Annales Geophysicae (ANGEO)
[SJR: 1.176] [H-I: 63] [13 followers] Follow
Open Access journal
ISSN (Print) 0992-7689 - ISSN (Online) 1432-0576
Published by European Geosciences Union [8 journals]
- Optimization of Saturn paraboloid magnetospheric field model
parameters using Cassini equatorial magnetic field data
Abstract: Optimization of Saturn paraboloid magnetospheric field model parameters using Cassini equatorial magnetic field data
Elena S. Belenkaya, Vladimir V. Kalegaev, Stanley W. H. Cowley, Gabrielle Provan, Marina S. Blokhina, Oleg G. Barinov, Alexander A. Kirillov, and Maria S. Grigoryan
Ann. Geophys., 34, 641-656, doi:10.5194/angeo-34-641-2016, 2016
The paraboloid model of Saturn’s magnetosphere describes the magnetic field of the planet, the ring current, magnetopause current, and the tail current. The model parameters are determined by comparison with the Cassini magnetic field data from 18 near-equatorial passes that span wide ranges of LT. The best-fit model parameters are employed to determine how the parameters vary with the subsolar distance of the magnetopause, governed by pressure balance at the magnetospheric boundary.
- Multi-year GNSS monitoring of atmospheric IWV over Central and South
America for climate studies
Abstract: Multi-year GNSS monitoring of atmospheric IWV over Central and South America for climate studies
Clara Eugenia Bianchi, Luciano Pedro Oscar Mendoza, Laura Isabel Fernández, María Paula Natali, Amalia Margarita Meza, and Juan Francisco Moirano
Ann. Geophys., 34, 623-639, doi:10.5194/angeo-34-623-2016, 2016
Long-term monitoring of the amount of water vapour in the lower atmosphere is essential for climate studies. We analysed satellite observations, at hundreds of locations in Central and South America, to look for changes in this parameter over several years. We found evidence of drying of the troposphere in temperate regions, and also evidence of slow moistening over the tropics. Moreover, we openly provide the complete data collection to the scientific community.
- Two-point observations of low-frequency waves at 67P/Churyumov-Gerasimenko
during the descent of PHILAE: comparison of RPCMAG and ROMAP
Abstract: Two-point observations of low-frequency waves at 67P/Churyumov-Gerasimenko during the descent of PHILAE: comparison of RPCMAG and ROMAP
Ingo Richter, Hans-Ulrich Auster, Gerhard Berghofer, Chris Carr, Emanuele Cupido, Karl-Heinz Fornaçon, Charlotte Goetz, Philip Heinisch, Christoph Koenders, Bernd Stoll, Bruce T. Tsurutani, Claire Vallat, Martin Volwerk, and Karl-Heinz Glassmeier
Ann. Geophys., 34, 609-622, doi:10.5194/angeo-34-609-2016, 2016
We have analysed the magnetic field measurements performed on the ROSETTA orbiter and the lander PHILAE during PHILAE's descent to comet 67P/Churyumov-Gerasimenko on 12 November 2014. We observed a new type of low-frequency wave with amplitudes of ~ 3 nT, frequencies of 20–50 mHz, wavelengths of ~ 300 km, and propagation velocities of ~ 6 km s−1. The waves are generated in a ~ 100 km region around the comet a show a highly correlated behaviour, which could only be determined by two-point observations.
- Solar energetic particle interactions with the Venusian atmosphere
Abstract: Solar energetic particle interactions with the Venusian atmosphere
Christina Plainaki, Pavlos Paschalis, Davide Grassi, Helen Mavromichalaki, and Maria Andriopoulou
Ann. Geophys., 34, 595-608, doi:10.5194/angeo-34-595-2016, 2016
In the context of planetary space weather, we estimate the ion production rates in the Venusian atmosphere due to the interactions of solar energetic particles (SEPs) with gas. The assumed concept for our estimations is based on two cases of SEP events, previously observed in near-Earth space: the event in October 1989 and the event in May 2012. For both cases, we assume that the directional properties of the flux and the interplanetary magnetic field configuration would have allowed the SEPs' arrival at Venus and their penetration to the planet's atmosphere. For the event in May 2012, we consider the solar particle properties (integrated flux and rigidity spectrum) obtained by the Neutron Monitor Based Anisotropic GLE Pure Power Law (NMBANGLE PPOLA) model (Plainaki et al., 2010, 2014) applied previously for the Earth case and scaled to the distance of Venus from the Sun. For the simulation of the actual cascade in the Venusian atmosphere initiated by the incoming particle fluxes, we apply the DYASTIMA code, a Monte Carlo (MC) application based on the Geant4 software (Paschalis et al., 2014). Our predictions are afterwards compared to other estimations derived from previous studies and discussed. Finally, we discuss the differences between the nominal ionization profile due to galactic cosmic-ray–atmosphere interactions and the profile during periods of intense solar activity, and we show the importance of understanding space weather conditions on Venus in the context of future mission preparation and data interpretation.
- Daytime twin-peak structures observed at southern African and European
middle latitudes on 8–13 April 2012
Abstract: Daytime twin-peak structures observed at southern African and European middle latitudes on 8–13 April 2012
Zama T. Katamzi, John Bosco Habarulema, and Nigussie M. Giday
Ann. Geophys., 34, 581-590, doi:10.5194/angeo-34-581-2016, 2016
Daytime twin-peak structures, also known as bite-out or diurnal double-maxima structures, are ionospheric phenomena in which the diurnal ionospheric trend shows two peaks (instead of the normal one) during the daytime. This study reports on first simultaneous observations of these structures in the Global Positioning System and ionosonde measurements from the southern African and European middle-latitude stations during a mostly quiet geomagnetic condition period of 8–13 April 2012.
- Critical pitch angle for electron acceleration in a collisionless shock
Abstract: Critical pitch angle for electron acceleration in a collisionless shock layer
Y. Narita, H. Comişel, and U. Motschmann
Ann. Geophys., 34, 591-593, doi:10.5194/angeo-34-591-2016, 2016
Collisionless shock waves in space and astrophysical plasmas can accelerate electrons along the shock layer by an electrostatic potential, and scatter or reflect electrons back to the upstream region by the amplified magnetic field or turbulent fluctuations. The notion of the critical pitch angle is introduced for non-adiabatic electron acceleration by balancing the two timescales under a quasi-perpendicular shock wave geometry in which the upstream magnetic field is nearly perpendicular to the shock layer normal direction. An analytic expression of the critical pitch angle is obtained as a function of the electron velocity parallel to the magnetic field, the ratio of the electron gyro- to plasma frequency, the cross-shock potential, the width of the shock transition layer, and the shock angle (which is the angle between the upstream magnetic field and the shock normal direction). For typical non-relativistic solar system applications, the critical pitch angle is predicted to be about 10°. An efficient acceleration is expected below the critical pitch angle.
- Secondary electron emission from meteoric smoke particles inside the polar
Abstract: Secondary electron emission from meteoric smoke particles inside the polar ionosphere
Carsten Baumann, Markus Rapp, and Antti Kero
Ann. Geophys., 34, 573-580, doi:10.5194/angeo-34-573-2016, 2016
Meteor smoke particles (MSPs), originating from evaporated meteoric matter at 60–110 km altitude, are present in the whole atmosphere including polar regions. As electron precipitation is present at high latitudes, these MSPs are bombarded by energetic electrons. The energetic electrons can enter the MSPs and excite secondary electrons. That can lead to a change of the charge state of these MSPs. The study finds that other charging processes, e.g., electron attachment, are more important.
- Calculating ultra-low-frequency wave power of the compressional magnetic
field vs. L and time: multi-spacecraft analysis using the Van Allen
probes, THEMIS and GOES
Abstract: Calculating ultra-low-frequency wave power of the compressional magnetic field vs. L and time: multi-spacecraft analysis using the Van Allen probes, THEMIS and GOES
Theodore E. Sarris and Xinlin Li
Ann. Geophys., 34, 565-571, doi:10.5194/angeo-34-565-2016, 2016
Ultra-low-frequency (ULF) pulsations are critical in radial diffusion processes of energetic particles, and the power spectral density (PSD) of these fluctuations is an integral part of the radial diffusion coefficients and of assimilative models of the radiation belts. Using simultaneous measurements from two Geostationary Operational Environmental Satellites (GOES) geosynchronous satellites, three satellites of the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft constellation and the two Van Allen probes during a 10-day period of intense geomagnetic activity and ULF pulsations of October 2012, we calculate the PSDs of ULF pulsations at different L shells. By following the time history of measurements at different L it is shown that, during this time, ULF wave power is not enhanced uniformly throughout the magnetosphere but instead is mostly enhanced in the outer L shells, close to the magnetopause, and to a lesser extent in the inner magnetosphere, closer to the plasmapause. Furthermore, by using phase differences between two GOES geosynchronous satellite pairs, we estimate the daily-averaged distribution of power at different azimuthal wave numbers. These results can have significant implications in better defining the effect of radial diffusion in the phase space density of energetic particles for different wave numbers or L shell distributions of ULF power.
- Generalised partition functions: inferences on phase space distributions
Abstract: Generalised partition functions: inferences on phase space distributions
Rudolf A. Treumann and Wolfgang Baumjohann
Ann. Geophys., 34, 557-564, doi:10.5194/angeo-34-557-2016, 2016
It is demonstrated that the statistical mechanical partition function can be used to construct various different forms of phase space distributions. This indicates that its structure is not restricted to the Gibbs–Boltzmann factor prescription based on counting statistics. Consequences concerning generalised Lorentzians and more general distribution functions are discussed.
- A multi-platform investigation of midlatitude sporadic E and
its ties to
E–F coupling and meteor activity
Abstract: A multi-platform investigation of midlatitude sporadic E and its ties to E–F coupling and meteor activity
Ann. Geophys., 34, 529-541, doi:10.5194/angeo-34-529-2016, 2016
This paper details observed connections between dense, transient layers within the lower ionosphere (sporadic E) and both meteor activity and irregularities higher in the ionosphere. The coupling between these layers and wavelike disturbances in the middle ionosphere seems to be shorted out when extremely dense “clouds” are present, which possible disrupt the stability of the layers.
- Properties of inertia-gravity waves in the lowermost stratosphere
as observed by the PANSY radar over Syowa Station in the Antarctic
Abstract: Properties of inertia-gravity waves in the lowermost stratosphere as observed by the PANSY radar over Syowa Station in the Antarctic
Maria Mihalikova, Kaoru Sato, Masaki Tsutsumi, and Toru Sato
Ann. Geophys., 34, 543-555, doi:10.5194/angeo-34-543-2016, 2016
Inertia-gravity waves (IGWs) are an important component for the dynamics of the middle atmosphere. However, observational studies needed to constrain their forcing are still insufficient especially in the remote areas of the Antarctic region. One year of observational data (January to December 2013) by the PANSY radar of the wind components (vertical resolution of 150 m and temporal resolution of 30 min) are used to derive statistical analysis of the properties of IGWs with short vertical wavelengths ( ≤ 4 km) and ground-based periods longer than 4 h in the lowermost stratosphere (height range 10 to 12 km) with the help of the hodograph method. The annual change of the IGWs parameters are inspected but no pronounced year cycle is found. The year is divided into two seasons (summer and winter) based on the most prominent difference in the ratio of Coriolis parameter (f) to intrinsic frequency (ω^) distribution. Average of f∕ω^ for the winter season is 0.40 and for the summer season 0.45 and the average horizontal wavelengths are 140 and 160 km respectively. Vertical wavelengths have an average of 1.85 km through the year. For both seasons the properties of IGWs with upward and downward propagation of the energy are also derived and compared. The percentage of downward propagating waves is 10.7 and 18.4 % in the summer and winter season respectively. This seasonal change is more than the one previously reported in the studies from mid-latitudes and model-based studies. It is in agreement with the findings of past radiosonde data-based studies from the Antarctic region. In addition, using the so-called dual-beam technique, vertical momentum flux and the variance of the horizontal perturbation velocities of IGWs are examined. Tropospheric disturbances of synoptic-scale are suggested as a source of episodes of IGWs with large variance of horizontal perturbation velocities, and this is shown in a number of cases.
- The dawn–dusk asymmetry of ion density in the dayside magnetosheath
and its annual variability measured by THEMIS
Abstract: The dawn–dusk asymmetry of ion density in the dayside magnetosheath and its annual variability measured by THEMIS
Andrew P. Dimmock, Tuija I. Pulkkinen, Adnane Osmane, and Katariina Nykyri
Ann. Geophys., 34, 511-528, doi:10.5194/angeo-34-511-2016, 2016
Ion densities measured on the dawn-side magnetosheath flank were higher than the dusk-flank. The asymmetry was measured close to the magnetopause, but it became more ambiguous in the central magnetosheath. We show that the asymmetry was at its maximum at the 2009 solar minimum (~ 20 %), but then decreased in the rising stage of the next solar cycle (
- Multi-satellite simultaneous observations of magnetopause and
atmospheric losses of radiation belt electrons during an intense solar
wind dynamic pressure pulse
Abstract: Multi-satellite simultaneous observations of magnetopause and atmospheric losses of radiation belt electrons during an intense solar wind dynamic pressure pulse
Zheng Xiang, Binbin Ni, Chen Zhou, Zhengyang Zou, Xudong Gu, Zhengyu Zhao, Xianguo Zhang, Xiaoxin Zhang, Shenyi Zhang, Xinlin Li, Pingbing Zuo, Harlan Spence, and Geoffrey Reeves
Ann. Geophys., 34, 493-509, doi:10.5194/angeo-34-493-2016, 2016
We used 14 satellites(GOES, POES, THEMIS, RBSP, FENGYUN, REPTile) measurement to investigate the loss mechanisms of a electron dropout event during a intense solar wind dynamic pressure pulse. The observations demonstrated that magnetopause shadowing and atmospheric loss both play important roles in electron flux dropout. Moreover, substrom injections and convection strongly enhanced the energetic electron fluxes, which may delay other than avoid the occurrence of electron flux dropout.
- Extreme value analysis of the time derivative of the horizontal magnetic
field and computed electric field
Abstract: Extreme value analysis of the time derivative of the horizontal magnetic field and computed electric field
Peter Wintoft, Ari Viljanen, and Magnus Wik
Ann. Geophys., 34, 485-491, doi:10.5194/angeo-34-485-2016, 2016
Extreme value analysis has been applied to 1-minute-resolution magnetic fields and computed electric fields over Europe. We find that on average the largest disturbances of the fields are observed close to the auroral oval, as expected. However, the analysis indicates that as we move south from Scandinavia to northern continental Europe the distribution becomes more extreme. This could be due to that strong storms regularly occur at high latitudes, while the extreme storms push the oval south.
- Hydromagnetic waves in a compressed-dipole field via field-aligned
Abstract: Hydromagnetic waves in a compressed-dipole field via field-aligned Klein–Gordon equations
Jinlei Zheng, Qiang Hu, Gary M. Webb, and James F. McKenzie
Ann. Geophys., 34, 473-484, doi:10.5194/angeo-34-473-2016, 2016
This work provides an alternative approach to examine one commonly occurring type of electromagnetic waves in Earth's inner magnetosphere. In certain wave modes, the waves propagate along individual field lines of Earth's magnetic field. Governed by the coupled system between the magnetic field and ionized gas of low temperature, the waves show certain characteristics similar to standing waves along an elastic string. We present solutions in agreement with spacecraft observations.
- The solar activity dependence of nonmigrating tides in electron density
at low and middle latitudes observed by CHAMP and GRACE
Abstract: The solar activity dependence of nonmigrating tides in electron density at low and middle latitudes observed by CHAMP and GRACE
Yun-Liang Zhou, Li Wang, Chao Xiong, Hermann Lühr, and Shu-Ying Ma
Ann. Geophys., 34, 463-472, doi:10.5194/angeo-34-463-2016, 2016
The solar activity dependence of nonmigrating tides in electron density at low and middle latitudes observed by CHAMP and GRACE are investigated. The absolute amplitudes of DE3 at low latitudes as well as DE1, D0 and DW2 at middle latitudes are highly related to the solar activity, while their relative amplitudes show little dependence on the solar activity. A clear modulation by the QBO is found in the relative amplitudes of DE3 at low latitudes.
- Effect of data gaps: comparison of different spectral analysis methods
Abstract: Effect of data gaps: comparison of different spectral analysis methods
Costel Munteanu, Catalin Negrea, Marius Echim, and Kalevi Mursula
Ann. Geophys., 34, 437-449, doi:10.5194/angeo-34-437-2016, 2016
We investigate the effect of data gaps for various methods of estimating the amplitude spectrum of a time series. We probe the effects of a single data gap of varying size and of numerous small gaps distributed within the time series. We use synthetic data sets and magnetic field measurements from the Venus Express spacecraft. For multiple gaps and turbulent magnetic data, we show that some advanced methods overestimate the high frequencies, while FFT slightly underestimates them.
- An alternative way to identify local geomagnetically quiet days: a case
study using wavelet analysis
Abstract: An alternative way to identify local geomagnetically quiet days: a case study using wavelet analysis
Virginia Klausner, Andrés Reinaldo Rodriguez Papa, Cláudia Maria Nicole Cândido, Margarete Oliveira Domingues, and Odim Mendes
Ann. Geophys., 34, 451-462, doi:10.5194/angeo-34-451-2016, 2016
This paper proposes a new method to evaluate geomagnetic activity based on wavelet analysis during the solar minimum activity (2007). In order to accomplish this task, a newly developed algorithm called effectiveness wavelet coefficient (EWC) was applied. Furthermore, a comparison between the 5 geomagnetically quiet days determined by the Kp-based method and by wavelet-based method was performed. This paper provides a new insight since the geomagnetic activity indexes are mostly designed to quantify the extent of disturbance rather than the quietness. The results suggest that the EWC can be used as an alternative tool to accurately detect quiet days, and consequently, it can also be used as an alternative to determine the Sq baseline to the current Kp-based 5 quietest days method. Another important aspect of this paper is that most of the quietest local wavelet candidate days occurred in an interval 2 days prior to the high-speed-stream-driven storm events. In other words, the EWC algorithm may potentially be used to detect the quietest magnetic activity that tends to occur just before the arrival of high-speed-stream-driven storms.
- Modelling natural electromagnetic interference in man-made conductors
for space weather applications
Abstract: Modelling natural electromagnetic interference in man-made conductors for space weather applications
Ann. Geophys., 34, 427-436, doi:10.5194/angeo-34-427-2016, 2016
Power transmission lines above the ground, cables and pipelines, and, in general, all man-made long grounded conductors are exposed to the variations of natural electromagnetic field of wide frequency range. This interference often can compromise the systems operations. Paper offers frequency dependent approach in modelling the response of these systems to the geomagnetic variations. The formulas were proposed, analysed, verified and recommended for use in space weather applications.
- The influence of resistivity gradients on shock conditions for a Petschek
Abstract: The influence of resistivity gradients on shock conditions for a Petschek reconnection geometry
Christian Nabert and Karl-Heinz Glassmeier
Ann. Geophys., 34, 421-425, doi:10.5194/angeo-34-421-2016, 2016
Electrical resistivity can influence the occurrence of shock waves. We derive analytically necessary conditions for shocks in a nonuniform resistive magnetohydrodynamic plasma. The nonuniform resistivity significantly modifies the characteristic velocity of wave propagation. A sufficient gradient of the resistivity in a diffusion region can satisfy the necessary condition for the occurrence of slow shocks, which is related to Petschek reconnection.