Bibliography
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Found 400 entries in the Bibliography.
Showing entries from 1 through 50
| 2021 |
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Abstract Simultaneous observations from Van Allen Probes (RBSP) in Earth’s outer radiation belt (∼4-6 RE) and Magnetospheric Multiscale (MMS) in the magnetotail plasma sheet at >20 RE geocentric distance are used to compare relative levels of relativistic electron phase space density (PSD) for constant values of the first adiabatic invariant, M. We present new evidence from two events showing: i) at times, there is sufficient PSD in the central plasma sheet to provide a source of >1 MeV electrons into the outer belt; ii) the most intense levels of relativistic electrons are not accelerated in the solar wind or transported from the inner magnetosphere and thus must be accelerated rapidly (within ∼minutes or less) and efficiently across a broad region of the magnetotail itself; and iii) the highest intensity relativistic electrons observed by MMS were confined within only the central plasma sheet. The answer to the title question here is: yes, it can, however whether Earth’s plasma sheet actually does provide a source of several 100s keV to >1 MeV electrons to the outer belt and how often it does so remain important outstanding questions. Turner, Drew; Cohen, Ian; Michael, Adam; Sorathia, Kareem; Merkin, Slava; Mauk, Barry; Ukhorskiy, Sasha; Murphy, Kyle; Gabrielse, Christine; Boyd, Alexander; Fennell, Joseph; Blake, Bernard; Claudepierre, Seth; Drozdov, Alexander; Jaynes, Allison; Ripoll, Jean-Francois; Reeves, Geoffrey; Published by: Geophysical Research Letters Published on: 09/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021GL095495 Radiation belts; plasma sheet; Particle acceleration; relativistic electrons; inner magnetosphere; magnetotail; Van Allen Probes |
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Realistic electron diffusion rates and lifetimes due to scattering by electron holes AbstractPlasma sheet electron precipitation into the diffuse aurora is critical for magnetosphere-ionosphere coupling. Recent studies have shown that electron phase space holes can pitch-angle scatter electrons and may produce plasma sheet electron precipitation. These studies have assumed identical electron hole parameters to estimate electron scattering rates (Vasko et al., 2018). In this study, we have re-evaluated the efficiency of this scattering by incorporating realistic electron hole properties from direct spacecraft observations into computing electron diffusion rates and lifetimes. The most important electron hole properties in this evaluation are their distributions in velocity and spatial scale and electric field root-mean-square intensity (). Using direct measurements of electron holes during a plasma injection event observed by the Van Allen Probe at , we find that when 4 mV/m electron lifetimes can drop below one hour and are mostly within strong diffusion limits at energies below 10 keV. During an injection observed by the THEMIS spacecraft at , electron holes with even typical intensities (1 mV/m) can deplete low-energy (a few keV) plasma sheet electrons within tens of minutes following injections and convection from the tail. Our results confirm that electron holes are a significant contributor to plasma sheet electron precipitation during injections. Shen, Yangyang; Vasko, Ivan; Artemyev, Anton; Malaspina, David; Chu, Xiangning; Angelopoulos, Vassilis; Zhang, Xiao-Jia; Published by: Journal of Geophysical Research: Space Physics Published on: 08/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021JA029380 diffuse aurora; electron pitch-angle scattering; electron phase space hole; Wave-particle interaction; electron lifetimes; broadband electrostatic fluctuations; Van Allen Probes |
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Trapping and amplification of unguided mode EMIC waves in the radiation belt AbstractElectromagnetic ion cyclotron (EMIC) waves can cause the scattering loss of the relativistic electrons in the radiation belt. They can be classified into the guided mode and the unguided mode, according to waves propagation behavior. The guided mode waves have been widely investigated in the radiation belt, but the observation of the unguided mode waves have not been expected. Based on the observations of Van Allen Probes, we demonstrate for the first time the existence of the intense unguided L-mode EMIC waves in the radiation belt according to the polarization characteristics. Growth rate analyses indicate that the hot protons with energies of a few hundred keV may provide the free energy for wave growth. The reflection interface formed by the spatial locations of local helium cutoff frequencies can be nearly parallel to the equatorial plane when the proton abundance ratio decreases sharply with -shell. This structure combined with hot protons may lead to the trapping and significant amplification of the unguided mode waves. These results may help to understand the nature of EMIC waves and their dynamics in the radiation belt. Wang, Geng; Gao, Zhonglei; Wu, MingYu; Wang, GuoQiang; Xiao, SuDong; Chen, YuanQiang; Zou, Zhengyang; Zhang, TieLong; Published by: Journal of Geophysical Research: Space Physics Published on: 08/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021JA029322 EMIC waves; unguided mode; Radiation belt; ion abundance ratios; Wave trapping; growth rate; Van Allen Probes |
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PreMevE Update: Forecasting Ultra-relativistic Electrons inside Earth’s Outer Radiation Belt Abstract Energetic electrons inside Earth’s Van Allen belts pose a major radiation threat to space-borne electronics that often play vital roles in modern society. Ultra-relativistic electrons with energies greater than or equal to two Megaelectron-volt (MeV) are of particular interest, and thus forecasting these ≥2 MeV electrons has significant meaning to all space sectors. Here we update the latest development of the predictive model for MeV electrons in the outer radiation belt. The new version, called PreMevE-2E, forecasts ultra-relativistic electron flux distributions across the outer belt, with no need for in-situ measurements of the trapped MeV electron population except at geosynchronous (GEO) orbit. Model inputs include precipitating electrons observed in low-Earth-orbits by NOAA satellites, upstream solar wind speeds and densities from solar wind monitors, as well as ultra-relativistic electrons measured by one Los Alamos GEO satellite. We evaluated 32 supervised machine learning models that fall into four different classes of linear and neural network architectures, and successfully tested ensemble forecasting by using groups of top-performing models. All models are individually trained, validated, and tested by in-situ electron data from NASA’s Van Allen Probes mission. It is shown that the final ensemble model outperforms individual models at most L-shells, and this PreMevE-2E model can provide 25-hr (∼1-day) and 50-hr (∼2-day) forecasts with high mean performance efficiency and correlation values. Our results also suggest this new model is dominated by nonlinear components at L-shells < ∼4 for ultra-relativistic electrons, different from the dominance of linear components for 1 MeV electrons as previously discovered. Sinha, Saurabh; Chen, Yue; Lin, Youzuo; de Lima, Rafael; Published by: Space Weather Published on: 08/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021SW002773 Supervised Machine Learning; Van Allen electron radiation belt; Predicting ultra-relativistic electrons; Van Allen Probes |
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Global Survey of Electron Precipitation due to Hiss Waves in the Earth s Plasmasphere and Plumes Abstract We present a global survey of energetic electron precipitation from the equatorial magnetosphere due to hiss waves in the plasmasphere and plumes. Using Van Allen Probes measurements, we calculate the pitch angle diffusion coefficients at the bounce loss cone, and evaluate the energy spectrum of precipitating electron flux. Our ∼6.5-year survey shows that, during disturbed times, hiss inside the plasmasphere primarily causes the electron precipitation at L > 4 over 8 h < MLT < 18 h, and hiss waves in plumes cause the precipitation at L > 5 over 8 h < MLT < 14 h and L > 4 over 14 h < MLT < 20 h. The precipitating energy flux increases with increasing geomagnetic activity, and is typically higher in the plasmaspheric plume than the plasmasphere. The characteristic energy of precipitation increases from ∼20 keV at L = 6 to ∼100 keV at L = 3, potentially causing the loss of electrons at several hundred keV. Ma, Q.; Li, W.; Zhang, X.-J.; Bortnik, J.; Shen, X.-C.; Connor, H.; Boyd, A.; Kurth, W.; Hospodarsky, G.; Claudepierre, S.; Reeves, G.; Spence, H.; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021JA029644 electron precipitation; hiss wave; plasmasphere; plasmaspheric plume; Precipitating Energy Flux; Van Allen Probes Survey; Van Allen Probes |
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Observational evidence of the excitation of magnetosonic waves by an He ion ring distribution Abstract We report plasma wave observations of equatorial magnetosonic waves at integer harmonics of the local gyrofrequency of doubly-ionized helium (He). The waves were observed by Van Allen Probe A on 08 Feb 2014 when the spacecraft was in the afternoon magnetic local time sector near inside of the plasmasphere. Analysis of the complementary in-situ energetic ion measurements (1-300 keV) reveals the presence of a helium ion ring distribution centered near 30 keV. Theoretical linear growth rate calculations suggest that the local plasma and field conditions can support the excitation of the magnetosonic waves from the unstable ring distribution. This represents the first report of the generation of magnetosonic equatorial noise via a ring distribution in energetic He ions in the near-Earth space plasma environment. Claudepierre, S.; Liu, X.; Chen, L.; Takahashi, K.; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021JA029532 magnetosonic waves; ion Bernstein waves; ring distribution; alpha particles; Plasma instability; ring current; Van Allen Probes |
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Abstract The coupling response between solar wind structures and the magnetosphere is highly complex, leading to different effects in the outer radiation belt electron fluxes. Most Coronal Mass Ejections cause strong geomagnetic storms with short recovery phases, often 1-2 days. By contrast, High-Speed Solar Wind Streams lead to moderate and weak storms often with much longer recovery phases, from several to ∼10 days. The magnetosphere receives energy for a long time under the influence of the HSSs, considerably changing its dynamics. This in turn has an effect on the charged particles trapped in the outer radiation belt. Although the high-energy electron flux enhancements have received considerable attention, the high-energy electron flux enhancement pattern (L > 4) has not. This paper identifies 37 events with this enhancement pattern in the high-energy electron flux during the Van Allen Probes era. We find the enhancements coincident with HSS occurrence. The interplanetary magnetic field (IMF) exhibits north/south Bz fluctuations of Alfvénic nature with moderate amplitudes. The high-energy electron flux enhancements also correspond to long periods of auroral activity indicating a relationship to magnetotail dynamics. However, the AE index only reaches moderate values. Ultra-Low Frequency waves were present in all of the events and whistler-mode chorus waves were present in 89.1\% of the events, providing a convenient scenario for wave-particle interactions. The radial gradient of the ULF wave power related to the L, under the influence of the HSSs, is necessary to trigger the physical processes responsible for this type of high-energy electron flux enhancement pattern. This article is protected by copyright. All rights reserved. Da Silva, L.; Shi, J.; Alves, L.; Sibeck, D.; Marchezi, J.; Medeiros, C.; Vieira, L.; Agapitov, O.; Cardoso, F.; Souza, V.; Dal Lago, A.; Jauer, P.; Wang, C.; Li, H.; Liu, Z.; Alves, M.; Rockenbach, M.; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021JA029363 outer radiation belt; high-energy electron flux; high speed solar wind stream; ultra low frequency waves; whistler-mode chorus waves; Electron flux enhancement; Van Allen Probes |
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ULF-modulation of whistler-mode waves in the inner magnetosphere during solar wind compression Abstract The solar wind plays important roles on terrestrial magnetosphere dynamics, including the particle population and plasma waves generation. Here we report an interesting event that ULF waves are enhanced right after solar wind compression and the compressional mode ULF wave subsequently modulates both the intensity and energy flux direction of whistler-mode waves. Quasi-periodic whistler-mode wave packets are observed around L=5.6 at noon sector by Van Allen Probes. Growth rate calculation demonstrates that the compressional mode ULF wave can modulate the whistler-mode wave intensity by modulating the energetic electron anisotropy. Moreover, the direction of wave energy flux is observed to alternate between northward and southward at equator, which is probably because the intense ULF waves periodically alter the relative direction of the wave source region respect to the spacecraft. The current results provide a chain of observational evidences to illustrate how the generation and propagation of whistler-mode waves in the inner magnetosphere are affected by ULF waves during the solar wind dynamic pressure enhancement. This article is protected by copyright. All rights reserved. Shang, Xiongjun; Liu, Si; Chen, Lunjin; Gao, Zhonglei; Wang, Geng; He, Qian; Li, Tong; Xiao, Fuliang; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021JA029353 |
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ULF-modulation of whistler-mode waves in the inner magnetosphere during solar wind compression Abstract The solar wind plays important roles on terrestrial magnetosphere dynamics, including the particle population and plasma waves generation. Here we report an interesting event that ULF waves are enhanced right after solar wind compression and the compressional mode ULF wave subsequently modulates both the intensity and energy flux direction of whistler-mode waves. Quasi-periodic whistler-mode wave packets are observed around L=5.6 at noon sector by Van Allen Probes. Growth rate calculation demonstrates that the compressional mode ULF wave can modulate the whistler-mode wave intensity by modulating the energetic electron anisotropy. Moreover, the direction of wave energy flux is observed to alternate between northward and southward at equator, which is probably because the intense ULF waves periodically alter the relative direction of the wave source region respect to the spacecraft. The current results provide a chain of observational evidences to illustrate how the generation and propagation of whistler-mode waves in the inner magnetosphere are affected by ULF waves during the solar wind dynamic pressure enhancement. This article is protected by copyright. All rights reserved. Shang, Xiongjun; Liu, Si; Chen, Lunjin; Gao, Zhonglei; Wang, Geng; He, Qian; Li, Tong; Xiao, Fuliang; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021JA029353 |
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Direct evidence reveals transmitter signal propagation in the magnetosphere AbstractSignals from very-low-frequency transmitters on the ground are known to induce energetic electron precipitation from the Earth’s radiation belts. The effectiveness of this mechanism depends on the propagation characteristics of those signals in the magnetosphere, and in particular whether the signals are ducted or nonducted along channels of enhanced plasma density, analogous to optical fibres. Here we perform a statistical analysis of in-situ waveform data collected by the Van Allen Probes satellites that shows that nonducted propagation dominates over ducted propagation in both the occurrence and intensity of the waves. Ray tracing confirms that the latitudinal distribution of wavevectors corresponds to nonducted as opposed to ducted propagation. Our results show the dominant mode of propagation needed to quantify transmitter-induced precipitation and improve the forecast of electron radiation belt dynamics for the safe operation of satellites. Gu, Wenyao; Chen, Lunjin; Xia, Zhiyang; Horne, Richard; Published by: Geophysical Research Letters Published on: 07/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021GL093987 VLF transmitters; ducted propagation; nonducted propagation; Magnetosphere; Van Allen Probes |
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Abstract Density irregularities near the plasmapause are commonly observed and play an important role in whistler-mode wave excitation and propagation. In this study, we report a frequency-dependent modulation event of whistler-mode waves by background density irregularities during a geomagnetic storm. Higher-frequency whistler waves (near 0.5 fce, where fce is the equatorial electron cyclotron frequency) are trapped in the density trough regions due to the small refractive index near the parallel direction, while lower-frequency whistler waves (below 0.02 fce) are trapped in the density crest regions due to the refractive index maximum along the parallel direction. In addition to the modulation, we also find that, quantitatively, the wave amplitude of the higher- (lower-) frequency whistler-mode waves is anti-correlated (correlated) with the relative plasma density variation. Our study suggests the importance of density irregularity dynamics in controlling whistler-mode wave intensity, and thus radiation belt dynamics. Liu, Xu; Gu, Wenyao; Xia, Zhiyang; Chen, Lunjin; Horne, Richard; Published by: Geophysical Research Letters Published on: 07/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021GL093095 |
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The Characteristics of Three-belt Structure of Sub-MeV Electrons in the Radiation Belts Abstract After the launch of Van Allen Probes, the three-belt structures of ultra-relativistic electrons are discovered. In this study, we investigate the three-belt structures of sub-MeV electrons, which may form under different mechanism compared with those of ultra-relativistic electrons and are worth in-depth analysis. Based on the differential flux data from MagEIS onboard RBSP-B satellite, we find 54 events, in which two comparable peaks of sub-MeV electron fluxes and a slot appear where there should be the outer radiation belt. Through the statistical analysis, the three-belt structures of sub-MeV electrons are found to be closely related to SYM-H and AE indices. The 2-day SYM-H minimum and AE maximum before the event have a linear trend with the remnant belt and the “second slot” locations. The L values of the remnant belt and the “second slot” of different energy electrons decrease as energy increases in general and show interesting characteristics during their temporal evolution. Moreover, the lifetime of the remnant belt of different energy electrons increases as energy increases. We find similarities and differences between sub-MeV and ultra-relativistic electrons three-belt events, which provides a new perspective in three-belt structure study. Li, Yu-Xuan; Yue, Chao; Hao, Yi-Xin; Zong, Qiu-Gang; Zhou, Xu-Zhi; Fu, Sui-Yan; Chen, Xing-Ran; Zhao, Xing-Xin; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021JA029385 |
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Abstract We present a comparison of magnetospheric plasma mass/electron density observations during an 11-day interval which includes the geomagnetic storm of 22 June 2015. For this study we used: equatorial plasma mass density derived from geomagnetic field line resonances (FLRs) detected by Van Allen Probes and at the ground-based magnetometer networks EMMA and CARISMA; in situ electron density inferred by the Neural-network-based Upper hybrid Resonance Determination algorithm applied to plasma wave Van Allen Probes measurements. The combined observations at L ∼ 4, MLT ∼ 16 of the two longitudinally-separated magnetometer networks show a temporal pattern very similar to that of the in situ observations: a density decrease by an order of magnitude about 1 day after the Dst minimum, a partial recovery a few hours later, and a new strong decrease soon after. The observations are consistent with the position of the measurement points with respect to the plasmasphere boundary as derived by a plasmapause test particle simulation. A comparison between plasma mass densities derived from ground and in situ FLR observations during favourable conjunctions shows a good agreement. We find however, for L < ∼3, the spacecraft measurements to be higher than the corresponding ground observations with increasing deviation with decreasing L, which might be related to the rapid outbound spacecraft motion in that region. A statistical analysis of the average ion mass using simultaneous spacecraft measurements of mass and electron density indicates values close to 1 amu in plasmasphere and higher values (∼ 2-3 amu) in plasmatrough. This article is protected by copyright. All rights reserved. Vellante, M.; Takahashi, K.; Del Corpo, A.; Zhelavskaya, I.; Goldstein, J.; Mann, I.; Pietropaolo, E.; Reda, J.; Heilig, B.; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021JA029292 magnetoseismology; plasmasphere; Field line resonance; ground-based magnetometers; Van Allen Probes; Swarm satellites |
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Abstract We present a comparison of magnetospheric plasma mass/electron density observations during an 11-day interval which includes the geomagnetic storm of 22 June 2015. For this study we used: equatorial plasma mass density derived from geomagnetic field line resonances (FLRs) detected by Van Allen Probes and at the ground-based magnetometer networks EMMA and CARISMA; in situ electron density inferred by the Neural-network-based Upper hybrid Resonance Determination algorithm applied to plasma wave Van Allen Probes measurements. The combined observations at L ∼ 4, MLT ∼ 16 of the two longitudinally-separated magnetometer networks show a temporal pattern very similar to that of the in situ observations: a density decrease by an order of magnitude about 1 day after the Dst minimum, a partial recovery a few hours later, and a new strong decrease soon after. The observations are consistent with the position of the measurement points with respect to the plasmasphere boundary as derived by a plasmapause test particle simulation. A comparison between plasma mass densities derived from ground and in situ FLR observations during favourable conjunctions shows a good agreement. We find however, for L < ∼3, the spacecraft measurements to be higher than the corresponding ground observations with increasing deviation with decreasing L, which might be related to the rapid outbound spacecraft motion in that region. A statistical analysis of the average ion mass using simultaneous spacecraft measurements of mass and electron density indicates values close to 1 amu in plasmasphere and higher values (∼ 2-3 amu) in plasmatrough. This article is protected by copyright. All rights reserved. Vellante, M.; Takahashi, K.; Del Corpo, A.; Zhelavskaya, I.; Goldstein, J.; Mann, I.; Pietropaolo, E.; Reda, J.; Heilig, B.; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021JA029292 magnetoseismology; plasmasphere; Field line resonance; ground-based magnetometers; Van Allen Probes; Swarm satellites |
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Observation of unusual chorus elements by Van Allen Probes AbstractWhistler mode chorus waves play an important role in the radiation belt dynamics, which usually appear as discrete elements with frequency sweeping. Finer structure analysis shows that a chorus element is composed of several frequency-sweeping subelements, and such two-level structures can be successfully reproduced by modeling based on nonlinear theories. Previous observations and models suggest that an element and its subelements should have the same frequency-sweep direction. However, we here present two unexpected chorus rising tone events within which the subelements exhibit clearly reversed, falling frequency-sweep. Moreover, the subelements consist of several wave packets that also show falling frequency-sweep features. The three-level structured chorus elements are distinctly different from all the reported observations and seem to bring challenges to the existing theories. We propose a possible scenario that the falling tone subelements are formed by nonlinear process with much shorter timescale and the starting frequency of each subelement is controlled by fast varying electron distribution. This study may inspire more studies toward a thorough understanding of the chorus generation process. Liu, Si; Gao, Zhonglei; Xiao, Fuliang; He, Qian; Li, Tong; Shang, Xiongjun; Zhou, Qinghua; Yang, Chang; Zhang, Sai; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021JA029258 |
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Origin of Electron Boomerang Stripes: Statistical Study Abstract In the outer radiation belt, localized ULF waves can interact with energetic electrons by drift resonance, leading to quasiperiodic oscillations. The oscillations in the pitch angle spectrum can be characterized by either boomerang-shaped or straight stripes. Previous studies have shown that boomerang-shaped stripes evolve from straight ones when electrons drift away from the localized wave interaction region. Based on the time-of-flight technique on the pitch angle-dependent drift velocity, the origin can be remotely identified from the pitch angle dispersion. We report 27 straight stripe events and 86 boomerang-shaped events observed by Van Allen Probes from 2013/01/01 to 2017/12/31. Statistical study shows a good coincidence between the locations of straight ones and traceback regions from boomerang-shaped ones. These locations, mainly located in noon-to-dusk region, coincide well with the plasmaspheric plumes. Thus localized ULF waves trapped in the plume may result in the preference of localized ULF waves-electron interactions at noon-to-dusk region. Zhao, X.; Hao, Y.; Zong, Q.; Zhou, X.; Yue, Chao; Chen, X.; Liu, Y.; Liu, Z.-Y.; Blake, J.; Claudepierre, S.; Reeves, G.; Published by: Geophysical Research Letters Published on: 05/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021GL093377 Localized ULF waves; Energetic Elctrons; drift resonance; Time-of-flight Technique; source region; boomerang-shaped stripes; Van Allen Probes |
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A Multi-instrument Study of a Dipolarization Event in the Inner Magnetosphere Abstract A dipolarization of the background magnetic field was observed during a conjunction of the Magnetospheric Multiscale (MMS) spacecraft and Van Allen Probe B on 22 September 2018. The spacecraft were located in the inner magnetosphere at L ∼ 6 − 7 just before midnight magnetic local time (MLT). The radial separation between MMS and Probe B was ∼ 1RE. Gradual dipolarization or an increase of the northward component BZ of the background field occurred on a timescale of minutes. Exploration of energization and Radiation in Geospace (ERG) located 0.5 MLT eastward at a similar L shell also measured a gradual increase. The spatial scale was of the order of 1 RE. On top of that, MMS and Probe B measured BZ increases, and a decrease in one case, on a timescale of seconds, accompanied by large electric fields with amplitudes > several tens of mV/m. Spatial scale lengths were of the order of the ion inertial length and the ion gyroradius. The inertial term in the momentum equation and the Hall term in the generalized Ohm’s law were sometimes non-negligible. These small-scale variations are discussed in terms of the ballooning/interchange instability (BICI) and kinetic Alfvén waves among others. It is inferred that physics of multiple scales was involved in the dynamics of this dipolarization event. This article is protected by copyright. All rights reserved. Matsui, H.; Torbert, R.; Spence, H.; Argall, M.; Cohen, I.; Cooper, M.; Ergun, R.; Farrugia, C.; Fennell, J.; Fuselier, S.; Gkioulidou, M.; Khotyaintsev, Yu.; Lindqvist, P.-A.; Matsuoka, A.; Russell, C.; Shoji, M.; Strangeway, R.; Turner, D.; Vaith, H.; Wygant, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021JA029294 Dipolarization; inner magnetosphere; Multiple Scale Dynamics; Van Allen Probes |
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Abstract Radiation belt flux dropout events are sudden and often significant reductions in high-energy electrons from Earth’s outer radiation belts. These losses are theorized to be due to interactions with the dayside magnetopause and possibly connected to observations of escaping magnetospheric particles. This study focuses on radiation belt losses during a moderate-strength, nonstorm dropout event on 21 November 2016. The potential loss mechanisms and the linkage to dayside escape are investigated using combined energetic electron observations throughout the dayside magnetosphere from the MMS and Van Allen Probes spacecraft along with global magnetohydronamic and test particle simulations. In particular, this nonstorm-time event simplifies the magnetospheric conditions and removes ambiguity in the interpretation of results, allowing focus on subequent losses from enhanced outward radial transport that can occur after initial compression and relaxation of the magnetopause boundary. The evolution of measured phase space density profiles suggest a total loss of approximately 60\% of the initial radiation belt content during the event. Together the in-situ observations and high-resolution simulations help to characterize the loss by bounding the following parameters: 1) the duration of the loss, 2) the relative distribution of losses and surface area of the magnetopause over which loss occurs, and 3) the escaping flux (i.e., loss) rate across the magnetopause. In particular, this study is able to estimate the surface area of loss to less than 2.9×106 RE2 and the duration of loss to greater than six hours, while also demonstrating the MLT-dependence of the escaping flux and energy spectrum . Cohen, I.; Turner, D.; Michael, A.; Sorathia, K.; Ukhorskiy, A; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021JA029261 Radiation belt; Magnetospheric escape; energetic electrons; Flux dropout events; test particle simulations; Van Allen Probes |
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A Statistical Study of Lower Hybrid Waves In the Earth’s Magnetosphere by Van Allen Probes Abstract The lower hybrid (LH) waves are electrostatic emissions near the LH resonant frequency. They propagate perpendicularly with a small wavelength comparable to Larmor radius of thermal particles and can heat both ions and electrons. In this paper, we statistically study the global distribution of LH waves in the inner magnetosphere by using Van Allen Probes observation from 2012 to 2018. We find that (1) LH waves are commonly observed in the inner magnetosphere. Most LH waves are confined near the magnetic equator with typical amplitudes of 0.02 ∼ 0.2 mV/m and occurrence rates up to 10\%. (2) LH waves extend to inner L regions with increasing wave amplitudes as AE* increases. (3) Weak LH waves occur at the nightside inside the plasmapause. Moderate and strong LH waves occur at the nightside and noon inside the plasmapause. As AE* increases, they extend to all MLTs inside the plasmapause and dawnside outside the plasmapause. Liu, Xu; Chen, Lunjin; Ma, Qianli; Published by: Geophysical Research Letters Published on: 05/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021GL093168 |
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Abstract Auroral kilometric radiations (AKR) are strong radio emission phenomena, and can prduce significant acceleration or scattering of radiation belt electrons. The variation of AKR wave amplitude with the latitude (λ) has not been reported so far owing to lack of measurements. Here, using observations of the Arase satellite and Van Allen Probes from 23 March 2017 to 31 July 2019, we present the first statistical study on the AKR electric field amplitude (Et) in the radiation belts for |λ| = 0° − 40° and L-shell L = 3.0−6.2. Results (totally 14,770 samples) show that Et can be described by a concise formula: Et(λ) = E0 exp(ξ sin |λ|), decreasing with decreasing latitude. Fitting parameters E0 and ξ are limited in the ranges: E0 = 0.054−0.340 mV/m and ξ = 3.0−4.2. Wave amplitudes are greater (smaller) under intense (weak) geomagnetic conditions. This study helps to better quantify the gyroresonance between AKR and radiation belt electrons. Zhang, Sai; Liu, Si; Li, Wentao; He, Yihua; Yang, Qiwu; Xiao, Fuliang; Kumamoto, Atsushi; Miyoshi, Yoshizumi; Nakamura, Yosuke; Tsuchiya, Fuminori; Kasahara, Yoshiya; Shinohara, Iku; Published by: Geophysical Research Letters Published on: 04/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021GL092805 AKR; wave amplitude; geomagnetic latitude; Radiation belt; field-aligned; Van Allen Probes |
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Abstract We investigate relativistic electron precipitation events detected by POES in low-Earth orbit in close conjunction with Van Allen Probe A observations of EMIC waves near the geomagnetic equator. We show that the occurrence rate of > 0.7 MeV electron precipitation recorded by POES during those times strongly increases, reaching statistically significant levels when the minimum electron energy for cyclotron resonance with hydrogen or helium band EMIC waves at the equator decreases below ≃ 1.0 − 2.5 MeV, as expected from quasi-linear theory. Both hydrogen and helium band EMIC waves can be effective in precipitating MeV electrons. However, > 0.7 MeV electron precipitation is more often observed (at statistically significant levels) when the minimum electron energy for cyclotron resonance with hydrogen band waves is low (Emin = 0.6 − 1.0 MeV), whereas it is more often observed when the minimum electron energy for cyclotron resonance with helium band waves is slightly larger (Emin = 1.0 − 2.5 MeV), indicative of warm plasma effects for waves approaching the He+ gyrofrequency. We further show that most precipitation events had energies > 0.7 − 1.0 MeV, consistent with the estimated minimum energy (Emin ∼ 0.6 − 2.5 MeV) of cyclotron resonance with the observed EMIC waves during the majority of these events. However, 4 out of the 12 detected precipitation events cannot be explained by electron quasi-linear scattering by the observed EMIC waves, and 12 out of 20 theoretically expected precipitation events were not detected by POES, suggesting the possibility of nonlinear effects likely present near the magnetic equator, or warm plasma effects, and/or narrowly localized bursts of EMIC waves. This article is protected by copyright. All rights reserved. Zhang, X.-J.; Mourenas, D.; Shen, X.-C.; Qin, M.; Artemyev, A.; Ma, Q.; Li, W.; Hudson, M.; Angelopoulos, V.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021JA029193 EMIC waves; relativistic electron precipitation; minimum resonant energy; Van Allen Probes; POES; Radiation belts |
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Abstract With Van Allen Probes data, we present the observational support for whistler waves guided by the plasmapause based on a case study and statistical analyses. Due to the combined effects of inhomogeneous magnetic fields and plasma densities, whistler waves near the inner edge of plasmapause (plasmasphere side) will be guided by a HDD-like (HDD, high density duct) density gradient, and tend to have very small wave normal angles (WNAs ≤20°). In contrast, whistler waves around the outer edge of the plasmapause (plasmatrough side) guided by a LDD-like (LDD, low density duct) density gradient, tend to have quite large WNAs (≥∼60°). Moreover, the statistical analysis reveals the remarkably different properties of whistler waves around inner and outer edges of plasmapause. We suggest that the plasmapause density gradients may play a significant role in the distribution of whistler waves. Chen, Rui; Gao, Xinliang; Lu, Quanming; Tsurutani, Bruce; Wang, Shui; Published by: Geophysical Research Letters Published on: 03/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021GL092652 Plasmapause; whistler wave; ducting effect; inner edge; outer edge; wave normal angle; Van Allen Probes |
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Whistler-mode waves trapped by density irregularities in the Earth s magnetosphere Abstract Whistler-mode waves are electromagnetic waves pervasively observed in the Earth s and other planetary magnetospheres. They are considered to be mainly responsible for producing the hazardous radiation and diffuse aurora, which heavily relies on their properties. Density irregularities, frequently observed in the Earth s magnetospheres, are found to change largely the properties of whistler-mode waves. Here we report, using Van Allen Probes measurements, whistler-mode waves strongly modulated by two different density enhancements. With particle-in-cell simulations, we propose wave trapping caused by field-aligned density irregularities (ducts) may account for this phenomenon. Simulation results show that whistler-mode waves can be trapped inside the enhanced density ducts. These trapped waves remain quasi-parallel and usually get much larger amplitudes than those unducted whistler waves during propagation away from the magnetic equator, and tend to focus at a spatially narrow channel, consistent with observations. Our results imply density irregularities may be significant to modulate radiation-belt electrons. This article is protected by copyright. All rights reserved. Ke, Yangguang; Chen, Lunjin; Gao, Xinliang; Lu, Quanming; Wang, Xueyi; Chen, Rui; Chen, Huayue; Wang, Shui; Published by: Geophysical Research Letters Published on: 03/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020GL092305 WHISTLER-MODE WAVES; density irregularities; Magnetosphere; Radiation belts; particle-in-cell simulation; Wave trapping; Van Allen Probes |
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Whistler-mode waves trapped by density irregularities in the Earth s magnetosphere Abstract Whistler-mode waves are electromagnetic waves pervasively observed in the Earth s and other planetary magnetospheres. They are considered to be mainly responsible for producing the hazardous radiation and diffuse aurora, which heavily relies on their properties. Density irregularities, frequently observed in the Earth s magnetospheres, are found to change largely the properties of whistler-mode waves. Here we report, using Van Allen Probes measurements, whistler-mode waves strongly modulated by two different density enhancements. With particle-in-cell simulations, we propose wave trapping caused by field-aligned density irregularities (ducts) may account for this phenomenon. Simulation results show that whistler-mode waves can be trapped inside the enhanced density ducts. These trapped waves remain quasi-parallel and usually get much larger amplitudes than those unducted whistler waves during propagation away from the magnetic equator, and tend to focus at a spatially narrow channel, consistent with observations. Our results imply density irregularities may be significant to modulate radiation-belt electrons. This article is protected by copyright. All rights reserved. Ke, Yangguang; Chen, Lunjin; Gao, Xinliang; Lu, Quanming; Wang, Xueyi; Chen, Rui; Chen, Huayue; Wang, Shui; Published by: Geophysical Research Letters Published on: 03/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020GL092305 WHISTLER-MODE WAVES; density irregularities; Magnetosphere; Radiation belts; particle-in-cell simulation; Wave trapping; Van Allen Probes |
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Whistler-mode waves trapped by density irregularities in the Earth s magnetosphere Abstract Whistler-mode waves are electromagnetic waves pervasively observed in the Earth s and other planetary magnetospheres. They are considered to be mainly responsible for producing the hazardous radiation and diffuse aurora, which heavily relies on their properties. Density irregularities, frequently observed in the Earth s magnetospheres, are found to change largely the properties of whistler-mode waves. Here we report, using Van Allen Probes measurements, whistler-mode waves strongly modulated by two different density enhancements. With particle-in-cell simulations, we propose wave trapping caused by field-aligned density irregularities (ducts) may account for this phenomenon. Simulation results show that whistler-mode waves can be trapped inside the enhanced density ducts. These trapped waves remain quasi-parallel and usually get much larger amplitudes than those unducted whistler waves during propagation away from the magnetic equator, and tend to focus at a spatially narrow channel, consistent with observations. Our results imply density irregularities may be significant to modulate radiation-belt electrons. This article is protected by copyright. All rights reserved. Ke, Yangguang; Chen, Lunjin; Gao, Xinliang; Lu, Quanming; Wang, Xueyi; Chen, Rui; Chen, Huayue; Wang, Shui; Published by: Geophysical Research Letters Published on: 03/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020GL092305 WHISTLER-MODE WAVES; density irregularities; Magnetosphere; Radiation belts; particle-in-cell simulation; Wave trapping; Van Allen Probes |
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A comparative study on the distributions of incoherent and coherent plasmaspheric hiss Abstract We perform a comparative study on the distributions of incoherent and coherent plasmaspheric hiss, based on the Van Allen Probe data. The statistics show that incoherent hiss ( ∼10–20 pT) is widely distributed in dayside plasmasphere, with peak frequencies below 500 Hz; intense coherent hiss (amplitudes up to 80 pT) occurs in outer plasmasphere of L > 4 (L denotes the L-shell.), whose frequency increases with ambient magnetic field significantly. The Poynting flux analysis indicates that incoherent hiss generally propagates omni-directionally inside the plasmasphere, with features of external sources; the coherent hiss propagates away from the equatorial region in outer plasmasphere and has a reversed direction in inner plasmasphere, indicating two different wave sources by local generation and ducted lightning generated whistler (LGW) respectively. This comparative study helps us to better understand the origination of plasmaspheric hiss. This article is protected by copyright. All rights reserved. He, Zhaoguo; Yu, Jiang; Li, Kun; Liu, Nigang; Chen, Zewen; Cui, Jun; Published by: Geophysical Research Letters Published on: 03/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021GL092902 |
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A comparative study on the distributions of incoherent and coherent plasmaspheric hiss Abstract We perform a comparative study on the distributions of incoherent and coherent plasmaspheric hiss, based on the Van Allen Probe data. The statistics show that incoherent hiss ( ∼10–20 pT) is widely distributed in dayside plasmasphere, with peak frequencies below 500 Hz; intense coherent hiss (amplitudes up to 80 pT) occurs in outer plasmasphere of L > 4 (L denotes the L-shell.), whose frequency increases with ambient magnetic field significantly. The Poynting flux analysis indicates that incoherent hiss generally propagates omni-directionally inside the plasmasphere, with features of external sources; the coherent hiss propagates away from the equatorial region in outer plasmasphere and has a reversed direction in inner plasmasphere, indicating two different wave sources by local generation and ducted lightning generated whistler (LGW) respectively. This comparative study helps us to better understand the origination of plasmaspheric hiss. This article is protected by copyright. All rights reserved. He, Zhaoguo; Yu, Jiang; Li, Kun; Liu, Nigang; Chen, Zewen; Cui, Jun; Published by: Geophysical Research Letters Published on: 03/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021GL092902 |
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In situ Observations of Whistler-mode Chorus Waves Guided by Density Ducts Abstract In this paper, we report the proof of the existence of density ducts in the Earth’s magnetosphere by studying in situ observations of whistler-mode chorus waves using NASA’s Van Allen Probe-A data. Chorus waves, originally excited inside the density ducts with wave normal angles (WNAs) smaller than the Gendrin angle at near equator region, are efficiently confined to a limited area inside density ducts (i.e., ducted regions), and remain with small WNAs as they propagate towards high latitudes. The ducted region becomes narrower for the higher-frequency waves. Chorus waves with WNAs larger than the Gendrin angle are not guided by density ducts. Our study reveals that density ducts can effectively control the property and distribution of chorus waves, and may ultimately regulate electron dynamics in the Earth’s or other planetary radiation belts. This article is protected by copyright. All rights reserved. Chen, Rui; Gao, Xinliang; Lu, Quanming; Chen, Lunjin; Tsurutani, Bruce; Li, Wen; Ni, Binbin; Wang, Shui; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA028814 Radiation belt; Chorus wave; density duct; ducted region; Van Allen Probes |
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In situ Observations of Whistler-mode Chorus Waves Guided by Density Ducts Abstract In this paper, we report the proof of the existence of density ducts in the Earth’s magnetosphere by studying in situ observations of whistler-mode chorus waves using NASA’s Van Allen Probe-A data. Chorus waves, originally excited inside the density ducts with wave normal angles (WNAs) smaller than the Gendrin angle at near equator region, are efficiently confined to a limited area inside density ducts (i.e., ducted regions), and remain with small WNAs as they propagate towards high latitudes. The ducted region becomes narrower for the higher-frequency waves. Chorus waves with WNAs larger than the Gendrin angle are not guided by density ducts. Our study reveals that density ducts can effectively control the property and distribution of chorus waves, and may ultimately regulate electron dynamics in the Earth’s or other planetary radiation belts. This article is protected by copyright. All rights reserved. Chen, Rui; Gao, Xinliang; Lu, Quanming; Chen, Lunjin; Tsurutani, Bruce; Li, Wen; Ni, Binbin; Wang, Shui; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA028814 Radiation belt; Chorus wave; density duct; ducted region; Van Allen Probes |
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A Comparison of the Location of the Mid-latitude Trough and Plasmapause Boundary Abstract We have compared the location of the mid-latitude trough observed in two dimensional vertical total electron content (vTEC) maps with four plasmapause boundary models, Radiation Belt Storm Probes observations, and IMAGE EUV observations all mapped to the ionosphere pierce point using the Tsyganenko [1996] magnetic field line model. For this study we examine four events over North America: one just after the 13 October 2012 storm, one during the 20 April 2002 double storm, another during a large substorm on 26 January 2013, and one quiet event on 19 May 2001. We have found that in general, the equatorward edge of the mid-latitude trough is within several degrees in geographic latitude of the mapped model plasmapause boundary location, the plasmapause boundary identified with IMAGE EUV, and the location identified by the Radiation Belt Storm Probes spacecraft. When the mid-latitude trough is mapped to the inner magnetosphere, the observed boundary agrees with the plasmapause boundary models within 2 Earth Radii at nearly all local times in the nightside and the observed mid-latitude boundary is within the uncertainty of the observations at most local times in the nightside. Furthermore, during dynamic solar wind conditions of 20 April 2002, the mid-latitude trough observed in the vTEC maps propagates equatorward as the plasmapause boundary identified with IMAGE EUV moves earthward. Our results indicate that the mid-latitude trough observed within the vTEC maps represents an additional means of identifying the plasmapause boundary location, which could result in improved plasmapause boundary models. This article is protected by copyright. All rights reserved. Weygand, J.M.; Zhelavskaya, I.; Shprits, Y.; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA028213 mid-latitude trough; plasmapause boundary; vTECs; plasmapause models; Van Allen Probes |
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Reconstruction of the Radiation Belts for Solar Cycles 17 – 24 (1933 – 2017) AbstractWe present a reconstruction of the dynamics of the radiation belts from Solar Cycles 17 – 24 which allows us to study how radiation belt activity has varied between the different solar cycles. The radiation belt simulations are produced using the Versatile Electron Radiation Belt (VERB)-3D code. The VERB-3D code simulations incorporate radial, energy, and pitch angle diffusion to reproduce the radiation belts. Our simulations use the historical measurements of Kp (available since Solar Cycle 17, i.e., 1933) to model the evolution radiation belt dynamics between L* = 1 – 6.6. A nonlinear auto regressive network with exogenous inputs (NARX) neural network was trained off GOES 15 measurements (Jan. 2011 – March 2014) and used to supply the upper boundary condition (L* = 6.6) over the course of Solar Cycles 17 – 24 (i.e., 1933 – 2017). Comparison of the model with long term observations of the Van Allen Probes and CRRES demonstrates that our model, driven by the NARX boundary, can reconstruct the general evolution of the radiation belt fluxes. Solar Cycle 24 (Jan 2008 – 2017) has been the least active of the considered solar cycles which resulted in unusually low electron fluxes. Our results show that Solar Cycle 24 should not be used as a representative solar cycle for developing long term environment models. The developed reconstruction of fluxes can be used to develop or improve empirical models of the radiation belts.This article is protected by copyright. All rights reserved. Saikin, A.; Shprits, Y; Drozdov, A; Landis, D.; Zhelavskaya, I.; Cervantes, S.; Published by: Space Weather Published on: 02/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020SW002524 Radiation belts; numerical modeling; Particle acceleration; Magnetosphere: inner; forecasting; Van Allen Probes |
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Determining the Temporal and Spatial Coherence of Plasmaspheric Hiss Waves in the Magnetosphere Abstract Plasmaspheric hiss is one of the most important plasma waves in the Earth s magnetosphere to contribute to radiation belt dynamics by pitch-angle scattering energetic electrons via wave-particle interactions. There is growing evidence that the temporal and spatial variability of wave-particle interactions are important factors in the construction of diffusion-based models of the radiation belts. Hiss amplitudes are thought to be coherent across large distances and on long timescales inside the plasmapause, which means that hiss can act on radiation belt electrons throughout their drift trajectories for many hours. In this study, we investigate both the spatial and temporal coherence of plasmaspheric hiss between the two Van Allen Probes from November 2012 to July 2019. We find ∼3,264 events where we can determine the correlation of wave amplitudes as a function of both spatial distance and time lag in order to study the spatial and temporal coherence of plasmaspheric hiss. The statistical results show that both the spatial and temporal correlation of plasmaspheric hiss decrease with increasing L-shell, and become incoherent at L > ∼4.5. Inside of L = ∼4.5, we find that hiss is coherent to within a spatial extent of up to ∼1,500 km and a time lag up to ∼10 min. We find that the spatial and temporal coherence of plasmaspheric hiss does not depend strongly on the geomagnetic index (AL*) or magnetic local time. We discuss the ramifications of our results with relevance to understanding the global characteristics of plasmaspheric hiss waves and their role in radiation belt dynamics. Zhang, Shuai; Rae, Jonathan; Watt, Clare; Degeling, Alexander; Tian, Anmin; Shi, Quanqi; Shen, Xiao-Chen; Smith, Andy; Wang, Mengmeng; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA028635 |
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Periodic Rising and Falling Tone ECH Waves from Van Allen Probes Observations AbstractElectron cyclotron harmonic (ECH) waves are known to precipitate plasma sheet electrons into the upper atmosphere and generate diffuse aurorae. In this study, we report quasi-periodic rising (3 events) and falling tone (22 events) ECH waves observed by Van Allen Probes, and evaluate their properties. These rising and falling tone ECH waves prefer to occur during quiet geomagnetic conditions over the dusk to midnight sector in relatively high-density (10–80 cm-3) regions. Their repetition periods increase with increasing L shell at L < 6, ranging from ∼60 to 110 s. The wave element duration varies from 10 s to 130 s peaking at ∼40 s and the chirping rate peaks at ∼50 (∼-50) Hz/s for rising (falling) tones. Our findings reveal intriguing features of the ECH wave properties, which provide new insights into their generation and potential effects on electron precipitation. Shen, Xiao-Chen; Li, Wen; Ma, Qianli; Published by: Geophysical Research Letters Published on: 02/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020GL091330 ECH wave; falling tone; rising tone; Magnetosphere; plasma wave; Van Allen Probes |
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A combined neural network- and physics-based approach for modeling plasmasphere dynamics AbstractIn recent years, feedforward neural networks (NNs) have been successfully applied to reconstruct global plasmasphere dynamics in the equatorial plane. These neural network-based models capture the large-scale dynamics of the plasmasphere, such as plume formation and erosion of the plasmasphere on the nightside. However, their performance depends strongly on the availability of training data. When the data coverage is limited or non-existent, as occurs during geomagnetic storms, the performance of NNs significantly decreases, as networks inherently cannot learn from the limited number of examples. This limitation can be overcome by employing physics-based modeling during strong geomagnetic storms. Physics-based models show a stable performance during periods of disturbed geomagnetic activity, if they are correctly initialized and configured. In this study, we illustrate how to combine the neural network- and physics-based models of the plasmasphere in an optimal way by using data assimilation. The proposed approach utilizes advantages of both neural network- and physics-based modeling and produces global plasma density reconstructions for both quiet and disturbed geomagnetic activity, including extreme geomagnetic storms. We validate the models quantitatively by comparing their output to the in-situ density measurements from RBSP-A for an 18-month out-of-sample period from 30 June 2016 to 01 January 2018, and computing performance metrics. To validate the global density reconstructions qualitatively, we compare them to the IMAGE EUV images of the He+ particle distribution in the Earth s plasmasphere for a number of events in the past, including the Halloween storm in 2003.This article is protected by copyright. All rights reserved. Zhelavskaya, I.; Aseev, N.; Shprits, Y; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA028077 plasmasphere; plasma density; neural networks; data assimilation; Kalman Filter; Machine learning; Van Allen Probes |
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Observations of Particle Loss due to Injection-Associated EMIC Waves AbstractWe report on observations of electromagnetic ion cyclotron (EMIC) waves and their interactions with injected ring current particles and high energy radiation belt electrons. The magnetic field experiment aboard the twin Van Allen Probes spacecraft measured EMIC waves near L = 5.5 − 6. Particle data from the spacecraft show that the waves were associated with particle injections. The wave activity was also observed by a ground-based magnetometer near the spacecraft geomagnetic footprint over a more extensive temporal range. Phase space density (PSD) profiles, calculated from directional differential electron flux data from Van Allen Probes, show that there was a significant energy-dependent relativistic electron dropout over a limited L-shell range during and after the EMIC wave activity. In addition, the NOAA spacecraft observed relativistic electron precipitation associated with the EMIC waves near the footprint of the Van Allen Probes spacecraft. The observations suggest EMIC wave-induced relativistic electron loss in the radiation belt. Kim, Hyomin; Schiller, Quintin; Engebretson, Mark; Noh, Sungjun; Kuzichev, Ilya; Lanzerotti, Louis; Gerrard, Andrew; Kim, Khan-Hyuk; Lessard, Marc; Spence, Harlan; Lee, Dae-Young; Matzka, Jürgen; Fromm, Tanja; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA028503 EMIC waves; ring current; Radiation belt; wave particle interaction; injection; Particle precipitation; Van Allen Probes |
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AbstractThe two Van Allen Probes simultaneously recorded a coherently modulated quasiperiodic (QP) emission that persisted for 3 hours. The magnetic field pulsation at the locations of the two satellites showed a substantial difference, and their frequencies were close to but did not exactly match the repetition frequency of QP emissions for most of the time, suggesting that those coherent QP emissions probably originated from a common source, which then propagated over a broad area in the magnetosphere. The QP emissions were amplified by local anisotropic electron distributions, and their large-scale amplitudes were modulated by the plasma density. A novel observation of this event is that chorus waves at frequencies above QP emissions exhibit a strong correlation with QP emissions. Those chorus waves intensified when the QP emissions reach their peak frequency. This indicates that embryonic QP emissions may be critical for its own intensification as well as chorus waves under certain circumstances. The low-earth-orbit POES satellite observed enhanced energetic electron precipitation in conjunction with the Van Allen Probes, providing direct evidence that QP emissions precipitate energetic electrons into the atmosphere. This scenario is quantitatively confirmed by our quasilinear diffusion simulation results. Li, Jinxing; Bortnik, Jacob; Ma, Qianli; Li, Wen; Shen, Xiaochen; Nishimura, Yukitoshi; An, Xin; Thaller, Scott; Breneman, Aaron; Wygant, John; Kurth, William; Hospodarsky, George; Hartley, David; Reeves, Geoffrey; Funsten, Herbert; Blake, Bernard; Spence, Harlan; Baker, Daniel; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA028484 quasiperiodic emissions; electron precipitation; Radiation belt; chorus waves; Van Allen Probes; ULF wave |
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Using seven years of data from the HOPE instrument on the Van Allen Probes, equatorial pitch angle distributions (PADs) of 1 – 50 keV electrons in Earth s inner magnetosphere are investigated statistically. An empirical model of electron equatorial PADs as a function of radial distance, magnetic local time, geomagnetic activity, and electron energy is constructed using the method of Legendre polynomial fitting. Model results show that most equatorial PADs of 1 – 10s of keV electrons in Earth s inner magnetosphere are pancake PADs, and the lack of butterfly PADs is likely due to their relatively flat or positive flux radial gradients at higher altitudes. During geomagnetically quiet times, more anisotropic distributions of 1 – 10s of keV electrons at dayside than nightside are observed, which could be responsible for moderate chorus wave activities at dayside during quiet times as reported by previous studies. During active times, the anisotropy of 1 – 10s of keV electrons significantly enhances, consistent with the enhanced chorus wave activity during active times and suggesting the critical role of 1 – 10s of keV electrons in generating chorus waves in Earth s inner magnetosphere. Different enhanced anisotropy patterns of different energy electrons are also observed during active times: at R>∼4 RE, keV electrons are more anisotropic at dawn to noon, while 10s of keV electrons have larger anisotropy at midnight to dawn. These differences, combined with the statistical distribution of chorus waves shown in previous studies, suggest the differential roles of electrons with different energies in generating chorus waves with different properties. This article is protected by copyright. All rights reserved. Zhao, H.; Friedel, R.; Chen, Y.; Baker, D.; Li, X.; Malaspina, D.; Larsen, B.; Skoug, R.; Funsten, H.; Reeves, G.; Boyd, A.; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028322 Pitch angle distribution; energetic electrons; Earth s inner magnetosphere; Anisotropy; Chorus wave; statistical analysis; Van Allen Probes |
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Magnetospheric ELF/VLF waves have an important role in the acceleration and loss of energetic electrons in the magnetosphere through wave-particle interaction. It is necessary to understand the spatiotemporal development of magnetospheric ELF/VLF waves to quantitatively estimate this effect of wave-particle interaction, a global process not yet well understood. We investigated spatiotemporal development of magnetospheric ELF/VLF waves using 6 PWING ground-based stations at subauroral latitudes, ERG and RBSP satellites, POES/MetOp satellites, and the RAM-SCB model, focusing on the March and November 2017 storms driven by corotating interaction regions in the solar wind. Our results show that the ELF/VLF waves are enhanced over a longitudinal extent from midnight to morning and dayside associated with substorm electron injections. In the main to early storm recovery phase, we observe continuous ELF/VLF waves from ∼0 to ∼12 MLT in the dawn sector. This wide extent seems to be caused by frequent occurrence of substorms. The wave region expands eastward in association with the drift of source electrons injected by substorms from the nightside. We also observed dayside ELF/VLF wave enhancement, possibly driven by magnetospheric compression by solar wind, over an MLT extent of at least 5 hours. Ground observations tend not to observe ELF/VLF waves in the post-midnight sector, although other methods clearly show the existence of waves. This is possibly due to Landau damping of the waves, the absence of the plasma density duct structure, and/or enhanced auroral ionization of the ionosphere in the post-midnight sector. Takeshita, Yuhei; Shiokawa, Kazuo; Miyoshi, Yoshizumi; Ozaki, Mitsunori; Kasahara, Yoshiya; Oyama, Shin-Ichiro; Connors, Martin; Manninen, Jyrki; Jordanova, Vania; Baishev, Dmitry; Oinats, Alexey; Kurkin, Vladimir; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028216 ELF/VLF wave; Arase; Van Allen Probes; PWING; RAM-SCB simulation; subauroral latitudes |
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Results from the NASA Van Allen Probes mission indicate extensive observations of mirror/drift-mirror (M/D-M hereafter) unstable plasma regions in the nightside inner magnetosphere. Said plasmas lie on the threshold between the kinetic and frozen-in plasma regimes and have favorable conditions for the formation of M/D-M modes and subsequent ultra-low frequency (ULF) wave signatures in the surrounding plasma. We present the results of a climatological analysis of plasma-γ (anisotropy measure) and total plasma-β (ratio of particle to magnetic field pressure) in regard to the satisfaction of instability conditions on said M/D-M modes under bi-Maxwellian distribution assumption, and ascertain the most likely region for such plasmas to occur. Our results indicate a strong preference for the pre-midnight sector of the nightside magnetosphere, with events ranging in time scales from half a minute (roughly 200 km in scale size) to several hours (multiple Earth radii). The statistical distribution of these plasma regions explicitly identifies the source region of “storm time Pc5 ULF waves” and suggests an alternative mechanism for their generation in the nightside inner magnetosphere. Cooper, M.; Gerrard, A.; Lanzerotti, L.; Soto-Chavez, A.; Kim, H.; Kuzichev, I.; Goodwin, L.; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028773 Mirror mode-unstable plasma; ULF waves; magnetotail injections; inner magnetosphere; Van Allen Probes |
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TWINS Observations of the Dynamics of Ring Currents Ion Spectra on 17th March and 7th October 2015 Direct comparisons between RBSP (Van Allen Probes or Radiation Belt Storm Probes) and TWINS (Two Wide-angle Imaging Neutral-atom Spectrometers) for the main phase of two storms, 17th March and 7th October 2015, showed agreement between the in–situ ion measurements and the ion spectra from the deconvolved energetic neutral atom (ENA) measurements, except when O+ ions were significant. Spatial evolution of individual energy peaks in the ion spectra are studied using TWINS data. O+ ions are seen to result in intense peaks at 5–10 keV/amu in the TWINS ion spectra. These ion populations are confined to low L shells (L < 5) and localized in the pre midnight sector. When H+ ions are significant, the low energy peaks ( < 25 keV/amu) are found to be less intense than the high energy peaks ( > 25 keV/amu), located at L > 4 and localized within the premidnight sector. During times of rapidly varying AE indices, two spatially distinct peaks, between 3–5RE and 6–8RE, are observed for the ions with energies > 25 keV/amu. The outer peak appears for a few hours and fades while the inner peak is more stable. These structures are found to be consistent with particle injections observed in the RBSP data. When double peaked structures are swept off, low energy ions accumulate in the pre midnight to midnight sectors whereas high energy ions are located pre to post midnight sectors. Faster drift orbits of > 25 keV/amu ions may cause this kind of distribution.This article is protected by copyright. All rights reserved. Shekhar, S.; Perez, J.; Ferradas, C.; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028156 Ring Currents; Magnetosphere; energy dependent drift; ion nose; Substorm Injections; Ion Spectra; Van Allen Probes |
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Ring current decay during storm recovery phase may be affected by different loss processes. In this study, we have investigated the lifetimes of ring current ions (H+ and O+) of energies from 1 keV to several hundred keV at L shell from 3 to 6 during the storm recovery phase through a statistical survey. The observational data of 48 geomagnetic storms from March 2013 to May 2019 are collected based on Van Allen Probe observations. We find that (1) the observed lifetimes of H+ and O+ in general increase with L shell and (2) the lifetimes of H+ is short than that of O+ when E < ∼50 keV while the situation is reversed when E > ∼50 keV. In addition, we have made use of the charge exchange theory, combined with previous experimental results on the charge exchange cross section and two distribution models of neutral hydrogen atoms in the exosphere, so as to directly estimate the ring current ions decay caused by charge exchange mechanism only. Through the comparison between the model predictions of charge exchange lifetime and the observed lifetimes, we find that (3) the observed lifetimes are in general consistent with model results, which confirms that charge exchange is a dominant loss mechanism of ring current ions during storm recovery phase. Chen, Ao; Yue, Chao; Chen, HongFei; Zong, Qiugang; Fu, Suiyan; Wang, Yongfu; Ren, Jie; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028500 charge exchange; lifetime; ring current decay; Van Allen Probes |
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Ring current decay during storm recovery phase may be affected by different loss processes. In this study, we have investigated the lifetimes of ring current ions (H+ and O+) of energies from 1 keV to several hundred keV at L shell from 3 to 6 during the storm recovery phase through a statistical survey. The observational data of 48 geomagnetic storms from March 2013 to May 2019 are collected based on Van Allen Probe observations. We find that (1) the observed lifetimes of H+ and O+ in general increase with L shell and (2) the lifetimes of H+ is short than that of O+ when E < ∼50 keV while the situation is reversed when E > ∼50 keV. In addition, we have made use of the charge exchange theory, combined with previous experimental results on the charge exchange cross section and two distribution models of neutral hydrogen atoms in the exosphere, so as to directly estimate the ring current ions decay caused by charge exchange mechanism only. Through the comparison between the model predictions of charge exchange lifetime and the observed lifetimes, we find that (3) the observed lifetimes are in general consistent with model results, which confirms that charge exchange is a dominant loss mechanism of ring current ions during storm recovery phase. Chen, Ao; Yue, Chao; Chen, HongFei; Zong, Qiugang; Fu, Suiyan; Wang, Yongfu; Ren, Jie; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028500 charge exchange; lifetime; ring current decay; Van Allen Probes |
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Fast magnetosonic (MS) waves are excited by the ring distribution of energetic protons preferably when the ring velocity (VR) is within a factor of 2 above or below the local Alfvén speed (VA). Here we examine the global distributions of MS waves and proton rings with 0.5VA ≤ VR ≤ 2VA based on 64 months (from October 25, 2012 to February 28, 2018) of Van Allen Probes observations. The statistical results show that MS waves are present over a broad region of L = 1.2–6.0 and 00–24 magnetic local time (MLT), with a higher occurrence rate at L = 2.5–5.5 on the dayside. Proton rings occur mainly on the dayside of L > 5.0. During active geomagnetic periods, both MS waves and proton rings occur more frequently and extend to low L-shells. The current results provide the further observational evidence that MS waves can be excited by proton rings at a distant region and propagate to low L-shells. Zhou, Qinghua; Jiang, Zheng; Yang, Chang; He, Yihua; Liu, Si; Xiao, Fuliang; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028354 Fast Magnetosonic Waves; global occurrences; proton ring distribution; Radiation belt; Van Allen Probe observation; Van Allen Probes |
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Statistical Study of Chorus Modulations by Background Magnetic Field and Plasma Density In this study, we use observations of THEMIS and Van Allen Probes to statistically study the modulations of chorus emissions by variations of background magnetic field and plasma density in the ultra low frequency range. The modulation events are identified automatically and divided into three types according to whether the chorus intensity correlates to the variations of the magnetic field only (Type B), plasma density only (Type N), or both (Type NB). For the THEMIS observations, the occurrences of the Types B and N are larger than Type NB, while for the Van Allen Probes observations, most events are of Type N. The chorus intensity is mostly correlated to the magnetic field strength negatively and plasma density positively. The chorus intensity tends to increase when the magnitude of the magnetic field perturbation increases, but little dependence on plasma density perturbation amplitude is found. Xia, Zhiyang; Chen, Lunjin; Li, Wen; Published by: Geophysical Research Letters Published on: 11/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020GL089344 |
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Alpha Transmitter Signal Reflection and Triggered Emissions Russian Alpha radio navigation system (RSDN-20) emits F1 = 11.9 kHz signals into the magnetosphere which propagate as whistler mode waves. Observed by waveform continuous burst mode from Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) on Van Allen Probes, a case is presented and featured with ducted propagation, multiple reflections, and triggered emissions. Both risers and fallers appear in the triggered emissions. We use a ray tracing method to demonstrate ducted propagation, which has a similar wave normal angle near 150° as the observation. The arrival time of reflected signals is estimated using propagation analysis and compared with the observed signal arrival time. To test the nonlinear cyclotron resonance theory, the interaction region scale and the order of chirping rate in triggered emission are estimated. The estimated interaction region scale of MLAT = −3° is smaller than the observed MLAT = −6°. The discrepancy may be caused by the parallel propagation assumption and background field model. Gu, Wenyao; Chen, Lunjin; Xia, Zhiyang; An, Xin; Horne, Richard; Published by: Geophysical Research Letters Published on: 11/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020GL090165 VLF transmitter; ducted propagation; triggered emission; Van Allen Probes |
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On 31 January 2016, the flux of >2 MeV electrons observed by Geostationary Operational Environmental Satellite (GOES)-13 dropped to the background level during a minor storm main phase (−48 nT). Then, a second storm (−53 nT) occurred on 2 February; during the 3 days after its main phase, the flux remained at background level. Using data from various instruments on the GOES, Polar Operational Environmental Satellites (POES), Radiation Belt Storm Probes (RBSP), Meteor-M2, and Fengyun-series spacecraft, we study this long-term dropout of MeV electrons during two sequential storms of similar magnitude under lightly disturbed solar wind conditions. Observations from low-altitude satellites show that the fluxes decreased first at higher L-shells and then gradually propagated inward. Moreover, the fluxes were almost completely lost and dropped to the background level at L > 5, while the fluxes at 4 < L < 5 were partly lost, as observed by RBSP and low-altitude satellites. Finally, observations show that on 5 February, only the fluxes at L > 5.5 recovered, while the fluxes at 4 < L < 5 did not return to the prestorm levels. These observations indicate that the loss and recovery processes developed first at higher L-shells. Phase space density (PSD) analysis shows that radial outward diffusion was the main reason for the dropout at higher L-shells. Regarding electron enhancement, stronger inward diffusion was accompanied by ultra-low-frequency (ULF) wave activities at higher L-shells, and chorus waves observed at outer L-shells provided conditions for relativistic electron flux recovery to the prestorm levels. Wu, H.; Chen, T.; Kalegaev, V.; Panasyuk, M.; Vlasova, N.; Duan, S.; Zhang, X.; He, Z.; Luo, J.; Wang, C.; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028098 Radiation belt; relativistic electron dropout; Geomagnetic storm; Van Allen Probes |
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On 31 January 2016, the flux of >2 MeV electrons observed by Geostationary Operational Environmental Satellite (GOES)-13 dropped to the background level during a minor storm main phase (−48 nT). Then, a second storm (−53 nT) occurred on 2 February; during the 3 days after its main phase, the flux remained at background level. Using data from various instruments on the GOES, Polar Operational Environmental Satellites (POES), Radiation Belt Storm Probes (RBSP), Meteor-M2, and Fengyun-series spacecraft, we study this long-term dropout of MeV electrons during two sequential storms of similar magnitude under lightly disturbed solar wind conditions. Observations from low-altitude satellites show that the fluxes decreased first at higher L-shells and then gradually propagated inward. Moreover, the fluxes were almost completely lost and dropped to the background level at L > 5, while the fluxes at 4 < L < 5 were partly lost, as observed by RBSP and low-altitude satellites. Finally, observations show that on 5 February, only the fluxes at L > 5.5 recovered, while the fluxes at 4 < L < 5 did not return to the prestorm levels. These observations indicate that the loss and recovery processes developed first at higher L-shells. Phase space density (PSD) analysis shows that radial outward diffusion was the main reason for the dropout at higher L-shells. Regarding electron enhancement, stronger inward diffusion was accompanied by ultra-low-frequency (ULF) wave activities at higher L-shells, and chorus waves observed at outer L-shells provided conditions for relativistic electron flux recovery to the prestorm levels. Wu, H.; Chen, T.; Kalegaev, V.; Panasyuk, M.; Vlasova, N.; Duan, S.; Zhang, X.; He, Z.; Luo, J.; Wang, C.; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028098 Radiation belt; relativistic electron dropout; Geomagnetic storm; Van Allen Probes |
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Precipitation Loss of Radiation Belt Electrons by Two-Band Plasmaspheric Hiss Waves A two-band plasmaspheric hiss consisting of a low-frequency band (normal hiss with the frequency below 2 kHz) and a high-frequency band (locally generated hiss with the frequency up to 10 kHz) was observed on 6 January 2014 by the Van Allen Probes (He et al., 2019, https://doi.org/10.1029/2018GL081578). The electron scattering effect driven by this kind of two-band plasmaspheric hiss is evaluated by the quasi-linear diffusion simulation for the first time. Realistic wave characteristic parameters of the two-band plasmaspheric hiss from statistics are adopted for driving our simulation. The pitch angle diffusion rates of the low-frequency band hiss present a “gap” with minimum magnitude at pitch angle αe ∼ 70°, a condition not favoring the transport of large pitch angle electrons toward the loss cone. However, the diffusion rates of the high-frequency band hiss have peak values at αe ∼ 70°, filling up for the “gap” of the low-frequency hiss diffusion rates. The realistic wave-driven electron PSD evolutions demonstrate that the collaborated effect of the low-frequency band and high-frequency band hiss can cause significant precipitation losses of energetic electrons of tens to several hundred keV within 2 days. He, Zhaoguo; Yan, Qi; Zhang, Xiaoping; Yu, Jiang; Ma, Yonghui; Cao, Yong; Cui, Jun; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028157 two-band hiss; radiation belt electron; loss; Van Allen Probes |
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The local generation of high-frequency plasmaspheric hiss has recently been reported by a case study (He et al., 2019, https://doi.org/10.1029/2018GL081578). In this research, we perform statistics of global distributions of the locally generated high-frequency plasmaspheric hiss (LHFPH) for different levels of substorm activity, using 6-year observational data from Van Allen Probes. The statistics find that the LHFPH amplitude presents a strong magnetic local time (MLT) asymmetry and highly depends on substorm activity, and intense LHFPHs occur from predawn to dusk side and can penetrate into inner plasmasphere of L ∼ 3 during AE > 300 nT. The statistical LHFPH spectrum shows that its frequency increases with the ambient magnetic field, with peaked wave powers between 0.1 and 0.5 fce. Based on the statistical properties of LHFPH, we evaluate the electron diffusion coefficients using quasi-linear theory. Those results suggest that electron pitch angle scattering driven by LHFPH could be a potential mechanism for the precipitation loss of suprathermal electrons of 0.1 keV to tens of keV, which can impact the ionization and chemical changes in the upper atmosphere. He, Zhaoguo; Yu, Jiang; Chen, Lunjin; Xia, Zhiyang; Wang, Wenrui; Li, Kun; Cui, Jun; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028526 |
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The local generation of high-frequency plasmaspheric hiss has recently been reported by a case study (He et al., 2019, https://doi.org/10.1029/2018GL081578). In this research, we perform statistics of global distributions of the locally generated high-frequency plasmaspheric hiss (LHFPH) for different levels of substorm activity, using 6-year observational data from Van Allen Probes. The statistics find that the LHFPH amplitude presents a strong magnetic local time (MLT) asymmetry and highly depends on substorm activity, and intense LHFPHs occur from predawn to dusk side and can penetrate into inner plasmasphere of L ∼ 3 during AE > 300 nT. The statistical LHFPH spectrum shows that its frequency increases with the ambient magnetic field, with peaked wave powers between 0.1 and 0.5 fce. Based on the statistical properties of LHFPH, we evaluate the electron diffusion coefficients using quasi-linear theory. Those results suggest that electron pitch angle scattering driven by LHFPH could be a potential mechanism for the precipitation loss of suprathermal electrons of 0.1 keV to tens of keV, which can impact the ionization and chemical changes in the upper atmosphere. He, Zhaoguo; Yu, Jiang; Chen, Lunjin; Xia, Zhiyang; Wang, Wenrui; Li, Kun; Cui, Jun; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028526 |