, D. M. Gillies, E. Donovan, J. K. Burchill
      Abstract: Auroral arcs occur in regions of upward field-aligned currents (FACs), however the relation is not one-to-one, since kinetic energy of the current-carrying electrons is also important in the production of auroral luminosity. Multiple auroral arc systems provide an opportunity to study the relation between FACs and auroral brightness in detail. In this study, we have identified two types of FAC configurations in multiple parallel arc systems using ground-based optical data from the THEMIS all-sky imagers (ASIs), magnetometers and electric field instruments onboard the Swarm satellites. In “unipolar FAC" events, each arc is an intensification within a broad, unipolar current sheet and downward return currents occur outside of this broad sheet. In “multipolar FAC" events, multiple arc systems represent a collection of multiple up/down current pairs. By collecting 17 events with unipolar FAC and 12 events with multipolar FACs, we find that (1) Unipolar FAC events occur most frequently between 20-21 MLT and multipolar FAC events tend to occur around local midnight and within 1 hour after substorm onset. (2) Arcs in unipolar FAC systems have a typical width of 10-20 km and a spacing of 25-50 km. Arcs in multipolar FAC systems are wider and more separated. (3) Upward currents with more arcs embedded have larger intensities and widths. (4) Electric fields are strong and highly structured on the edges of multiple arc system with unipolar FAC. The fact that arcs with unipolar FAC are much more highly structured than the associated currents suggests that arc multiplicity is indicative not of a structured generator deep in the magnetosphere, but rather of the magnetosphere-ionosphere coupling process.
      PubDate: 2017-09-29T18:55:29.064517-05:
      DOI: 10.1002/2017JA024439
       
  • Pulsations in the Earth's Lower Ionosphere Synchronized with Solar Flare
           Emission
    • Authors: Laura A. Hayes; Peter T. Gallagher, Joseph McCauley, Brian R. Dennis, Jack Ireland, Andrew Inglis
      Abstract: Solar flare emission at X-ray and extreme ultraviolet (EUV) energies can cause substantial enhancements in the electron density in the Earth's lower ionosphere. It has now become clear that flares exhibit quasi-periodic pulsations with timescales of minutes at X-ray energies, but to date, it has not been known if the ionosphere is sensitive to this variability. Here, using a combination of Very Low Frequency (24 kHz) measurement together with space-based X-ray and EUV observations, we report pulsations of the ionospheric D-region, which are synchronized with a set of pulsating flare loops. Modeling of the ionosphere show that the D-region electron density varies by up to an order of magnitude over the timescale of the pulsations (∼ 20 mins). Our results reveal that the Earth's ionosphere is more sensitive to small-scale changes in solar soft X-ray flux than previously thought, and implies that planetary ionospheres are closely coupled to small-scale changes in solar/stellar activity.
      PubDate: 2017-09-29T18:55:27.154372-05:
      DOI: 10.1002/2017JA024647
       
  • Whistler-mode waves below LHR frequency - generation and spectral features
    • Authors: D. R. Shklyar; M. A. Balikhin
      Abstract: Equatorial noise in the frequency range below the lower hybrid resonance frequency, whose structure is shaped by high proton cyclotron harmonics, has been observed by the Cluster spacecraft. We develop a model of this wave phenomenon which assumes (as, in general, has been suggested long ago) that the observed spectrum is excited due to loss-cone instability of energetic ions in the equatorial region of the magnetosphere. The wave field is represented as a sum of constant frequency wave packets which cross a number of cyclotron resonances while propagating in a highly oblique mode along quite specific trajectories. The growth (damping) rate of these wave packets varies both in sign and magnitude along the ray path, making the wave net amplification, but not the growth rate, the main characteristic of the wave generation process. The growth rates and the wave amplitudes along the ray paths, determined by the equations of geometrical optics, have been calculated for a 3D set of wave packets with various frequencies, initial L-shells, and initial wave normal angles at the equator. It is shown that the dynamical spectrum resulting from the proposed model qualitatively matches observations.
      PubDate: 2017-09-29T18:55:22.536356-05:
      DOI: 10.1002/2017JA024416
       
  • The characteristic response of whistler mode waves to interplanetary
           shocks
    • Authors: Chao Yue; Lunjin Chen, Jacob Bortnik, Qianli Ma, Richard M. Thorne, Vassilis Angelopoulos, Jinxing Li, Xin An, Chen Zhou, Craig Kletzing, Geoffrey D. Reeves, Harlan E. Spence
      Abstract: Magnetospheric whistler mode waves play a key role in regulating the dynamics of the electron radiation belts. Recent satellite observations indicate a significant influence of interplanetary (IP) shocks on whistler mode wave power in the inner magnetosphere. In this study, we statistically investigate the response of whistler mode chorus and plasmaspheric hiss to IP shocks based on Van Allen Probes and THEMIS satellite observations. Immediately after the IP shock arrival, chorus wave power is usually intensified, often at post-midnight to pre-noon sector, while plasmaspheric hiss wave power predominantly decreases near the dayside but intensifies near the nightside. We conclude that chorus wave intensification outside the plasmasphere is probably associated with the suprathermal electron flux enhancement caused by the IP shock. Through a simple ray tracing modeling assuming the scenario that plasmaspheric hiss is originated from chorus, we find that the solar wind dynamic pressure increase changes the magnetic field configuration to favor ray penetration in the nightside and promote ray refraction away from the dayside, potentially explaining the magnetic local time (MLT) dependent responses of plasmaspheric hiss waves following IP shock arrivals.
      PubDate: 2017-09-29T18:55:20.345838-05:
      DOI: 10.1002/2017JA024574
       
  • Thermosphere global time response to geomagnetic storms caused by coronal
           mass ejections
    • Authors: D. M. Oliveira; E. Zesta, P. W. Schuck, E. K. Sutton
      Abstract: We investigate, for the first time with a spatial superposed epoch analysis study, the thermosphere global time response to 159 geomagnetic storms caused by CMEs observed in the solar wind at Earth's orbit during the period of September 2001 to September 2011. The thermosphere neutral mass density is obtained from the CHAMP and GRACE spacecraft. All density measurements are inter-calibrated against densities computed by the Jacchia-Bowman 2008 empirical model under the regime of very low geomagnetic activity. We explore both the effects of the pre-CME shock impact on the thermosphere and of the storm main phase onset by taking their times of occurrence as zero epoch times (CME impact and IMF Bz southward turning) for each storm. We find that the shock impact produces quick and transient responses at the two high latitude regions with minimal propagation toward lower latitudes. In both cases, thermosphere is heated in very high latitude regions within several minutes. The Bz southward turning of the storm onset has a fast heating manifestation at the two high latitude regions and it takes approximately 3 hours for that heating to propagate down to equatorial latitudes and to globalize in the thermosphere. This heating propagation is presumably accomplished, at least in part, with traveling atmospheric disturbances (TADs) and complex meridional wind structures. Current models use longer lag times in computing thermosphere density dynamics during storms. Our results suggest that the thermosphere response time scales are shorter, and should be accordingly adjusted in thermospheric empirical models.
      PubDate: 2017-09-28T17:42:10.363657-05:
      DOI: 10.1002/2017JA024006
       
  • Simultaneous measurements of substorm-related electron energization in the
           ionosphere and the plasma sheet
    • Authors: N. Sivadas; J. Semeter, Y. Nishimura, A. Kero
      Abstract: On 26 March 2008, simultaneous measurements of a large substorm were made using the Poker Flat Incoherent Scatter Radar, THEMIS spacecraft and all sky cameras. After the onset, electron precipitation reached energies ≳100 keV leading to intense D-region ionization. Identifying the source of energetic precipitation has been a challenge due to lack of quantitative and magnetically conjugate measurements of loss-cone electrons. In this study, we use the maximum entropy inversion technique to invert altitude profiles of ionization measured by the radar to estimate the loss-cone energy spectra of primary electrons. By comparing them with magnetically conjugate measurements from THEMIS-D spacecraft in the night-side plasma sheet, we constrain the source location and acceleration mechanism of precipitating electrons of different energy ranges. Our analysis suggests that the observed electrons ≳100 keV are a result of pitch angle scattering of electrons originating from or tailward of the inner plasma sheet at ~9 RE, possibly through interaction with Electromagnetic Ion Cyclotron waves. The electrons of energy 10-100 keV are produced by pitch angle scattering due to a potential drop of ≲10 kV in the Auroral Acceleration Region (AAR) as well as wave-particle interactions in and tailward of the AAR. This work demonstrates the utility of magnetically conjugate ground- and space-based measurements in constraining the source of energetic electron precipitation. Unlike in-situ spacecraft measurements, ground-based incoherent scatter radars combined with an appropriate inversion technique can be used to provide remote and continuous-time estimates of loss-cone electrons in the plasma sheet.
      PubDate: 2017-09-28T09:07:45.872556-05:
      DOI: 10.1002/2017JA023995
       
  • Interesting equatorial plasma bubbles observed by all-sky imagers in the
           equatorial region of China
    • Authors: Kun Wu; Jiyao Xu, Wenbin Wang, Longchang Sun, Xiao Liu, Wei Yuan
      Abstract: This paper reports some interesting equatorial plasma bubbles (EPBs) on 04-05 October 2013 and 29-30 September 2013 observed by two all-sky imagers located in the magnetically equatorial region of Hainan (19.5°N; 9.5° geomagnetic latitude) and Guiping (23.8°N; 13.9° geomagnetic latitude), China. The case of 04-05 October 2013 shows that: 1. EPBs had planar wave-like structures and their wavefronts were parallel to each other before midnight. 2. The angle between the wavefronts of those EPBs and the geomagnetic meridian were ~30°. 3. Near midnight, the higher latitude part of one EPB suddenly began to rotate with a large eastward zonal drift, resulting in an unusual C-shaped EPB that was observed for the first time by an all-sky imager. 4. After midnight, one EPB merged into another EPB and formed an integrated EPB. The other EPB case on 29-30 Sept. 2013 shows that: 1. The images captured the full evolution processes of an ‘I’ shaped EPB with an angle of ~30° with respect to the geomagnetic meridian. The imagers also observed ‘S’ and ‘Y’ shaped EPBs. 2. The change of EPBs’ shape was directly related to the change of EPBs’ zonal drift velocities. 3. The angle between the ‘I’ shaped EPBs and the geomagnetic meridian was likely caused by the change of the latitudinal gradient of zonal neutral wind velocities and ionospheric conductivity. 4. The zonal velocity of each branch of the ‘Y’ shape EPB was different, which could be related to the polarization electric fields within each branch.
      PubDate: 2017-09-27T16:00:27.382158-05:
      DOI: 10.1002/2017JA024561
       
  • The modulation of the quasi-two day wave on Total Electron Content as
           revealed by BeiDou GEO and meteor radar observations over central China
    • Authors: Sheng-Yang Gu; Jiuhou Lei, Xiankang Dou, Xianghui Xue, Fuqing Huang, Mingjiao Jia
      Abstract: The ground-based Total Electron Content (TEC) observations from BeiDou Geostationary Orbit (GEO) satellites provide more accurate temporal ionospheric variations nearly at the fixed ionospheric pierce points as compared with the non-GEO TEC. BeiDou GEO TEC measurements during 2016, along with the horizontal wind observations from a collocated meteor radar, are utilized to quantitatively study the ionospheric response to the quasi-two day wave (QTDW) in the neutral atmosphere at MengCheng (116.6°E, 33.3°N) over central China. The QTDW peaks during July with amplitudes of ~25-30 m/s for both zonal and meridional winds. It is suggested that the nonlinear interactions between the QTDW and tides and their influences on TEC are insignificant for this QTDW event. Nevertheless, the diurnal tide decreases by ~40-60% during the QTDW episode, which is most likely related to the change of background wind induced by the QTDW. Correspondingly, the 24-hour oscillations in TEC decrease by ~18%. In addition, the wind perturbations of the QTDW can also possibly modulate the mid-latitude electric dynamo and result in a quasi-two-day oscillation (QTDO) of ~1.2 TECU, about ~10% of the background TEC. Our analysis also shows that the background TEC decreases by ~1 TECU (~8%) when the QTDW reaches maximum amplitude. This is probably related to the thermospheric composition changes (e.g., O and N2) induced by the QTDW dissipation.
      PubDate: 2017-09-27T16:00:23.823125-05:
      DOI: 10.1002/2017JA024349
       
  • Energetic proton spectra measured by the Van Allen Probes
    • Authors: Danny Summers; Run Shi, Mark J. Engebretson, Kjellmar Oksavik, Jerry W. Manweiler, Donald G. Mitchell
      Abstract: We test the hypothesis that pitch-angle scattering by electromagnetic ion cyclotron (EMIC) waves can limit ring current proton fluxes. For two chosen magnetic storms, during March 17-20, 2013 and March 17-20, 2015, we measure proton energy spectra in the region 3 ≤ L ≤ 6 using the RBSPICE B instrument on the Van Allen Probes. The most intense proton spectra are observed to occur during the recovery periods of the respective storms. Using proton precipitation data from the POES (NOAA and MetOp) spacecraft, we deduce that EMIC wave action was prevalent at the times and L-shell locations of the most intense proton spectra. We calculate limiting ring current proton energy spectra from recently developed theory. Comparisons between the observed proton energy spectra and the theoretical limiting spectra show reasonable agreement. We conclude that the measurements of the most intense proton spectra are consistent with self-limiting by EMIC wave scattering.
      PubDate: 2017-09-26T18:15:52.905559-05:
      DOI: 10.1002/2017JA024484
       
  • Ion-Scale Wave Properties and Enhanced Ion Heating across the Low-Latitude
           Boundary Layer during Kelvin-Helmholtz Instability
    • Authors: T. W. Moore; K. Nykyri, A. P. Dimmock
      Abstract: In the Earth's magnetosphere, the magnetotail plasma sheet ions are much hotter than in the shocked solar wind. On the dawn-sector, the cold-component ions are more abundant and hotter by 30-40 percent when compared to the dusk sector. Recent statistical studies of the flank magnetopause and magnetosheath have shown that the level of temperature asymmetry of the magnetosheath is unable to account for this, so additional physical mechanisms must be at play, either at the magnetopause or plasma sheet that contribute to this asymmetry. In this study, we perform a statistical analysis on the ion-scale wave properties in the three main plasma regimes common to flank magnetopause boundary crossings when the boundary is unstable to KHI: hot and tenuous magnetospheric, cold and dense magnetosheath and mixed [Hasegawa et al., 2004]. These statistics of ion-scale wave properties are compared to observations of fast magnetosonic wave modes that have recently been linked to Kelvin-Helmholtz (KH) vortex centered ion heating [Moore et al., 2016]. The statistical analysis shows that during KH events there is enhanced non-adiabatic heating calculated during ion scale wave intervals when compared to non-KH events. This suggests that during KH events there is more free energy for ion-scale wave generation, which in turn can heat ions more effectively when compared to cases when KH waves are absent. This may contribute to the dawn favored temperature asymmetry of the plasma sheet, recent studies suggest KH waves favor the dawn flank during Parker-Spiral (PS) interplanetary magnetic field (IMF).
      PubDate: 2017-09-26T18:15:48.64994-05:0
      DOI: 10.1002/2017JA024591
       
  • High Latitude Neutral Mass Density Maxima
    • Authors: C. Y. Huang; Y. Huang, Y.-J. Su, T. Huang, E. K. Sutton
      Abstract: Recent studies have reported that thermospheric effects due to solar wind driving can be observed poleward of auroral latitudes. In these papers, the measured neutral mass density perturbations appear as narrow, localized maxima in the cusp and polar cap. They conclude that Joule heating below the spacecraft is the cause of the mass density increases which are sometimes associated with local field-aligned current structures, but not always.In this paper we investigate neutral mass densities measured by accelerometers on the CHAllenging Minisatellite Payload (CHAMP) and Gravity Recovery and Climate Experiment (GRACE) spacecraft from launch until years 2010 (CHAMP) and 2012 (GRACE), approximately 10 years of observations from each satellite. We extract local maxima in neutral mass densities over the background using a smoothing window with size of one quarter of the orbit. The maxima have been analyzed for each year, and also for the duration of each set of satellite observations. We show where they occur, under what solar wind conditions, and their relation to magnetic activity. The region with the highest frequency of occurrence coincides approximately with the cusp and mantle, with little direct evidence of an auroral zone source. Our conclusions agree with the “hot polar cap” observations which have been reported and studied in the past.
      PubDate: 2017-09-26T18:15:45.17038-05:0
      DOI: 10.1002/2017JA024334
       
  • Modeling Particle Acceleration and Transport at a 2D CME-Driven Shock
    • Authors: Junxiang Hu; Gang Li, Xianzhi Ao, Gary P. Zank, Olga Verkhoglyadova
      Abstract: We extend our earlier Particle Acceleration and Transport in the Heliosphere (PATH) model to study particle acceleration and transport at a CME-driven shock. We model the propagation of a CME-driven shock in the ecliptic plane using the ZEUS-3D code from 20 solar radii to 2 AU. As in the previous PATH model, the initiation of the CME-driven shock is simplified and modelled as a disturbance at the inner boundary. Different from the earlier PATH model, the disturbance is now longitudinally dependent. Particles are accelerated at the 2D shock via the diffusive shock acceleration (DSA) mechanism. The acceleration depends on both the parallel and perpendicular diffusion coefficients κ and κ⊥ and is therefore shock-obliquity dependent. Following the procedure used in Li et al. [2012a], we obtain the particle injection energy, the maximum energy and the accelerated particle spectra at the shock front. Once accelerated, particles diffuse and convect in the shock complex. The diffusion and convection of these particles are treated using a refined 2-D shell model in an approach similar to Zank et al. [2000], When particles escape from the shock, they propagate along and across the interplanetary magnetic field (IMF). The propagation is modelled using a focused transport equation with the addition of perpendicular diffusion. We solve the transport equation using a backward stochastic differential equation method where adiabatic cooling, focusing, pitch angle scattering, and cross field diffusion effects are all included. Time intensity profiles and instantaneous particle spectra as well as particle pitch angle distributions are shown for two example CME shocks.
      PubDate: 2017-09-26T18:15:42.018997-05:
      DOI: 10.1002/2017JA024077
       
  • Ion heating in the Martian ionosphere
    • Authors: C. M. Fowler; R. E. Ergun, L. Andersson, W. K. Peterson, T. Hara, J. McFadden, J. Espley, J. Halekas, D. L. Mitchell, C. Mazelle, B. M. Jakosky
      Abstract: Energetic O+ and O2+ ions with energies of up to a few hundred eV are observed in the Martian ionosphere. Corresponding ion velocity distributions show ion conics, suggesting that the observed ion populations have been heated perpendicular to the local magnetic field before experiencing a magnetic mirror force. Magnetic field observations support these interpretations: wave power at the local O+ and O2+ gyrofrequencies in the spacecraft frame is observed coincident with the energetic ions, within an apparent magnetic field bottle-like topology.Analysis of the observed ion conics leads to estimates of ion temperatures of 10-30 eV. We suggest that the ion populations are initially heated perpendicular to the local magnetic field by wave power propagating inward from the Mars-solar wind interaction. The local magnetic field “balloons out” in response to these enhanced ion temperatures and pressures. The resultant magnetic field topology is bottle-like; the transversely heated ions would subsequently experience a magnetic mirror force in the converging field regions, agreeing with the reported observations.Such strong heating events that significantly increase the ion temperature and pressure, thereby decreasing the net magnetic field, are rare and seem to occur under specific interplanetary magnetic field orientations. Events were observed to span the upper exobase region and just above, a region characterized by significant ion densities in an increasingly collisionless domain. Ion heating in this region has the potential to drive significant ion outflows, thus contributing to atmospheric loss from the planet.
      PubDate: 2017-09-26T18:15:37.728303-05:
      DOI: 10.1002/2017JA024578
       
  • A numerical investigation on tidal and gravity wave contributions to the
           summer time Na variations in the mid-latitude E region
    • Authors: Xuguang Cai; Tao Yuan, J. Vincent Eccles
      Abstract: The Na density variations in the E region have been studied over the past few decades. Although considerable progress in understanding and in modeling the metal layer observations has been made, Na density features above 100 km have yet to be explained. Various studies have linked them to the Na+ variations, a major reservoir for Na in E region. But the lack of comprehensive modeling investigations and of wind and temperature observations prevents further understanding on this important ion-neutral coupling topic. In this study, we conduct a numerical simulation on the summer time Na density behavior in the mid-latitude E region, where both the ion density and the neutral atmosphere are modulated by tidal and gravity waves. Simulation results show good agreement with Na lidar measurements and reveal that atmospheric waves can transport Na upward to generate Na layers and variations in E region considerably. The vertical wind component of the large amplitude tidal wave can extend the Na layer above 120 km into the thermosphere. The simulation also demonstrates that the modulation of large amplitude gravity (GW) wave can generate small scale sporadic Na layers (Nas) in the E region. Finally, eddy diffusion enhancement in the GW saturation process can significantly alter the Nas spatial and temporal structures.
      PubDate: 2017-09-26T18:15:32.615476-05:
      DOI: 10.1002/2016JA023764
       
  • Multipoint observations of energetic particle injections and substorm
           activity during a conjunction between Magnetospheric Multiscale (MMS) and
           Van Allen Probes
    • Authors: D. L. Turner; J. F. Fennell, J. B. Blake, S. G. Claudepierre, J. H. Clemmons, A. N. Jaynes, T. Leonard, D. N. Baker, I. J. Cohen, M. Gkioulidou, A. Y. Ukhorskiy, B. H. Mauk, C. Gabrielse, V. Angelopoulos, R. J. Strangeway, C. A. Kletzing, O. Le Contel, H. E. Spence, R. B. Torbert, J. L. Burch, G. D. Reeves
      Abstract: This study examines multipoint observations during a conjunction between MMS and Van Allen Probes on 07 April 2016 in which a series of energetic particle injections occurred. With complementary data from THEMIS, Geotail, and LANL-GEO (16 spacecraft in total), we develop new insights on the nature of energetic particle injections associated with substorm activity. Despite this case involving only weak substorm activity (max. AE < 300 nT) during quiet geomagnetic conditions in steady, below-average solar wind, a complex series of at least six different electron injections was observed throughout the system. Intriguingly, only one corresponding ion injection was clearly observed. All ion and electron injections were observed at < 600 keV only. MMS reveals detailed substructure within the largest electron injection. A relationship between injected electrons with energy < 60 keV and enhanced whistler-mode chorus wave activity is also established from Van Allen Probes and MMS. Drift mapping using a simplified magnetic field model provides estimates of the dispersionless injection boundary locations as a function of universal time, magnetic local time, and L-shell. The analysis reveals that at least five electron injections, which were localized in magnetic local time, preceded a larger injection of both electrons and ions across nearly the entire nightside of the magnetosphere near geosynchronous orbit. The larger, ion and electron injection did not penetrate to L < 6.6, but several of the smaller, electron injections penetrated to L < 6.6. Due to the discrepancy between the number, penetration depth, and complexity of electron vs. ion injections, this event presents challenges to the current conceptual models of energetic particle injections.
      PubDate: 2017-09-25T21:35:28.940644-05:
      DOI: 10.1002/2017JA024554
       
  • Influence of velocity fluctuations on the Kelvin-Helmholtz instability and
           its associated mass transport
    • Authors: Katariina Nykyri; Xuanye Ma, Andrew Dimmock, Claire Foullon, Antonius Otto, Adnane Osmane
      Abstract: Kelvin-Helmholtz instability (KHI) and associated magnetic reconnection and diffusion processes provide plasma transport from solar wind into the magnetosphere. The efficiency of this transport depends on the magnetosheath and magnetospheric plasma and field properties at the vicinity of the magnetopause. Our recent statistical study using data from the Time History of Events and Macroscale Interactions during Substorms spacecraft indicates that the amplitude of the magnetosheath velocity fluctuations perpendicular to the magnetopause can be substantial. We have performed a series of local macroscale 2.5-dimensional magnetohydrodynamic simulations of the KHI during strongly northward interplanetary magnetic field and with the initial plasma parameters typical to the dayside magnetopause by perturbing the initial equilibrium with time-dependent perpendicular velocity field fluctuations. The effect of the single-mode and multimode seed spectrums at different frequencies and amplitudes is studied. The plasma transport in Kelvin-Helmholtz vortices is quantified. The results show that when large-amplitude, low-frequency seed velocity fluctuations exist in the magnetosheath, the resulting KH waves grow faster, get larger in size, and can transport more plasma through magnetic boundary, resulting in diffusion coefficient of the order 109 m2/s. The relevance of these findings to the solar wind-magnetosphere coupling is discussed.
      PubDate: 2017-09-23T07:51:47.060271-05:
      DOI: 10.1002/2017JA024374
       
  • Ultra-low Frequency Waves Deep inside the Inner Magnetosphere Driven by
           Dipolarizing Flux Bundles
    • Authors: Jiang Liu; V. Angelopoulos, X. -J. Zhang, A. Runov, A. Artemyev, F. Plaschke, Song Fu, San Lu, Yi-Hsin Liu, Xiangning Chu
      Abstract: Dipolarizing flux bundles (DFBs) are small flux tubes (typical cross-tail scale of 1−3 RE) in the nightside magnetosphere that have magnetic field more dipolar than the background. They are generated at or beyond 20 RE downtail and then travel earthward. Although DFBs usually stop before reaching the geosynchronous orbit (GEO), they may still transfer some portion of their energy into the inner magnetosphere by radiating ULF waves. We show the clearest evidence of this process, to date, using in-situ data from a fleet of spacecraft and ground stations. We illustrate that a typical DFB stopped before reaching GEO but excited Pi2 waves which filled a volume of space extending from the plasma sheet to deep inside the plasmasphere. This event provides the first in-situ, direct link between stopped DFBs and ULF waves deep inside the inner magnetosphere (as deep as L=3). The waves were attenuated when travelling away from the DFB, but even at L=3 (XGSM=−2.2), they were still travelling with a significant earthward Poynting flux. In addition, we observed evidence of interaction between these waves and electrons at GEO.
      PubDate: 2017-09-21T20:08:20.515639-05:
      DOI: 10.1002/2017JA024270
       
  • Mercury's solar wind interaction as characterized by magnetospheric plasma
           mantle observations with MESSENGER
    • Authors: Jamie M. Jasinski; James A. Slavin, Jim M. Raines, Gina A. DiBraccio
      Abstract: We analyze 94 traversals of Mercury's southern magnetospheric plasma mantle using data from the MESSENGER spacecraft. The mean and median proton number density in the mantle are 1.5 and 1.3 cm-3, respectively. For sodium number density these values are 0.004 and 0.002 cm-3. Moderately higher densities are observed on the magnetospheric dusk side. The mantle supplies up to 1.5x108 cm-2 s-1 and 0.8 x 108cm-2 s-1 of proton and sodium flux to the plasma sheet, respectively. We estimate the cross-electric magnetospheric potential from each observation and find a mean of ~19 kV (standard deviation of 16 kV) and a median of ~13 kV. This is an important result as it is lower than previous estimations and shows that Mercury's magnetosphere is at times not as highly driven by the solar wind as previously thought. Our values are comparable to the estimations for the ice giant planets, Uranus and Neptune, but lower than Earth. The estimated potentials do have a very large range of values (1 – 74 kV), showing that Mercury's magnetosphere is highly dynamic. A correlation of the potential is found to the interplanetary magnetic field (IMF) magnitude, supporting evidence that dayside magnetic reconnection can occur at all shear angles at Mercury. But we also see that Mercury has an Earth-like magnetospheric response, favoring –BZ IMF orientation. We find evidence that –BX orientations in the IMF favor the southern cusp and southern mantle. This is in agreement with telescopic observations of exospheric emission, but in disagreement with modeling.
      PubDate: 2017-09-21T20:08:16.945064-05:
      DOI: 10.1002/2017JA024594
       
  • Solar wind plasma parameter variability across solar cycles 23 and 24:
           from turbulence to extremes
    • Authors: E. Tindale; S. C. Chapman
      Abstract: Solar wind variability spans a wide range of amplitudes and timescales, from turbulent fluctuations to the 11 year solar cycle. We apply the data quantile-quantile (DQQ) method to NASA/Wind observations spanning solar cycles 23 and 24, to study how the uniqueness of each cycle maximum and minimum manifests in the changing statistical distribution of plasma parameters in fast and slow solar wind. The DQQ method allows us to discriminate between two distinct components of the distribution: the core region simply tracks the solar cycle in its moments, but shows little sensitivity to solar wind state or the specific activity of each cycle. This would be consistent with an underlying in-situ process such as turbulence driving the evolution of fluctuations up to an outer scale. In contrast, the tail component of the distribution is sensitive both to the differences between the maxima and minima of cycles 23 and 24, and the fast or slow state of the solar wind. The tail component varies over the solar cycle in such a way as to maintain a constant functional form, with only its moments varying with solar activity. Finally, after isolating the core region of the distribution, we test its lognormality over the solar cycle in each solar wind state, and find the lognormal provides a more robust description of the statistics in slow wind than fast, however in both states the goodness of fit is significantly reduced at solar maximum.
      PubDate: 2017-09-21T20:08:06.842117-05:
      DOI: 10.1002/2017JA024412
       
  • Time-Integral Correlations of Multiple Variables with the
           Relativistic-Electron Flux at Geosynchronous Orbit: The Strong Roles of
           Substorm-Injected Electrons and the Ion Plasma Sheet
    • Authors: Joseph E. Borovsky
      Abstract: Time-integral correlations are examined between the geosynchronous relativistic-electron flux index Fe1.2 and 31 variables of the solar wind and magnetosphere. An “evolutionary algorithm” is used to maximize correlations. Time integrations (into the past) of the variables are found to be superior to time-lagged variables for maximizing correlations with the radiation belt. Physical arguments are given as to why. Dominant correlations are found for the substorm-injected electron flux at geosynchronous orbit and for the pressure of the ion plasma sheet. Different sets of variables are constructed and correlated with Fe1.2: some sets maximize the correlations, some sets are based on purely solar-wind variables. Examining known physical mechanisms that act on the radiation belt, sets of correlations are constructed (1) using magnetospheric variables that control those physical mechanisms and (2) using the solar-wind variables that control those magnetospheric variables. Fe1.2-increasing intervals are correlated separately from Fe1.2-decreasing intervals and the introduction of autoregression into the time-integral correlations is explored. A great impediment to discerning physical cause and effect from the correlations is the fact that all solar-wind variables are intercorrelated and carry much of the same information about the time sequence of the solar wind that drives the time sequence of the magnetosphere.
      PubDate: 2017-09-21T20:05:30.517528-05:
      DOI: 10.1002/2017JA024476
       
  • Cold ionospheric ions in the magnetic reconnection outflow region
    • Authors: W. Y. Li; M. André, Yu. V. Khotyaintsev, A. Vaivads, S. A. Fuselier, D. B. Graham, S. Toledo-Redondo, B. Lavraud, D. L. Turner, C. Norgren, B. B. Tang, C. Wang, P.-A. Lindqvist, D. T. Young, M. Chandler, B. Giles, C. Pollock, R. Ergun, C. T. Russell, R. Torbert, T. Moore, J. Burch
      Abstract: Magnetosheath plasma usually determines properties of asymmetric magnetic reconnection at the subsolar region of Earth's magnetopause. However, cold plasma that originated from the ionosphere can also reach the magnetopause, and modify the kinetic physics of asymmetric reconnection. We present a magnetopause crossing with high-density (10-60 cm−3) cold ions and ongoing reconnection from the observation of the Magnetospheric Multiscale (MMS) spacecraft. The magnetopause crossing is estimated to be 300 ion-inertial lengths south of the X line. Two distinct ion populations are observed on the magnetosheath edge of the ion jet. One population with large parallel velocities (200-300 km/s) is identified to be cold ion beams, and the other population is the magnetosheath ions. In the deHoffman-Teller frame, the field-aligned magnetosheath ions are Alfvénic and move towards the jet region, while the field-aligned cold ion beams move towards the magnetosheath boundary layer, with much small speeds. These cold ion beams are suggested to be from the cold ions entering the jet close to the X line. This is the first observation of the cold ionospheric ions in the reconnection outflow region, including the reconnection jet and the magnetosheath boundary layer.
      PubDate: 2017-09-20T17:16:04.617643-05:
      DOI: 10.1002/2017JA024287
       
  • Simulated prompt acceleration of multi-MeV electrons by the 17 March 2015
           interplanetary shock
    • Authors: Mary Hudson; Allison Jaynes, Brian Kress, Zhao Li, Maulik Patel, Xiaochen Shen, Scott Thaller, Michael Wiltberger, John Wygant
      Abstract: Prompt enhancement of relativistic electron flux at L = 3−5 has been reported from Van Allen Probes Relativistic Electron Proton Telescope (REPT) measurements associated with the 17 March 2015 interplanetary shock compression of the dayside magnetosphere. Acceleration by ∼ 1 MeV is inferred on less than a drift time scale as seen in prior shock compression events, which launch a magetosonic azimuthal electric field impulse tailward. This impulse propagates from the dayside around the flanks accelerating electrons in drift resonance at the dusk flank. Such longitudinally localized acceleration events produce a drift echo signature which was seen at>1 MeV energy on both Van Allen Probe spacecraft, with sustained observations by Probe B outbound at L = 5 at 2100 MLT at the time of impulse arrival, measured by the Electric Fields and Waves instrument. MHD-test particle simulations are presented which reproduce drift echo features observed in the REPT measurements at Probe B, including the energy and pitch angle dependence of drift echoes observed. While the flux enhancement was short-lived for this event due to subsequent inward motion of the magnetopause, stronger events with larger electric field impulses, as observed in March 1991 and the Halloween 2003 storm, produce enhancements which can be quantified by the inward radial transport and energization determined by the induction electric field resulting from dayside compression.
      PubDate: 2017-09-20T17:15:42.074016-05:
      DOI: 10.1002/2017JA024445
       
  • Signatures of Ultrarelativistic Electron Loss in the Heart of the Outer
           Radiation Belt Measured by Van Allen Probes
    • Authors: N. A. Aseev; Y. Y. Shprits, A. Y. Drozdov, A. C. Kellerman, M. E. Usanova, D. Wang, I. S. Zhelavskaya
      Abstract: Up until recently, signatures of the ultrarelativistic electron loss driven by electromagnetic ion cyclotron (EMIC) waves in the Earth's outer radiation belt have been limited to direct or indirect measurements of electron precipitation or the narrowing of normalized pitch angle distributions in the heart of the belt. In this study, we demonstrate additional observational evidence of ultrarelativistic electron loss that can be driven by resonant interaction with EMIC waves. We analyzed the profiles derived from Van Allen Probe particle data as a function of time and three adiabatic invariants between 9 October and 29 November 2012. New local minimums in the profiles are accompanied by the narrowing of normalized pitch angle distributions and ground-based detection of EMIC waves. Such a correlation may be indicative of ultrarelativistic electron precipitation into the Earth's atmosphere caused by resonance with EMIC waves.
      PubDate: 2017-09-19T17:51:32.093258-05:
      DOI: 10.1002/2017JA024485
       
  • Hybrid simulations of positively and negatively charged pickup ions and
           cyclotron wave generation at Europa
    • Authors: R. T. Desai; M. M. Cowee, H. Wei, X. Fu, S. P. Gary, M. Volwerk, A. J. Coates
      Abstract: In the vicinity of Europa, Galileo observed bursty Alfvén-cyclotron wave power at the gyrofrequencies of a number of species including K+, 2+, Na+, and Cl+, indicating the localised pickup of these species. Additional evidence for the presence of Chlorine was the occurrence of both left-hand (LH) and right-hand (RH) polarised transverse wave power near the Cl+ gyrofrequency, thought to be due to the pickup of both Cl+ and the easily formed Chlorine anion, Cl−. To test this hypothesis we use one-dimensional hybrid (kinetic ion, massless fluid electron) simulations for both positive and negative pickup ions and self-consistently reproduce the growth of both LH and RH Alfvén-cyclotron waves in agreement with linear theory. We show how the simultaneous generation of LH and RH waves can result in non-gyrotropic ion distributions and increased wave amplitudes, and how even trace quantities of negative pickup ions are able to generate an observable RH signal. Through comparing simulated and observed wave amplitudes, we are able to place the first constraints on the densities of Chlorine pickup ions in localised regions at Europa.
      PubDate: 2017-09-19T17:51:23.198718-05:
      DOI: 10.1002/2017JA024479
       
  • Scaling features of high latitude geomagnetic field fluctuations at Swarm
           altitude: Impact of IMF orientation
    • Authors: Paola De Michelis; Giuseppe Consolini, Roberta Tozzi, Maria Federica Marcucci
      Abstract: This paper attempts to explore the statistical scaling features of high latitude geomagnetic field fluctuations at Swarm altitude. Data for this study are low resolution (1 Hz) magnetic data recorded by the vector field magnetometer onboard Swarm A satellite over one year (from April 15, 2014 to April 15, 2015). The 1st and 2nd order structure function scaling exponents and the degree of intermittency of the fluctuations of the intensity of the horizontal component of the magnetic field at high Northern latitudes have been evaluated for different interplanetary magnetic field orientations in the GSM Y-Z plane and seasons. In the case of the 1st order structure function scaling exponent, a comparison between the average spatial distributions of the obtained values and the statistical convection patterns obtained using a SuperDARN dynamic model (CS10 model) has been also considered. The obtained results support the idea that the knowledge of the scaling features of the geomagnetic field fluctuations can help in the characterization of the different ionospheric turbulence regimes of the medium crossed by Swarm A satellite. This study shows that different turbulent regimes of the geomagnetic field fluctuations exist in the regions characterized by a double-cell convection pattern and in those regions near the border of the convective structures.
      PubDate: 2017-09-19T17:51:18.815115-05:
      DOI: 10.1002/2017JA024156
       
  • Constraining Balmer-alpha Fine-Structure Excitation Measured in Geocoronal
           Hydrogen Observations
    • Authors: D. D. Gardner; E. J. Mierkiewicz, F. L. Roesler, S. M. Nossal, L. M. Haffner
      Abstract: Cascade contributions to geocoronal Balmer α airglow line profiles are directly proportional to the Balmer β/α line ratio and can therefore be determined with near simultaneous Balmer β observations. Due to scattering differences for solar Lyman β and Lyman γ (responsible for the terrestrial Balmer α and Balmer β fluorescence, respectively) there is an expected trend for the cascade emission to become a smaller fraction of the Balmer α intensity at larger shadow altitudes. Near coincident Balmer α and Balmer β data sets, obtained from the Wisconsin Hα Mapper (WHAM) Fabry–Perot, are used to determine the cascade contribution to the Balmer α line profile, and to show, for the first time, the Balmer β/α line ratio, as a function of shadow altitude. We show that this result is in agreement with direct cascade determinations from Balmer α line profile fits obtained independently by high resolution Fabry–Perot at Pine Bluff, WI. We also demonstrate with radiative transport forward modeling that a solar cycle influence on cascade is expected, and that the Balmer β/α line ratio poses a tight constraint on retrieved aeronomical parameters (such as hydrogen's evaporative escape rate and exobase density). Index Terms: Hydrogen Geocorona, Balmer-alpha Line Profile, Fabry–Perot Interferometry
      PubDate: 2017-09-19T17:51:13.207338-05:
      DOI: 10.1002/2017JA024055
       
  • Elves Accompanying Terrestrial Gamma Ray Flashes
    • Authors: Ningyu Liu; Joseph R. Dwyer, Steven A. Cummer
      Abstract: This paper reports a modeling study of the optical phenomenon in the lower ionosphere known as elves that may accompany terrestrial gamma ray flashes (TGFs). Recent research has indicated that the in-cloud (IC) discharge processes, termed energetic in-cloud pulses (EIPs), associated with some TGFs can produce a current moment waveform with a peak of hundreds of kA-km and a duration of 10 μs. Simulations using the source current moment waveform associated with a Fermi TGF indicate that the radiated electric field at ionospheric altitudes reaches a few times the threshold electric field to excite the optical emissions. A bright elve is therefore induced, with the intensity reaching tens of MegaRayleighs, comparable to the brightest elves caused by cloud-to-ground lightning. Because of the strong electromagnetic field radiated, significant blue emissions from the second positive band system of N2 and the first negative band system of N2+ are excited, besides the dominant red emissions from the first positive band system of N2. The elves caused by EIPs with durations of ∼10 μs are elve doublets. For EIPs of longer durations, e.g., 30-40 μs, elve multiplets greater than two can be produced. We conclude that elves can be produced by an IC lightning process previously unconnected to elves, and that at least some TGFs should have accompanying optical signatures in the lower ionosphere. In addition, TGFs of short durations are more likely to have accompanying elves, because their source currents vary more rapidly.
      PubDate: 2017-09-19T17:51:10.954207-05:
      DOI: 10.1002/2017JA024344
       
  • Ring Current He-Ion Control by Bounce Resonant ULF Waves
    • Authors: Hyomin Kim; Andrew J. Gerrard, Louis J. Lanzerotti, Rualdo Soto-Chavez, Ross J. Cohen, Jerry W. Manweiler
      Abstract: Ring current energy He-ion (∼65 keV to ∼520 keV) differential flux data from the Radiation Belt Storm Probe Ion Composition Experiment (RBSPICE) instrument aboard the Van Allan Probes spacecraft show considerable variability during quiet solar wind and geomagnetic time periods. Such variability is apparent from orbit to orbit (∼9 hours) of the spacecraft and is observed to be ∼50–100% of the nominal flux. Using data from the Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) instrument, also aboard the Van Allen Probes spacecraft, we identify that a dominant source of this variability is from ULF waveforms with periods of 10's of sec. These periods correspond to the bounce resonant timescales of the ring current He-ions being measured by RBSPICE. A statistical survey using the particle and field data for one full spacecraft precession period (approximately two years) shows that the wave and He-ion flux variations are generally anti-correlated, suggesting the bounce resonant pitch-angle scattering process as a major component in the scattering of He-ions.
      PubDate: 2017-09-19T17:50:44.882328-05:
      DOI: 10.1002/2017JA023958
       
  • Global three-dimensional simulation of Earth's dayside reconnection using
           a two-way coupled magnetohydrodynamics with embedded particle-in-cell
           model: initial results
    • Authors: Yuxi Chen; Gábor Tóth, Paul Cassak, Xianzhe Jia, Tamas I. Gombosi, James A. Slavin, Stefano Markidis, Ivy Bo Peng, Vania K. Jordanova, Michael G. Henderson
      Abstract: We perform a three-dimensional (3D) global simulation of Earth's magnetosphere with kinetic reconnection physics to study the flux transfer events (FTEs) and dayside magnetic reconnection with the recently developed magnetohydrodynamics with embedded particle-in-cell model (MHD-EPIC). During the one-hour long simulation, the FTEs are generated quasi-periodically near the subsolar point and move toward the poles. We find the magnetic field signature of FTEs at their early formation stage is similar to a ‘crater FTE’, which is characterized by a magnetic field strength dip at the FTE center. After the FTE core field grows to a significant value, it becomes an FTE with typical flux rope structure. When an FTE moves across the cusp, reconnection between the FTE field lines and the cusp field lines can dissipate the FTE. The kinetic features are also captured by our model. A crescent electron phase space distribution is found near the reconnection site. A similar distribution is found for ions at the location where the Larmor electric field appears. The lower hybrid drift instability (LHDI) along the current sheet direction also arises at the interface of magnetosheath and magnetosphere plasma. The LHDI electric field is about 8 mV/m and its dominant wavelength relative to the electron gyroradius agrees reasonably with MMS observations.
      PubDate: 2017-09-18T18:56:26.034516-05:
      DOI: 10.1002/2017JA024186
       
  • Neutron monitors and cosmogenic isotopes as cosmic ray energy-integration
           detectors: Effective yield functions, effective energy and its dependence
           on the local interstellar spectrum
    • Authors: Eleanna Asvestari; Agnieszka Gil, Gennady A. Kovaltsov, Ilya G. Usoskin
      Abstract: The method of assessment of GCR variability over different time scales, using energy-integrating ground-based detectors such as a NM and cosmogenic isotopes 10Be and 14C stored in natural archives, is revisited here. The effective yield functions for cosmogenic 14C (globally mixed in the atmosphere) and 10Be (realistically deposited in the polar region) are calculated and provided, in a tabulated form, in the Supplementary information. The effective energy of a detector is re-defined so that the variability of the flux of GCR particles at this energy is equal to that of the detector's count rate. The effective energy is found as 11–12 GeV/nuc for the standard polar neutron monitor, and 6–7 GeV/nuc and 5.5–6 GeV/nuc for 14C and 10Be, respectively. New ‘calibration’ relations between the force-field modulation potentials, based on different models of local interstellar spectra (LIS) are provided. While such relations are typically based on re-fitting the modelled cosmic ray spectra with a prescribed LIS model, the method introduced here straightforwardly accounts for the exact type of the detector used to assess the spectrum. The relations are given separately for ground-based neutron monitors and cosmogenic isotopes. This work allows for harmonization of different works related to variability of galactic cosmic ray flux in the vicinity of Earth, on long-term scale.
      PubDate: 2017-09-18T18:56:17.631028-05:
      DOI: 10.1002/2017JA024469
       
  • MMS Observations of Reconnection at Dayside Magnetopause Crossings During
           Transitions of the Solar Wind to Sub-Alfvénic Flow
    • Authors: C. J. Farrugia; N. Lugaz, L. Alm, B. Vasquez, M. R. Argall, H. Kucharek, H. Matsui, R. B. Torbert, B. Lavraud, O. Le Contel, I. J. Cohen, J. L. Burch, C. T. Russell, R. J. Strangeway, J. Shuster, J. C. Dorelli, J. P. Eastwood, R. E. Ergun, S. A. Fuselier, D. J. Gershman, B. L. Giles, Y. V. Khotyaintsev, P. A. Lindqvist, G. T. Marklund, K. Paulson, S. M. Petrinec, T. D. Phan, C. J. Pollock
      Abstract: We present MMS observations during two dayside magnetopause crossings under hitherto unexamined conditions: (i) when the bow shock is weakening and the solar wind transitioning to sub-Alfvénic flow, and (ii) when it is reforming. Interplanetary conditions consist of a magnetic cloud with (i) a strong B(∼20 nT) pointing south, and (ii) a density profile with episodic decreases to values of ∼0.3 cm−3 followed by moderate recovery. During the crossings the magnetosheath magnetic field is stronger than the magnetosphere field by a factor of ∼2.2. As a result, during the outbound crossing through the ion diffusion region, MMS observed an inversion of the relative positions of the X and stagnation (S) lines from that typically the case: the S line was closer to the magnetosheath side. The S-line appears in the form of a slow expansion fan near which most of the energy dissipation is taking place. While in the magnetosphere between the crossings, MMS observed strong field and flow perturbations, which we argue to be due to kinetic Alfvén waves. During the reconnection interval, whistler mode waves generated by an electron temperature anisotropy (Te⊥>Te∥) were observed. Another aim of the paper is to distinguish bow shock-induced field and flow perturbations from reconnection-related signatures. The high resolution MMS data together with 2D hybrid simulations of bow shock dynamics helped us to distinguish between the two sources. We show examples of bow shock-related effects (such as heating) and reconnection effects such as accelerated flows satisfying the Walén relation.
      PubDate: 2017-09-18T18:56:15.863784-05:
      DOI: 10.1002/2017JA024563
       
  • Scaling the ion inertial length and its implications for modeling
           reconnection in global simulations
    • Authors: Gábor Tóth; Yuxi Chen, Tamas I. Gombosi, Paul Cassak, Stefano Markidis, Ivy Bo Peng
      Abstract: We investigate the use of artificially increased ion and electron kinetic scales in global plasma simulations. We argue that as long as the global and ion inertial scales remain well separated, 1) the overall global solution is not strongly sensitive to the value of the ion inertial scale, while 2) the ion inertial scale dynamics will also be similar to the original system, but it occurs at a larger spatial scale, and 3) structures at intermediate scales, such as magnetic islands, grow in a self-similar manner. To investigate the validity and limitations of our scaling hypotheses, we carry out many simulations of a two-dimensional magnetosphere with the magnetohydrodynamics with embedded particle-in-cell (MHD-EPIC) model. The PIC model covers the dayside reconnection site. The simulation results confirm that the hypotheses are true as long as the increased ion inertial length remains less than about 5% of the magnetopause standoff distance. Since the theoretical arguments are general, we expect these results to carry over to three dimensions. The computational cost is reduced by the third and fourth powers of the scaling factor in two- and three-dimensional simulations, respectively, which can be many orders of magnitude. The present results suggest that global simulations that resolve kinetic scales for reconnection are feasible. This is a crucial step for applications to the magnetospheres of Earth, Saturn and Jupiter and to the solar corona.
      PubDate: 2017-09-18T18:55:46.586477-05:
      DOI: 10.1002/2017JA024189
       
  • Imprints of quasi-adiabatic ion dynamics on the current sheet structures
           observed in the Martian magnetotail by MAVEN
    • Authors: E. E. Grigorenko; S. D. Shuvalov, H. V. Malova, E. Dubinin, V. Yu. Popov, L. M. Zelenyi, J. Espley, Mc Fadden J.P.
      Abstract: Numerous studies of the Current Sheets (CS) in the Earth magnetotail showed that quasi-adiabatic ion dynamics plays an important role in formation of complicated multilayered current structures. In order to check whether the similar mechanisms operate in the Martian magnetotail we analyzed 80 CS crossings using MAVEN measurements on the nightside of Mars at radial distances ~1.0–2.8RM. We found that CS structures experience the similar dependence on the value of the normal component of the magnetic field at the neutral plane (BN) and on the ratio of the ion drift velocity outside the CS to the thermal velocity (VT/VD) as it was observed for the CSs in the Earth’s magnetotail. For the small values of BN a thin and intense CS embedded in a thicker one is observed. The half-thickness of this layer is L~30–100km ≤ ρH+ (ρH+ is a gyroradius of thermal protons outside the CS). With the increase of BN the L also increases up to several hundred km (~ρO+, ρO2+), the current density decreases and the embedding feature disappears. Our statistical analysis showed a good agreement between L values observed by MAVEN and the CS scaling obtained from the quasi-adiabatic model, if the plasma characteristics in Martian CSs are used as input parameters. Thus, we may conclude that, in spite of the differences in magnetic topology, ion composition and plasma thermal characteristics observed in the Earth’s and Martian magnetotails, similar quasi-adiabatic mechanisms contribute to the formation of the CSs in the magnetotails of both planets.
      PubDate: 2017-09-18T18:55:24.317393-05:
      DOI: 10.1002/2017JA024216
       
  • In Situ Analysis of Heliospheric Current Sheet Propagation
    • Authors: Jun Peng; Yong C.-M. Liu, Jia Huang, Hui Li, Berndt Klecker, Antoinette B. Galvin, Kristin Simunac, Charles Farrugia, L. K. Jian, Yang Liu, Jie Zhang
      Abstract: The heliospheric current sheet (HCS) is an important structure not only for understanding the physics of interplanetary space but also for space weather prediction. We investigate the differences of the HCS arrival time between three spacecraft separated in heliolongitude, heliolatitude and radial distance from the Sun (STEREO A, STEREO B and ACE) to understand the key factors controlling the HCS propagation. By assuming that the source of the solar wind does not evolve except for the effects of solar rotation, we first test the first order approach method (ignoring latitudinal differences), using STEREO observation during the year 2007, when the Sun was quiet and the two STEREO spacecraft were separated in heliolongitude by less than 44°. The first order approach method matches well with observations for many events except for those events when the HCS has a small inclination angle to the ecliptic plane. The latitudinal effect is suggested to account for such discrepancies. The predictions are not improved much by considering the HCS inclination angle obtained from the potential field source surface (PFSS) model. However, the predictions match well with the observations when the HCS inclination angle at 1 AU is obtained from the time differences of HCS arrival times between the STEREO B and ACE spacecraft. An improved model of calculating the inclination of the heliospheric current sheet other than PFSS is needed.
      PubDate: 2017-09-14T19:01:22.796675-05:
      DOI: 10.1002/2017JA024194
       
  • Equatorial ionospheric response to different estimated disturbed electric
           fields as investigated using SUPIM-INPE
    • Authors: M. A. Bravo; I. S. Batista, J. R. Souza, A. J. Foppiano
      Abstract: Good ionospheric modeling is important to understand anomalous effects, mainly during geomagnetic storm events. Ionospheric electric fields, thermospheric winds and neutral composition are affected at different degrees, depending on the intensity of the magnetic disturbance which, in turns, affects the electron density distribution at all latitudes. The most important disturbed parameter for the equatorial ionosphere is the electric field, which is responsible for the Equatorial Ionization Anomaly. Here, various electric fields measurements and models are analyzed: (1) measured by the Jicamarca incoherent scattering radar (ISR), (2) from Jicamarca Unattended Long-Term studies of the Ionosphere and Atmosphere (JULIA) radar, (3) deduced from magnetometers, (4) calculated from the time variations of the F layer height (dh’F/dt) and (5) deduced from interplanetary electric field determinations. The response of ionospheric parameters foF2 and hmF2 to the electric fields simulated using the Sheffield University Plasmasphere Ionosphere Model version available at INPE is compared with observations for two locations, during the geomagnetic storm events of 17-18 April 2002 and 7-10 November 2004. Results are found to be consistent with the observations in such a way that a hierarchy among the different types of drifts used can be established. When no ISR measurements are available, the drifts deduced from magnetometers or measured by the JULIA are best when including the contribution derived from dh’F/dt for the 18-24 LT time interval. However, when none of these drifts are available, drifts inferred from the interplanetary electric field seem to be a good alternative for some purposes.
      PubDate: 2017-09-14T19:00:58.643853-05:
      DOI: 10.1002/2017JA024265
       
  • Directivity functions of neutron monitors
    • Authors: G. G. Karapetyan
      Abstract: We derive directivity function (DF) of neutron monitor (NM). It represents the distribution of count rate by asymptotic directions of primary cosmic ray protons, providing the detailed and accurate description of directional sensitivity of a NM. We present the DFs of several NM stations, located at high and low geographical latitudes, clarifying the features of their acceptance cones. The knowledge of DFs will help in research of galactic and solar cosmic rays based on neutron monitors. Particularly, using DFs we estimated the times of maximum for diurnal variations of several stations and showed that they are consistent with the observed data
      PubDate: 2017-09-14T19:00:55.282005-05:
      DOI: 10.1002/2017JA023907
       
  • Interaction of magnetic flux ropes via magnetic reconnection observed at
           the magnetopause
    • Authors: Rongsheng Wang; Quanming Lu, Rumi Nakamura, Wolfgang Baumjohann, C. T. Russell, J. L. Burch, R. E. Ergun, P. A. Lindqvist, Shui Wang, Barbara Giles, Dan Gershman
      Abstract: Using the high resolution field and plasma data obtained from the Magnetospheric Multiscale mission (MMS) at the magnetopause, a series of three flux transfer events was observed one after another inside southward ion flows, without time gap between any two successive flux ropes. Using the plasma measurements, the current densities within the flux ropes were studied in detail. The currents within the first two flux ropes, dubbed Fr1 and Fr2, was composed of a series of well-separated filamentary currents. The thickness of the filamentary currents and the gap between them were sub-ion scale, occasionally dropped down to electron-scale. In the third flux rope Fr3 which was closest to the expected reconnection X-line, the current displayed a singular compact current layer, was ion scale in width and concentrated on its center. Considering the location of the flux ropes relative to the reconnection X-line, we suggested the current density could be a singular structure when the flux rope was just created and then fragmented into a series of filamentary currents as time. By examining the inter-regions between Fr1 and Fr2, and between Fr2 and Fr3, reconnection was only confirmed to occur between Fr2 and Fr3 and no reconnection signature was found between Fr1 and Fr2. It seems that magnetic field compression resulted from collision of two neighboring flux ropes is one necessary condition for the occurrence of the coalescence.
      PubDate: 2017-09-14T19:00:53.407279-05:
      DOI: 10.1002/2017JA024482
       
  • Observations and simulations of eddy diffusion and tidal effects on the
           semi-annual oscillation in the ionosphere
    • Authors: Qian Wu; W. S. Schreiner, S.-P. Ho, H.-L. Liu, Liying Qian
      Abstract: We use the NCAR TIEGCM (Thermosphere Ionosphere Electrodynamics General Circulation Model) model to investigate the eddy diffusion and tidal effects on the ionosphere SAO (semiannual oscillation). We also use the COSMIC (Constellation Observing System for Meteorology, Ionosphere, and Climate) satellite GPS radio occultation (RO) observations to validate the simulation results. The TIEGCM is driven at the 97 km lower boundary by tidal and gravity wave (eddy diffusion coefficient) inputs. The eddy diffusion input can be constant or with a SAO modulation [Qian et al., 2009] and the tidal input has on and off options. The TIEGCM simulation with a SAO modulated eddy diffusion (with tidal input) agrees better with the COSMIC observation than that without the SAO. Turning off the tides at the lower boundary makes the TIEGCM simulated ionospheric density much higher than the COSMIC observation. The simulations showed two results: 1) the need to add the SAO modulation to the eddy diffusion, and 2) how tides reduce the ionospheric density and SAO. As to how much of the SAO should be added to the eddy diffusion is dependent on the amplitudes of the tides since both can have effects on the ionospheric density. The TIEGCM results also demonstrate that the ionospheric density diurnal signal is mostly in-situ excited, while the semidiurnal signal comes from lower atmosphere.
      PubDate: 2017-09-14T19:00:51.063804-05:
      DOI: 10.1002/2017JA024341
       
  • Characterization of Low Altitude Nightside Martian Magnetic Topology Using
           Electron Pitch Angle Distributions
    • Authors: Tristan Weber; David Brain, David Mitchell, Shaosui Xu, Jack Connerney, Jasper Halekas
      Abstract: Magnetic field lines at Mars act as direct pathways for both energy inflow and ion escape. Local variations in magnetic field topology can therefore directly impact the interaction between the solar wind and the Martian ionosphere. One method of analyzing magnetic topology is through the use of electron pitch angle distributions (PADs). Previous PAD investigations have characterized magnetic topology in the Martian system using data from the Mars Global Surveyor (MGS) spacecraft, but these studies were orbitally constrained to ∼400km altitude and 2 AM/2 PM local time. With the Mars Atmosphere and Volatile Evolution (MAVEN) mission, we are now able to extend this analysis to a larger range of altitudes and local times. Here we use electron PADs measured using the Solar Wind Electrostatic Analyzer (SWEA) and Magnetometer (MAG) instruments on MAVEN to analyze the magnetic topology of the nightside Martian environment. We use several characteristic PAD shapes to determine where Martian magnetic field lines are open or closed to the solar wind, and present frequency maps of how these PAD shapes vary both geographically and with altitude. Finally, we present an initial analysis of the variation of the PAD shapes with local time, finding that trapped electron distributions become increasingly frequent as crustal fields rotate from dusk to dawn across the nightside of Mars.
      PubDate: 2017-09-14T19:00:43.350822-05:
      DOI: 10.1002/2017JA024491
       
  • Latitude dependence of low-altitude O+ ion upflow: Statistical results
           from FAST observations
    • Authors: K. Zhao; K. W. Chen, Y. Jiang, W. J. Chen, L. F. Huang, S. Fu
      Abstract: We introduce a statistical model to explain the latitudinal dependence of the occurrence rate and energy flux of the ionospheric escaping ions, taking advantage of advances in the spatial coverage and accuracy of FAST observations. We use a weighted piecewise Gaussian function to fit the dependence, because two probability peaks are located in the dayside polar cusp source region and the nightside auroral oval zone source region. The statistical results show that: (1) the Gaussian Mixture Model (GMM) suitably describes the dayside polar cusp upflows, and the dayside and the nightside auroral oval zone upflows. (2) The magnetic latitudes of the ionospheric upflow source regions expand toward the magnetic equator as Kp increases, from 81° MLat (cusp upflows) and 63° MLat (auroral oval upflows) during quiet times to 76° MLat and 61° MLat, respectively. (3) The dayside polar cusp region provides only 3-5% O+ upflows among all the source regions, which include the dayside auroral oval zone, dayside polar cusp, nightside auroral oval zone and even the polar cap. However, observations show that more than 70% of upflows occur in the auroral oval zone and that the occurrence probability increases at the altitudes of 3500 - 4200 km, which is considered to be the lower altitude boundary of ion beams. This observed result suggests that soft electron precipitation and transverse wave heating are the most efficient ion energization/acceleration mechanisms at the altitudes of FAST orbit, and that the parallel acceleration caused by field-aligned potential drops become effective above that altitude.
      PubDate: 2017-09-12T18:51:23.396111-05:
      DOI: 10.1002/2017JA024075
       
  • A simulation study of the equatorial ionospheric response to the October
           2013 geomagnetic storm
    • Authors: Dexin Ren; Jiuhou Lei
      Abstract: The ionospheric observation from ionosonde at Sao Luis (2.5° S, 44.2° W; 6.68° S dip latitude) around the magnetic equator showed that the nighttime ionospheric F2 layer was uplifted by more than 150 km during the October 2013 geomagnetic storm. The changes of the F2 peak height (hmF2) at the magnetic equator were generally attributed to the variations of vertical drift associated with zonal electric fields. In this paper, the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM) simulation results are utilized to explore the possible physical mechanisms responsible for the observed increase of hmF2 at Sao Luis. The TIEGCM generally reproduced the changes of F2 peak electron density (NmF2) and its height (hmF2) during the main and recovery phases of the October 2013 storm. A series of controlled simulations revealed that storm-time hmF2 changes at the magnetic equator are not purely associated with the changes of electric fields; horizontal plasma transport due to meridional winds and thermospheric expansion also contributed significantly to the profound increase of nighttime hmF2 observed at Sao Luis on 2 October. Moreover, the changes of meridional winds and neutral temperature in the equatorial region are associated with storm-time travelling atmospheric disturbances originating from high latitudes.
      PubDate: 2017-09-11T19:03:01.634162-05:
      DOI: 10.1002/2017JA024286
       
  • The Martian photoelectron boundary as seen by MAVEN
    • Authors: P. Garnier; M. Steckiewicz, C. Mazelle, S. Xu, D. Mitchell, M. K. G. Holmberg, J. S. Halekas, L. Andersson, D. A. Brain, J. E. P. Connerney, J. R. Espley, R. J. Lillis, J. G. Luhmann, J.-A. Sauvaud, B. M. Jakosky
      Abstract: Photoelectron peaks in the 20-30 eV energy range are commonly observed in the planetary atmospheres, produced by the intense photoionization from solar 30.4 nm photons. At Mars, these photoelectrons are known to escape the planet down its tail, making them tracers for the atmospheric escape. Furthermore, their presence or absence allow to define the so-called PhotoElectron Boundary (PEB), that separates the photoelectron dominated ionosphere from the external environment. We provide here a detailed statistical analysis of the location and properties of the PEB based on the Mars Atmosphere and Volatile Evolution (MAVEN) electron and magnetic field data obtained from September 2014 until May 2016 (including 1696 PEB crossings).The PEB appears as mostly sensitive to the solar wind dynamic and crustal fields pressures. Its variable altitude thus leads to a variable wake cross section for escape (up to ∼+50%), which is important for deriving escape rates. The PEB is not always sharp, and is characterized on average by : a magnetic field topology typical for the end of Magnetic Pile Up Region above it, more field aligned fluxes above than below, and a clear change of the altitude slopes of both electron fluxes and total density (that appears different from the ionopause). The PEB thus appears as a transition region between two plasma and fields configurations determined by the draping topology of the interplanetary magnetic field around Mars and much influenced by the crustal field sources below, whose dynamics also impacts the estimated escape rate of ionospheric plasma.
      PubDate: 2017-09-11T19:02:59.315308-05:
      DOI: 10.1002/2017JA024497
       
  • Observation of Three-dimensional Magnetic Reconnection in the Terrestrial
           Magnetotail
    • Authors: Meng Zhou; Maha Ashour-Abdalla, Xiaohua Deng, Ye Pang, Huishan Fu, Raymond Walker, Giovanni Lapenta, Shiyong Huang, Xiaojun Xu, Rongxin Tang
      Abstract: Study of magnetic reconnection has been focused on two-dimensional geometry in the past decades, whereas three-dimensional structures and dynamics of reconnection X-line are poorly understood. In this paper, we report Cluster multi-spacecraft observations of a three-dimensional magnetic reconnection X-line with a weak guide field (~25% of the upstream magnetic field) in the Earth's magnetotail. We find that the X-line not only retreated tailward but also expanded across the tail following the electron flow direction with a maximum average speed of (0.04 - 0.15) VA,up, where VA,up is the upstream Alfvén speed, or (0.14 - 0.57) Vde, where Vde is the electron flow speed in the out-of-plane direction. An ion diffusion region was observed by two spacecraft that were separated about 10 ion inertial lengths along the out-of-plane direction; however, these two spacecraft observed distinct magnetic structures associated with reconnection: one spacecraft observed dipolarization fronts while the other one observed flux ropes. This indicates that reconnection proceeds in drastically different ways in different segments along the X-line only a few ion inertial lengths apart.
      PubDate: 2017-09-11T19:02:54.740026-05:
      DOI: 10.1002/2017JA024597
       
  • Polar thermospheric winds and temperature observed by Fabry-Perot
           Interferometer at Jang Bogo Station, Antarctica
    • Authors: Changsup Lee; Geonhwa Jee, Qian Wu, Ja Soon Shim, Damian Murphy, In-Sun Song, Hyuck-Jin Kwon, Jeong-Han Kim, Yong Ha Kim
      Abstract: Upper atmospheric neutral winds and temperature have been observed by the Fabry-Perot Interferometer (FPI) which was installed at Jang Bogo Station (JBS), Antarctica in 2014. Since JBS is mostly located within the polar cap region, the observed thermospheric winds at 250 km show strong diurnal variations with notable anti-sunward motions due to the effects of plasma convection. The winds at 87 km, on the other hand, show semidiurnal variations due to the lower atmospheric tidal effects. We found that the winds from green line emission show largely diurnal variations, unlike the other independent observations, which might be due to the auroral contamination. The HWM14 winds at 250 km show reasonable agreement with FPI winds while large discrepancies exist at 87 km in terms of seasonal variations. There is a distinctive asymmetric seasonal variation of the thermospheric zonal wind in the dusk and dawn sectors. FPI temperatures at 250 km show a fairly close correlation with Kp index, especially in 2015 when the geomagnetic activity is stronger. However, the temperatures at 87 km are mostly independent on Kp index. Finally, during the intense geomagnetic storm, thermospheric winds and temperature are significantly disturbed and TIECM simulations are in surprisingly good agreement with observation for winds but the temperatures are significantly underestimated during the whole storm period.
      PubDate: 2017-09-11T19:02:25.901458-05:
      DOI: 10.1002/2017JA024408
       
  • ssImpact of sudden stratospheric warming of 2009 on the equatorial and
           low-latitude ionosphere of the Indian longitudes: A case study
    • Authors: Sneha Yadav; Tarun K. Pant, R. K. Choudhary, C. Vineeth, Surendra Sunda, K. K. Kumar, P. R. Shreedevi, S. Mukherjee
      Abstract: Using the Equatorial Electrojet (EEJ) induced surface magnetic field and Total Electron Content (TEC) measurements, we investigated the impact of the Sudden Stratospheric Warming (SSW) of January 2009 on the equatorial electrodynamics and low-latitude ionosphere over the Indian longitudes. Results indicate that the intensity of EEJ and the TEC over low-latitudes (extending up to 30°N) exhibit significant perturbations during and after the SSW peak. One of the interesting features is the deviation of EEJ and TEC from the normal quiet time behaviour well before the onset of the SSW. This is found to be coincided with the beginning of enhanced planetary wave (PW) activity over high-latitudes. The substantial amplification of the semidiurnal perturbation after the SSW peak is seen to be coinciding with the onset of new and full moon. The response of TEC to SSW is found to be latitude dependent as the near-equatorial (NE) stations show the semidiurnal perturbation only after the SSW peak. Another notable feature is the presence of reduced ionization in the night sector over the NE and low-latitude regions, appearing as an ‘ionization hole’, well after the SSW peak. The investigation revealed the existence of a quasi-16 day wave in the TEC over low-latitudes similar to the one present in the EEJ strength. These results have been discussed in the light of changes in the dynamical background because of enhanced PW activity during SSW, which creates favourable conditions for the amplification of lunar tides, and their subsequent interaction with the lower thermospheric tidal fields.
      PubDate: 2017-09-11T19:02:22.582524-05:
      DOI: 10.1002/2017JA024392
       
  • Characterization of a Double Mesospheric Bore Over Europe
    • Authors: Steven M. Smith; Gunter Stober, Christoph Jacobi, Jorge L. Chau, Michael Gerding, Martin G. Mlynczak, James M. Russell, Jeffrey L. Baumgardner, Michael Mendillo, Monica Lazzarin, Gabriel Umbriaco
      Abstract: Observations of a pair of mesospheric bore disturbances that propagated through the nighttime mesosphere over Europe are presented. The observations were made at the Padua Observatory, Asiago (45.9°N, 11.5°E) by the Boston University all-sky imager on 11 March 2013. The bores appeared over the north-west horizon, approximately 30 minutes apart, and propagated towards the south-east. Using additional satellite and radar data, we present evidence indicating the bores originated in the mesosphere from a single, larger-scale mesospheric disturbance propagating through the mesopause region. Furthermore, the large-scale mesospheric disturbance appeared to be associated with an intense weather disturbance that moved southeastwards over the United Kingdom and Western Europe during 10 and 11 March.
      PubDate: 2017-09-11T19:02:16.962219-05:
      DOI: 10.1002/2017JA024225
       
  • Hot ion flows in the distant magnetotail: ARTEMIS observations from lunar
           orbit to ∼−200RE.
    • Authors: A. V. Artemyev; V. Angelopoulos, A. Runov, I. Y. Vasko
      Abstract: Plasma energization in Earth's magnetotail is supported by acceleration processes in (and around) magnetic reconnection regions. Hot plasma flows and strong electromagnetic waves, generated by magnetic energy release during reconnection, transport energy necessary for current system intensification and particle acceleration in the inner magnetosphere. Earth's magnetotail configuration includes two main reconnection regions (X-lines): the near-Earth X-line, which has been well studied by several multispacecraft missions, and the distant X-line, which has been much less investigated. In this paper, we utilize the unique dataset gathered by two ARTEMIS spacecraft in 2010 at radial distances between lunar orbit and ∼200RE (Earth radii). We identify an X-line at around ∼80RE and collect statistics on hot plasma flows observed around and beyond this distance. Ion spectra within these flows are well fitted by a power-law with the exponential tail starting above an energy ϵ0∼2 − 5 keV. Assuming that these spectra are originated at the distant X-line, we examine the characteristics of the acceleration at the distant tail reconnection region.
      PubDate: 2017-09-06T17:11:22.168405-05:
      DOI: 10.1002/2017JA024433
       
  • Rapid loss of radiation belt relativistic electrons by EMIC waves
    • Authors: Zhenpeng Su; Zhonglei Gao, Huinan Zheng, Yuming Wang, Shui Wang, H. E. Spence, G. D. Reeves, D. N. Baker, J. R. Wygant
      Abstract: How relativistic electrons are lost is an important question surrounding the complex dynamics of the Earth's outer radiation belt. Radial loss to the magnetopause and local loss to the atmosphere are two main competing paradigms. Here, on the basis of the analysis of a radiation belt storm event on 27 February 2014, we present new evidence for the EMIC wave-driven local precipitation loss of relativistic electrons in the heart of the outer radiation belt. During the main phase of this storm, the radial profile of relativistic electron phase space density was quasi-monotonic, qualitatively inconsistent with the prediction of radial loss theory. The local loss at low L-shells was required to prevent the development of phase space density peak resulting from the radial loss process at high L-shells. The rapid loss of relativistic electrons in the heart of outer radiation belt was observed as a dip structure of the electron flux temporal profile closely related to intense EMIC waves. Our simulations further confirm that the observed EMIC waves within a quite limited longitudinal region was able to reduce the off-equatorially mirroring relativistic electron fluxes by up to 2 orders of magnitude within about 1.5 h.
      PubDate: 2017-08-31T17:22:21.491807-05:
      DOI: 10.1002/2017JA024169
       
  • The effect of storm driver and intensity on magnetospheric ion
           temperatures
    • Authors: Amy M. Keesee; Roxanne M. Katus, Earl E. Scime
      Abstract: Energy deposited in the magnetosphere during geomagnetic storms drives ion heating and convection. Ions are also heated and transported via internal processes throughout the magnetosphere. Injection of the plasma sheet ions to the inner magnetosphere drives the ring current and, thus, the storm intensity. Understanding the ion dynamics is important to improving our ability to predict storm evolution. In this study, we perform superposed epoch analyses of ion temperatures during storms, comparing ion temperature evolution by storm driver and storm intensity. The ion temperatures are calculated using energetic neutral atom measurements from the TWINS mission. The global view of these measurements provide both spatial and temporal information. We find that storms driven by coronal mass ejections (CMEs) tend to have higher ion temperatures throughout the main phase than storms driven by corotating interaction regions (CIRs), but that the temperatures increase during the recovery phase of CIR-driven storms. Ion temperatures during intense CME-driven storms have brief intervals of higher ion temperatures than those during moderate CME-driven storms, but have otherwise comparable ion temperatures. The highest temperatures during CIR-driven storms are centered at 18 MLT, and occur on the dayside for moderate CME-driven storms. During the second half of the main phase, ion temperatures tend to decrease in the post-midnight to dawn sector for CIR storms, but an increase is observed for CME storms. This increase begins with a sharp peak in ion temperatures for intense CME storms, likely a signature of substorm activity that drives the increased ring current.
      PubDate: 2017-08-31T17:21:49.158863-05:
      DOI: 10.1002/2017JA023973
       
  • The characteristic pitch angle distributions of 1 eV to 600 keV protons
           near the equator based on Van Allen Probes observations
    • Authors: Chao Yue; Jacob Bortnik, Richard M. Thorne, Qianli Ma, Xin An, C. R. Chappell, Andrew J. Gerrard, Louis J. Lanzerotti, Quanqi Shi, Geoffrey D. Reeves, Harlan E. Spence, Donald G. Mitchell, Matina Gkioulidou, Craig A. Kletzing
      Abstract: Understanding the source and loss processes of various plasma populations is greatly aided by having accurate knowledge of their pitch angle distributions (PADs). Here, we statistically analyze ~1 eV to 600 keV hydrogen (H+) PADs near the geomagnetic equator in the inner magnetosphere based on Van Allen Probes measurements, to comprehensively investigate how the H+ PADs vary with different energies, magnetic local times (MLTs), L-shells, and geomagnetic conditions. Our survey clearly indicates four distinct populations with different PADs: (1) a pancake distribution of the plasmaspheric H+ at low L-shells except for dawn sector; (2) a bi-directional field-aligned distribution of the warm plasma cloak; (3) pancake or isotropic distributions of ring current H+; (4) radiation belt particles show pancake, butterfly and isotropic distributions depending on their energy, MLT and L-shell. Meanwhile, the pancake distribution of ring current H+ moves to lower energies as L-shell increases which is primarily caused by adiabatic transport. Furthermore, energetic H+ (> 10 keV) PADs become more isotropic following the substorm injections, indicating wave-particle interactions. The radiation belt H+ butterfly distributions are identified in a narrow energy range of 100 < E < 400 keV at large L (L> 5), which are less significant during quiet times and extend from dusk to dawn sector through midnight during substorms. The different PADs near the equator provide clues of the underlying physical processes that produce the dynamics of these different populations.
      PubDate: 2017-08-31T17:21:33.195228-05:
      DOI: 10.1002/2017JA024421
       
  • Pulsating auroras produced by interactions of electrons and time domain
           structures
    • Authors: F. S. Mozer; O. V. Agapitov, A. Hull, S. Lejosne, I. Y. Vasko
      Abstract: Previous evidence has suggested that either lower band chorus waves or kinetic Alfven waves scatter equatorial kilovolt electrons that propagate to lower altitudes where they precipitate or undergo further low-altitude scattering to make pulsating auroras. Recently, time domain structures (TDSs) were shown, both theoretically and experimentally, to efficiently scatter equatorial electrons. To assess the relative importance of these three mechanisms for production of pulsating auroras, 11 intervals of equatorial THEMIS data and a 4 h interval of Van Allen Probe measurements have been analyzed. During these events, lower band chorus waves produced only negligible modifications of the equatorial electron distributions. During the several TDS events, the equatorial 0.1–3 keV electrons became magnetic field-aligned. Kinetic Alfven waves may also have had a small electron scattering effect. The conclusion of these studies is that time domain structures caused the most important equatorial scattering of ~1 keV electrons toward the loss cone to provide the main electron contribution to pulsating auroras. Chorus wave scattering may have provided part of the highest energy (>10 keV) electrons in such auroras.
      PubDate: 2017-08-31T01:46:16.441119-05:
      DOI: 10.1002/2017JA024223
       
  • Daytime zonal drifts in the ionospheric 150 km and E regions
           estimated using EAR observations
    • Authors: P. Pavan Chaitanya; A. K. Patra, Y. Otsuka, T. Yokoyama, M. Yamamoto, R. A. Stoneback, R. A. Heelis
      Abstract: Multibeam observations of the 150 km echoes made using the Equatorial Atmosphere Radar (EAR), located at Kototabang, Indonesia, provide unique opportunity to study both vertical and zonal E × B plasma drifts in the equatorial ionosphere. In this paper, we focus on estimating daytime zonal drifts at the 150 km (140–160 km) and E (100–110 km) regions using multibeam observations of 150 km and E region echoes made using the EAR and study the daytime zonal drifts covering all seasons not studied before from Kototabang. Zonal drifts in the 150 km and E regions are found to be westward and mostly below −80 m s−1 and −60 m s−1, respectively. While the zonal drifts in the 150 km and E regions do not go hand in hand on a case-by-case basis, the seasonal mean drifts in the two height regions are found to be in good agreement with each other. Zonal drifts at the 150 km region show seasonal variations with three maxima peaking around May, September, and January. The zonal drifts at the 150 km region are found to be smaller than the F region drifts obtained from Coupled Ion Neutral Dynamics Investigation (CINDI) onboard Communication and Navigation Outage Forecasting System (C/NOFS) by about 25 m s−1 consistent with the height variations of F region zonal drifts observed by the Jicamarca radar. These results constitute the first comprehensive study of zonal drifts at the 150 km and E regions from Kototabang, Indonesia, and the results are discussed in the light of current understanding on the low-latitude electrodynamics and coupling.
      PubDate: 2017-08-31T01:41:04.656897-05:
      DOI: 10.1002/2017JA024589
       
  • Magnetospheric ion influence at the dayside magnetopause
    • Authors: S. A. Fuselier; J. L. Burch, J. Mukherjee, K. J. Genestreti, S. K. Vines, R. Gomez, J. Goldstein, K. J. Trattner, S. M. Petrinec, B. Lavraud, R. J. Strangeway
      Abstract: Magnetospheric ions have the potential to affect magnetic reconnection at the magnetopause. The results of a survey of magnetospheric ions near the magnetopause are reported here. Composition measurements from the Magnetospheric Multiscale (MMS) mission are used to determine the total mass density of all magnetospheric ions and distinguish two populations of magnetospheric ions: the warm plasma cloak and the plasmaspheric drainage plume. The warm plasma cloak can contain substantial O+, and the plasmaspheric plume can contain substantial He+. The results of the survey show that, for nominal magnetospheric activity, the warm plasma cloak and plasmaspheric plume will reduce the normalized reconnection rate at the magnetopause by greater than 20% only a few percent of the time.
      PubDate: 2017-08-31T01:40:41.798354-05:
      DOI: 10.1002/2017JA024515
       
  • Thunderstorm-/lightning-induced ionospheric perturbation: An observation
           from equatorial and low-latitude stations around Hong Kong
    • Authors: Sanjay Kumar; Wu Chen, Mingli Chen, Zhizhao Liu, R. P. Singh
      Abstract: Total electron content (TEC) computed from the network of Global Positioning System over Hong Kong area known as Hong Kong Sat-Ref-network has been used to study perturbation in the ionosphere from thunder storm activity. Data for geomagnetic quiet day (Kp 
      PubDate: 2017-08-31T01:36:19.79021-05:0
      DOI: 10.1002/2017JA023914
       
  • Application of a global magnetospheric-ionospheric current model for
           dayside and terminator Pi2 pulsations
    • Authors: S. Imajo; A. Yoshikawa, T. Uozumi, Shin. Ohtani, A. Nakamizo, P. J. Chi
      Abstract: Pi2 magnetic oscillations on the dayside are considered to be produced by the ionospheric current that is driven by Pi2-associated electric fields from the high-latitude region, but this idea has not been quantitatively tested. The present study numerically tested the magnetospheric-ionospheric current system for Pi2 consisting of field-aligned currents (FACs) localized in the nightside auroral region, the perpendicular magnetospheric current flowing in the azimuthal direction, and horizontal ionospheric currents driven by the FACs. We calculated the spatial distribution of the ground magnetic field produced by these currents using the Biot-Savart law in a stationary state. The calculated magnetic field reproduced the observational features reported by previous studies: (1) the sense of the H component does not change a wide range of local time sectors at low latitudes, (2) the amplitude of the H component on the dayside is enhanced at the equator, (3) the D component reverses its phase near the dawn and dusk terminators, (4) the meridian of the D component phase reversal near the dusk terminator is shifted more sunward than that near the dawn terminator, and (5) the amplitude of the D component in the morning is larger than that in the early evening. We also derived the global distributions of observed equivalent currents for two Pi2 events. The spatial patterns of dayside equivalent currents were similar to the spatial pattern of numerically derived equivalent currents. The results indicate that the oscillation of the magnetospheric-ionospheric current system is a plausible explanation of Pi2s on the dayside and near the terminator.
      PubDate: 2017-08-31T01:32:38.612268-05:
      DOI: 10.1002/2017JA024246
       
  • The Empirical Canadian High Arctic Ionospheric Model (E-CHAIM): NmF2 and
           hmF2
    • Authors: David R. Themens; P. T. Jayachandran, Ivan Galkin, Chris Hall
      Abstract: We present here the Empirical Canadian High Arctic Ionospheric Model (E-CHAIM) quiet NmF2, perturbation NmF2, and quiet hmF2 models. These models provide peak ionospheric characteristics for a domain above 50°N geomagnetic latitude. Model fitting is undertaken using all available ionosonde and radio occultation electron density data, constituting a data set of over 28 million observations. A comprehensive validation of the model is undertaken, and performance is compared to that of the International Reference Ionosphere (IRI). In the case of the quiet NmF2 model, the E-CHAIM model provides a systematic improvement over the IRI Union Radio Scientifique Internationale maps. At all stations within the polar cap, we see drastic RMS error improvements over the IRI by up to 1.3 MHz in critical frequency (up to 60% in NmF2). These improvements occur primarily during equinox periods and at low solar activities, decreasing somewhat as one tends to lower latitudes. Qualitatively, the E-CHAIM is capable of representing auroral enhancements in NmF2, as well as the location and extent of the main ionospheric trough, not reproduced by the IRI. The included NmF2 storm model demonstrates improvements over the IRI by up to 35% and over the quiet time E-CHAIM model by up to 30%. In terms of hmF2, over the validation periods used in this study, we found overall RMS errors of ~13 km for E-CHAIM, with IRI2007 overall hmF2 errors ranging between 16 km and 22 km. The E-CHAIM performs comparably to or slightly better than the IRI within the polar cap; however, significant improvements are found within the auroral oval.
      PubDate: 2017-08-31T01:31:50.579358-05:
      DOI: 10.1002/2017JA024398
       
  • Statistical Study of Relations Between the Induced Magnetosphere, Ion
           Composition, and Pressure Balance Boundaries around Mars Based on MAVEN
           Observations
    • Authors: Kazunari Matsunaga; Kanako Seki, David A. Brain, Takuya Hara, Kei Masunaga, James P. McFadden, Jasper S. Halekas, David L. Mitchell, Christian Mazelle, J. R. Espley, Jacob Gruesbeck, Bruce M. Jakosky
      Abstract: Direct interaction between the solar wind (SW) and the Martian upper atmosphere forms a characteristic region, called the induced magnetosphere between the magnetosheath and the ionosphere. Since the SW deceleration due to increasing mass loading by heavy ions plays an important role in the induced magnetosphere formation, the ion composition is also expected to change around the induced magnetosphere boundary (IMB). Here we report on relations of the IMB, the ion composition boundary (ICB), and the pressure balance boundary based on a statistical analysis of about 8-months of simultaneous ion, electron, and magnetic field observations by Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. We chose the period when MAVEN observed the SW directly near its apoapsis to investigate their dependence on SW parameters. Results show that IMBs almost coincide with ICBs on the dayside and locations of all three boundaries are affected by the SW dynamic pressure. A remarkable feature is that all boundaries tend to locate at higher altitudes in the southern hemisphere than in the northern hemisphere on the nightside. This clear geographical asymmetry is permanently seen regardless of locations of the strong crustal B fields in the southern hemisphere, while the boundary locations become higher when the crustal B fields locate on the dayside. On the nightside, IMBs usually locate at higher altitude than ICBs. However, ICBs are likely to be located above IMBs in the nightside, southern, and downward ESW hemisphere when the strong crustal B fields locate on the dayside.
      PubDate: 2017-08-30T19:26:13.015382-05:
      DOI: 10.1002/2017JA024217
       
  • Understanding the Mechanisms of Radiation Belt Dropouts Observed by Van
           Allen Probes
    • Authors: Zheng Xiang; Weichao Tu, Xinlin Li, Binbin Ni, S. K. Morley, D. N. Baker
      Abstract: To achieve a better understanding of the dominant loss mechanisms for the rapid dropouts of radiation belt electrons, three distinct radiation belt dropout events observed by Van Allen Probes are comprehensively investigated. For each event, observations of the pitch angle distribution of electron fluxes and electromagnetic ion cyclotron (EMIC) waves are analyzed to determine the effects of atmospheric precipitation loss due to pitch angle scattering induced by EMIC waves. Last closed drift shells (LCDS) and magnetopause standoff position are obtained to evaluate the effects of magnetopause shadowing loss. Evolution of electron phase space density (PSD) versus L* profiles and the μ and K (first and second adiabatic invariants) dependence of the electron PSD drops are calculated to further analyze the dominant loss mechanisms at different L*. Our findings suggest that these radiation belt dropouts can be classified into distinct classes in terms of dominant loss mechanisms: magnetopause shadowing dominant, EMIC wave scattering dominant, and combination of both mechanisms. Different from previous understanding, our results show that magnetopause shadowing can deplete electrons at L* < 4, while EMIC waves can efficiently scatter electrons at L*> 4. Compared to the magnetopause standoff position, it is more reliable to use LCDS to evaluate the impact of magnetopause shadowing. The evolution of electron PSD versus L* profile and the μ, K dependence of electron PSD drops can provide critical and credible clues regarding the mechanisms responsible for electron losses at different L* over the outer radiation belt.
      PubDate: 2017-08-30T19:25:50.06423-05:0
      DOI: 10.1002/2017JA024487
       
  • Sources of Ionospheric Variability at Mars
    • Authors: Michael Mendillo; Clara Narvaez, Marissa F. Vogt, Majd Mayyasi, Jeffrey Forbes, Marina Galand, Edward Thiemann, Mehdi Benna, Francis Eparvier, Phillip Chamberlin, Paul Mahaffy, Laila Andersson
      Abstract: During the MAVEN mission's deep-dip #2 campaign of 17-22 April 2015, spacecraft instruments observed all of the physical parameters needed to assess the photo-chemical-equilibrium (PCE) explanation for ionospheric variability at a fixed altitude (135 km) near the peak of the martian ionosphere. MAVEN measurements of electron density, electron temperature, neutral CO2 density and solar irradiance were collected during 28 orbits. When inserted into the PCE equation, the measurements of varying PCE drivers correlated with the observed electron density variations to within instrumental uncertainty levels. The dominant source of this positive correlation was the variability of CO2 densities associated with the longitudinal wave-2 component of non-migrating tides in the martian thermosphere.
      PubDate: 2017-08-30T19:25:43.16013-05:0
      DOI: 10.1002/2017JA024366
       
  • A statistical study of kinetic-size magnetic holes in turbulent
           magnetosheath: MMS observations
    • Authors: S. Y. Huang; J. W. Du, F. Sahraoui, Z. G. Yuan, J. S. He, J. S. Zhao, O. Le Contel, H. Breuillard, D. D. Wang, X. D. Yu, X. H. Deng, H. S. Fu, M. Zhou, C. J. Pollock, R. B. Torbert, C. T. Russell, J. L. Burch
      Abstract: Kinetic-size magnetic holes (KSMHs) in the turbulent magnetosheath are statistically investigated using high time resolution data from the Magnetospheric Multiscale mission. The KSMHs with short duration (i.e.,
      PubDate: 2017-08-29T21:51:28.449789-05:
      DOI: 10.1002/2017JA024415
       
  • An explanation of auroral intensification during the substorm expansion
           phase
    • Authors: Zhonghua Yao; I. J. Rae, A. T. Y. Lui, K. R. Murphy, C. J. Owen, Z. Y. Pu, C. Forsyth, D. Grodent, Q.-G. Zong, A. M. Du, N. M. E. Kalmoni
      Abstract: A multiple auroral onset substorm on 28 March 2010 provides an opportunity to understand the physical mechanism in generating auroral intensifications during a substorm expansion phase. Conjugate observations of magnetic fields and plasma from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft, of field-aligned currents (FACs) from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) satellites, and from ground-based magnetometers and aurora are all available. The comprehensive measurements allow us to further our understanding of the complicated causalities among dipolarization, FAC generation, particle acceleration, and auroral intensification. During the substorm expansion phase, the plasma sheet expanded and was perturbed leading to the generation of a slow mode wave, which modulated electron flux in the outer plasma sheet. During this current sheet expansion, field-aligned currents formed, and geomagnetic perturbations were simultaneously detected by ground-based instruments. However, a magnetic dipolarization did not occur until about 3 min later in the outer plasma sheet observed by THEMIS-A spacecraft (THA). We believe that this dipolarization led to an efficient Fermi acceleration to electrons and consequently the cause of a significant auroral intensification during the expansion phase as observed by the All-Sky Imagers (ASIs). This Fermi acceleration mechanism operating efficiently in the outer plasma sheet during the expansion phase could be a common explanation of the poleward auroral development after substorm onset. These results also show a good agreement between the upward FAC derived from AMPERE measurements and the auroral brightening observed by the ASIs.
      PubDate: 2017-08-29T21:51:05.820966-05:
      DOI: 10.1002/2017JA024029
       
  • The solar wind proton ejection mechanism: Experiments with ultradense
           hydrogen agree with observed velocity distributions
    • Authors: Leif Holmlid
      Abstract: Ultradense hydrogen H(0) is a very dense hydrogen cluster phase with H-H distances in the picometer range. It has been studied experimentally in several publications from our group. A theoretical model exists which agrees well with laser-pulse-induced time-of-flight spectra and with rotational spectroscopy emission spectra. Coulomb explosions in H(0) in spin state s = 1 generate protons with kinetic energies larger than the retaining gravitational energy at the photosphere of the Sun. The required proton kinetic energy above 2 keV has been directly observed in published experiments. Such protons may be ejected from the Sun and are proposed to form the solar wind. The velocity distributions of the protons are calculated for three different ejecting modes from spin state s = 1. They agree well with both the fast and the slow solar winds. The best agreement is found for H(0) cluster sizes of 3 and 20–50 atoms; such clusters have been studied experimentally previously. The properties of ultradense hydrogen H(0) give also a few novel possibilities to explain the high corona temperature of the Sun.
      PubDate: 2017-08-29T21:50:27.731077-05:
      DOI: 10.1002/2017JA024498
       
  • Analyses of electron runaway in front of the negative streamer channel
    • Authors: L. P. Babich; E. I. Bochkov, I. M. Kutsyk, T. Neubert, O. Chanrion
      Abstract: X-ray and γ-ray emissions, observed in correlation with negative leaders of lightning and long sparks of high-voltage laboratory experiments, are conventionally connected with the bremsstrahlung of high-energy runaway electrons (REs). Here we extend a focusing mechanism, analyzed in our previous paper, which allows the electric field to reach magnitudes, required for a generation of significant RE fluxes and associated bremsstrahlung, when the ionization wave propagates in a narrow, ionized channel created by a previous streamer. Under such conditions we compute the production rate of REs per unit streamer length as a function of the streamer velocity and predict that, once a streamer is formed with the electric field capable of producing REs ahead of the streamer front, the ionization induced by the REs is capable of creating an ionized channel that allows for self-sustained propagation of the RE-emitting ionization wave independent of the initial electron concentration. Thus, the streamer coronas of the leaders are probable sources of REs producing the observed high-energy radiation. To prove these predictions, new simulations are planned, which would show explicitly that the preionization in front of the channel via REs will lead to the ionization wave propagation self-consistent with RE generation.
      PubDate: 2017-08-29T21:45:34.582659-05:
      DOI: 10.1002/2017JA023917
       
  • The characteristics and generation mechanism of small-amplitude and
           large-amplitude ESF irregularities observed by the C/NOFS satellite
    • Authors: Chao-Song Huang
      Abstract: It is well understood that equatorial plasma bubbles are initiated in the bottomside F region and grow into the topside F region, producing equatorial spread F (ESF) irregularities in both bottomside and topside F regions. However, it is not known whether small-amplitude and large-amplitude irregularities have the same occurrence pattern and how the generation of small-amplitude and large-amplitude irregularities is related to the postsunset vertical plasma drift and potential seeding processes. In this study, we use ion density and velocity data measured by the Communications/Navigation Outage Forecasting System satellite during May 2008 to July 2014 to derive the longitude-month distributions of the occurrence probability of ESF irregularities at different amplitudes. It is found that the occurrence probability of large-amplitude irregularities is well correlated with the postsunset vertical plasma drift and that small-amplitude irregularities do not show a clear pattern at low solar activity but is anticorrelated with that of large-amplitude irregularities at moderate solar activity. That is, the months and longitudes with high occurrence probability of large-amplitude irregularities are exactly those with low occurrence probability of small-amplitude irregularities, and vice versa. ESF irregularities are mostly limited below 500 km during low solar activity in 2008–2010, but large-amplitude irregularities can reach 700–800 km in altitude during moderate solar activity in 2011–2014. The generation of large-amplitude ESF irregularities is controlled by the postsunset vertical plasma drift at both low and moderate solar activities. In contrast, small-amplitude ESF irregularities at moderate solar activity occur more frequently in the areas where the postsunset vertical plasma drift is small.
      PubDate: 2017-08-29T21:41:02.632127-05:
      DOI: 10.1002/2017JA024041
       
  • Nonlinear generation mechanism of EMIC falling tone emissions
    • Authors: Masafumi Shoji; Yoshiharu Omura
      Abstract: We have conducted a self-consistent hybrid simulation, successfully reproducing EMIC emissions with falling-tone frequencies. The hybrid simulation is implemented with a parabolic ambient magnetic field. In the simulation, strong oxygen band EMIC emissions are generated through nonlinear wave growth. The cold ion density is modulated by electrostatic structures which are induced by the forward and backward propagating oxygen band EMIC waves. Along with the growth of the oxygen band, the helium band waves also grow because of the initial linear growth followed by the nonlinear growth. The nonlinear growth of the helium band waves is affected by the cold plasma density modulation, and there appear short wave packets of helium band emissions. The short wave packets entrap energetic protons efficiently, resulting in electromagnetic proton hills in the velocity phase space. The proton hill forms a nonlinear resonant current causing the falling frequency of the EMIC waves. We find strong deformation of the velocity distribution function of the energetic protons due to the proton hill being guided by the increasing resonance velocity.
      PubDate: 2017-08-29T19:35:34.886852-05:
      DOI: 10.1002/2017JA023883
       
  • Annual and interannual variations in global 6.5DWs from 20 to 110 km
           during 2002–2016 observed by TIMED/SABER
    • Authors: Y. Y. Huang; S. D. Zhang, C. Y. Li, H. J. Li, K. M. Huang, C. M. Huang
      Abstract: Using version 2.0 of the TIMED/SABER kinetic temperature data, we have conducted a study on the annual and interannual variations of 6.5DWs at 20–110 km, from 52°S to 52°N for 2002–2016. First, we obtained global annual variations in the spectral power and amplitudes of 6.5DWs. We found that strong wave amplitudes emerged from 25°S/N to 52°S/N and peaked in the altitudes of the stratosphere, mesosphere, and the lower thermosphere. The annual variations in the 6.5DWs are similar in both hemispheres but different at various altitudes. At 40–50 km, the annual maxima emerge mostly in winters. In the MLT, annual peaks occurred twice every half year. At 80–90 km, 6.5DWs appeared mainly in equinoctial seasons and winters. At 100–110 km, 6.5DWs emerged mainly in equinoctial seasons. Second, we continued the study of the interannual variations in 6.5DW amplitudes from 2002 to 2016. Frequency spectra of the monthly mean amplitudes showed that main dynamics in the long-term variations of 6.5DWs were AO and SAO in both hemispheres. In addition, 4 month period signals were noticed in the MLT of the NH. The amplitudes of SAO and AO were obtained using a band-pass filter and were found to increase with altitude, as do the 6.5DW amplitudes. In both hemispheres, the relative importance of SAO and AO changes with altitude. At 40–50 and 100–110 km, AO play a dominant role, while at 80–90 km, they are weaker than SAO. Our results show that both the annual and interannual variations in 6.5DWs are mainly caused by the combined action of SAO and AO.
      PubDate: 2017-08-29T00:17:50.265317-05:
      DOI: 10.1002/2017JA023886
       
  • Electric and magnetic variations in the near-Mars environment
    • Authors: C. M. Fowler; L. Andersson, J. Halekas, J. R. Espley, C. Mazelle, E. R. Coughlin, R. E. Ergun, D. J. Andrews, J. E. P. Connerney, B. Jakosky
      Abstract: For the first time at Mars the statistical distribution of (1-D) electric field wave power in the magnetosphere is presented, along with the distribution of magnetic field wave power, as observed by the Mars Atmosphere and Volatile EvolutioN spacecraft from the first 14.5 months of the mission. Wave power in several different frequency bands was investigated, and the strongest wave powers were observed at the lowest frequencies. The presented statistical studies suggest that the full thermalization of ions within the magnetosheath does not appear to occur, as has been predicted by previous studies. Manual inspection of 140 periapsis passes on the dayside shows that Poynting fluxes (at 2–16 Hz) between ∼10−11 and 10−8 Wm−2 reach the upper ionosphere for all 140 cases. Wave power is not observed in the ionosphere for integrated electron densities greater than 1010.8 cm−2, corresponding to typical depths of 100–200 km. The observations presented support previous suggestions that energy from the Mars-solar wind interaction can propagate into the upper ionosphere and may provide an ionospheric heating source. Upstream of the shock, the orientation of the solar wind interplanetary magnetic field was shown to significantly affect the statistical distribution of wave power, based on whether the spacecraft was likely magnetically connected to the shock or not—something that is predicted but has not been quantitatively shown at Mars before. In flight performance and caveats of the Langmuir Probe and Waves electric field power spectra are also discussed.
      PubDate: 2017-08-29T00:16:06.62129-05:0
      DOI: 10.1002/2016JA023411
       
  • Energy budget and mechanisms of cold ion heating in asymmetric magnetic
           reconnection
    • Authors: Sergio Toledo-Redondo; Mats André, Yuri V. Khotyaintsev, Benoit Lavraud, Andris Vaivads, Daniel B. Graham, Wenya Li, Denise Perrone, Stephen Fuselier, Daniel J. Gershman, Nicolas Aunai, Jeremy Dargent, Barbara Giles, Olivier Le Contel, Per-Arne Lindqvist, Robert E. Ergun, Christopher T. Russell, James L. Burch
      Abstract: Cold ions (few tens of eV) of ionospheric origin are commonly observed on the magnetospheric side of the Earth's dayside magnetopause. As a result, they can participate in magnetic reconnection, changing locally the reconnection rate and being accelerated and heated. We present four events where cold ion heating was observed by the Magnetospheric Multiscale mission, associated with the magnetospheric Hall E field region of magnetic reconnection. For two of the events the cold ion density was small compared to the magnetosheath density, and the cold ions were heated roughly to the same temperature as magnetosheath ions inside the exhaust. On the other hand, for the other two events the cold ion density was comparable to the magnetosheath density and the cold ion heating observed was significantly smaller. Magnetic reconnection converts magnetic energy into particle energy, and ion heating is known to dominate the energy partition. We find that at least 10 - 25% of the energy spent by reconnection into ion heating, went into magnetospheric cold ion heating. The total energy budget for cold ions may be even higher when properly accounting for the heavier species, namely Helium and Oxygen. Large E field fluctuations are observed in this cold ion heating region, i.e., gradients and waves, that are likely the source of particle energization.
      PubDate: 2017-08-28T17:57:27.018853-05:
      DOI: 10.1002/2017JA024553
       
  • Traveling foreshocks and transient foreshock phenomena
    • Authors: P. Kajdič; X. Blanco-Cano, N. Omidi, D. Rojas-Castillo, D. G. Sibeck, L. Billingham
      Abstract: We use the multi-spacecraft capabilities of the Cluster and THEMIS missions to show that two types of foreshock may be detected in spacecraft data. One is the global foreshock that appears upstream of the Earth's quasi-parallel bow-shock under steady or variable interplanetary magnetic field. Another type is a traveling foreshock that is bounded by two rotational discontinuities in the interplanetary magnetic field and propagates along the bow-shock. Foreshock compressional boundaries are found at the edges of both types of foreshock. We show that isolated foreshock cavities are a subset of the traveling foreshock that form when two bounding rotational discontinuities are so close that the ultra-low frequency waves do not develop in the region between them. We also report observations of a spontaneous hot flow anomaly inside a traveling foreshock. This means that other phenomena, such as foreshock cavitons, may also exist inside this type of foreshock. In the second part of this work we present statistical properties of phenomena related to the foreshock, namely foreshock cavities, cavitons, spontaneous hot flow anomalies and foreshock compressional boundaries. We show that spontaneous hot flow anomalies are the most depleted transient structures in terms of the B-field and plasma density inside them and that the foreshock compressional boundaries and foreshock cavities are closely related structures.
      PubDate: 2017-08-28T17:57:19.338124-05:
      DOI: 10.1002/2017JA023901
       
  • Modeling polar region atmospheric ionization induced by the giant solar
           storm on 20 January 2005
    • Authors: W. Mitthumsiri; A. Seripienlert, U. Tortermpun, P.-S. Mangeard, A. Sáiz, D. Ruffolo, R. Macatangay
      Abstract: Ionization in Earth's troposphere is mainly due to Galactic cosmic rays. Occasionally, solar storms produce intense relativistic ion beams that significantly increase such ionization. One of the largest recorded solar radiation storms, on 20 January 2005, resulted in up to 55-fold increases in the count rates of ground-based particle detectors in polar regions. We use McMurdo and Inuvik neutron monitor data to estimate accurate time profiles of ion energy spectra above the atmosphere at each location. Using data-driven atmospheric models, we perform Monte Carlo simulations of particle-air interactions and calculate atmospheric ionization and potential biological dosage versus altitude and time for each location. We found that if airplane passengers had traversed the south polar region, they could have been exposed to the typical annual cosmic radiation dosage at sea level within 1 h. These techniques can help evaluate possible influences of solar activity on atmospheric properties.
      PubDate: 2017-08-26T08:21:01.630312-05:
      DOI: 10.1002/2017JA024125
       
  • Modeling radiation belt dynamics using a 3-D layer method code
    • Authors: C. Wang; Q. Ma, X. Tao, Y. Zhang, S. Teng, J. M. Albert, A. A. Chan, W. Li, B. Ni, Q. Lu, S. Wang
      Abstract: A new 3-D diffusion code using a recently published layer method has been developed to analyze radiation belt electron dynamics. The code guarantees the positivity of the solution even when mixed diffusion terms are included. Unlike most of the previous codes, our 3-D code is developed directly in equatorial pitch angle (α0), momentum (p), and L shell coordinates; this eliminates the need to transform back and forth between (α0,p) coordinates and adiabatic invariant coordinates. Using (α0,p,L) is also convenient for direct comparison with satellite data. The new code has been validated by various numerical tests, and we apply the 3-D code to model the rapid electron flux enhancement following the geomagnetic storm on 17 March 2013, which is one of the Geospace Environment Modeling Focus Group challenge events. An event-specific global chorus wave model, an AL-dependent statistical plasmaspheric hiss wave model, and a recently published radial diffusion coefficient formula from Time History of Events and Macroscale Interactions during Substorms (THEMIS) statistics are used. The simulation results show good agreement with satellite observations, in general, supporting the scenario that the rapid enhancement of radiation belt electron flux for this event results from an increased level of the seed population by radial diffusion, with subsequent acceleration by chorus waves. Our results prove that the layer method can be readily used to model global radiation belt dynamics in three dimensions.
      PubDate: 2017-08-26T08:20:35.68337-05:0
      DOI: 10.1002/2017JA024143
       
  • SAPS/SAID revisited: A causal relation to the substorm current wedge
    • Authors: Evgeny Mishin; Yukitoshi Nishimura, John Foster
      Abstract: We present multispacecraft observations of enhanced flow/electric field channels in the inner magnetosphere and conjugate subauroral ionosphere, i.e., subauroral polarization streams (SAPS) near dusk and subauroral ion drifts (SAID) near midnight. The channels collocate with ring current (RC) injections lagging the onset of substorms by a few to ∼20 min, i.e., significantly shorter than the gradient-curvature drift time of tens of keV ions. The time lag is of the order of the propagation time of reconnection-injected hot plasma jets to the premidnight plasmasphere and the substorm current wedge (SCW) to dusk. The observations confirm and expand on the previous results on the SAID features that negate the paradigm of voltage and current generators. Fast-time duskside SAPS/RC injections appear intimately related to a two-loop circuit of the substorm current wedge (SCW2L). We suggest that the poleward electric field inherent in the SCW2L circuit, which demands closure of the Region 1 and Region 2 sense field-aligned currents via meridional currents, is the ultimate cause of fast RC injections and SAPS on the duskside.
      PubDate: 2017-08-26T08:11:46.551615-05:
      DOI: 10.1002/2017JA024263
       
  • Quasi-thermal noise spectroscopy: The art and the practice
    • Authors: N. Meyer-Vernet; K. Issautier, M. Moncuquet
      Abstract: Quasi-thermal noise spectroscopy is an efficient tool for measuring in situ macroscopic plasma properties in space, using a passive wave receiver at the ports of an electric antenna. This technique was pioneered on spinning spacecraft carrying very long dipole antennas in the interplanetary medium—like ISEE-3 and Ulysses—whose geometry approached a “theoretician's dream.” The technique has been extended to other instruments in various types of plasmas on board different spacecraft and will be implemented on several missions in the near future. Such extensions require different theoretical modelizations, involving magnetized, drifting, or dusty plasmas with various particle velocity distributions and antennas being shorter, biased, or made of unequal wires. We give new analytical approximations of the plasma quasi-thermal noise (QTN) and study how the constraints of the real world in space can (or cannot) be compatible with plasma detection by QTN spectroscopy. We consider applications to the missions Wind, Cassini, BepiColombo, Solar Orbiter, and Parker Solar Probe.
      PubDate: 2017-08-26T08:10:49.170651-05:
      DOI: 10.1002/2017JA024449
       
  • Validation of single spacecraft methods for collisionless shock velocity
           estimation
    • Authors: Stefanos Giagkiozis; Simon N. Walker, Simon A. Pope, Glyn Collinson
      Abstract: The velocity of a collisionless shock (CS) is an important parameter in the determination of the spatial scales of the shock. The spatial scales of the shock determine the processes that guide the energy dissipation, which is related to the nature of the shock. During the pre-ISEE era, estimations of relative shock-spacecraft velocity (VSh) were based on spatial scales of the shock front regions, in particularly the foot. Multispacecraft missions allow more reliable identification of VSh. The main objective of this study is to examine the accuracy of two single spacecraft methods, which use the foot region of quasi-perpendicular shocks in order determine VSh. This is important for observational shock studies based on a single spacecraft data such as Venus Express (VEX) and THOR, a proposed single spacecraft mission of European Space Agency. It is shown that neither method provides estimates with an accuracy comparable to multipoint measurements of VSh. In the absence of alternative techniques to identify the VSh and therefore the spatial scales of the shocks, the methods can be used to provided order of magnitude estimations for the spatial scales of the shock front. Observations of the Venusian bow shock from VEX data have been used as an illustrative example for the application of these methods to estimate the shock spatial scale and the corresponding errors of this estimation. It is shown that the spatial width of the ramp of the observed shock is L ∼ 3.4 ± 1.4c/ωpe.
      PubDate: 2017-08-26T08:10:28.105569-05:
      DOI: 10.1002/2017JA024502
       
  • Equinoctial asymmetry in the zonal distribution of scintillation as
           observed by GPS receivers in Indonesia
    • Authors: P. Abadi; Y. Otsuka, K. Shiokawa, A. Husin, Huixin Liu, S. Saito
      Abstract: We investigate the azimuthal distribution of amplitude scintillation observed by Global Positioning System (GPS) ground receivers at Pontianak (0.0°S, 109.3°E; magnetic latitude: 9.8°S) and Bandung (6.9°S, 107.6°E; magnetic latitude: 16.7°S) in Indonesia in March and September from 2011 to 2015. The scintillation is found to occur more to the west than to the east in March at both stations, whereas no such zonal difference is found in September. We also analyze the zonal scintillation drift as estimated using three closely spaced single-frequency GPS receivers at Kototabang (0.2°S, 100.3°E; magnetic latitude: 9.9°S) in Indonesia during 2003–2015 and the zonal thermospheric neutral wind as measured by the CHAMP satellite at longitudes of 90°–120°E during 2001–2008. We find that the velocities of both the zonal scintillation drift and the neutral wind decrease with increasing latitudes. Interestingly, the latitudinal gradients of both the zonal scintillation drift and the neutral wind are steeper in March than in September. These steeper March gradients may be responsible for the increased westward altitudinal and latitudinal tilting of plasma bubbles in March. This equinoctial asymmetry could be responsible for the observed westward bias in scintillation in March, because the scintillation is more likely to occur when radio waves pass through longer lengths of plasma irregularities in the plasma bubbles.
      PubDate: 2017-08-24T10:21:08.936274-05:
      DOI: 10.1002/2017JA024146
       
  • EMIC wave parameterization in the long-term VERB code simulation
    • Authors: A. Y. Drozdov; Y. Y. Shprits, M. E. Usanova, N. A. Aseev, A. C. Kellerman, H. Zhu
      Abstract: Electromagnetic ion cyclotron (EMIC) waves play an important role in the dynamics of ultrarelativistic electron population in the radiation belts. However, as EMIC waves are very sporadic, developing a parameterization of such wave properties is a challenging task. Currently, there are no dynamic, activity-dependent models of EMIC waves that can be used in the long-term (several months) simulations, which makes the quantitative modeling of the radiation belt dynamics incomplete. In this study, we investigate Kp, Dst, and AE indices, solar wind speed, and dynamic pressure as possible parameters of EMIC wave presence. The EMIC waves are included in the long-term simulations (1 year, including different geomagnetic activity) performed with the Versatile Electron Radiation Belt code, and we compare results of the simulation with the Van Allen Probes observations. The comparison shows that modeling with EMIC waves, parameterized by solar wind dynamic pressure, provides a better agreement with the observations among considered parameterizations. The simulation with EMIC waves improves the dynamics of ultrarelativistic fluxes and reproduces the formation of the local minimum in the phase space density profiles.
      PubDate: 2017-08-24T10:20:49.012587-05:
      DOI: 10.1002/2017JA024389
       
  • Linear response of field-aligned currents to the interplanetary electric
           field
    • Authors: D. R. Weimer; T. R. Edwards, Nils Olsen
      Abstract: Many studies that have shown that the ionospheric, polar cap electric potentials (PCEPs) exhibit a “saturation” behavior in response to the level of the driving by the solar wind. As the magnitudes of the interplanetary magnetic field (IMF) and electric field (IEF) increase, the PCEP response is linear at low driving levels, followed with a rollover to a more constant level. While there are several different theoretical explanations for this behavior, so far, no direct observational evidence has existed to confirm any particular model. In most models of this saturation, the interaction of the field-aligned currents (FACs) with the solar wind/magnetosphere/ionosphere system has a role. As the FACs are more difficult to measure, their behavior in response to the level of the IEF has not been investigated as thoroughly. In order to resolve the question of whether or not the FAC also exhibit saturation, we have processed the magnetic field measurements from the Ørsted, CHAMP, and Swarm missions, spanning more than a decade. As the amount of current in each region needs to be known, a new technique is used to separate and sum the current by region, widely known as R0, R1, and R2. These totals are found separately for the dawnside and duskside. Results indicate that the total FAC has a response to the IEF that is highly linear, continuing to increase well beyond the level at which the electric potentials saturate. The currents within each region have similar behavior.
      PubDate: 2017-08-24T10:15:46.688423-05:
      DOI: 10.1002/2017JA024372
       
  • Interplanetary magnetic field properties and variability near Mercury's
           orbit
    • Authors: Matthew K. James; Suzanne M. Imber, Emma J. Bunce, Timothy K. Yeoman, Mike Lockwood, Mathew J. Owens, James A. Slavin
      Abstract: The first extensive study of interplanetary magnetic field (IMF) characteristics and stability at Mercury is undertaken using MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) magnetometer data. Variations in IMF and solar wind conditions have a direct and rapid effect upon Mercury's highly dynamic magnetosphere; hence, understanding of the time scales over which these variations occur is crucial because they determine the duration of magnetospheric states. We characterize typical distributions of IMF field strength, clock angle, and cone angle throughout the duration of MESSENGER's mission. Clock and cone angle distributions collected during the first Earth year of the mission indicate that there was a significant north-south asymmetry in the location of the heliospheric current sheet during this period. The stability of IMF magnitude, clock angle, cone angle, and IMF Bz polarity is quantified for the entire mission. Changes in IMF Bz polarity and magnitude are found to be less likely for higher initial field magnitudes. Stability in IMF conditions is also found to be higher at aphelion (heliocentric distance r ∼ 0.31 AU) than at perihelion (r ∼ 0.47 AU).
      PubDate: 2017-08-24T10:11:28.384856-05:
      DOI: 10.1002/2017JA024435
       
  • Midlatitude ionospheric D region: Height, sharpness, and solar zenith
           angle
    • Authors: Neil R. Thomson; Mark A. Clilverd, Craig J. Rodger
      Abstract: VLF radio amplitude and phase measurements are used to find the height and sharpness of the D region of the ionosphere at a mid to high geomagnetic dip latitude of ~52.5°. The two paths used are both from the 23.4 kHz transmitter, DHO, in north Germany with the first path being northward and mainly over the sea along the west coast of Denmark over a range of ~320–425 km, and the second, also mainly all-sea, to a single fixed recording receiver at Eskdalemuir in Scotland (~750 km). From plots of the measured amplitudes and phases versus distance for the first of these paths compared with calculations using the U.S. Navy code, ModeFinder, the Wait height and sharpness parameters of the D region at midday in summer 2015 are found to be H′ = 72.8 ± 0.2 km and β = 0.345 ± 0.015 km−1 at a solar zenith angle ~33°. From phase and amplitude measurements at other times of day on the second path, the daytime changes in H′ and β as functions of solar zenith angle are determined from shortly after dawn to shortly before dusk. Comparisons are also made between the modal ModeFinder calculations and wave hop calculations, with both giving similar results. The parameters found here should be useful in understanding energy inputs to the D region from the radiation belts, solar flares, or transient luminous events. The midday values may be sufficiently precise to be useful for monitoring climate change.
      PubDate: 2017-08-24T10:10:46.487621-05:
      DOI: 10.1002/2017JA024455
       
  • Characterizing the source properties of terrestrial gamma ray flashes
    • Authors: Joseph R. Dwyer; Ningyu Liu, J. Eric Grove, Hamid Rassoul, David M. Smith
      Abstract: Monte Carlo simulations are used to determine source properties of terrestrial gamma ray flashes (TGFs) as a function of atmospheric column depth and beaming geometry. The total mass per unit area traversed by all the runaway electrons (i.e., the total grammage) during a TGF, Ξ, is introduced, defined to be the total distance traveled by all the runaway electrons along the electric field lines multiplied by the local air mass density along their paths. It is shown that key properties of TGFs may be directly calculated from Ξ and its time derivative, including the gamma ray emission rate, the current moment, and the optical power of the TGF. For the calculations presented in this paper, a standard TGF gamma ray fluence, F0 = 0.1 cm−2 above 100 keV for a spacecraft altitude of 500 km, and a standard total grammage, Ξ0 = 1018 g/cm2, are introduced, and results are presented in terms of these values. In particular, the current moments caused by the runaway electrons and their accompanying ionization are found for a standard TGF fluence, as a function of source altitude and beaming geometry, allowing a direct comparison between the gamma rays measured in low-Earth orbit and the VLF-LF radio frequency emissions recorded on the ground. Such comparisons should help test and constrain TGF models and help identify the roles of lightning leaders and streamers in the production of TGFs.
      PubDate: 2017-08-24T10:10:34.125246-05:
      DOI: 10.1002/2017JA024141
       
  • Contribution of energetic and heavy ions to the plasma pressure: Storm
           September 27 - October 3, 2002
    • Authors: E. A. Kronberg; L. M. Kistler, D. Welling, C. Mouikis, P. W. Daly, E. E. Grigorenko, B. Klecker, I. Dandouras
      Abstract: Magnetospheric plasma sheet ions drift towards the Earth and populate the ring current. The ring current plasma pressure distorts the terrestrial internal magnetic field at the surface and this disturbance strongly affects the strength of a magnetic storm. The contribution of energetic ions (>40 keV) and of heavy ions to the total plasma pressure in the near-Earth plasma sheet is not always considered. In this study, we evaluate the contribution of low-energy and energetic ions of different species to the total plasma pressure for the storm observed by the Cluster mission from September 27 until October 3 in 2002. We show that the contribution of energetic ions (>40 keV) and of heavy ions to the total plasma pressure is ≃76–98.6% in the ring current and ≃14–59% in the magnetotail. The main source of oxygen ions, responsible for ≃56% of the plasma pressure of the ring current, is located at distances Earthward of XGSE≃-13.5 RE during the main phase of the storm. The contribution of the ring current particles agrees with the observed Dst index. We model the magnetic storm using the Space Weather Modeling Framework (SWMF). We assess the plasma pressure output in the ring current for two different ion outflow models in the SWMF through comparison with observations. Both models yield reasonable results. The model which produces the most heavy ions agrees best with the observations. However, the data suggests that there is still potential for refinement in the simulations.
      PubDate: 2017-08-23T16:37:52.393736-05:
      DOI: 10.1002/2017JA024215
       
  • Erosion of the plasmasphere during a storm
    • Authors: J. Krall; J. D. Huba, S. Sazykin
      Abstract: The erosion of the plasmasphere during a storm is analyzed using the Naval Research Laboratory (NRL) Sami3 is Also a Model of the Ionosphere (SAMI3) ionosphere/plasmasphere code, coupled to the Rice Convection Model (RCM) of the inner magnetosphere and ring current. We reproduce the commonly-observed post-storm plasmasphere profile, with strong erosion outside of a sharp, post-storm plasmapause and weak erosion inside the plasmapause. We find that inclusion of the ring current E field sharpens the post-storm plasmapause. In the case of a weak storm, erosion inside the post-storm plasmapause might not occur. In all cases, plasma flows are dominated by E × B drifts. For strong storms, we find that erosion, both inside and outside of the post-storm plasmapause, is caused by outward E × B drifts.
      PubDate: 2017-08-21T20:19:25.925781-05:
      DOI: 10.1002/2017JA024450
       
  • CIMI simulations with newly developed multi-parameter chorus and
           plasmaspheric hiss wave models
    • Authors: Homayon Aryan; David G. Sibeck, Suk-Bin Kang, Michael A. Balikhin, Mei-Ching Fok, Oleksiy Agapitov, Colin M. Komar, Shrikanth G. Kanekal, Tsugunobu Nagai
      Abstract: Numerical simulation studies of the Earth's radiation belts are important to understand the acceleration and loss of energetic electrons. The Comprehensive Inner Magnetosphere-Ionosphere (CIMI) model considers the effects of the ring current and plasmasphere on the radiation belts to obtain plausible results. The CIMI model incorporates pitch angle, energy, and cross diffusion of electrons, due to chorus and plasmaspheric hiss waves. These parameters are calculated using statistical wave distribution models of chorus and plasmaspheric hiss amplitudes. However, currently these wave distribution models are based only on a single parameter, geomagnetic index (AE), and could potentially underestimate the wave amplitudes. Here we incorporate recently developed multi-parameter chorus and plasmaspheric hiss wave models based on geomagnetic index and solar wind parameters. We then perform CIMI simulations for two geomagnetic storms and compare the flux enhancement of MeV electrons with data from the Van Allen Probes and Akebono satellites. We show that the relativistic electron fluxes calculated with multi-parameter wave models resembles the observations more accurately than the relativistic electron fluxes calculated with single-parameter wave models. This indicates that wave models based on a combination of geomagnetic index and solar wind parameters are more effective as inputs to radiation belt models.
      PubDate: 2017-08-21T20:19:06.821585-05:
      DOI: 10.1002/2017JA024159
       
  • Energetic Particle Loss Through the Magnetopause: A Combined Global MHD
           and Test-Particle Study
    • Authors: K. A. Sorathia; V. G. Merkin, A. Y. Ukhorskiy, B. H. Mauk, D. G. Sibeck
      Abstract: We study the spatiotemporal characteristics of energetic particle losses from the magnetosphere using test-particle trajectories in electromagnetic fields from a global magnetosphere magnetohydrodynamic (MHD) simulation. We use a dynamically evolving distribution of high-resolution electromagnetic fields from the Lyon-Fedder-Mobarry (LFM) global MHD model and trace large ensembles of 100 keV hydrogen and oxygen ions as well as electrons from a near-Earth plasma sheet location through their escape from the magnetosphere. In agreement with recent MMS observations, we demonstrate that both ions and electrons have access to and escape throughout the dayside magnetopause, including magnetically drift-shadowed regions. Also in agreement with MMS observations, the depth of penetration and persistence of particles in the magnetosheath has a clear mass dependence, heavier particles penetrating further and lingering longer. We demonstrate both magnetic local time and latitude dependence of particles losses as manifested by their crossings of the open-closed boundary, and relate them to the complex field topology. Finally, we establish a significant role of Kelvin-Helmholtz instability in facilitating particle losses at the magnetopause flanks.
      PubDate: 2017-08-17T16:26:22.231946-05:
      DOI: 10.1002/2017JA024268
       
  • Local Ensemble Transform Kalman Filter for Ionospheric Data Assimilation:
           Observation Influence Analysis During a Geomagnetic Storm Event
    • Authors: Juan Durazo; Eric J. Kostelich, Alex Mahalov
      Abstract: We propose a targeted observation strategy, based on the influence matrix diagnostic, that optimally selects where additional observations may be placed to improve ionospheric forecasts. This strategy is applied in data assimilation observing system experiments, where synthetic electron density vertical profiles, which mimic those of Constellation Observing System for Meteorology, Ionosphere, and Climate/Formosa satellite 3 (COSMIC), are assimilated into the Thermosphere-Ionosphere-Electrodynamics Global Circulation Model (TIEGCM) using the Local Ensemble Transform Kalman Filter (LETKF) during the 26 September 2011 geomagnetic storm. During each analysis step, the observation vector is augmented with five synthetic vertical profiles optimally placed to target electron density errors, using our targeted observation strategy. Forecast improvement due to assimilation of augmented vertical profiles is measured with the root mean square error (RMSE) of analyzed electron density, averaged over 600 km regions centered around the augmented vertical profile locations. Assimilating vertical profiles with targeted locations yields about 60%-80% reduction in electron density RMSE, compared to a 15% average reduction when assimilating randomly placed vertical profiles. Assimilating vertical profiles whose locations target the zonal component of neutral winds (Un) yields on average a 25% RMSE reduction in Un estimates, compared to a 2% average improvement obtained with randomly placed vertical profiles. These results demonstrate that our targeted strategy can improve data assimilation efforts during extreme events by detecting regions where additional observations would provide the largest benefit to the forecast.
      PubDate: 2017-08-15T15:50:43.155187-05:
      DOI: 10.1002/2017JA024274
       
  • Revisting the structure of low Mach number, low beta, quasi-perpendicular
           shocks
    • Authors: L. B. Wilson III; A. Koval, A. Szabo, M. L. Stevens, J. C. Kasper, C. A. Cattell, V. V. Krasnoselskikh
      Abstract: A study of the structure of 145 low Mach number (M ≤ 3), low beta (β≤ 1), quasi-perpendicular interplanetary collisionless shock waves observed by the Wind spacecraft has provided strong evidence that these shocks have large amplitude whistler precursors. The common occurrence and large amplitudes of the precursors raise doubts about the standard assumption that such shocks can be classified as laminar structures. This directly contradicts standard models. In 113 of the 145 shocks (∼78%), we observe clear evidence of magnetosonic-whistler precursor fluctuations with frequencies ∼0.1–7 Hz. We find no dependence on the upstream plasma beta, or any other shock parameter, for the presence or absence of precursors. The majority (∼66%) of the precursors propagate at ≤45∘ with respect to the upstream average magnetic field and most (∼87%) propagate ≥30∘ from the shock normal vector. Further, most (∼79%) of the waves propagate at least 20° from the coplanarity plane. The peak-to-peak wave amplitudes (δBpk − pk) are large with a range of maximum values for the 113 precursors of ∼0.2–13 nT with an average of ∼3 nT. When we normalize the wave amplitudes to the upstream averaged magnetic field and the shock ramp amplitude, we find average values of ∼50% and ∼80%, respectively.
      PubDate: 2017-08-03T19:50:58.394779-05:
      DOI: 10.1002/2017JA024352
       
  • The Dependence of Magnetospheric Plasma Mass Loading on Geomagnetic
           Activity Using Cluster
    • Authors: J. K. Sandhu; T. K. Yeoman, I. J. Rae, R. C. Fear, I. Dandouras
      Abstract: Understanding changes in the magnetospheric mass density during disturbed geomagnetic conditions provides valuable insight into the dynamics and structure of the environment. The mass density plays a significant role in a variety of magnetospheric processes, such as wave propagation, magnetic reconnection rates and radiation belt dynamics. In this study, the spatial variations of total plasma mass density are explored through the analysis of Cluster observations. Data from the WHISPER (Waves of High frequency and Sounder for Probing of Electron density by Relaxation) and CODIF (ion Composition and Distribution Function analyser) instruments, on board the four Cluster spacecraft for a time interval spanning 2001 - 2012, are used to determine empirical models describing the distribution of the total plasma mass density along closed geomagnetic field lines. The region considered covers field lines within 5.9≤L < 9.5, corresponding to the outer plasmasphere, plasmatrough, and near-Earth plasma sheet. This study extends previous work to examine and quantify spatial variations in the electron density, average ion mass, and total plasma mass density with Dst index. The results indicate that during periods of enhanced ring current strength, electron density is observed to decrease and average ion mass is observed to increase, compared with quiet geomagnetic conditions. The combination of these variations show that although heavy ion concentration is enhanced, the decrease in plasma number density results in a general decrease in total plasma mass density during disturbed geomagnetic conditions. The observed decrease in mass density is in contrast to prevailing understanding and, due to the dependence of the Alfvén speed on mass density, has important implications for a range of plasma processes during storm time conditions (e.g. propagation of wave modes).
      PubDate: 2017-08-03T19:50:36.02805-05:0
      DOI: 10.1002/2017JA024171
       
  • Statistical analysis of MMS observations of energetic electron escape
           observed at/beyond the dayside magnetopause
    • Authors: Ian J. Cohen; Barry H. Mauk, Brian J. Anderson, Joseph H. Westlake, David G. Sibeck, Drew L. Turner, Joseph F. Fennell, J. Bern Blake, Allison N. Jaynes, Trevor W. Leonard, Daniel N. Baker, Harlan E. Spence, Geoff D. Reeves, Barbara J. Giles, Robert J. Strangeway, Roy B. Torbert, James L. Burch
      Abstract: Observations from the Energetic Particle Detector (EPD) instrument suite aboard the Magnetospheric Multiscale (MMS) spacecraft show that energetic (>10s of keV) magnetospheric particle escape into the magnetosheath occurs commonly across the dayside. This includes the surprisingly frequent observation of magnetospheric electrons in the duskside magnetosheath, an unexpected result given assumptions regarding magnetic drift shadowing. 238 events have been identified during the first MMS dayside season that exhibit strongly anisotropic pitch angle distributions indicating mono-hemispheric field-aligned streaming away from the magnetopause in the 40 keV electron energy channel. A review of the extremely rich literature of energetic electron observations beyond the magnetopause is provided to place these new observations into historical context. Despite the extensive history of such research, these new observations provide a more comprehensive dataset that includes unprecedented magnetic local time (MLT) coverage of the dayside equatorial magnetopause/magnetosheath. These data clearly highlight the common escape of energetic electrons along magnetic field lines concluded to have been reconnected across the magnetopause. While these streaming escape events agree with prior studies which show strong correlation with geomagnetic activity (suggesting a magnetotail source) and occur most frequently during periods of southward IMF, the high number of duskside events is unexpected and previously unobserved. Although the lowest electron energy channel was the focus of this study, the events reported here exhibit pitch angle anisotropies indicative of streaming up to 200 keV, which could represent the magnetopause loss of>1 MeV electrons from the outer radiation belt.
      PubDate: 2017-08-01T23:20:37.522046-05:
      DOI: 10.1002/2017JA024401
       
  • Enhancement and modulation of cosmic noise absorption in the afternoon
           sector at sub-auroral location (L = 5) during the recovery phase of 17th
           March 2015 geomagnetic storm
    • Authors: Jayanta K. Behera; Ashwini K. Sinha, Geeta Vichare, Ankush Bhaskar, Farideh Honary, Rahul Rawat, Rajesh Singh
      Abstract: The present study has focused on the intense production of cosmic noise absorption(CNA) at Maitri, Antarctica (L = 5;CGM −62∘ S 55∘ E ) during the early recovery phase of the largest storm of the current solar cycle commenced on 17th March,2015 St. Patrick Day. The enhancement of CNA during 15 − 18 UT(14 − 17 MLT); (MLT=UT-1 at Maitri) was as large as the CNA enhancement occurred during the main phase of the storm. During this time the CNA pattern also exhibits oscillation in the Pc5(2 − 7 mHz) range and is in simultaneity with geomagnetic pulsations in the same frequency range. We observed the amplitude of CNA pulsation is well correlated with the level of CNA production. High amplitude Pc5 oscillations were observed in the vicinity of auroral oval near Maitri. Absence of Electro-Magnetic Ion-Cyclotron(EMIC) waves is marked suggesting the possible role of VLF waves in precipitation. The reason for the intense CNA production is found to be the precipitation caused mainly by hiss-driven sub-relativistic electrons. The CNA enhancement event is located well inside the dusk plasmaspheric bulge region as suggested by Tsurutani et al. [2015]. Signature of enhanced eastward electrojet at Maitri during 14 − 17 MLT could be an additional factor for such large CNA. In order to establish the cause and effect relationship between the geomagnetic and CNA oscillations at Maitri, Transfer Entropy method has been used, which confirmed the modulation of CNA by geomagnetic pulsations.
      PubDate: 2017-07-31T18:33:16.555007-05:
      DOI: 10.1002/2017JA024226
       
  • A statistical survey of heat input parameters into the cusp thermosphere
    • Authors: Åsmund Steen Skjæveland; Herbert C. Carlson, JÃÿran I. Moen
      Abstract: Based on three winters of observational data, we present those ionosphere parameters deemed most critical to realistic space weather ionosphere and thermosphere representation and prediction, in regions impacted by variability in the cusp. The CHAMP spacecraft revealed large variability in cusp thermosphere densities, measuring frequent satellite drag enhancements, up to doublings. The community recognizes a clear need for more realistic representation of plasma flows and electron densities near the cusp. Existing average-value models produce order of magnitude errors in these parameters, resulting in large underestimations of predicted drag. We fill this knowledge gap with statistics-based specification of these key parameters over their range of observed values. The EISCAT Svalbard Radar (ESR) tracks plasma flow Vi, electron density Ne, and electron, ion temperatures Te, Ti, with consecutive 2–3 minute windshield-wipe scans of 1000x500 km areas. This allows mapping the maximum Ti of a large area within or near the cusp with high temporal resolution. In magnetic field-aligned mode the radar can measure high-resolution profiles of these plasma parameters. By deriving statistics for Ne and Ti, we enable derivation of thermosphere heating deposition under background and frictional-drag-dominated magnetic reconnection conditions. We separate our Ne and Ti profiles into quiescent and enhanced states, which are not closely correlated due to the spatial structure of the reconnection footpoint. Use of our data-based parameter inputs can make order of magnitude corrections to input data driving thermosphere models, enabling removal of previous twofold drag errors.
      PubDate: 2017-07-31T18:32:35.846259-05:
      DOI: 10.1002/2016JA023594
       
  • Electron density extrapolation above F2 peak by the linear Vary-Chap model
           supporting new GNSS-LEO occultation missions
    • Authors: Manuel Hernández-Pajares; Miquel Garcia-Fernàndez, Antonio Rius, Riccardo Notarpietro, Axel von Engeln, Germán Olivares-Pulido, Àngela Aragón-Àngel, Alberto García-Rigo
      Abstract: The new radio-occultation (RO) instrument on-board the future EUMETSAT Polar System 2nd Generation (EPS-SG) satellites, flying at a height of 820 km, is primarily focusing on neutral atmospheric profiling. It will also provide an opportunity for RO ionospheric sounding, but only below impact heights of 500 km, in order to guarantee a full data gathering of the neutral part. This will leave a gap of 320 km, which impedes the application of the direct inversion techniques to retrieve the electron density profile. To contribute to overcome this challenge, we have looked for new ways (accurate and simple) of extrapolating the electron density (also applicable to other Low-Earth-Orbiting, LEO, missions like CHAMP): a new Vary-Chap Extrapolation Technique (VCET). VCET is based on the scale height behaviour, linearly dependent on the altitude above hmF2 . This allows the electron density profile extrapolation for impact heights above its peak height (this is the case for EPS-SG), up to the satellite orbital height. VCET has been assessed with more than 3700 complete electron density profiles obtained in 4 representative scenarios of FORMOSAT-3/COSMIC occultations, in solar maximum and minimum conditions, and geomagnetically disturbed conditions, by applying an updated Improved Abel Transform Inversion technique to dual-frequency GPS measurements. It is shown that VCET performs much better than other classical Chapman models, with 60% of occultations showing relative extrapolation errors below 20%, in contrast with conventional Chapman model extrapolation approaches with 10% or less of the profiles with relative error below 20%.
      PubDate: 2017-07-20T20:41:15.813061-05:
      DOI: 10.1002/2017JA023876
       
  • Transition from global to local control of dayside reconnection from
           ionospheric-sourced mass loading
    • Authors: B. Zhang; O. J. Brambles, P. A. Cassak, J. E. Ouellette, M. Wiltberger, W. Lotko, J. G. Lyon
      Abstract: We have conducted a series of controlled numerical simulations to investigate the response of dayside reconnection to idealized, ionosphere-sourced mass loading processes to determine whether they affect the integrated dayside reconnection rate. Our simulation results show that the coupled solar wind-magnetosphere (SW-M) system may exhibit both local and global control behaviors depending on the amount of mass loading. With a small amount of mass loading, the changes in local reconnection rate affects magnetosheath properties only weakly and the geoeffective length in the upstream solar wind is essentially unchanged, resulting in the same integrated dayside reconnection rate. With a large amount of mass loading, however, the magnetosheath properties and the geoeffective length are significantly affected by slowing down the local reconnection rate, resulting in an increase of the magnetic pressure in the magnetosheath, with a significant reduction in the geoeffective length in the upstream solar wind and in the integrated dayside reconnection rate. In this controlled simulation setup, the behavior of dayside reconnection potential is determined by the role of the enhanced magnetic pressure in the magnetospheath due to magnetospheric mass loading. The reconnection potential starts to decrease significantly when the enhanced magnetic pressure alters the thickness of the magnetosheath.
      PubDate: 2017-07-17T17:51:16.021505-05:
      DOI: 10.1002/2016JA023646
       
  • Data-derived optimization of sensitivity requirements for upcoming auroral
           imaging missions
    • Authors: Eric Donovan; Vadim M. Uritsky, Craig Unick, Vladimir Troyan
      Abstract: Using an extensive database of ultraviolet images of the night-time sector of the northern auroral oval obtained from the POLAR spacecraft, and data analysis tools adopted from statistical mechanics of turbulent flows, we identify scaling relations describing substorm - time variability of the auroral intensity as a function of spatial scale and auroral intensity level. By extrapolating these relations to scales smaller than those resolved by previously flown auroral missions, we derive contrast and sensitivity constraints for a next-generation global auroral imager. The outcomes of this analysis, combined with the results reported by Uritsky et al. [2010], make it possible to optimize sensitivity and resolution requirements for future auroral imaging missions intended to observe auroral structure and dynamics across wide ranges of spatial and temporal scales.
      PubDate: 2017-07-14T16:50:23.974348-05:
      DOI: 10.1002/2017JA024106
       
  • Occurrence of electrostatic solitary waves in the lunar wake
    • Authors: R. Rubia; S. V. Singh, G. S. Lakhina
      Abstract: An alternative generation mechanism for the electrostatic waves observed in the lunar wake during the first flyby of the ARTEMIS mission in terms of slow and fast ion-acoustic and electron-acoustic solitons is proposed. The lunar wake plasma is modelled by fluid multicomponent magnetized plasma comprising of hot protons, hot heavier ions (α-particles, He++), electron beam and suprathermal electrons following kappa distribution. The electric fields associated with the slow and fast ion-acoustic and electron-acoustic solitons are in the range of ∼(0.003 − 17) mV m−1. This is in excellent agreement with observed electrostatic wave electric field of 5 to 15 mV m−1. The fast Fourier transform (FFT) of soliton electric fields generate broadband spectra having peak frequencies (corresponding to peak in the power spectra) in the range of ∼(3 − 1800) Hz. This corresponds to wave frequencies being in the range of ∼(0.001 − 0.56)fpe, where fpe is the electron plasma frequency. This matches well with the observed frequency range of (0.01 − 0.4)fpe. Further, the widths and velocities of these solitons are in the range ∼(100 − 8000) m and ∼(30 − 1300) km s−1, respectively. Both, soliton widths and velocities, match well with the estimated wavelengths (a few hundred meters to a couple of thousand meters) and estimated phase velocities (of the order of 1000 km s−1) of the electrostatic waves in the lunar wake.
      PubDate: 2017-07-13T15:55:43.336131-05:
      DOI: 10.1002/2017JA023972
       
  • On the Relationship Between Electron Flux Oscillations and ULF Wave-Driven
           Radial Transport
    • Authors: Theodore E. Sarris; Xinlin Li, Michael Temerin, Hong Zhao, Sam Califf, Wenlong Liu, Robert Ergun
      Abstract: The objective of this study is to investigate the relationship between the levels of electron flux oscillations and radial diffusion for different Phase Space Density (PSD) gradients, through observation and particle tracing simulations under the effect of model Ultra Low Frequency (ULF) fluctuations. This investigation aims to demonstrate that electron flux oscillation is associated with and could be used as an indicator of ongoing radial diffusion. To this direction, flux oscillations are observed through the Van Allen Probes’ MagEIS energetic particle detector; subsequently, flux oscillations are produced in a particle tracing model that simulates radial diffusion by using model magnetic and electric field fluctuations that are approximating measured magnetic and electric field fluctuations as recorded by the Van Allen Probes’ EMFISIS and EFW instruments, respectively. The flux oscillation amplitudes are then correlated with Phase Space Density gradients in the magnetosphere and with the ongoing radial diffusion process.
      PubDate: 2017-06-09T20:35:21.134959-05:
      DOI: 10.1002/2016JA023741
       
  • Issue Information
    • Pages: 7849 - 7853
      Abstract: No abstract is available for this article.
      PubDate: 2017-09-25T12:18:11.327168-05:
      DOI: 10.1002/jgra.52920
       
  • Global kinetic hybrid simulation for radially expanding solar wind
    • Authors: S. Dyadechkin; V. S. Semenov, E. Kallio, N. V. Erkaev, M. Alho, H. Lammer
      Pages: 7854 - 7864
      Abstract: We present the results of a 1-D global kinetic simulation of the solar wind in spherical coordinates without a magnetic field in the region from the Sun to the Earth's orbit. Protons are considered as particles while electrons are considered as a massless fluid, with a constant temperature, in order to study the relation between the hybrid and hydrodynamic solutions. It is shown that the strong electric field in the hybrid model accelerates the protons. Since the electric field in the model is related to electron pressure, each proton in the initial Maxwellian velocity distribution function moves under the same forces as in the classical Parker Solar wind model. The study shows that the hybrid model results in very similar velocity and number density distributions along the radial distance as in the Parker model. In the hybrid simulations, the proton temperature is decreased with distance in 1 order of magnitude. The effective polytropic index of the proton population slightly exceeds 1 at larger distances with the maximum value ∼1.15 in the region near the Sun. A highly non-Maxwellian type of distribution function is initially formed. Further from the Sun, a narrow beam of the escaping protons is created which does not change much in later expansion. The results of our study indicates that already a nonmagnetized global hybrid model is capable of reproducing some fundamental features of the expanding solar wind shown in the Parker model and additional kinetic effects in the solar wind.
      PubDate: 2017-08-11T16:16:20.480923-05:
      DOI: 10.1002/2017JA023992
       
  • Interplanetary coronal mass ejection observed at STEREO-A, Mars, comet
           67P/Churyumov-Gerasimenko, Saturn, and New Horizons en route to Pluto:
           Comparison of its Forbush decreases at 1.4, 3.1, and 9.9 AU
    • Authors: O. Witasse; B. Sánchez-Cano, M. L. Mays, P. Kajdič, H. Opgenoorth, H. A. Elliott, I. G. Richardson, I. Zouganelis, J. Zender, R. F. Wimmer-Schweingruber, L. Turc, M. G. G. T. Taylor, E. Roussos, A. Rouillard, I. Richter, J. D. Richardson, R. Ramstad, G. Provan, A. Posner, J. J. Plaut, D. Odstrcil, H. Nilsson, P. Niemenen, S. E. Milan, K. Mandt, H. Lohf, M. Lester, J.-P. Lebreton, E. Kuulkers, N. Krupp, C. Koenders, M. K. James, D. Intzekara, M. Holmstrom, D. M. Hassler, B. E. S. Hall, J. Guo, R. Goldstein, C. Goetz, K. H. Glassmeier, V. Génot, H. Evans, J. Espley, N. J. T. Edberg, M. Dougherty, S. W. H. Cowley, J. Burch, E. Behar, S. Barabash, D. J. Andrews, N. Altobelli
      Pages: 7865 - 7890
      Abstract: We discuss observations of the journey throughout the Solar System of a large interplanetary coronal mass ejection (ICME) that was ejected at the Sun on 14 October 2014. The ICME hit Mars on 17 October, as observed by the Mars Express, Mars Atmosphere and Volatile EvolutioN Mission (MAVEN), Mars Odyssey, and Mars Science Laboratory (MSL) missions, 44 h before the encounter of the planet with the Siding-Spring comet, for which the space weather context is provided. It reached comet 67P/Churyumov-Gerasimenko, which was perfectly aligned with the Sun and Mars at 3.1 AU, as observed by Rosetta on 22 October. The ICME was also detected by STEREO-A on 16 October at 1 AU, and by Cassini in the solar wind around Saturn on the 12 November at 9.9 AU. Fortuitously, the New Horizons spacecraft was also aligned with the direction of the ICME at 31.6 AU. We investigate whether this ICME has a nonambiguous signature at New Horizons. A potential detection of this ICME by Voyager 2 at 110–111 AU is also discussed. The multispacecraft observations allow the derivation of certain properties of the ICME, such as its large angular extension of at least 116°, its speed as a function of distance, and its magnetic field structure at four locations from 1 to 10 AU. Observations of the speed data allow two different solar wind propagation models to be validated. Finally, we compare the Forbush decreases (transient decreases followed by gradual recoveries in the galactic cosmic ray intensity) due to the passage of this ICME at Mars, comet 67P, and Saturn.
      PubDate: 2017-08-14T16:22:57.51721-05:0
      DOI: 10.1002/2017JA023884
       
  • Proton velocity ring-driven instabilities and their dependence on the ring
           speed: Linear theory
    • Authors: Kyungguk Min; Kaijun Liu, S. Peter Gary
      Pages: 7891 - 7906
      Abstract: Linear dispersion theory is used to study the Alfvén-cyclotron, mirror and ion Bernstein instabilities driven by a tenuous (1%) warm proton ring velocity distribution with a ring speed, vr, varying between 2vA and 10vA, where vA is the Alfvén speed. Relatively cool background protons and electrons are assumed. The modeled ring velocity distributions are unstable to both the Alfvén-cyclotron and ion Bernstein instabilities whose maximum growth rates are roughly a linear function of the ring speed. The mirror mode, which has real frequency ωr=0, becomes the fastest growing mode for sufficiently large vr/vA. The mirror and Bernstein instabilities have maximum growth at propagation oblique to the background magnetic field and become more field-aligned with an increasing ring speed. Considering its largest growth rate, the mirror mode, in addition to the Alfvén-cyclotron mode, can cause pitch angle diffusion of the ring protons when the ring speed becomes sufficiently large. Moreover, because the parallel phase speed, v∥ph, becomes sufficiently small relative to vr, the low-frequency Bernstein waves can also aid the pitch angle scattering of the ring protons for large vr. Potential implications of including these two instabilities at oblique propagation on heliospheric pickup ion dynamics are discussed.
      PubDate: 2017-08-23T16:38:24.927075-05:
      DOI: 10.1002/2017JA023944
       
  • Current-driven flare and CME models
    • Authors: D. B. Melrose
      Pages: 7963 - 7978
      Abstract: Roles played by the currents in the impulsive phase of a solar flare and in a coronal mass ejection (CME) are reviewed. Solar flares are magnetic explosions: magnetic energy stored in unneutralized currents in coronal loops is released into energetic electrons in the impulsive phase and into mass motion in a CME. The energy release is due to a change in current configuration effectively reducing the net current path. A flare is driven by the electromotive force (EMF) due to the changing magnetic flux. The EMF drives a flare-associated current whose cross-field closure is achieved by redirection along field lines to the chromosphere and back. The essential roles that currents play are obscured in the “standard” model and are described incorrectly in circuit models. A semiquantitative treatment of the energy and the EMF is provided by a multicurrent model, in which the currents are constant and the change in the current paths is described by time-dependent inductances. There is no self-consistent model that includes the intrinsic time dependence, the EMF, the flare-associated current, and the internal energy transport during a flare. The current, through magnetic helicity, plays an important role in a CME, with twist converted into writhe allowing the kink instability plus reconnection to lead to a new closed loop and with the current-current force accelerating the CME through the torus instability.
      PubDate: 2017-08-03T14:00:25.423312-05:
      DOI: 10.1002/2017JA024035
       
  • Eruptive event generator based on the Gibson-Low magnetic configuration
    • Authors: D. Borovikov; I. V. Sokolov, W. B. Manchester, M. Jin, T. I. Gombosi
      Pages: 7979 - 7984
      Abstract: Coronal mass ejections (CMEs), a kind of energetic solar eruptions, are an integral subject of space weather research. Numerical magnetohydrodynamic (MHD) modeling, which requires powerful computational resources, is one of the primary means of studying the phenomenon. With increasing accessibility of such resources, grows the demand for user-friendly tools that would facilitate the process of simulating CMEs for scientific and operational purposes. The Eruptive Event Generator based on Gibson-Low flux rope (EEGGL), a new publicly available computational model presented in this paper, is an effort to meet this demand. EEGGL allows one to compute the parameters of a model flux rope driving a CME via an intuitive graphical user interface. We provide a brief overview of the physical principles behind EEGGL and its functionality. Ways toward future improvements of the tool are outlined.
      PubDate: 2017-08-03T14:10:24.518716-05:
      DOI: 10.1002/2017JA024304
       
  • The tails of the satellite auroral footprints at Jupiter
    • Authors: B. Bonfond; J. Saur, D. Grodent, S. V. Badman, D. Bisikalo, V. Shematovich, J.-C. Gérard, A. Radioti
      Pages: 7985 - 7996
      Abstract: The electromagnetic interaction between Io, Europa, and Ganymede and the rotating plasma that surrounds Jupiter has a signature in the aurora of the planet. This signature, called the satellite footprint, takes the form of a series of spots located slightly downstream of the feet of the field lines passing through the moon under consideration. In the case of Io, these spots are also followed by an extended tail in the downstream direction relative to the plasma flow encountering the moon. A few examples of a tail for the Europa footprint have also been reported in the northern hemisphere. Here we present a simplified Alfvénic model for footprint tails and simulations of vertical brightness profiles for various electron distributions, which favor such a model over quasi-static models. We also report here additional cases of Europa footprint tails, in both hemispheres, even though such detections are rare and difficult. Furthermore, we show that the Ganymede footprint can also be followed by a similar tail. Finally, we present a case of a 320° long Io footprint tail, while other cases in similar configurations do not display such a length.
      PubDate: 2017-08-02T17:27:36.444314-05:
      DOI: 10.1002/2017JA024370
       
  • Comparing the Dynamic Global Core Plasma Model with ground-based plasma
           mass density observations
    • Authors: Anders M. Jorgensen; Balazs Heilig, Massimo Vellante, Janos Lichtenberger, Jan Reda, Fridrich Valach, Igor Mandic
      Pages: 7997 - 8013
      Abstract: The Dynamic Global Core Plasma Model (DGCPM) is an empirical dynamical model of the plasmasphere which, despite its simple mathematical form, or perhaps because of its simple mathematical form, has enjoyed wide use in the space physics modeling community. In this paper we present some recent observations from the European quasi-Meridional Magnetometer Array (EMMA) and compare these with the DGCPM. The observations suggest more rapid daytime refilling and loss than what is described in the DGCPM. We then modify the DGCPM by changing the values of some of its parameters, leaving the functional form intact. The modified DGCPM agrees much better with the EMMA observations. The modification resulted in an order-of-magnitude faster daytime refilling and nighttime loss. These results are also consistent with previous observations of daytime refilling.
      PubDate: 2017-08-03T13:40:43.657989-05:
      DOI: 10.1002/2016JA023229
       
  • Ion velocity distributions in dipolarization events: Distributions in the
           central plasma sheet
    • Authors: J. Birn; A. Runov, X.-Z. Zhou
      Pages: 8014 - 8025
      Abstract: Using combined MHD/test particle simulations, we further explore characteristic ion velocity distributions in the central plasma sheet (CPS) in relation to dipolarization events. Distributions in the CPS within the dipolarized flux bundle (DFB) that follows the passage of a dipolarization front typically show two opposing low subthermal-energy beams with a ring-like component perpendicular to the magnetic field at about twice the thermal energy. The dominance of the perpendicular anisotropy and a field-aligned peak at lower energy agree qualitatively with ion distribution functions derived from “Time History of Events and Macroscale Interactions during Substorms” observations. At locations somewhat off the equatorial plane the field-aligned peaks are shifted by a field-aligned component of the bulk flow, such that one peak becomes centered near zero net velocity, which makes it less likely to be observed. The origins of the field-aligned peaks are low-energy lobe (or near plasma sheet boundary layer) regions, while the ring distribution originates mostly from thermal plasma sheet particles on extended field lines. The acceleration mechanisms are also quite different: the beam ions are accelerated first by the E × B drift motion of the DFB and then by a slingshot effect of the earthward convecting DFB (akin to first-order Fermi, type B, acceleration), which causes an increase in field-aligned speed. In contrast, the ring particles are accelerated by successive, betatron-like acceleration after entering the high electric field region of an earthward propagating DFB.
      PubDate: 2017-08-03T13:26:53.260018-05:
      DOI: 10.1002/2017JA024230
       
  • Ion velocity distributions in dipolarization events: Beams in the vicinity
           of the plasma sheet boundary
    • Authors: J. Birn; M. Chandler, T. Moore, A. Runov
      Pages: 8026 - 8036
      Abstract: Using combined MHD/test particle simulations, we further explore characteristic ion velocity distributions in relation to magnetotail reconnection and dipolarization events, focusing on distributions at and near the plasma sheet boundary layer (PSBL). Simulated distributions right at the boundary are characterized by a single earthward beam, as discussed earlier. However, farther inside, the distributions consist of multiple beams parallel and antiparallel to the magnetic field, remarkably similar to recent Magnetospheric Multiscale observations. The simulations provide insight into the mechanisms: the lowest earthward beam results from direct acceleration at an earthward propagating dipolarization front (DF), with a return beam at somewhat higher energy. A higher-energy earthward beam results from dual acceleration, first near the reconnection site and then at the DF, again with a corresponding return beam resulting from mirroring closer to Earth. Multiple acceleration at the X line or the propagating DF with intermediate bounces may produce even higher-energy beams. Particles contributing to the lower energy beams are found to originate from the PSBL with thermal source energies, increasing with increasing beam energy. In contrast, the highest-energy beams consist mostly of particles that have entered the acceleration region via cross-tail drift with source energies in the suprathermal range.
      PubDate: 2017-08-03T13:25:51.882843-05:
      DOI: 10.1002/2017JA024231
       
  • Electron dropout echoes induced by interplanetary shock: A statistical
           study
    • Authors: Z. Y. Liu; Q.-G. Zong, Y. X. Hao, X.-Z. Zhou, X. H. Ma, Y. Liu
      Pages: 8037 - 8050
      Abstract: “Electron dropout echo” as indicated by repeated moderate dropout and recovery signatures of the flux of energetic electron in the outer radiation belt region has been investigated systematically. The electron moderate dropout and its echoes are usually found for higher-energy (>300 keV) channel fluxes, whereas the flux enhancements are obvious for lower energy electrons simultaneously after the interplanetary shock arrives at the Earth's geosynchronous orbit. The electron dropout echo events are found to be usually associated with the interplanetary shocks arrival. The 104 dropout echo events have been found from 215 interplanetary shock events from 1998 to 2007 based on the Los Alamos National Laboratory satellite data. In analogy to substorm injections, these 104 events could be naturally divided into two categories: dispersionless (49 events) or dispersive (55 events) according to the energy dispersion of the initial dropout. It is found that locations of dispersionless events are distributed mainly in the duskside magnetosphere. Further, the obtained locations derived from dispersive events with the time-of-flight technique of the initial dropout regions are mainly located at the duskside as well. Statistical studies have shown that the effect of shock normal, interplanetary magnetic field Bz and solar wind dynamic pressure may be insignificant to these electron dropout events. We suggest that the ∼1 min electric field impulse induced by the interplanetary shock produces a more pronounced inward migration of electrons at the duskside, resulting in the observed duskside moderate dropout of electron flux and its consequent echoes.
      PubDate: 2017-08-03T13:26:16.652178-05:
      DOI: 10.1002/2017JA024045
       
  • Global Mars-solar wind coupling and ion escape
    • Authors: Robin Ramstad; Stas Barabash, Yoshifumi Futaana, Hans Nilsson, Mats Holmström
      Pages: 8051 - 8062
      Abstract: Loss of the early Martian atmosphere is often thought to have occurred due to an effective transfer of the solar wind energy through the Martian induced magnetic barrier to the ionosphere. We have quantified the coupling efficiency by comparing the power of the heavy ion outflow with the available power supplied by the upstream solar wind. Constraining upstream solar wind density nsw, velocity vsw, and EUV intensity IEUV/photoionizing flux FXUV in varying intervals reveals a decrease in coupling efficiency, k, with solar wind dynamic pressure as k∝pdyn−0.74±0.13 and with FXUV as k∝FXUV−2.28±0.30. Despite the decrease in coupling efficiency, higher FXUV enhances the cold ion outflow, increasing the total ion escape rate as Q(FXUV) = 1010(0.82 ± 0.05)FXUV. The discrepancy between coupling and escape suggests that ion escape from Mars is primarily production limited in the modern era, though decreased coupling may lead to an energy-limited solar wind interaction under early Sun conditions.
      PubDate: 2017-08-03T13:31:29.270457-05:
      DOI: 10.1002/2017JA024306
       
  • Cassini observations of aperiodic waves on Saturn's magnetodisc
    • Authors: C. J. Martin; C. S. Arridge
      Pages: 8063 - 8077
      Abstract: The location and motion of Saturn's equatorial current sheet is the result of an interplay between a quasi-static deformation that varies in radial distance and local time, impulsive perturbations that produce large-scale displacements, quasiperiodic perturbations near the planetary rotation period, and wave-like structures on shorter timescales. This study focuses on the latter, aperiodic wave pulses with periods from 1 to 30 min, which are unrelated to the quasiperiodic “flapping” with a period near that of Saturn's rotation. Cassini magnetometer data were surveyed for these aperiodic structures and then fitted to a simple model in order to estimate the properties of the waves. The model consists of a modified Harris current sheet model deformed by a Gaussian pulse wave function. This then allows for the extraction of wave parameters and current sheet properties. In particular, we show an increase in current sheet scale height with radial distance from Saturn, an increase in the wave amplitude with radial distance, and the resolution of propagation directions using the wave vector fitted by the model. The dominant propagation direction is found to be radially outward from Saturn.
      PubDate: 2017-08-03T13:30:43.070297-05:
      DOI: 10.1002/2017JA024293
       
  • Ion leakage at dayside magnetopause in case of high and low magnetic
           shears
    • Authors: I. P. Kirpichev; E. E. Antonova, M. Stepanova
      Pages: 8078 - 8095
      Abstract: The nature of energetic ions in the magnetosheath of the Earth is studied using the data of the Time History of Events and Macroscale Interactions during Substorms mission. Three intervals of the multiple crossings of the magnetopause during northward orientation of the interplanetary magnetic field and quiet geomagnetic conditions were selected to illustrate the behavior of ion distribution functions near the subsolar region in case of high and low magnetic shears. For all analyzed events, the velocity and thickness of the magnetopause was estimated using the simultaneous measurements in two satellites. The ion spectra in the magnetosphere and magnetosheath were fitted by kappa and bi-kappa distributions, respectively. It was found that during high shear events the energetic part of the ion spectra is practically identical inside and outside the magnetopause. On the other side, for low shear events the energetic fluxes of ions in the magnetosheath are lower. We argue that in case of high magnetic shear, the magnetopause becomes transparent when the ion Larmor radii is comparable or larger than the thickness of the magnetopause. It may explain coincidence of the energetic part of spectra inside and outside the magnetosphere. We discuss the reason for the changes of spectra at low magnetic shear.
      PubDate: 2017-08-03T13:31:13.897843-05:
      DOI: 10.1002/2016JA023735
       
  • Occurrence characteristics of relativistic electron microbursts from
           SAMPEX observations
    • Authors: Emma Douma; Craig J. Rodger, Lauren W. Blum, Mark A. Clilverd
      Pages: 8096 - 8107
      Abstract: We study the occurrence of relativistic microbursts observed by the Solar Anomalous Magnetospheric Particle Explorer (SAMPEX) satellite. An algorithm is used to identify 193,694 relativistic microbursts in the> 1.05 MeV electron fluxes occurring across the time period 23 August 1996 to 11 August 2007, nearly a full solar cycle. Our observations are normalized to provide the change in absolute occurrence rates with various parameters. We find that relativistic microbursts are mostly confined to the outer radiation belt, from L = 3–8, occurring primarily on the morningside, between 0 and 13 magnetic local time (MLT). This L and MLT distribution is consistent with the L and MLT distribution of whistler mode chorus amplitude. Thus, our observations favor whistler mode chorus wave activity as a driver of relativistic microbursts. Relativistic microbursts become more frequent as the geomagnetic activity level increases and are more frequent during equinoxes than during the solstices. The peak occurrence frequency of the relativistic microbursts moves to lower L as the geomagnetic activity increases, reaching a peak occurrence rate of one microburst every 10.4 s (on average) at L = 4 for 6.6 ≤ Kp ≤ 8.7. Microbursts primarily occur outside of the plasmapause and track the inward movement of the plasmapause with increasing geomagnetic activity. The L and MLT distribution of the relativistic microbursts exhibits a peak occurrence of one microburst every 8.6 (98.0) s during active (disturbed) conditions, with the peak located at L = 5 (L = 5.5) and 08 (08) MLT.
      PubDate: 2017-08-03T13:45:32.091159-05:
      DOI: 10.1002/2017JA024067
       
  • The magnetic local time distribution of energetic electrons in the
           radiation belt region
    • Authors: Hayley J. Allison; Richard B. Horne, Sarah A. Glauert, Giulio Del Zanna
      Pages: 8108 - 8123
      Abstract: Using 14 years of electron flux data from the National Oceanic and Atmospheric Administration Polar Operational Environmental Satellites, a statistical study of the magnetic local time (MLT) distribution of the electron population is performed across a range of activity levels, defined by AE, AE*, Kp, solar wind velocity (Vsw), and VswBz. Three electron energies (>30,>100, and>300 keV) are considered. Dawn-dusk flux asymmetries larger than order of magnitude were observed for>30 and>100 keV electrons. For>300 keV electrons, dawn-dusk asymmetries were primarily due to a decrease in the average duskside flux beyond L* ∼ 4.5 that arose with increasing activity. For the>30 keV population, substorm injections enhance the dawnside flux, which may not reach the duskside as the electrons can be on open drift paths and lost to the magnetopause. The asymmetries in the>300 keV population are attributed to the combination of magnetopause shadowing and>300 keV electron injections by large electric fields. We suggest that 3-D radiation belt models could set the minimum energy boundary (Emin) to 30 keV or above at L* ∼ 6 during periods of low activity. However, for more moderate conditions, Emin should be larger than 100 keV and, for very extreme activities, ∼300 keV. Our observations show the extent that in situ electron flux readings may vary during active periods due to the MLT of the satellite and highlight the importance of 4-D radiation belt models to fully understand radiation belt processes.
      PubDate: 2017-08-03T13:50:44.766042-05:
      DOI: 10.1002/2017JA024084
       
  • Peculiarities of VLF wave propagation in the Earth's magnetosphere in the
           presence of artificial large-scale inhomogeneity
    • Authors: D. L. Pasmanik; A. G. Demekhov
      Pages: 8124 - 8135
      Abstract: We study specific features of VLF waves propagation in the Earth's ionosphere and magnetosphere in the presence of large-scale field-aligned plasma inhomogeneities (ducts). These inhomogeneities can, e.g., be formed during the ionosphere heating by high-power HF facilities such as High Frequency Active Auroral Research Program and “Sura.” They can extend up to altitudes of several thousand kilometers along geomagnetic field lines and have transverse scales of about 1° determined by the heated region scale. We analyze ray trajectories of VLF waves with frequencies of 1 to 15 kHz starting from about 100 km altitude and use the plasma parameters obtained within the framework of the SAMI2 simulation model (Huba et al., 2000). This model employs MHD equations for thermal plasma and allows one to obtain the plasma parameters along the entire magnetic flux tube in a fixed meridional plane. By knowing the ray trajectories, we calculate and compare the amplitude variation along the ray paths for the cases of unperturbed and heated ionosphere. We show that the presence of a large-scale density disturbance produced by the HF heating can lead to significant changes of wave propagation trajectories. In particular, efficient guiding of VLF waves in this region can take place, which in turn can result in the appearance of several wave focusing regions and a drastic local increase of the VLF wave amplitude in these regions (up to ∼10 times as compared to the case of unperturbed plasma). The number of focusing regions is determined by an extension of an artificial duct along the geomagnetic field.
      PubDate: 2017-08-03T13:55:38.991838-05:
      DOI: 10.1002/2017JA024118
       
  • Flux ropes in the Hermean magnetotail: Distribution, properties, and
           formation
    • Authors: A. W. Smith; J. A. Slavin, C. M. Jackman, G.-K. Poh, R. C. Fear
      Pages: 8136 - 8153
      Abstract: An automated method was applied to identify magnetotail flux rope encounters in MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) magnetometer data. The method identified significant deflections of the north-south component of the magnetic field coincident with enhancements in the total field or dawn-dusk component. Two hundred forty-eight flux ropes are identified that possess well-defined minimum variance analysis (MVA) coordinate systems, with clear rotations of the field. Approximately 30% can be well approximated by the cylindrically symmetric, linearly force-free model. Flux ropes are most common moving planetward, in the postmidnight sector. Observations are intermittent, with the majority (61%) of plasma sheet passages yielding no flux ropes; however, the peak rate of flux ropes during a reconnection episode is ∼5 min−1. Overall, the peak postmidnight rate is ∼0.25 min−1. Only 25% of flux ropes are observed in isolation. The radius of flux ropes is comparable to the ion inertial length within Mercury's magnetotail plasma sheet. No clear statistical separation is observed between tailward and planetward moving flux ropes, suggesting the near-Mercury neutral line (NMNL) is highly variable. Flux ropes are more likely to be observed if the preceding lobe field is enhanced over background levels. A very weak correlation is observed between the flux rope core field and the preceding lobe field orientation; a stronger relationship is found with the orientation of the field within the plasma sheet. The core field strength measured is ∼6 times stronger than the local dawn-dusk plasma sheet magnetic field.
      PubDate: 2017-08-03T14:00:58.444511-05:
      DOI: 10.1002/2017JA024295
       
  • Generation of rising-tone chorus in a two-dimensional mirror field by
           using the general curvilinear PIC code
    • Authors: Yangguang Ke; Xinliang Gao, Quanming Lu, Xueyi Wang, Shui Wang
      Pages: 8154 - 8165
      Abstract: Recently, the generation of rising-tone chorus has been implemented with one-dimensional (1-D) particle-in-cell (PIC) simulations in an inhomogeneous background magnetic field, where both the propagation of waves and motion of electrons are simply forced to be parallel to the background magnetic field. In this paper, we have developed a two-dimensional (2-D) general curvilinear PIC simulation code and successfully reproduced rising-tone chorus waves excited from an anisotropic electron distribution in a 2-D mirror field. Our simulation results show that whistler waves are mainly generated around the magnetic equator and continuously gain growth during their propagation toward higher-latitude regions. The rising-tone chorus waves are observed off the magnetic equator, which propagate quasi-parallel to the background magnetic field with the wave normal angle smaller than 25°. Due to the propagating effect, the wave normal angle of chorus waves is increasing during their propagation toward higher-latitude regions along an enough curved field line. The chirping rate of chorus waves is found to be larger along a field line with a smaller curvature.
      PubDate: 2017-08-03T14:11:33.160126-05:
      DOI: 10.1002/2017JA024178
       
  • Self-consistent formation of a 0.5 cyclotron frequency gap in
           magnetospheric whistler mode waves
    • Authors: H. Ratcliffe; C. E. J. Watt
      Pages: 8166 - 8180
      Abstract: Decades of in situ observations of whistler mode waves in Earth's magnetosphere reveal that there is frequently a gap in the spectral power at around half the local electron gyrofrequency. Recent theoretical and kinetic simulation studies have suggested that the gap arises due to the presence of temperature anisotropy in both a “warm” and a “hot” electron population, leading to two separate (and independent) regions of wave growth in frequency space. We present two-dimensional kinetic plasma simulations using the powerful EPOCH (Extendable PIC Open Collaboration) particle-in-cell code that offer an alternative explanation. After an initial linear-growth period, our simulations show self-consistent formation of a gap feature. In most cases this arises where linear theory predicts the maximum growth rate and is associated with subtle local structuring of the hot electron distributions. This feature persists in multiple simulations with varying hot electron parameters. We discuss these results in the context of in situ observations of both waves and electron distribution functions and argue that the rapid reorganization of electron distributions in a small, but key, region of phase space during the growth of whistler mode waves naturally results in the spectral gap often observed at half the electron gyrofrequency.
      PubDate: 2017-08-03T14:10:41.799253-05:
      DOI: 10.1002/2017JA024399
       
  • Identifying the 630 nm auroral arc emission height: A comparison of the
           triangulation, FAC profile, and electron density methods
    • Authors: D. Megan Gillies; D. Knudsen, E. Donovan, B. Jackel, R. Gillies, E. Spanswick
      Pages: 8181 - 8197
      Abstract: We present a comprehensive survey of 630 nm (red-line) emission discrete auroral arcs using the newly deployed Redline Emission Geospace Observatory. In this study we discuss the need for observations of 630 nm aurora and issues with the large-altitude range of the red-line aurora. We compare field-aligned currents (FACs) measured by the Swarm constellation of satellites with the location of 10 red-line (630 nm) auroral arcs observed by all-sky imagers (ASIs) and find that a characteristic emission height of 200 km applied to the ASI maps gives optimal agreement between the two observations. We also compare the new FAC method against the traditional triangulation method using pairs of all-sky imagers (ASIs), and against electron density profiles obtained from the Resolute Bay Incoherent Scatter Radar-Canadian radar, both of which are consistent with a characteristic emission height of 200 km.
      PubDate: 2017-08-05T15:11:17.412239-05:
      DOI: 10.1002/2016JA023758
       
  • A hybrid approach to empirical magnetosphere modeling
    • Authors: N. A. Tsyganenko; V. A. Andreeva
      Pages: 8198 - 8213
      Abstract: A new approach has been devised and explored to reconstruct magnetospheric configurations, based on spacecraft data and a synthesis of two methods of modeling the magnetic field of extraterrestrial currents. The main idea is to combine within a single framework (1) a modular structure explicitly representing separate contributions to the total field from the magnetopause, ring, tail, and field-aligned currents, and (2) a system of densely distributed field sources, modeled by the radial basis functions (RBF). In such an arrangement, the modular part takes on a role of the principal component representing the gross large-scale structure of the magnetosphere, whereas the RBF part serves as a higher-order correction that compensates for the lack of flexibility of the modular component. The approach has been tested on four subsets of spacecraft data, corresponding to four phases of a geomagnetic storm, and was shown to tangibly improve the model's performance. In particular, it allows proper representation of magnetic effects of the field-aligned currents both at low altitudes and in the distant magnetosphere, as well as inclusion of extensive high-latitude field depressions associated with diamagnetism of the polar cusp plasma, missing in earlier empirical models. It also helps to more accurately model the nightside magnetosphere, so that most of the large-scale magnetotail field is compactly described by a dedicated module inherited from an earlier empirical model, while the RBF component's task is to resolve finer details in the inner magnetosphere.
      PubDate: 2017-08-05T15:26:11.847292-05:
      DOI: 10.1002/2017JA024359
       
  • Survey of Saturn electrostatic cyclotron harmonic wave intensity
    • Authors: J. D. Menietti; T. F. Averkamp, W. S. Kurth, S.-Y. Ye, D. A. Gurnett, B. Cecconi
      Pages: 8214 - 8227
      Abstract: We conduct a survey of electrostatic electron cyclotron harmonic (ECH) emissions observed at Saturn by the radio and plasma wave science investigation on board the Cassini spacecraft. These emissions are known to be effective at interacting with electrons in the terrestrial inner magnetosphere, producing electron scattering into the loss cone and acceleration (cf. Horne and Thorne, 2000; Thorne et al., 2010). At Saturn ECH emission occurs with high probability and at strong intensity near the magnetic equator, outside the Enceladus torus in the range ~5 
      PubDate: 2017-08-09T15:37:12.559286-05:
      DOI: 10.1002/2017JA023929
       
  • The occurrence and wave properties of EMIC waves observed by the
           Magnetospheric Multiscale (MMS) mission
    • Authors: X. Y. Wang; S. Y. Huang, R. C. Allen, H. S. Fu, X. H. Deng, M. Zhou, J. L. Burch, R. B. Torbert
      Pages: 8228 - 8240
      Abstract: Electromagnetic ion cyclotron (EMIC) waves can precipitate the ring current ions and relativistic electrons and heat the cold electrons in the magnetosphere. This requires comprehensive knowledge of the occurrence and wave properties of EMIC waves. In the present study, we used the data from one new mission, the Magnetospheric Multiscale (MMS) mission launched in March 2015, to investigate the occurrence and wave properties of H+-band and He+-band EMIC waves in the magnetosphere. Our statistical results show the following: (1) H+-band EMIC waves mostly occur in the higher L-shells (L > 5) while He+-band EMIC waves are mostly observed in the lower L-shells (L 
      PubDate: 2017-08-09T15:37:45.313609-05:
      DOI: 10.1002/2017JA024237
       
  • Survey of Voyager plasma science ions at Jupiter: 1. Analysis method
    • Authors: F. Bagenal; L. P. Dougherty, K. M. Bodisch, J. D. Richardson, J. M. Belcher
      Pages: 8241 - 8256
      Abstract: The Voyagers 1 and 2 spacecraft flew by Jupiter in March and July of 1979, respectively. The Plasma Science instrument (PLS) acquired detailed measurements of the plasma environment in the equatorial region of the magnetosphere between 4.9 and 4 RJ. While bulk plasma properties such as charge density, ion temperature, and bulk flow were reasonably well determined, the ion composition was only well constrained in occasional regions of cold plasma. The ion data obtained by the PLS instrument have been reanalyzed using physical chemistry models to constrain the composition and reduce the number of free parameters, particularly in regions of hotter plasma. This paper describes the method used for fitting the plasma data and presents the results versus time. Two companion papers describe the composition of heavy ions and present analysis of protons plus other minor ions.
      PubDate: 2017-08-10T19:11:24.409391-05:
      DOI: 10.1002/2016JA023797
       
  • Survey of Voyager plasma science ions at Jupiter: 2. Heavy ions
    • Authors: L. P. Dougherty; K. M. Bodisch, F. Bagenal
      Pages: 8257 - 8276
      Abstract: We take the plasma parameters derived by Bagenal et al. (2017) from Voyager plasma science data in the Jovian magnetosphere and examine the radial profiles of density, temperature, composition, and azimuthal flow. The plasma sheet shows a relatively uniform structure of decreasing electron density (Ne) and increasing temperature out to about 20 RJ, but beyond about 15 RJ there is increasing disorder with sporadic blobs of cold plasma. These small (~0.5 RJ) blobs of cold (~20 eV) plasma make a minor contribution to the net outward flux of iogenic plasma. The ion composition in the cold blobs is consistent with the ion abundances derived from physical chemistry models extending from 6 to ~9 RJ, whereupon the collisional reactions slow down and radial transport speeds up, effectively freezing in the ion composition to the following abundances: O+/Ne = 15–22%, S++/Ne = 10–19%, O++/Ne = 4–8%, S+++/Ne = 4–6%, and S+/Ne = 1–5%. Beyond about 7 RJ the component of hot (suprathermal, approximately hundreds of eV) ions becomes a significant fraction of the total density. The radial profile of the plasma's azimuthal flow speed shows that corotation begins to breakdown at about 9 RJ, dipping down to about 20% below corotation before increasing back up to corotation briefly (~17–20 RJ), reaching an asymptotic value of about 225 km/s (corresponding to rigid corotation at ~18 RJ). We present a 2-D model of the plasma sheet beyond 6 RJ based on simple functions for the equatorial profiles of plasma properties and steady state diffusive equilibrium along magnetic flux tubes. Cold plasma blobs in the Jovian plasma sheet show ion composition consistent with physical chemistry models. Azimuthal flow speeds dip below corotation 9–15 Jovian radii. Radial profiles of plasma properties are combined to make a 2-D model of plasma sheet.
      PubDate: 2017-08-10T09:59:37.926644-05:
      DOI: 10.1002/2017JA024053
       
  • Survey of Voyager plasma science ions at Jupiter: 3. Protons and minor
           ions
    • Authors: K. M. Bodisch; L. P. Dougherty, F. Bagenal
      Pages: 8277 - 8294
      Abstract: When the Voyager 1 and 2 spacecraft flew through the Jovian system in March and July 1979, the Plasma Science instruments measured ions and electrons in the Io plasma torus and plasma sheet between 4.9 and 42 RJ. The dominant ions in the Jovian magnetosphere comprise the first few ionization states of atomic sulfur and oxygen. We present here an analysis of minor ion species H+, Na+, and SO2+. Protons are 1–20% of the plasma between 5 and 30 RJ with variable temperatures ranging by a factor of 10 warmer or colder than the heavy ions. We suggest that these protons, measured deep inside the magnetosphere, are consistent with a source from the ionosphere of ~1.5–7.5 × 1027 protons s−1 (2.5–13 kg/s). Na+ ions are detected between 5 and 40 RJ at an abundance of 1 to 10%, produced by the ionization of the extended neutral cloud emanating from Io that has been observed since 1974. SO2+ ions are detected between 5.31 and 5.07 RJ at an abundance of 0.1–0.6%. These ions clearly come from the plasma interaction with Io's atmosphere, but the exact processes whereby atmospheric molecules escape Io and end up as ions well inside Io's orbit are not clear.
      PubDate: 2017-08-10T19:10:58.144238-05:
      DOI: 10.1002/2017JA024148
       
  • The ion temperature gradient: An intrinsic property of Earth's magnetotail
    • Authors: San Lu; A. V. Artemyev, V. Angelopoulos, Y. Lin, X. Y. Wang
      Pages: 8295 - 8309
      Abstract: Although the ion temperature gradient along (XGSM) and across (ZGSM) the Earth's magnetotail, which plays a key role in generating the cross-tail current and establishing pressure balance with the lobes, has been extensively observed by spacecraft, the mechanism responsible for its formation is still unknown. We use multispacecraft observations and three-dimensional (3-D) global hybrid simulations to reveal this mechanism. Using THEMIS (Time History of Events and Macroscale Interactions during Substorms), Geotail, and ARTEMIS (Acceleration, Reconnection, Turbulence and Electrodynamics of Moon's Interaction with the Sun) observations during individual, near-simultaneous plasma sheet crossings from 10 to 60 RE, we demonstrate that the ion temperature ZGSM profile is bell-shaped at different geocentric distances. This ZGSM profile is also prevalent in statistics of ~200 THEMIS current sheet crossings in the near-Earth region. Using 3-D global hybrid simulations, we show that mapping of the XGSM gradient of ion temperature along magnetic field lines produces such a bell-shaped profile. The ion temperature mapping along magnetic field lines in the magnetotail enables construction of two-dimensional distributions of these quantities from vertical (north-south) spacecraft crossings. Our findings suggest that the ion temperature gradient is an intrinsic property of the magnetotail that should be considered in kinetic descriptions of the magnetotail current sheet. Toward this goal, we use theoretical approaches to incorporate the temperature gradient into kinetic current sheet models, making them more realistic.
      PubDate: 2017-08-10T09:59:17.834037-05:
      DOI: 10.1002/2017JA024209
       
  • Simulation of Mercury's magnetosheath with a combined hybrid-paraboloid
           model
    • Authors: David Parunakian; Sergey Dyadechkin, Igor Alexeev, Elena Belenkaya, Maxim Khodachenko, Esa Kallio, Markku Alho
      Pages: 8310 - 8326
      Abstract: In this paper we introduce a novel approach for modeling planetary magnetospheres that involves a combination of the hybrid model and the paraboloid magnetosphere model (PMM); we further refer to it as the combined hybrid model. While both of these individual models have been successfully applied in the past, their combination enables us both to overcome the traditional difficulties of hybrid models to develop a self-consistent magnetic field and to compensate the lack of plasma simulation in the PMM. We then use this combined model to simulate Mercury's magnetosphere and investigate the geometry and configuration of Mercury's magnetosheath controlled by various conditions in the interplanetary medium. The developed approach provides a unique comprehensive view of Mercury's magnetospheric environment for the first time. Using this setup, we compare the locations of the bow shock and the magnetopause as determined by simulations with the locations predicted by stand-alone PMM runs and also verify the magnetic and dynamic pressure balance at the magnetopause. We also compare the results produced by these simulations with observational data obtained by the magnetometer on board the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft along a dusk-dawn orbit and discuss the signatures of the magnetospheric features that appear in these simulations. Overall, our analysis suggests that combining the semiempirical PMM with a self-consistent global kinetic model creates new modeling possibilities which individual models cannot provide on their own.
      PubDate: 2017-08-14T17:53:17.118742-05:
      DOI: 10.1002/2017JA024105
       
  • Statistical study of the storm time radiation belt evolution during Van
           Allen Probes era: CME- versus CIR-driven storms
    • Authors: Xiao-Chen Shen; Mary K. Hudson, Allison N. Jaynes, Quanqi Shi, Anmin Tian, Seth G. Claudepierre, Mu-Rong Qin, Qiu-Gang Zong, Wei-Jie Sun
      Pages: 8327 - 8339
      Abstract: Coronal mass ejection (CME)-driven or corotating interaction region (CIR)-driven storms can change the electron distributions in the radiation belt dramatically, which can in turn affect the spacecraft in this region or induce geomagnetic effects. The Van Allen Probes twin spacecraft, launched on 30 August 2012, orbit near the equatorial plane and across a wide range of L∗ with apogee at 5.8 RE and perigee at 620 km. Electron data from Van Allen Probes MagEIS and REPT instruments have been binned every 6 h at L∗=3 (defined as 2.5 < L∗
      PubDate: 2017-08-14T17:52:07.914702-05:
      DOI: 10.1002/2017JA024100
       
  • Statistical properties of low-frequency plasmaspheric hiss
    • Authors: David M. Malaspina; Allison N. Jaynes, George Hospodarsky, Jacob Bortnik, Robert E. Ergun, John Wygant
      Pages: 8340 - 8352
      Abstract: Plasmaspheric hiss is an important wave mode for the dynamics of inner terrestrial magnetosphere plasma populations. It acts to scatter high-energy electrons out of trapped orbits about Earth and into the atmosphere, defining the inner edge of the radiation belts over a range of energies. A low-frequency component of hiss was recently identified and is important for its ability to interact with higher-energy electrons compared to typically considered hiss frequencies. This study compares the statistical properties of low- and high-frequency plasmaspheric hiss in the terrestrial magnetosphere, demonstrating that they are statistically distinct wave populations. Low-frequency hiss shows different behavior in frequency space, different spatial localization (in magnetic local time and radial distance), and different amplitude distributions compared to high-frequency hiss. The observed statistical properties of low-frequency hiss are found to be consistent with recently developed theories for low-frequency hiss generation. The results presented here suggest that careful consideration of low-frequency hiss properties can be important for accurate inclusion of this wave population in predictive models of inner magnetosphere plasma dynamics.
      PubDate: 2017-08-14T17:57:50.918604-05:
      DOI: 10.1002/2017JA024328
       
  • Storm time empirical model of O+ and O6+ distributions in the
           magnetosphere
    • Authors: R. C. Allen; S. A. Livi, S. K. Vines, J. Goldstein, I. Cohen, S. A. Fuselier, B. H. Mauk, H. E. Spence
      Pages: 8353 - 8374
      Abstract: Recent studies have utilized different charge states of oxygen ions as a tracer for the origins of plasma populations in the magnetosphere of Earth, using O+ as an indicator of ionospheric-originating plasma and O6+ as an indicator of solar wind-originating plasma. These studies have correlated enhancements in O6+ to various solar wind and geomagnetic conditions to characterize the dominant solar wind injection mechanisms into the magnetosphere but did not include analysis of the temporal evolution of these ions. A sixth-order Fourier expansion model based empirically on a superposed epoch analysis of geomagnetic storms observed by Polar is presented in this study to provide insight into the evolution of both ionospheric-originating and solar wind-originating plasma throughout geomagnetic storms. At high energies (~200 keV) the flux of O+ and O6+ are seen to become comparable in the outer magnetosphere. Moreover, while the density of O+ is far higher than O6+, the two charge states have comparable pressures in the outer magnetosphere. The temperature of O6+ is generally higher than that of O+, because the O6+ is injected from preheated magnetosheath populations before undergoing further heating once in the magnetosphere. A comparison between the model results with O+ observations from the Magnetospheric Multiscale mission and the Van Allen Probes provides a validation of the model. In general, this empirical model agrees qualitatively well with the trends seen in both data sets. Quantitatively, the modeled density, pressure, and temperature almost always agree within a factor of at most 10, 5, and 2, respectively.
      PubDate: 2017-08-16T12:46:15.172317-05:
      DOI: 10.1002/2017JA024245
       
  • The role of the electron temperature on ion loss from Mars
    • Authors: Stephen H. Brecht; Stephen A. Ledvina, Bruce M. Jakosky
      Pages: 8375 - 8390
      Abstract: This paper reports the results of hybrid simulations of the Mars-solar wind interaction. The focus is on the role of the low altitude (
      PubDate: 2017-08-17T15:56:33.908651-05:
      DOI: 10.1002/2016JA023510
       
  • Ion escape rates from Mars: Results from hybrid simulations compared to
           MAVEN observations
    • Authors: Stephen A. Ledvina; Stephen H. Brecht, David A. Brain, Bruce M. Jakosky
      Pages: 8391 - 8408
      Abstract: Daily averaged heavy ion escape rates from HALFSHEL hybrid simulations of the solar wind interaction with the Martian ionosphere are compared to the ion escape rates reported by Brain et al. (2015). The simulation rates are found to be in agreement with the rates measured by Mars Atmosphere and Volatile EvolutioN (MAVEN). When the simulation rates are adjusted for known variability in the Martian system, the ion escape rates are within 40% of the MAVEN results. The ion escape rate is found to vary linearly with the solar wind speed. Using the simulation results to scale the MAVEN ion escape rate to include ions of all kinetic energies, we predict a total heavy ion escape rate of 1.2 × 1025 ions/s. The assumptions used to derive the total ion escape by Brain et al. (2015) are tested against the simulation results and are found to be excellent.
      PubDate: 2017-08-17T15:55:56.76545-05:0
      DOI: 10.1002/2016JA023521
       
  • Statistical study of low-frequency magnetic field fluctuations near Venus
           during the solar cycle
    • Authors: S. D. Xiao; T. L. Zhang, G. Q. Wang
      Pages: 8409 - 8418
      Abstract: We statistically investigate the solar cycle dependence of the magnetic field fluctuations in the frequency range 30–300 MHz based on Venus Express data. We present the spatial distributions of fluctuation properties during three typical periods of the solar cycle, and a comparative study is also performed. With the increase of solar activity, the magnetic field is still quiet in the magnetotail region and the wave intensity becomes weaker in the magnetosheath. The transverse component of fluctuations becomes stronger in the magnetosheath region and weaker in the tail region. The proportion of circularly polarized components to incoherent noise of the fluctuations decreases in the magnetosheath region. The proportion of dominant parallel propagation fluctuations tends to be larger in the nightside magnetosheath, and more perpendicular propagation component is shown in the tail region.
      PubDate: 2017-08-18T16:06:59.283191-05:
      DOI: 10.1002/2017JA023878
       
  • Coupling between Mercury and its nightside magnetosphere: Cross-tail
           current sheet asymmetry and substorm current wedge formation
    • Authors: Gangkai Poh; James A. Slavin, Xianzhe Jia, Jim M. Raines, Suzanne M. Imber, Wei-Jie Sun, Daniel J. Gershman, Gina A. DiBraccio, Kevin J. Genestreti, Andy W. Smith
      Pages: 8419 - 8433
      Abstract: We analyzed MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) magnetic field and plasma measurements taken during 319 crossings of Mercury's cross-tail current sheet. We found that the measured BZ in the current sheet is higher on the dawnside than the duskside by a factor of ≈3 and the asymmetry decreases with downtail distance. This result is consistent with expectations based upon MHD stress balance. The magnetic fields threading the more stretched current sheet in the duskside have a higher plasma beta than those on the dawnside, where they are less stretched. This asymmetric behavior is confirmed by mean current sheet thickness being greatest on the dawnside. We propose that heavy planetary ion (e.g., Na+) enhancements in the duskside current sheet provides the most likely explanation for the dawn-dusk current sheet asymmetries. We also report the direct measurement of Mercury's substorm current wedge (SCW) formation and estimate the total current due to pileup of magnetic flux to be ≈11 kA. The conductance at the foot of the field lines required to close the SCW current is found to be ≈1.2 S, which is similar to earlier results derived from modeling of Mercury's Region 1 field-aligned currents. Hence, Mercury's regolith is sufficiently conductive for the current to flow radially then across the surface of Mercury's highly conductive iron core. Mercury appears to be closely coupled to its nightside magnetosphere by mass loading of upward flowing heavy planetary ions and electrodynamically by field-aligned currents that transfer momentum and energy to the nightside auroral oval crust and interior. Heavy planetary ion enhancements in Mercury's duskside current sheet provide explanation for cross-tail asymmetries found in this study. The total current due to the pileup of magnetic flux and conductance required to close the SCW current is found to be ≈11 kA and 1.2 S. Mercury is coupled to magnetotail by mass loading of heavy ions and field-aligned currents driven by reconnection-related fast plasma flow.
      PubDate: 2017-08-19T13:03:08.874223-05:
      DOI: 10.1002/2017JA024266
       
  • Detailed characteristics of radiation belt electrons revealed by
           CSSWE/REPTile measurements: Geomagnetic activity response and
           precipitation observation
    • Authors: K. Zhang; X. Li, Q. Schiller, D. Gerhardt, H. Zhao, R. Millan
      Pages: 8434 - 8445
      Abstract: Earth's outer radiation belt electrons are highly dynamic. We study the detailed characteristics of relativistic electrons in the outer belt using measurements from the Colorado Student Space Weather Experiment (CSSWE) mission, a low Earth orbit (LEO) CubeSat, which traverses the radiation belt four times in one orbit (~1.5 h) and has the advantage of measuring the dynamic activities of the electrons including their rapid precipitation. We focus on the measured electron response to geomagnetic activity for different energies to show that there are abundant sub-MeV electrons in the inner belt and slot region. These electrons are further enhanced during active times, while there is a lack of>1.63 MeV electrons in these regions. We also show that the variation of measured electron flux at LEO is strongly dependent on the local magnetic field strength, which is far from a dipole approximation. Moreover, a specific precipitation band, which happened on 19 January 2013, is investigated based on the conjunctive measurement of CSSWE, the Balloon Array for Radiation belt Relativistic Electron Losses, and one of the Polar Operational Environmental Satellites. In this precipitation band event, the net loss of the 0.58–1.63 MeV electrons (L = 3.5–6) is estimated to account for 6.8% of the total electron content.
      PubDate: 2017-08-19T13:02:55.381498-05:
      DOI: 10.1002/2017JA024309
       
  • Propagation and evolution of electric fields associated with solar wind
           pressure pulses based on spacecraft and ground-based observations
    • Authors: N. Takahashi; Y. Kasaba, Y. Nishimura, A. Shinbori, T. Kikuchi, T. Hori, Y. Ebihara, N. Nishitani
      Pages: 8446 - 8461
      Abstract: We investigate spatial and temporal evolution of large-scale electric fields in the magnetosphere and ionosphere associated with sudden commencements (SCs) using multipoint equatorial magnetospheric (THEMIS, RBSP, and GOES) and ionospheric (C/NOFS) satellites with radars (SuperDARN). A distinct SC event on 17 March 2013 shows that the magnetospheric electric field in the equatorial plane propagates from dayside toward nightside as a fast-mode wave. The ionospheric electric field responds ~41 s after the onset of dayside magnetospheric electric field, which can be explained by the propagation of the Alfvén wave along magnetic field lines. The wavelet analysis shows that the Alfvén wave is dominant in the plasmasphere. Poynting fluxes toward the ionosphere support these propagations. From a statistical analysis of response time, tailward propagation speed is estimated at about 1000–1100 km/s. We also statistically derive a spatial distribution and time evolution of the magnetospheric electric field in the dawn-dusk direction (Ey). Our result shows that negative Ey (dawnward) propagates from noon toward the magnetotail, followed by positive Ey (duskward). The propagation characteristics of electric fields in the equatorial plane depend on magnetic local time. At noon, negative Ey lasts for about 1 min, and positive Ey becomes dominant about 2 min after the SC onset. Negative Ey soon attenuates in the nightside region, while the positive Ey propagates fairly well to the premidnight or postmidnight regions while maintaining a certain amplitude. The enhancement of positive Ey is due to the enhancement of magnetospheric convection associated with the main impulse of SCs.
      PubDate: 2017-08-23T16:21:34.700059-05:
      DOI: 10.1002/2017JA023990
       
  • Equatorial magnetic field of the near-Earth magnetotail
    • Authors: S. Ohtani; T. Motoba
      Pages: 8462 - 8478
      Abstract: The equatorial magnetic field of the nightside magnetosphere is critical for understanding not only the configuration of the magnetotail but also its state and dynamics. The present study observationally addresses various aspects of the equatorial magnetic field, such as its spatial distribution, possible antisunward gradients, and extremely weak magnetic fields, with emphasis on the transition region between dipolar and stretched magnetic configurations. The results are summarized as follows: (1) the transition of the tail magnetic field from a near-Earth dipolar configuration to a stretched one farther out takes place around −12 ≤ Xagsm ≤ −9 RE, although instantaneous configurations can vary significantly; (2) the average equatorial magnetic field in this transition region is noticeably weaker at solar minimum presumably reflecting weaker nightside magnetospheric currents closer to Earth; (3) the statistical comparison of equatorial magnetic fields measured simultaneously at two locations indicates that the gradient of the equatorial magnetic field is directed predominantly earthward, and it is suggested that apparent tailward gradients observed can be very often attributed to other factors such as structures in the Y direction and local fluctuations; (4) however, the gradient can be transiently directed tailward in association with the dipolarization of local magnetic field; (5) extremely weak (≤ 2 nT) magnetic fields are occasionally observed in the transition region during the substorm growth phase and during prolonged quiet intervals, but the association with steady magnetospheric convection, which was suggested before, cannot be confirmed possibly because of its rare occurrence.
      PubDate: 2017-08-23T16:50:22.886102-05:
      DOI: 10.1002/2017JA024115
       
  • Where is the magnetic energy for the expansion phase of auroral substorms
           accumulated' 2. The main body, not the magnetotail
    • Authors: Syun-Ichi Akasofu
      Pages: 8479 - 8487
      Abstract: It is suggested that the magnetosphere tries to stabilize itself by quickly unloading the magnetic energy accumulated within its main body, when the accumulated magnetic energy exceeds a limited amount, which can be identified as the energy for the expansion phase. It is this process which manifests as the impulsive expansion phase, during which auroral arcs advance well beyond the presubstorm latitude in the midnight sector. It was shown in the previous paper that the magnetotail does not have enough magnetic energy for a medium substorm (energy 5 × 1015 J; AE = 1000 nT). In this paper, it is shown that (1) the reason of the short lifetime (1–1.5 h) of the expansion phase is due to the fact that a limited amount of magnetic energy accumulated during the growth phase is dissipated in a period similar to the duration of the growth phase (1–1.5 h); the accumulation rate is similar to the dissipation rate during the expansion phase: (2) when the main body of the magnetosphere accumulates the magnetic energy, it is inflated; β (= (nkT/B2/8π)) even at XGSM = −6 RE becomes close to 1.0 for magnetic energy (2.9 × 1014 J) which is less than the amount consumed by a medium intensity substorm. (3) As a result, the plasma sheet current and thus the magnetosphere are expected to become unstable, unloading the accumulated excess magnetic energy and resulting in current reduction and deflation. (4) The resulting deflation can cause an earthward electric field of 5–50 mV/m, which can generate Bostrom's current system, which is mainly responsible in producing various phenomena of the expansion phase. (5) The large range of substorm intensity (AE = 100–2000 nT) is likely to be due to the location where the energy is accumulated; the closer is the distance to the Earth (XGSM between −10 RE and −4 RE), the more intense the substorm intensity is.
      PubDate: 2017-08-24T09:50:33.557892-05:
      DOI: 10.1002/2016JA023074
       
  • Ionospheric anomalies immediately before Mw7.0–8.0 earthquakes
    • Authors: Liming He; Kosuke Heki
      Pages: 8659 - 8678
      Abstract: Recent observations suggested that ionospheric anomalies appear immediately before large earthquakes with moment magnitudes (Mw) of 8.2 or more. Do similar phenomena precede smaller earthquakes' Here we answer this question by analyzing vertical total electron contents (VTEC) observed near the epicenters before and after 32 earthquakes with Mw7.0–8.0 using data from nearby Global Navigation Satellite Systems stations. To detect anomalies, we defined the reference curves to fit the observed VTEC and considered the departure from the curves as anomalies. In estimating the reference curves, we excluded time windows, prescribed for individual earthquakes considering Mw, possibly affected by earthquakes. We validated the method using synthetic VTEC data assuming both preseismic, coseismic, and postseismic anomalies. Out of the 32 Mw7.0–8.0 earthquakes, eight earthquakes showed possible preseismic anomalies starting 10–20 min before earthquakes. For earthquakes of this Mw range, we can observe preseismic ionospheric changes probably when the background VTEC is large, say 50 TECU (total electron content unit, 1 TECU = 1016 el m−2) or more.
      PubDate: 2017-08-02T17:23:23.507692-05:
      DOI: 10.1002/2017JA024012
       
  • Direct and indirect electron precipitation effect on nitric oxide in the
           polar middle atmosphere, using a full-range energy spectrum
    • Authors: Christine Smith-Johnsen; Hilde Nesse Tyssøy, Koen Hendrickx, Yvan Orsolini, Grandhi Kishore Kumar, Linn-Kristine Glesnes Ødegaard, Marit Irene Sandanger, Frode Stordal, Linda Megner
      Pages: 8679 - 8693
      Abstract: In April 2010, a coronal mass ejection and a corotating interaction region on the Sun resulted in an energetic electron precipitation event in the Earth's atmosphere. We investigate direct and indirect nitric oxide (NO) response to the electron precipitation. By combining electron fluxes from the Total Energy Detector and the Medium Energy Proton and Electron Detector on the National Oceanic and Atmospheric Administration's Polar-orbiting Operational Environmental Satellites, we obtain a continuous energy spectrum covering 1–750 keV. This corresponds to electrons depositing their energy at atmospheric altitudes 60–120 km. Based on the electron energy deposition, taking into account loss due to photolysis, the accumulated NO number density is estimated. When compared to NO measured at these altitudes by the Solar Occultation for Ice Experiment instrument on board the Aeronomy of Ice in the Mesosphere satellite, the NO direct effect was detected down to 55 km. The main variability at these altitudes is, however, dominated by the indirect effect, which is downward transported NO. We estimate the source of this descending NO to be in the upper mesosphere at ∼75–90 km.
      PubDate: 2017-08-02T17:46:58.232496-05:
      DOI: 10.1002/2017JA024364
       
  • Preearthquake anomalous ionospheric signatures observed at low-mid
           latitude Indian station, Delhi, during the year 2015 to early 2016:
           Preliminary results
    • Authors: Sumedha Gupta; A. K. Upadhayaya
      Pages: 8694 - 8719
      Abstract: We have analyzed five major earthquake events measuring greater than 6 on Richter scale (M > 6) that occurred during the year 2015 to early 2016, affecting Indian region ionosphere, using F2 layer critical parameters (foF2, hmF2) obtained using Digisonde from a low-mid latitude Indian station, Delhi (28.6°N, 77.2°E, 19.2°N geomagnetic latitude, 42.4°N dip). Normal day-to-day variability occurring in ionosphere is segregated by calculating F2 layer critical frequency and peak height variations (ΔfoF2, ΔhmF2) from the normal quiet time behavior apart from computing interquartile range. We find that the ionospheric F2 region across Delhi by and large shows some significant perturbations 3–4 days prior to these earthquake events, resulting in a large peak electron density variation of ~200%. These observed perturbations indicate towards a possibility of seismo-ionospheric coupling as the solar and geomagnetic indices were normally quiet and stable during the period of these events. It was also observed that the precursory effect of earthquake was predominantly seen even outside the earthquake preparation zone, as given by Dobrovolsky et al. (1979). The thermosphere neutral composition (O/N2) as observed by Global Ultraviolet Imager, across Delhi, during these earthquake events does not show any marked variation. Further, the effect of earthquake events on ionospheric peak electron density is compared to the lower atmosphere meteorological phenomenon of 2015 sudden stratospheric warming event.
      PubDate: 2017-08-02T17:48:49.900884-05:
      DOI: 10.1002/2017JA024192
       
  • Perturbations to the lower ionosphere by tropical cyclone Evan in the
           South Pacific Region
    • Authors: Sushil Kumar; Samir NaitAmor, Olivier Chanrion, Torsten Neubert
      Pages: 8720 - 8732
      Abstract: Very low frequency (VLF) electromagnetic signals from navigational transmitters propagate worldwide in the Earth-ionosphere waveguide formed by the Earth and the electrically conducting lower ionosphere. Changes in the signal properties are signatures of variations in the conductivity of the reflecting boundary of the lower ionosphere which is located in the mesosphere and lower thermosphere, and their analysis is, therefore, a way to study processes in these remote regions. Here we present a study on amplitude perturbations of local origin on the VLF transmitter signals (NPM, NLK, NAA, and JJI) observed during tropical cyclone (TC) Evan, 9–16 December 2012 when TC was in the proximity of the transmitter-receiver links. We observed a maximum amplitude perturbation of 5.7 dB on JJI transmitter during 16 December event. From Long Wave Propagation Capability model applied to three selected events we estimate a maximum decrease in the nighttime D region reference height (H′) by ~5.2 km (13 December, NPM) and maximum increase in the daytime D region H′ by 6.1 km and 7.5 km (14 and 16 December, JJI). The results suggest that the TC caused the neutral densities of the mesosphere and lower thermosphere to lift and sink (bringing the lower ionosphere with it), an effect that may be mediated by gravity waves generated by the TC. The perturbations were observed before the storm was classified as a TC, at a time when it was a tropical depression, suggesting the broader conclusion that severe convective storms, in general, perturb the mesosphere and the stratosphere through which the perturbations propagate.
      PubDate: 2017-08-03T14:15:47.338851-05:
      DOI: 10.1002/2017JA024023
       
  • A corotation electric field model of the Earth derived from Swarm
           satellite magnetic field measurements
    • Authors: Stefan Maus
      Pages: 8733 - 8754
      Abstract: Rotation of the Earth in its own geomagnetic field sets up a primary corotation electric field, compensated by a secondary electric field of induced electrical charges. For the geomagnetic field measured by the Swarm constellation of satellites, a derivation of the global corotation electric field inside and outside of the corotation region is provided here, in both inertial and corotating reference frames. The Earth is assumed an electrical conductor, the lower atmosphere an insulator, followed by the corotating ionospheric E region again as a conductor. Outside of the Earth's core, the induced charge is immediately accessible from the spherical harmonic Gauss coefficients of the geomagnetic field. The charge density is positive at high northern and southern latitudes, negative at midlatitudes, and increases strongly toward the Earth's center. Small vertical electric fields of about 0.3 mV/m in the insulating atmospheric gap are caused by the corotation charges located in the ionosphere above and the Earth below. The corotation charges also flow outward into the region of closed magnetic field lines, forcing the plasmasphere to corotate. The electric field of the corotation charges further extends outside of the corotating regions, contributing radial outward electric fields of about 10 mV/m in the northern and southern polar caps. Depending on how the magnetosphere responds to these fields, the Earth may carry a net electric charge.
      PubDate: 2017-08-03T13:51:14.123591-05:
      DOI: 10.1002/2017JA024221
       
  • WN4 variability in DMSP ion densities across season, solar cycle, and
           local time
    • Authors: J. M. Hawkins; P. C. Anderson
      Pages: 8755 - 8769
      Abstract: Nonmigrating tides are a major coupling mechanism between the different regions of the atmosphere and ionosphere. The wave number 4 (WN4) pattern in the ionosphere has been recognized as originating primarily with the diurnal eastward propagating wave-3 nonmigrating tide (DE3) in the troposphere, and significant effort has been devoted in recent years to understanding how tidal effects manifest in various physical parameters across a very wide range of altitudes. While DE3 and WN4 signatures have been much studied in the mesosphere-lower thermosphere region, relatively little is known about how WN4 impacts the ionosphere above the F peak. We present an analysis of WN4 in the topside ionosphere as measured by the Defense Meteorological Satellite Program (DMSP) spacecraft, using monthly averages of total ion densities and composition binned by latitude and longitude. We found that WN4 is most strongly present during September equinox. In May–August, ion densities near 180–270 geographic longitude (GLON) are enhanced and the WN4 pattern moves 5–10° north; in November–February, ion densities are reduced in this region and WN4 moves 5–10° south. No solar cycle effects were found in the magnitude of dN/N. The longitude position of the peaks (phase) was observed to vary by about 10° with F10.7, moving eastward with increasing F10.7. The latitude variation was less than 5° and did not show a trend with F10.7. The WN4 pattern changes rapidly near dawn but is very constant throughout the afternoon and evening in terms of dN/N and drifts eastward at about 2° GLON per hour magnetic local time.
      PubDate: 2017-08-03T14:01:41.596411-05:
      DOI: 10.1002/2017JA024065
       
  • Sixteen year variation of horizontal phase velocity and propagation
           direction of mesospheric and thermospheric waves in airglow images at
           Shigaraki, Japan
    • Authors: D. Takeo; K. Shiokawa, H. Fujinami, Y. Otsuka, T. S. Matsuda, M. K. Ejiri, T. Nakamura, M. Yamamoto
      Pages: 8770 - 8780
      Abstract: We analyzed the horizontal phase velocity of gravity waves and medium-scale traveling ionospheric disturbances (MSTIDs) by using the three-dimensional fast Fourier transform method developed by Matsuda et al. (2014) for 557.7 nm (altitude: 90–100 km) and 630.0 nm (altitude: 200–300 km) airglow images obtained at Shigaraki MU Observatory (34.8°N, 136.1°E, dip angle: 49°) over ∼16 years from 16 March 1999 to 20 February 2015. The analysis of 557.7 nm airglow images shows clear seasonal variation of the propagation direction of gravity waves in the mesopause region. In spring, summer, fall, and winter, the peak directions are northeastward, northeastward, northwestward, and southwestward, respectively. The difference in east-west propagation direction between summer and winter is probably caused by the wind filtering effect due to the zonal mesospheric jet. Comparison with tropospheric reanalysis data shows that the difference in north-south propagation direction between summer and winter is caused by differences in the latitudinal location of wave sources due to convective activity in the troposphere relative to Shigaraki. The analysis of 630.0 nm airglow images shows that the propagation direction of MSTIDs is mainly southwestward with a minor northeastward component throughout the 16 years. A clear negative correlation is seen between the yearly power spectral density of MSTIDs and F10.7 solar flux. This negative correlation with solar activity may be explained by the linear growth rate of the Perkins instability and secondary wave generation of gravity waves in the thermosphere.
      PubDate: 2017-08-05T15:20:55.887841-05:
      DOI: 10.1002/2017JA023919
       
  • Ionospheric electron heating associated with pulsating auroras: A Swarm
           survey and model simulation
    • Authors: Jun Liang; B. Yang, E. Donovan, J. Burchill, D. Knudsen
      Pages: 8781 - 8807
      Abstract: In this paper we report a study on the plasma signatures (electron temperature, plasma density, and field-aligned current) of patchy pulsating auroras in the upper F region ionosphere using Swarm satellite data. Via a survey of 38 patch crossing events, we repeatedly identify a strong electron temperature enhancement associated with the pulsating aurora. On average, the electron temperature at Swarm satellite altitudes (~460 km) increases from ~2200 K at subauroral latitudes to a peak of ~3000 K within the pulsating auroral patch. This indicates that pulsating auroras may act as an important heating source for the nightside ionosphere. On the other hand, no well-defined trend of plasma density variations associated with pulsating auroras is identified at Swarm altitudes. The field-aligned currents within the pulsating aurora patch are mostly upward, with mean magnitudes on order of ~1 μA/m2. We then perform a numerical simulation to explore the potential mechanisms underlying the strong electron heating associated with the pulsating aurora. Via simulations we find that to account for the realistic electron temperature observation in a major portion of our events, pulsating auroras are likely accompanied by substantial magnetospheric heat fluxes around the order of ~1010 eV/cm2. We propose that such magnetospheric heat fluxes may be pertinent to one long-hypothesized feature of pulsating auroras, namely, the coexistence of an enhanced low-energy plasma population in magnetic flux tubes threading the pulsating aurora, in addition to the energetic electron precipitation. Via a Swarm survey we repeatedly find a strong electron temperature enhancement associated with the pulsating aurora The field-aligned currents within pulsating auroras are moderately upward, with mean magnitudes on the order of ~1e−6 A/m2 To explain the observed electron heating, pulsating auroras are likely accompanied by magnetospheric heat fluxes around ~1E+10 eV/cm2/s.
      PubDate: 2017-08-05T15:21:43.469202-05:
      DOI: 10.1002/2017JA024127
       
  • Impact of M-solar flare-induced solar proton event on mesospheric Na layer
           over Utah (41.8°N,112°W)
    • Authors: Tikemani Bag
      Pages: 8808 - 8815
      Abstract: The influence of solar proton event, induced by M-solar flare, on the mesospheric sodium layer is studied over a midlatitude location Utah(41.8°N, 112°W) during 19 July 2012. The variation in sodium concentration (cm−3) is examined with temperature and atomic oxygen concentration obtained from NRLMSISE-00 empirical model. In the vicinity of peak sodium concentration, the temperature shows a strong negative correlation with sodium concentration, atomic oxygen concentration shows a positive correlation with sodium concentration. An enhancement in sodium concentration is observed during the solar proton event with highest concentration at the time of maximum proton flux. The altitude of peak sodium concentration shows a downward movement with lowest altitude corresponding to the time of maximum proton flux. However, the altitude of peak sodium concentration is found in the altitude region of 85–90 km throughout the solar proton event.
      PubDate: 2017-08-05T15:25:30.004149-05:
      DOI: 10.1002/2017JA024001
       
  • Ionospheric annual anomaly—New insights to the physical mechanisms
    • Authors: V. Sai Gowtam; S. Tulasi Ram
      Pages: 8816 - 8830
      Abstract: The ionospheric annual anomaly or nonseasonal anomaly of the ionosphere is characterized by globally increased ionization in December solstice than in June solstice. Though this phenomenon was reported several decades ago, the causal mechanisms have not been fully understood till today. In this paper, the F2 layer peak electron density (NmF2) data from Formosa satellite 3/Constellation Observing System for Meteorology, Ionosphere, and Climate-radio occultation observations during the low solar activity year 2009 were systematically analyzed to investigate the physical mechanisms responsible for annual anomaly and its local time, latitudinal, and longitudinal variability. It is found that the annual anomaly is primarily dominant at Southern Hemisphere at all local times, with significant enhancements at equatorial ionization anomaly crest latitudes during noon to afternoon hours and at high latitudes during nighttimes. The annual anomaly in Northern Hemisphere occurs with relatively smaller magnitudes and confined only to morning to early afternoon hours (08–14 LT). This study brings out the important roles of effective neutral winds due to the geomagnetic field configuration and the offset between geomagnetic equator and subsolar point for the enhanced plasma density in the Southern Hemisphere during December that majorly contributes to the ionospheric annual anomaly. These results provide new insights to the responsible mechanisms behind the ionospheric annual anomaly and its local time latitudinal, and longitudinal variation
      PubDate: 2017-08-10T09:41:30.323888-05:
      DOI: 10.1002/2017JA024170
       
  • Short-term variability in the ionosphere due to the nonlinear interaction
           between the 6 day wave and migrating tides
    • Authors: Quan Gan; Jens Oberheide, Jia Yue, Wenbin Wang
      Pages: 8831 - 8846
      Abstract: Using the thermosphere-ionosphere-mesosphere electrodynamics general circulation model simulations, we investigate the short-term ionospheric variability due to the child waves and altered tides produced by the nonlinear interaction between the 6 day wave and migrating tides. Via the Fourier spectral diagnostics and least squares fittings, the [21 h, W2] and [13 h, W1] child waves, generated by the interaction of the 6 day wave with the DW1 and SW2, respectively, are found to play the leading roles on the subdiurnal variability (e.g., ±10 m/s in the ion drift and ~50% in the NmF2) in the F region vertical ion drift changes through the dynamo modulation induced by the low-latitude zonal wind and the meridional wind at higher latitudes. The relatively minor contribution of the [11 h, W3] child wave is explicit as well. Although the [29 h, W0] child wave has the largest magnitude in the E region, its effect is totally absent in the vertical ion drift due to the zonally uniform structure. But the [29 h, W0] child wave shows up in the NmF2. It is found that the NmF2 short-term variability is attributed to the wave modulations on both E region dynamo and in situ F region composition. Also, the altered migrating tides due to the interaction will not contribute to the ionospheric changes significantly.
      PubDate: 2017-08-10T09:42:05.953542-05:
      DOI: 10.1002/2017JA023947
       
  • Stratosphere and lower mesosphere wind observation and gravity wave
           activities of the wind field in China using a mobile Rayleigh Doppler
           lidar
    • Authors: Ruocan Zhao; Xiankang Dou, Xianghui Xue, Dongsong Sun, Yuli Han, Chong Chen, Jun Zheng, Zimu Li, Anran Zhou, Yan Han, Guocheng Wang, Tingdi Chen
      Pages: 8847 - 8857
      Abstract: Since the mobile Rayleigh Doppler lidar of the University of Science and Technology of China was developed in 2013, more than 100 days of valid nighttime wind data from 15 to 60 km altitude were obtained during recent 3 years. The observation locations cover the northwest (midlatitude) of China: Delingha (37.371°N, 97.374°E), Xinzhou (38.425°N, 112.729°E), and Jiuquan (39.741°N, 98.495°E). Recently, we have extracted perturbations of the wind profiles from the wind field measurements and we have found that inertia gravity waves and mountain waves existed at the same time. The results of wind field and several gravity waves cases are shown in this paper. Typical characteristics of the gravity waves are analyzed in this midlatitude area of China. A 2-D fast Fourier transform of the wind perturbation shows that a dominant stationary wave mode and a downward wave mode exist simultaneously in the spectrum. A band-pass 2-D filter was applied to the spectrum followed by inverse fast Fourier transform to separate inertia gravity waves from stationary mountain waves. The horizontal wavelength is retrieved using hodograph methods, indicating that the inertia waves are generated thousands of kilometers away. Observed mountain waves from a combination of vertical wind and leaned line of sight wind measurements show a small-angle leaned wave front from the horizontal direction. This kind of gravity wave observation of the stratospheric wind field and its wave patterns is rare and significant for the study of atmospheric dynamics.
      PubDate: 2017-08-10T10:14:47.587475-05:
      DOI: 10.1002/2016JA023713
       
  • Characteristics of ionospheric flux rope at the terminator observed by
           Venus Express
    • Authors: Y. Q. Chen; T. L. Zhang, S. D. Xiao, G. Q. Wang
      Pages: 8858 - 8867
      Abstract: We investigate the characteristics of the magnetic flux rope in the Venusian ionosphere near the terminator observed by the Venus Express while previous works about flux rope by PVO are mainly in the subsolar region. The probability to observe the flux rope becomes larger as solar activity strengthens. A statistical work during solar maximum presents the following characteristics. (1) The flux ropes in the terminator region have a lower spatial occurrence compared with those in the subsolar region, and the spatial occurrence of the flux ropes is also getting smaller when altitude increases. (2) The scale size of the flux rope is larger in the terminator region than that in the subsolar region and becomes larger when altitude increases. (3) In the terminator region, the flux rope appears to have a quasi-horizontal orientation but with some cases can be vertical at low altitude. (4) The flux ropes in high solar zenith angle regions are confirmed to have a lower helicity compared with those in low solar zenith angle regions.
      PubDate: 2017-08-14T17:56:43.111668-05:
      DOI: 10.1002/2017JA023999
       
  • Observation and simulation of the ionosphere disturbance waves triggered
           by rocket exhausts
    • Authors: Charles C. H. Lin; Chia-Hung Chen, Mitsuru Matsumura, Jia-Ting Lin, Yoshihiro Kakinami
      Pages: 8868 - 8882
      Abstract: Observations and theoretical modeling of the ionospheric disturbance waves generated by rocket launches are investigated. During the rocket passage, time rate change of total electron content (rTEC) enhancement with the V-shape shock wave signature is commonly observed, followed by acoustic wave disturbances and region of negative rTEC centered along the trajectory. Ten to fifteen min after the rocket passage, delayed disturbance waves appeared and propagated along direction normal to the V-shape wavefronts. These observation features appeared most prominently in the 2016 North Korea rocket launch showing a very distinct V-shape rTEC enhancement over enormous areas along the southeast flight trajectory despite that it was also appeared in the 2009 North Korea rocket launch with the eastward flight trajectory. Numerical simulations using the physical-based nonlinear and nonhydrostatic coupled model of neutral atmosphere and ionosphere reproduce promised results in qualitative agreement with the characteristics of ionospheric disturbance waves observed in the 2009 event by considering the released energy of the rocket exhaust as the disturbance source. Simulations reproduce the shock wave signature of electron density enhancement, acoustic wave disturbances, the electron density depletion due to the rocket-induced pressure bulge, and the delayed disturbance waves. The pressure bulge results in outward neutral wind flows carrying neutrals and plasma away from it and leading to electron density depletions. Simulations further show, for the first time, that the delayed disturbance waves are produced by the surface reflection of the earlier arrival acoustic wave disturbances.
      PubDate: 2017-08-16T12:36:56.224046-05:
      DOI: 10.1002/2017JA023951
       
  • Long-term variations of exospheric temperature inferred from foF1
           observations: A comparison to ISR Ti trend estimates
    • Authors: L. Perrone; A. V. Mikhailov
      Pages: 8883 - 8892
      Abstract: June noontime monthly median foF1 ionosonde observations at Sodankylä (auroral zone), Juliusruh, and Rome (middle latitudes) were used to retrieve exospheric temperature, Tex long-term variations over the (1958–2015) period. After removing solar activity effects the residual linear trends were found to be small (0.05–0.6)% per decade and statistically insignificant at middle latitudes. Therefore, the revealed Tex long-term variations are mainly due to long-term variations of solar activity, i.e., they have a natural (not anthropogenic) origin. Large trends in ion temperature, Ti inferred from incoherent scatter radar (ISR) observations which the researchers identify with trends in neutral temperature, Tn may be related to the incoherent scatter method routinely based on a fixed model of ion composition (O+/Ne ratio and mean ion mass, correspondingly) under varying geophysical conditions. Mean ion mass number manifests a negative trend at 175 km which should correspond to a negative trend in Ti contrary the results obtained below 200 km with ISRs. Therefore, routine ISR observations based on a fixed model of ion composition may be not appropriate for long-term trend analyses.
      PubDate: 2017-08-23T16:37:57.475858-05:
      DOI: 10.1002/2017JA024193
       
  • Dependence of thermospheric zonal winds on solar flux, geomagnetic
           activity, and hemisphere as measured by CHAMP
    • Authors: Xiaofang Zhang; Libo Liu, Songtao Liu
      Pages: 8893 - 8914
      Abstract: The thermospheric zonal winds measured by the CHAllenging Minisatellite Payload (CHAMP) satellite are used to statistically determine the climatology under quiet and active geomagnetic conditions. By collectively analyzing the bin-averaged wind trend with F10.7 and the solar-induced difference in wind structures, the solar flux dependence of global thermosphere zonal wind is determined. The increase of solar flux enhances the eastward winds at low latitudes from dusk to midnight. The increased ion drag reduces the nighttime eastward wind in the subauroral latitudes, and the daytime westward winds from 06 to 08 MLT at all latitudes decrease with increasing solar flux. Zonal winds show coupled seasonal/extreme ultraviolet (EUV) dependency. The equatorial zonal winds from 18 to 04 magnetic local time (MLT) indicate weaker eastward winds during the June solstice at high solar flux levels. Quiet time eastward winds at subauroral latitudes from 16 to 20 MLT are further decreased in the winter hemisphere. Influenced by asymmetries in solar illumination and the magnetic field, zonal winds show hemispheric asymmetries. Quiet daytime winds are additionally influenced by solar illumination effects, and the westward winds at the middle and subauroral latitudes are always stronger in the summer. The nighttime eastward winds are higher in the winter hemisphere during the solstices, as in the Southern Hemisphere during equinoxes, with the winter-summer asymmetry lessened or receding at the solar maxima. Storm-induced subauroral westward disturbance winds are higher in the summer hemisphere and in the Northern Hemisphere during equinoxes. At a high level of solar flux, the westward disturbance winds are comparable in the two hemispheres during December solstice. Geomagnetic disturbance wind observations from CHAMP agree well with the empirical geomagnetic disturbance wind model, except for stronger subauroral westward jets. Westward winds during the afternoon may be enhanced in the auroral latitudes before the initial time of a storm main phase.
      PubDate: 2017-08-23T16:39:13.865786-05:
      DOI: 10.1002/2016JA023715
       
  • New DMSP database of precipitating auroral electrons and ions
    • Authors: Robert J. Redmon; William F. Denig, Liam M. Kilcommons, Delores J. Knipp
      Pages: 9056 - 9067
      Abstract: Since the mid-1970s, the Defense Meteorological Satellite Program (DMSP) spacecraft have operated instruments for monitoring the space environment from low Earth orbit. As the program evolved, so have the measurement capabilities such that modern DMSP spacecraft include a comprehensive suite of instruments providing estimates of precipitating electron and ion fluxes, cold/bulk plasma composition and moments, the geomagnetic field, and optical emissions in the far and extreme ultraviolet. We describe the creation of a new public database of precipitating electrons and ions from the Special Sensor J (SSJ) instrument, complete with original counts, calibrated differential fluxes adjusted for penetrating radiation, estimates of the total kinetic energy flux and characteristic energy, uncertainty estimates, and accurate ephemerides. These are provided in a common and self-describing format that covers 30+ years of DMSP spacecraft from F06 (launched in 1982) to F18 (launched in 2009). This new database is accessible at the National Centers for Environmental Information and the Coordinated Data Analysis Web. We describe how the new database is being applied to high-latitude studies of the colocation of kinetic and electromagnetic energy inputs, ionospheric conductivity variability, field-aligned currents, and auroral boundary identification. We anticipate that this new database will support a broad range of space science endeavors from single observatory studies to coordinated system science investigations.
      PubDate: 2017-08-10T11:30:30.65155-05:0
      DOI: 10.1002/2016JA023339
       
  • A new DMSP magnetometer and auroral boundary data set and estimates of
           field-aligned currents in dynamic auroral boundary coordinates
    • Authors: Liam M. Kilcommons; Robert J. Redmon, Delores J. Knipp
      Pages: 9068 - 9079
      Abstract: We have developed a method for reprocessing the multidecadal, multispacecraft Defense Meteorological Satellite Program Special Sensor Magnetometer (DMSP SSM) data set and have applied it to 15 spacecraft years of data (DMSP Flight 16–18, 2010–2014). This Level-2 data set improves on other available SSM data sets with recalculated spacecraft locations and magnetic perturbations, artifact signal removal, representations of the observations in geomagnetic coordinates, and in situ auroral boundaries. Spacecraft locations have been recalculated using ground-tracking information. Magnetic perturbations (measured field minus modeled main field) are recomputed. The updated locations ensure the appropriate model field is used. We characterize and remove a slow-varying signal in the magnetic field measurements. This signal is a combination of ring current and measurement artifacts. A final artifact remains after processing: step discontinuities in the baseline caused by activation/deactivation of spacecraft electronics. Using coincident data from the DMSP precipitating electrons and ions instrument (SSJ4/5), we detect the in situ auroral boundaries with an improvement to the Redmon et al. (2010) algorithm. We embed the location of the aurora and an accompanying figure of merit in the Level-2 SSM data product. Finally, we demonstrate the potential of this new data set by estimating field-aligned current (FAC) density using the Minimum Variance Analysis technique. The FAC estimates are then expressed in dynamic auroral boundary coordinates using the SSJ-derived boundaries, demonstrating a dawn-dusk asymmetry in average FAC location relative to the equatorward edge of the aurora. The new SSM data set is now available in several public repositories.
      PubDate: 2017-08-10T11:30:50.371772-05:
      DOI: 10.1002/2016JA023342
       
  • First observation of mesosphere response to the solar wind high-speed
           streams
    • Authors: Wen Yi; Iain M. Reid, Xianghui Xue, Joel P. Younger, Andrew J. Spargo, Damian J. Murphy, Tingdi Chen, Xiankang Dou
      Pages: 9080 - 9088
      Abstract: We present a first analysis of 9 and 6.75 day periodic oscillations observed in the neutral mesospheric density in 2005 and 2006. Mesospheric densities near 90 km are derived using data from the Davis meteor radar (68.5°S, 77.9°E; magnetic latitude, 74.6°S), Antarctica. Spectral analysis indicates that the pronounced periodicities of 9 and 6.75 days observed in the mesosphere densities are associated with variations in solar wind high-speed streams and recurrent geomagnetic activity. Neutral mesospheric winds and temperatures, simultaneously measured by the Davis meteor radar, also exhibit 9 and 6.75 day periodicities. A Morlet wavelet analysis shows that the time evolution of the 9 and 6.75 day oscillations in the neutral mesosphere densities and winds are similar to those in the solar wind and in planetary magnetic activity index, Kp in 2005 and 2006. These results demonstrate a direct coupling between Sun's corona (upper atmosphere) and the Earth's mesosphere.
      PubDate: 2017-08-18T16:07:23.202105-05:
      DOI: 10.1002/2017JA024446
       
 
 
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