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Journal Cover Journal of Atmospheric and Solar-Terrestrial Physics
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   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 1364-6826
   Published by Elsevier Homepage  [3089 journals]
  • Aliasing of Schumann resonance background signal by sprite-associated
           Q-bursts
    • Authors: Anirban Guha; Earle Williams; Robert Boldi; Gabriella Sátori; Tamás Nagy; József Bór; Joan Montanyà; Pascal Ortega
      Pages: 25 - 37
      Abstract: Publication date: Available online 4 November 2017
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Anirban Guha, Earle Williams, Robert Boldi, Gabriella Sátori, Tamás Nagy, József Bór, Joan Montanyà, Pascal Ortega
      The Earth's naturally occurring Schumann resonances (SR) are composed of a quasi-continuous background component and a larger-amplitude, short-duration transient component, otherwise called ‘Q-burst’ (Ogawa et al., 1967). Sprites in the mesosphere are also known to accompany the energetic positive ground flashes that launch the Q-bursts (Boccippio et al., 1995). Spectra of the background Schumann Resonances (SR) require a natural stabilization period of ∼10–12 min for the three conspicuous modal parameters to be derived from Lorentzian fitting. Before the spectra are computed and the fitting process is initiated, the raw time series data need to be properly filtered for local cultural noise, narrow band interference as well as for large transients in the form of global Q-bursts. Mushtak and Williams (2009) describe an effective technique called Isolated Lorentzian (I-LOR), in which, the contributions from local cultural and various other noises are minimized to a great extent. An automated technique based on median filtering of time series data has been developed. These special lightning flashes are known to have greater contribution in the ELF range (below 1 kHz) compared to general negative CG strikes [Huang et al., 1999; Cummer et al., 2006]. The global distributions of these Q-bursts have been studied by Huang et al. (1999) by wave impedance methods from single station ELF measurements at Rhode Island, USA and from Japan Hobara et al. (2006). The present work aims to demonstrate the effect of Q-bursts on SR background spectra using GPS time-stamped observation of TLEs. It is observed that the Q-bursts selected for the present work do alias the background spectra over a 5-s period, though the amplitudes of these Q-bursts are far below the background threshold of 16 Core Standard Deviation (CSD) so that they do not strongly alias the background spectra of 10–12 min duration. The examination of one exceptional Q-burst shows that appreciable spectral aliasing can occur even when 12-min spectral integrations are considered. The statistical result shows that for a 12-min spectrum, events above 16 CSD are capable of producing significant frequency aliasing of the modal frequencies, although, the intensity aliasing might have a negligible effect unless the events are exceptionally large (∼200 CSD). The spectral CSD methodology may be used to extract the time of arrival of the Q-burst transients. This methodology may be combined with a hyperbolic ranging, thus becoming an effective tool to detect TLEs globally with a modest number of networked observational stations.

      PubDate: 2017-11-18T23:24:18Z
      DOI: 10.1016/j.jastp.2017.11.003
      Issue No: Vol. 165-166 (2017)
       
  • Day and nighttime L-Band amplitude scintillations during low solar
           activity at a low latitude station in the South Pacific Region
    • Authors: Ramendra Prasad; Sushil Kumar
      Pages: 54 - 66
      Abstract: Publication date: Available online 13 November 2017
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Ramendra Prasad, Sushil Kumar
      A morphological study of GPS L-band amplitude scintillations observed at a low latitude station Suva (18.1°S, 178.4°E), Fiji, during low solar activity year 2010 of solar cycle 24, has been presented. Out of a total of 480 scintillation events recorded during 2010, 84.4% were weak (0.2 ≤ S 4  < 0.3), 14.6% moderate (0.3 ≤ S 4  < 0.45) and only 1% strong (0.45 ≤ S 4 ). The amplitude scintillations were most pronounced in the local daytime with January registering the highest occurrence. Seasonal analysis revealed maximum scintillation occurrence during summer as compared to winter and equinox seasons. The daytime scintillation with a maximum in the summer is consistent with localized blanketing sporadic E observations and could also be possibly due to lightning activity around the observing station. Annual percentage occurrence shows that scintillations occurred mostly in the daytime with peak occurrence at around 05:00–09:00 LT. The daytime strong scintillation events were not associated with TEC depletions and phase scintillations, but the signal to noise ratio during the scintillation events decreased with increase in scintillation index (S 4 ). However, the post-midnight strong amplitude scintillations were associated with TEC depletions and phase scintillations indicative of large scale irregularities (spread-F). The geomagnetic activity effect showed enhanced occurrence on geomagnetically disturbed days as compared to quite conditions. The geomagnetic storm effect on scintillations for 17 storms of different strengths (Dst ≤ 50 nT) during 2010–2011, in general, showed an increase in the occurrence of post-storm scintillations, on the days following the storm.

      PubDate: 2017-11-18T23:24:18Z
      DOI: 10.1016/j.jastp.2017.11.005
      Issue No: Vol. 165-166 (2017)
       
  • Experimental investigation of turbulent transport of momentum and heat in
           the atmospheric surface layer
    • Authors: Guowen Han; X.J. Zheng; Tianli Bo
      Pages: 18 - 28
      Abstract: Publication date: November 2017
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 164
      Author(s): Guowen Han, X.J. Zheng, Tianli Bo
      In our study, turbulent transport of momentum and heat is investigated in the neutral and unstable atmospheric surface layer (ASL) over the edge of a desert. Our results reveal that with the increase of wind speed the transport efficiencies for momentum and heat increased, furthermore, transport efficiency of momentum increases faster than that of heat. In addition, the method of quadrant analysis and turbulent events were used to analyze the moment flux and heat flux. Experimental results show that the influence of wind speed on moment flux and heat flux can be quite different, which maybe has a great impact on the turbulent transport of momentum and heat in ASL.

      PubDate: 2017-08-03T07:02:04Z
      DOI: 10.1016/j.jastp.2017.07.017
      Issue No: Vol. 164 (2017)
       
  • Stationary depletions in thermospheric atomic oxygen concentration and
           mass density observed with WINDII, GUVI, GOCE and simulated by NRLMSISE-00
           
    • Authors: Gordon G. Shepherd; Young-Min Cho
      Pages: 29 - 38
      Abstract: Publication date: November 2017
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 164
      Author(s): Gordon G. Shepherd, Young-Min Cho
      Observations of thermospheric atomic oxygen concentrations [O] by the Wind Imaging Interferometer (WINDII) and the Global Ultra Violet Imager (GUVI) derived from daytime airglow observations clearly show a persistent depletion in [O], for WINDII by about 63% below background, in the southern mid-latitudes, near 40° S latitude and 100° longitude. It appears less strongly in the northern hemisphere at about 250° longitude and is not evident in local winter for either hemisphere. The same feature appears strongly in the NRLMSISE-00 empirical model. Mass density observations by the Gravity field and steady-state Ocean Circulation Explorer (GOCE) available at dawn and dusk local times at times show similar depletions with a smaller reduction of about 20% but do not consistently agree with those of [O]. It has been shown elsewhere that Total Electron Content (TEC) observations are strongly related to the column ratio ΣO/N2. These observations clearly show the Weddell Sea Anomaly (WSA) enhancement as well as the [O] depletion at a similar latitude; these are oppositely phased and 180° apart in longitude, suggesting a common source.

      PubDate: 2017-08-03T07:02:04Z
      DOI: 10.1016/j.jastp.2017.07.016
      Issue No: Vol. 164 (2017)
       
  • Characteristics of longwave radiation through the statistical analysis of
           downward and upward longwave radiation and inter-comparison of two sites
           in Cyprus
    • Authors: S. Pashiardis; S.A. Kalogirou; A. Pelengaris
      Pages: 60 - 80
      Abstract: Publication date: November 2017
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 164
      Author(s): S. Pashiardis, S.A. Kalogirou, A. Pelengaris
      In this study, three years of hourly longwave downward and upward irradiance measurements for two sites in Cyprus representing two different climate regimes (inland vs coastal locations) are used to analyse and compare them. The quality control process was based on physically possible, extremely rare and climatological limits. Furthermore, comparison tests between the two longwave components as well as with air and ground surface temperatures were used to evaluate the hourly values of longwave irradiances. The annual mean daily downward longwave irradiation at Athalassa is 29.1 MJ m−2 and at Larnaca it is slightly higher (31.3 MJ m−2). On the other hand, the annual mean daily upward longwave irradiation at Athalassa is 38.2 MJ m−2, while at Larnaca it is slightly lower (37.4 MJ m−2). The performance of various models in estimating the daylight downward and upward longwave irradiances under clear-sky and all-sky conditions was evaluated. Root-mean-square errors, mean bias errors, and linear regression correlations have been used to compare measured and estimated values. The results of this comparison for the station of Athalassa, showed that Idso's model perform well and it can be used to estimate downward longwave irradiance under clear-sky conditions. Furthermore, Idso's model was extended to estimate the daylight downward longwave irradiance under all-sky conditions by taking into account the ratio of global to the clear-sky global solar irradiance. The RMSE of the local calibrated coefficients scheme of Idso's model was 17.70 W m−2. For the estimation of the daylight upward longwave irradiance under all-sky conditions, the calibrated Dognieux and Lemoine model was used which performed well. The RMSE in this case was 12.75 W m−2.

      PubDate: 2017-09-02T09:49:12Z
      DOI: 10.1016/j.jastp.2017.08.007
      Issue No: Vol. 164 (2017)
       
  • Three dimensional ray tracing technique for tropospheric water vapor
           tomography using GPS measurements
    • Authors: Saeid Haji Aghajany; Yazdan Amerian
      Pages: 81 - 88
      Abstract: Publication date: November 2017
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 164
      Author(s): Saeid Haji Aghajany, Yazdan Amerian
      Tropospheric water vapor has a key role in tropospheric processes and it is an important parameter in meteorology studies. Because of its non-uniform spatiotemporal distribution, modeling the spatiotemporal variations of water vapor is a challenging subject in meteorology. The GNSS tomography of the troposphere is a promising method to assess the spatiotemporal distribution of water vapor parameter in this layer. The tomography method efficiency is dependent on the ray tracing technique and GPS derived tropospheric slant wet delays. Implementing constraints and regularization methods are necessary in order to achieve the regularized solution in troposphere tomography. In this paper, the three dimensional (3D) ray tracing technique based on Eikonal equations and ERA-I data are used to perform the reconstruction the signal path, Iranian Permanent GPS Network (IPGN) measurements are used to calculate slant wet delays and the LSQR regularization technique is used to obtain a regularized tomographic solution for tropospheric water vapor. The modeled water vapor profiles are validated using radiosonde observations.

      PubDate: 2017-09-02T09:49:12Z
      DOI: 10.1016/j.jastp.2017.08.003
      Issue No: Vol. 164 (2017)
       
  • Is the “Earth-ionosphere capacitor” a valid component in the
           atmospheric global electric circuit'
    • Authors: Christos Haldoupis; Michael Rycroft; Earle Williams; Colin Price
      Pages: 127 - 131
      Abstract: Publication date: November 2017
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 164
      Author(s): Christos Haldoupis, Michael Rycroft, Earle Williams, Colin Price
      This paper examines whether the Earth-ionosphere capacitor (EIC) model is correct, by comparing observed atmospheric electrical properties with those expected for a spherical capacitor, as defined in electrostatics. The comparisons suggest that the EIC concept cannot be reconciled with, and hence cannot account for, the observations, particularly the rapid reduction of the atmospheric electric field with height that is measured. This means that the spherical EIC concept is incorrect by being too simplistic; it is thus misleading. The reason for this flawed concept is simple: the model disregards the non-uniform conductivity of the atmosphere which requires the presence of a net positive charge in the lower atmosphere that equals in magnitude the Earth's negative charge. This positive charge shields the action of the Earth's negative charge from polarizing the ionosphere positively. Thus, the lower D region ionosphere remains electrically neutral, which makes the EIC concept inappropriate.

      PubDate: 2017-09-02T09:49:12Z
      DOI: 10.1016/j.jastp.2017.08.012
      Issue No: Vol. 164 (2017)
       
  • Climatology of GW-TIDs in the magnetic equatorial upper thermosphere over
           India
    • Authors: G. Manju; R.P. Aswathy
      Pages: 142 - 148
      Abstract: Publication date: November 2017
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 164
      Author(s): G. Manju, R.P. Aswathy
      An analysis of Gravity wave induced travelling ionospheric disturbances (GW-TIDs) in the thermosphere during high and low solar epochs is undertaken using ionosonde data at Trivandrum (8.50N, 770E). Wavelet analysis is performed on the temporal variations of foF2 and the amplitudes of waves present in two period bands of (0.5–1.5) h and (2–4) h are extracted. The real height profiles are generated at 15 min internal for the whole day (for sample days) during high and low solar activity years. The study reveals that the GW-TID activity is significantly greater for solar minimum compared to solar maximum for the period 8.5–17.5 h. Diurnally the GW-TID activity in the (2–4) h period band peaks in the post sunset hours for both high and low solar epochs. For the 0.5–1.5 h period band, the diurnal maximum in GW-TID is occurring in the post sunset hours for high solar epoch while it occurs in the morning hours around 10 h LT for low solar epoch. Seasonally the day time GW-TID activity maximizes (minimizes) for winter (vernal equinox). The post sunset time GW-TID maximizes (minimizes) either for summer/winter (vernal equinox). The other interesting observation is the anti correlation of GW-TID in upper thermosphere with solar activity for day time and the correlation of the same with solar activity in the post sunset hours. The present results for daytime are in agreement with the equatorial daytime GW-TID behaviour reported from CHAMP satellite observations. The GW-TID activity during post sunset time for equatorial region upper thermosphere has not been reported so far.

      PubDate: 2017-09-02T09:49:12Z
      DOI: 10.1016/j.jastp.2017.08.015
      Issue No: Vol. 164 (2017)
       
  • The evolution of geomagnetotail magnetic flux in isolated substorms
    • Authors: Y.Y. Yang; C. Shen; Z.J. Rong; M. Dunlop; X.H. Shen; J.P. Huang; Z.Q. Chen
      Pages: 163 - 171
      Abstract: Publication date: November 2017
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 164
      Author(s): Y.Y. Yang, C. Shen, Z.J. Rong, M. Dunlop, X.H. Shen, J.P. Huang, Z.Q. Chen
      The magnetic field energy stored in geomagnetotail released during a substorm period, cause significant magnetic disturbance of the space environment. The quantitative relationship between the magnetic field energy and the level of substorm activity, however, is still unclear, although many studies have qualitatively revealed the correlation between them. Here, using data from four selected isolated substorm cases, the evolution of the magnetic flux (MF) in the magnetotail observed by Cluster is quantitatively surveyed. The results from the four cases demonstrate that the evolution of magnetotail MF is closely related to the phases of substorm development. For quiet time, the magnetotail is in the ground state with MF being about 0.6 GWb. During the growth phase, however, as the substorm develop the MF keeps increasing, the substorm onset is triggered when the MF has increased up to some threshold. The comparison between the four cases shows that the accumulation of more magnetic field energy corresponds to more released energy, and consistently, the more intense a substorm can be powered. The study also finds that there is an imbalance between the increased and decreased MF amplitude, indicating that the substorm may not be the only way to release the stored magnetotail energy.

      PubDate: 2017-09-02T09:49:12Z
      DOI: 10.1016/j.jastp.2017.08.016
      Issue No: Vol. 164 (2017)
       
  • Unusual lightning electric field waveforms observed in Kathmandu, Nepal,
           and Uppsala, Sweden
    • Authors: Pitri Bhakta Adhikari; Shriram Sharma; Kedarnath Baral; Vladimir A. Rakov
      Pages: 172 - 184
      Abstract: Publication date: November 2017
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 164
      Author(s): Pitri Bhakta Adhikari, Shriram Sharma, Kedarnath Baral, Vladimir A. Rakov
      Unusual lightning events have been observed in Uppsala, Sweden, and Kathmandu, Nepal, using essentially the same electric field measuring system developed at Uppsala University. They occurred in the storms that also generated “normal” lightning events. The unusual events recorded in Uppsala occurred on one thunderstorm day. Similar events were observed in Kathmandu on multiple thunderstorm days. The unusual events were analyzed in this study assuming them to be positive ground flashes (+CGs), although we cannot rule out the possibility that some or most of them were actually cloud discharges (ICs). The unusual events were each characterized by a relatively slow, negative (atmospheric electricity sign convention) electric field waveform preceded by a pronounced opposite-polarity pulse whose duration was some tens of microseconds. To the best of our knowledge, such unusual events have not been reported in the literature. The average amplitudes of the opposite-polarity pulses with respect to those of the following main waveform were found to be about 33% in Uppsala (N = 31) and about 38% in Kathmandu (N = 327). The average durations of the main waveform and the preceding opposite-polarity pulse in Uppsala were 8.24 ms and 57.1 μs, respectively, and their counterparts in Kathmandu were 421 μs and 39.7 μs. Electric field waveforms characteristic of negative ground flashes (-CGs) were also observed, and none of them exhibited an opposite-polarity pulse prior to the main waveform. Possible origins of the unusual field waveforms are discussed.

      PubDate: 2017-09-02T09:49:12Z
      DOI: 10.1016/j.jastp.2017.08.028
      Issue No: Vol. 164 (2017)
       
  • Longitudinal expansion of field line dipolarization
    • Authors: O. Saka; K. Hayashi
      Pages: 235 - 242
      Abstract: Publication date: November 2017
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 164
      Author(s): O. Saka, K. Hayashi
      We examine the substorm expansions that started at 1155 UT 10 August 1994 in the midnight sector focusing on the longitudinal (eastward) expansion of field line dipolarization in the auroral zone. Eastward expansion of the dipolarization region was observed in all of the H, D, and Z components. The dipolarization that started at 1155 UT (0027 MLT) from 260° of geomagnetic longitude (CMO) expanded to 351°(PBQ) in about 48 min. The expansion velocity was 0.03–0.04°/s, or 1.9 km/s at 62°N of geomagnetic latitude. The dipolarization region expanding to the east was accompanied by a bipolar event at the leading edge of the expansion in latitudes equatorward of the westward electrojet (WEJ). In the midnight sector at the onset meridian, the Magnetospheric Plasma Analyzer (MAP) on board geosynchronous satellite L9 measured electrons and ions between 10 eV and 40 keV. We conclude from the satellite observations that this dipolarization was characterized by the evolution of temperature anisotropies, an increase of the electron and ion temperatures, and a rapid change in the symmetry axis of the temperature tensor. The field line dipolarization and its longitudinal expansion were interpreted in terms of the slow MHD mode triggered by the current disruption. We propose a new magnetosphere-ionosphere coupling (MI-coupling) mechanism based on the scenario that transmitted westward electric fields from the magnetosphere in association with expanding dipolarization produced electrostatic potential (negative) in the ionosphere through differences in the mobility of collisional ions and collisionless electrons. The field-aligned currents that emerged from the negative potential region are arranged in a concentric pattern around the negative potential region, upward toward the center and downward on the peripheral.

      PubDate: 2017-09-14T10:17:30Z
      DOI: 10.1016/j.jastp.2017.09.009
      Issue No: Vol. 164 (2017)
       
  • Exploring noctilucent cloud variability using the nudged and extended
           version of the Canadian Middle Atmosphere Model
    • Authors: Maartje Kuilman; Bodil Karlsson; Susanne Benze; Linda Megner
      Pages: 276 - 288
      Abstract: Publication date: November 2017
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 164
      Author(s): Maartje Kuilman, Bodil Karlsson, Susanne Benze, Linda Megner
      Ice particles in the summer mesosphere – such as those connected to noctilucent clouds and polar mesospheric summer echoes - have since their discovery contributed to the uncovering of atmospheric processes on various scales ranging from interactions on molecular levels to global scale circulation patterns. While there are numerous model studies on mesospheric ice microphysics and how the clouds relate to the background atmosphere, there are at this point few studies using comprehensive global climate models to investigate observed variability and climatology of noctilucent clouds. In this study it is explored to what extent the large-scale inter-annual characteristics of noctilucent clouds are captured in a 30-year run - extending from 1979 to 2009 - of the nudged and extended version of the Canadian Middle Atmosphere Model (CMAM30). To construct and investigate zonal mean inter-seasonal variability in noctilucent cloud occurrence frequency and ice mass density in both hemispheres, a simple cloud model is applied in which it is assumed that the ice content is solely controlled by the local temperature and water vapor volume mixing ratio. The model results are compared to satellite observations, each having an instrument-specific sensitivity when it comes to detecting noctilucent clouds. It is found that the model is able to capture the onset dates of the NLC seasons in both hemispheres as well as the hemispheric differences in NLCs, such as weaker NLCs in the SH than in the NH and differences in cloud height. We conclude that the observed cloud climatology and zonal mean variability are well captured by the model.

      PubDate: 2017-09-25T11:18:52Z
      DOI: 10.1016/j.jastp.2017.08.019
      Issue No: Vol. 164 (2017)
       
  • κ distribution of carbon II doublet in the solar transition region
    • Authors: Jian He; Qingguo Zhang
      Pages: 289 - 293
      Abstract: Publication date: Available online 22 September 2017
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Jian He, Qingguo Zhang
      For accurate spectral diagnostics of the solar plasma in the transition region, the averaged collision strength of the κ distribution of electron energies is discussed for non-Maxwellian distribution, and the Maxwellian averaged collision strengths and the non-Maxwellian averaged collision strengths for κ  = 2, 3 and 5 from 104.4 to 106.0 K are calculated for Carbon II doublet in the transition region. Results are in agreement with those from the CHIANTI database, and the main error comes from the approximation of the collision strength. This calculation will be significant for spectral diagnostics of the solar plasma for non-Maxwellian distribution of the electron energies.

      PubDate: 2017-09-25T11:18:52Z
      DOI: 10.1016/j.jastp.2017.09.017
      Issue No: Vol. 164 (2017)
       
  • Surfatron acceleration of weakly relativistic electrons by electromagnetic
           wave packet in space plasma
    • Authors: R. Shkevov; N.S. Erokhin; V.M. Loznikov; N.N. Zolnikova; L.A. Mikhailovskaya
      Abstract: Publication date: Available online 5 November 2017
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): R. Shkevov, N.S. Erokhin, V.M. Loznikov, N.N. Zolnikova, L.A. Mikhailovskaya
      Resonant interactions between an electromagnetic wave packet and charged particles based on numerical calculations are investigated. The strong surfatron acceleration of weakly relativistic electrons by an electromagnetic wave packet in space plasma is studied. In the central area of the wave packet, the electric field amplitude is above a threshold value and this makes it possible to capture particles in the surfing mode. The work is carried out by exact solving of second order nonlinear, nonstationary equations for the wave packet phase on the particle's trajectory at the carrying frequency. Numerical modeling shows that the trapping of weakly relativistic electrons in strong acceleration mode occurs immediately for a wide enough range of favorable initial wave phase values (80% and more). Furthermore it has been demonstrated that the combination of ranges of the particle's initial parameters corresponding to the capturing in surfatron acceleration is large enough. Temporal dynamics of momentum components and velocities for accelerated particles, the particularities of their trajectory, taking into account cyclotron rotation at the initial stage and phase plane structure for numerically solved nonlinear equations, are considered. Simulation results let us drawing conclusions about the possibility of surfatron acceleration of weakly relativistic charged particles in space plasma by an electromagnetic wave packet.

      PubDate: 2017-11-18T23:24:18Z
      DOI: 10.1016/j.jastp.2017.11.001
       
  • IFC-Ed. board
    • Abstract: Publication date: November 2017
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 164


      PubDate: 2017-11-18T23:24:18Z
       
  • A simplified Suomi NPP VIIRS dust detection algorithm
    • Authors: Yikun Yang; Lin Sun Jinshan Zhu Jing Wei Qinghua Wenxiao
      Abstract: Publication date: November 2017
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 164
      Author(s): Yikun Yang, Lin Sun, Jinshan Zhu, Jing Wei, Qinghua Su, Wenxiao Sun, Fangwei Liu, Meiyan Shu
      Due to the complex characteristics of dust and sparse ground-based monitoring stations, dust monitoring is facing severe challenges, especially in dust storm-prone areas. Aim at constructing a high-precision dust storm detection model, a pixel database, consisted of dusts over a variety of typical feature types such as cloud, vegetation, Gobi and ice/snow, was constructed, and their distributions of reflectance and Brightness Temperatures (BT) were analysed, based on which, a new Simplified Dust Detection Algorithm (SDDA) for the Suomi National Polar-Orbiting Partnership Visible infrared Imaging Radiometer (NPP VIIRS) is proposed. NPP VIIRS images covering the northern China and Mongolian regions, where features serious dust storms, were selected to perform the dust detection experiments. The monitoring results were compared with the true colour composite images, and results showed that most of the dust areas can be accurately detected, except for fragmented thin dusts over bright surfaces. The dust ground-based measurements obtained from the Meteorological Information Comprehensive Analysis and Process System (MICAPS) and the Ozone Monitoring Instrument Aerosol Index (OMI AI) products were selected for comparison purposes. Results showed that the dust monitoring results agreed well in the spatial distribution with OMI AI dust products and the MICAPS ground-measured data with an average high accuracy of 83.10%. The SDDA is relatively robust and can realize automatic monitoring for dust storms.

      PubDate: 2017-11-18T23:24:18Z
       
  • Influence of air parcel trajectories on CO2 and CH4 concentrations in the
           northern plateau of the Iberian Peninsula
    • Authors: Isidro A. Pérez; M. Luisa Sánchez; M. Ángeles García; Nuria Pardo
      Abstract: Publication date: Available online 1 November 2017
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Isidro A. Pérez, M. Luisa Sánchez, M. Ángeles García, Nuria Pardo
      This study presents a simpler procedure for grouping air parcel back trajectories than others previously applied. Two-day air parcel back trajectories reaching an unpolluted site in the centre of the northern plateau of the Iberian Peninsula were calculated over a three-year period using the METEX model. A procedure based on the kernel density calculation was applied to the direction of each trajectory centroid to determine groups of trajectories. This method is much faster than the cluster procedure when it comes to retaining the directional details of groups. Seasonal analysis of six groups of trajectories revealed that the Atlantic origin prevailed against displacement from northern Europe. Moreover, Mediterranean and particularly African trajectories were infrequent, probably due to the rough peninsular orography in these directions. The location of air trajectories reaching the study site was described using a surface classification below the air parcels with improved spatial resolution compared to previous analyses. Local contribution was very marked, particularly in summer. Mean trajectories were calculated for each group together with meteorological features and CO2 and CH4 concentrations. Groups may be identified by their mean temperature, wind speed, elevation and distance values. However, only two groups should be considered when analysing the two trace gases, one for trajectories from the Atlantic Ocean and the second for trajectories from the continent. Contrasts of about 4 ppm for CO2 in summer and 0.023 ppm for CH4 in winter were observed, revealing that air trajectories from the Atlantic Ocean were cleaner than those arriving from the continent. These differences were attributed to higher air stagnation over land.

      PubDate: 2017-11-18T23:24:18Z
      DOI: 10.1016/j.jastp.2017.10.015
       
  • Particle tracing modeling of ion fluxes at geosynchronous orbit
    • Authors: Thiago V. Brito; Jesse Woodroffe; Vania K. Jordanova; Michael Henderson; Joachim Birn
      Abstract: Publication date: Available online 31 October 2017
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Thiago V. Brito, Jesse Woodroffe, Vania K. Jordanova, Michael Henderson, Joachim Birn
      The first results of a coupled MHD/particle tracing method to evaluate particle fluxes in the inner magnetosphere are presented. This setup is capable of capturing the earthward particle acceleration process resulting from dipolarization events in the tail region of the magnetosphere. On the period of study, the MHD code was able to capture a dipolarization event and the particle tracing algorithm was able to capture the results of these disturbances and calculate proton fluxes in the night side geosynchronous orbit region. The simulation captured dispersionless injections as well as the energy dispersion signatures that are frequently observed by satellites at geosynchronous orbit. Currently, ring current models rely on Maxwellian-type distributions based on either empirical flux values or sparse satellite data for their boundary conditions close to geosynchronous orbit. Despite some differences in intensity and timing, the setup presented here is able to capture substorm injections, which represents an improvement regarding a reverse way of coupling these ring current models with MHD codes through the use of boundary conditions.

      PubDate: 2017-11-18T23:24:18Z
      DOI: 10.1016/j.jastp.2017.10.008
       
  • Structure of magnetospheric current systems and mapping of high latitude
           magnetospheric regions to the ionosphere
    • Authors: E.E. Antonova; M. Stepanova; I.P. Kirpichev; I.L. Ovchinnikov; V.G. Vorobjev; O.I. Yagodkina; M.O. Riazanseva; V.V. Vovchenko; M.S. Pulinets; S.S. Znatkova; N.V. Sotnikov
      Abstract: Publication date: Available online 31 October 2017
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): E.E. Antonova, M. Stepanova, I.P. Kirpichev, I.L. Ovchinnikov, V.G. Vorobjev, O.I. Yagodkina, M.O. Riazanseva, V.V. Vovchenko, M.S. Pulinets, S.S. Znatkova, N.V. Sotnikov
      The structures of the main magnetospheric current systems are interesting to researchers because of their key role in magnetospheric physics, including the generation of geomagnetic storms and substorms. Ring current and tail current are usually considered as main sources of geomagnetic activity. We assume that the ring current is divided into the inner part located from ∼ 3 to ∼ < 7 R E and the outer part located from 7 R E to the magnetopause near noon and to ∼ 10–13 R E near midnight. We named the outer part of the ring current as the cut ring current (CRC). Due to compression of the geomagnetic field by the solar wind, the CRC is not concentrated near the equatorial plane at the noon sector, it spreads along field lines. We discuss the main properties of CRC and its role in the generation of field-aligned currents. We propose a method - based on the conservation of plasma pressure along a current line - that enables us to determine the position of the boundary between the ring and tail currents, and to determine the configuration of current lines which cross the magnetopause. At the same time, conservation of plasma pressure along a field line for plasmas in magnetostatic equilibrium enables us to analyze the auroral oval mapping into the equatorial plane regardless of any magnetic field model. It is well known that the auroral oval has a thick ring-like shape. We discuss that it is topologically impossible to map such a structure to a sheet band like structure in the tail. Our analysis showed that most of the auroral oval is mapped to the CRC region. We argue that including CRC as a part of the ring current allows to re-establish the traditional point of view, in which the ring current has a dominant role in Dst/SYM-H variations.

      PubDate: 2017-11-18T23:24:18Z
      DOI: 10.1016/j.jastp.2017.10.013
       
  • Planetary wave-like oscillations in the ionosphere retrieved with a
           longitudinal chain of ionosondes at high northern latitudes
    • Authors: Nora H. Stray; Patrick J. Espy
      Abstract: Publication date: Available online 29 October 2017
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Nora H. Stray, Patrick J. Espy
      This paper examines the influence of neutral dynamics on the high latitude ionosphere. Using a longitudinal chain of ionosondes at high northern latitudes (52°–65° N), planetary wave-like structures were observed in the spatial structure of the peak electron density in the ionosphere. Longitudinal wavenumbers S0, S1 and S2 have been extracted from these variations of the F layer. The observed wave activity in wavenumber one and two does not show any significant correlation with indices of magnetic activity, suggesting that this is not the primary driver. In addition, the motion of the S1 ionospheric wave structures parallels that of the S1 planetary waves observed in the winds of the mesosphere-lower-thermosphere derived from a longitudinal array of SuperDARN meteor-radar wind measurements. The time delay between the motions of the wave structures would indicate a indirect coupling, commensurate with the diffusion to the ionosphere of mesospheric atomic oxygen perturbations.

      PubDate: 2017-11-18T23:24:18Z
      DOI: 10.1016/j.jastp.2017.10.011
       
  • DMSP observations of high latitude Poynting flux during magnetic storms
    • Authors: Cheryl Y. Huang; Yanshi Huang; Yi-Jiun Su; Marc R. Hairston; Thomas Sotirelis
      Abstract: Publication date: Available online 21 September 2017
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Cheryl Y. Huang, Yanshi Huang, Yi-Jiun Su, Marc R. Hairston, Thomas Sotirelis
      Previous studies have demonstrated that energy can enter the high-latitude regions of the Ionosphere-Thermosphere (IT) system on open field lines. To assess the extent of high-latitude energy input, we have carried out a study of Poynting flux measured by the Defense Meteorological Satellite Program (DMSP) satellites during magnetic storms. We report sporadic intense Poynting fluxes measured by four DMSP satellites at polar latitudes during two moderate magnetic storms which occurred in August and September 2011. Comparisons with a widely used empirical model for energy input to the IT system show that the model does not adequately capture electromagnetic (EM) energy at very high latitudes during storms. We have extended this study to include more than 30 storm events and find that intense EM energy is frequently detected poleward of 75° magnetic latitude.

      PubDate: 2017-09-25T11:18:52Z
      DOI: 10.1016/j.jastp.2017.09.005
       
  • Impacts of spectral nudging on the simulated surface air temperature in
           summer compared with the selection of shortwave radiation and land surface
           model physics parameterization in a high-resolution regional atmospheric
           model
    • Authors: Jun Park; Seung-On Hwang
      Abstract: Publication date: Available online 6 September 2017
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Jun Park, Seung-On Hwang
      The impact of a spectral nudging technique for the dynamical downscaling of the summer surface air temperature in a high-resolution regional atmospheric model is assessed. The performance of this technique is measured by comparing 16 analysis-driven simulation sets of physical parameterization combinations of two shortwave radiation and four land surface model schemes of the model, which are known to be crucial for the simulation of the surface air temperature. It is found that the application of spectral nudging to the outermost domain has a greater impact on the regional climate than any combination of shortwave radiation and land surface model physics schemes. The optimal choice of two model physics parameterizations is helpful for obtaining more realistic spatiotemporal distributions of land surface variables such as the surface air temperature, precipitation, and surface fluxes. However, employing spectral nudging adds more value to the results; the improvement is greater than using sophisticated shortwave radiation and land surface model physical parameterizations. This result indicates that spectral nudging applied to the outermost domain provides a more accurate lateral boundary condition to the innermost domain when forced by analysis data by securing the consistency with large-scale forcing over a regional domain. This consequently indirectly helps two physical parameterizations to produce small-scale features closer to the observed values, leading to a better representation of the surface air temperature in a high-resolution downscaled climate.

      PubDate: 2017-09-08T10:00:34Z
      DOI: 10.1016/j.jastp.2017.09.001
       
  • Effects of atmospheric oscillations at different time scales on persistent
           autumn rainstorms in Hainan, China
    • Authors: Jiangnan Li; Qingwen Ye; Fangzhou Li; Chenghui Ding; Youlong Chen; Yanbin Huang
      Abstract: Publication date: Available online 6 September 2017
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Jiangnan Li, Qingwen Ye, Fangzhou Li, Chenghui Ding, Youlong Chen, Yanbin Huang
      In the autumn of 2008, 2010, and 2011, Hainan experienced anomalously persistent rainstorms. The objective of this study was to examine the roles of atmospheric oscillations at different time scales on these three rainstorm events. A wavelet analysis of daily rainfall data revealed that the 3–10-day synoptic-scale oscillations were the dominant mode in 2008 and 2011 and the 8–15-day quasi-biweekly oscillations were dominant in 2010. These three autumn rainstorm events can be divided into two major periods. Both the synoptic-scale and quasi-biweekly mode influenced the rainstorms, but their oscillation centers and propagation directions were completely different. There is a good corresponding relationship between the two heavy rain periods and the synoptic-scale oscillation cyclones and convection during the autumn of 2008 and 2011. During the first period, moisture mainly came from vapor convergence in the South China Sea (SCS), but during the second period, moisture came from the equatorial Indian Ocean. The major source of the synoptic-scale oscillation was the western North Pacific. The synoptic-scale oscillation cyclones and convection moved northwest to Hainan, resulting in heavy rainfall. Moisture during the first period mainly came from water vapor convergence in the SCS during the autumn of 2010, but moisture in the second period came from western North Pacific. The quasi-biweekly oscillation convection was generated and developed mainly over the equatorial Indian Ocean. Strong convection accompanying oscillation cyclones spread toward the northeast, triggering heavy precipitation in the Hainan region.

      PubDate: 2017-09-08T10:00:34Z
      DOI: 10.1016/j.jastp.2017.09.002
       
  • Considering the potential of IAR emissions for ionospheric sounding
    • Authors: A.S. Potapov; T.N. Polyushkina; B. Tsegmed; A.V. Oinats; A. Yu. Pashinin; I.K. Edemskiy; A.A. Mylnikova; K.G. Ratovsky
      Abstract: Publication date: Available online 4 September 2017
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): A.S. Potapov, T.N. Polyushkina, B. Tsegmed, A.V. Oinats, A. Yu. Pashinin, I.K. Edemskiy, A.A. Mylnikova, K.G. Ratovsky
      Knowledge of the ionospheric state allows us to adjust the forecasts of radio wave propagation, specify the environment models, and follow the changes of space weather. At present, probing of the ionosphere is produced by radio sounding with ground ionosondes, as well as by raying signals from satellites. We want to draw attention to the possibility of the diagnosis of the ionospheric parameters by detecting ultra-low frequency (ULF) electromagnetic emission generated in the so-called ionospheric Alfvén resonator (IAR). To do this, we present observations of the IAR emission made simultaneously for the first time at three stations using identical induction magnetometers. The stations are within one-hour difference of local time, two of them are mid-latitudinal; the third one is situated in the auroral zone. We compare frequency and frequency difference between adjacent harmonics of the observed multi-band emission with ionospheric parameters measured at the stations using ionosondes and GPS-observations. Diurnal variations of the ionospheric and ULF emission characteristics are also compared. The results show that there is quite a stable correlation between the resonant frequencies of the resonator bands and the critical frequency of the F2 layer of the ionosphere, namely, the frequency of the IAR emission varies inversely as the critical frequency of the ionosphere. This is due to the fact that the frequency of oscillation captured in the resonator is primarily determined by the Alfvén velocity (which depends on the plasma density) in the ionospheric F2 layer. The correlation is high; it varies at different stations, but is observed distinctly along the whole meridian. However, coefficients of a regression equation that connects the ionosphere critical frequency with DSB frequency vary significantly from day to day at all stations. The reason for such a big spread of the regression parameters is not clear and needs further investigation before we are able to develop a method for evaluating the ionosphere critical frequency using the IAR emission observations. Such a method may prove to be useful as an additional alternative to the basic method for probing the ionosphere using digisondes. This is especially important for auroral regions, where the presence of strong absorption, shielding by a lower layer, stratification, the presence of echoes, etc. make the sounding difficult.

      PubDate: 2017-09-08T10:00:34Z
      DOI: 10.1016/j.jastp.2017.08.026
       
  • Investigation of Kelvin wave periods during Hai-Tang typhoon using
           Empirical Mode Decomposition
    • Authors: P. Kishore; J. Jayalakshmi; Pay Liam-Lin; Isabella Velicogna; Tyler C. Sutterley; Enrico Ciracì; Yara Mohajerani; S. Balaji Kumar
      Abstract: Publication date: Available online 1 September 2017
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): P. Kishore, J. Jayalakshmi, Pay Liam-Lin, Isabella Velicogna, Tyler C. Sutterley, Enrico Ciracì, Yara Mohajerani, S. Balaji Kumar
      Equatorial Kelvin waves (KWs) are fundamental components of the tropical climate system. In this study, we investigate Kelvin waves (KWs) during the Hai-Tang typhoon of 2005 using Empirical Mode Decomposition (EMD) of regional precipitation, zonal and meridional winds. For the analysis, we use daily precipitation datasets from the Global Precipitation Climatology Project (GPCP) and wind datasets from the European Centre for Medium-Range Weather Forecasts (ECMWF) Interim Re-analysis (ERA-Interim). As an additional measurement, we use in-situ precipitation datasets from rain-gauges over the Taiwan region. The maximum accumulated precipitation was approximately 2400 mm during the period July 17–21, 2005 over the southwestern region of Taiwan. The spectral analysis using the wind speed at 950 hPa found in the 2nd, 3rd, and 4th intrinsic mode functions (IMFs) reveals prevailing Kelvin wave periods of ∼3 days, ∼4–6 days, and ∼6–10 days, respectively. From our analysis of precipitation datasets, we found the Kelvin waves oscillated with periods between ∼8 and 20 days.

      PubDate: 2017-09-02T09:49:12Z
      DOI: 10.1016/j.jastp.2017.07.025
       
  • GPS amplitude and phase scintillation associated with polar cap auroral
           forms
    • Authors: P.T. Jayachandran; A.M. Hamza; K. Hosokawa; H. Mezoui; K. Shiokawa
      Abstract: Publication date: Available online 1 September 2017
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): P.T. Jayachandran, A.M. Hamza, K. Hosokawa, H. Mezoui, K. Shiokawa
      Global Positioning System (GPS) signal amplitude and phase scintillation occurrence were observed in close association with polar cap auroral forms. Scintillation were present on most GPS ray paths irrespective of the ray path's location and orientation relative to arc alignment, motion and the direction of E × B drift. Spectra of amplitude and phase scintillation show similar power law behaviour with close to identical power law coefficients. The distribution of power law coefficients shows an average power law coefficient of ∼−2.3, which is different from the spectral characteristics of equatorial and low latitude scintillation.

      PubDate: 2017-09-02T09:49:12Z
      DOI: 10.1016/j.jastp.2017.08.030
       
  • Numerical study of heating the upper atmosphere by acoustic-gravity waves
           from a local source on the Earth's surface and influence of this heating
           on the wave propagation conditions
    • Authors: I.V. Karpov; S.P. Kshevetskii
      Abstract: Publication date: Available online 31 July 2017
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): I.V. Karpov, S.P. Kshevetskii
      The propagation of acoustic-gravity waves (AGW) from a source on the Earth's surface to the upper atmosphere is investigated with methods of mathematical modeling. The applied non-linear model of wave propagation in the atmosphere is based on numerical integration of a complete set of two-dimensional hydrodynamic equations. The source on the Earth's surface generates waves with frequencies near to the Brunt-Vaisala frequency. The results of simulation have revealed that some region of heating the atmosphere by propagated upward and dissipated AGWs arises above the source at altitudes nearby of 200 km. The horizontal scale of this heated region is about 1000 km in the case of the source that radiates AGWs during approximately 1 h. The appearing of the heated region has changed the conditions of AGW propagation in the atmosphere. When the heated region in the upper atmosphere has been formed, further a waveguide regime of propagation of waves with the periods shorter the Brunt-Vaisala period is realized. The upper boundary of the wave-guide coincides with the arisen heated region in the upper atmosphere. The considered mechanism of formation of large-scale disturbances in the upper atmosphere may be useful for explanation of connections of processes in the upper and lower atmospheric layers.

      PubDate: 2017-08-03T07:02:04Z
      DOI: 10.1016/j.jastp.2017.07.019
       
  • Characteristics of convective structures of sodium layer in lower
           thermosphere (105–120 km) at Haikou (19.99°N, 110.34°E), China
    • Authors: Jing Jiao; Guotao Yang; Jihong Wang; Tiemin Zhang; Hongyan Peng; Yuchang Xun; Zhengkuan Liu; Chi Wang
      Abstract: Publication date: Available online 29 July 2017
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Jing Jiao, Guotao Yang, Jihong Wang, Tiemin Zhang, Hongyan Peng, Yuchang Xun, Zhengkuan Liu, Chi Wang
      The atmospheric sodium layer normally occurs in the mesopause (80–105 km) region, but rarely in the lower thermosphere region (>105 km) at low latitude. We observed a kind of peculiar sodium layer in lower thermosphere at Haikou (19.99.00°N, 110.34°E)—the thermospheric convective sodium layer (TCSL) in a lidargram. The TCSL's sodium density unstably developed over time and appeared as several discontinuous convective shapes vertically. It is the first time convective sodium layer observed in the lower thermosphere region (105–120 km). Based on Haikou lidar data, we obtained 14 TCSL events during 180 nights from March 2010 to August 2012. Most of the apogees of the TCSL events are higher than 108 km. A TCSL event lasts several hours and is composed of several convective structures, with each veitical shape lasting ∼5–30 min. All TCSL events occurred during spring and summer, and generally appear near midnight (22:00–00:00 LT). The TCSL has potential regional feature and appears to be related to the thermospheric sporadic E (Es) layers, winds, and field-aligned ionospheric irregularities (FAI).

      PubDate: 2017-08-03T07:02:04Z
      DOI: 10.1016/j.jastp.2017.07.020
       
 
 
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