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Found 435 entries in the Bibliography.
Showing entries from 1 through 50
| 2021 |
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Inter-calibrated Measurements of Intense Whistlers by Arase and Van Allen Probes Abstract Measurements of electromagnetic waves in space plasmas are an important tool for our understanding of physical processes in this environment. Inter-calibration of data from different spacecraft missions is necessary for combining their measurements in empirical models or in case studies. We show results collected during a close conjunction of the Van Allen Probes and Arase spacecraft. The inter-calibration is based on a fortuitous case of common observations of strong whistlers at frequencies between a few hundred hertz and 10 kHz, which are generated by the same lightning strokes and which propagate along very similar paths to the two spacecraft. Measured amplitudes of the magnetic field fluctuations are the same within ∼14\% precision of our analysis, corresponding to 1.2 dB. Currently archived electric field measurements show twice larger amplitudes on Arase compared to Van Allen Probes but they start to match within ∼33\% precision (2.5 dB) once the newest results on the interface of the antennas to the surrounding plasma are included in the calibration procedures. Ray tracing simulations help us to build a consistent scenario of wave propagation to both spacecraft reflected by a successful inter-calibration of the polarization and propagation parameters obtained from multicomponent measurements. We succeed in linking the spacecraft observations to localizations of lightning return strokes by two different ground based networks which independently verify the correctness of the Universal Time tags of waveform measurements by both spacecraft missions, with an uncertainty better than 10 ms. This article is protected by copyright. All rights reserved. Santolik, O.; Miyoshi, Y.; Kolmašová, I.; Matsuda, S.; Hospodarsky, G.; Hartley, D.; Kasahara, Y.; Kojima, H.; Matsuoka, A.; Shinohara, I.; Kurth, W.; Kletzing, C.; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021JA029700 calibration of measeurements of electromagnetic waves; Whistlers; ducts; Van Allen Probes |
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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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Abstract We report on the relationship between a pulsating aurora and a relativistic electron microburst using simultaneous observations of ground-based fast auroral imagers with the FIREBIRD-� � CubeSat for the first time. We conducted a detailed analysis of an event on October 8, 2018 and found that the occurrence of the pulsating aurora with internal modulations corresponds to the flux enhancement of electrons with energy ranging from ∼220 keV to >1 MeV detected with Flight Unit 4, one of FIREBIRD’s CubeSat, with a time delay of ∼585 ms. Combining of this time delay result and time of flight model, we suggest that the theory the pulsating aurora and the microburst occur due to the chorus waves at different latitudes along the same field-line by Miyoshi et al. (2020). Kawamura, Miki; Sakanoi, Takeshi; Fukizawa, Mizuki; Miyoshi, Yoshizumi; Hosokawa, Keisuke; Tsuchiya, Fuminori; Katoh, Yuto; Ogawa, Yasunobu; Asamura, Kazushi; Saito, Shinji; Spence, Harlan; Johnson, Arlo; Oyama, Shin’ichiro; Brändström, Urban; Published by: Geophysical Research Letters Published on: 09/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021GL094494 pulsating aurora; Microbursts; chorus waves; Van Allen Probes |
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Plain Language Summary The plasmasphere is the region filled with cold, dense ionized gas in geospace. The ionized gas mainly consists in protons, helium ions, oxygen ions and electrons, which come from Earth’s ionosphere and fill in magnetic flux tubes. The density distribution of the ionized gas along the flux tube provides important information to understand how the ions and electrons have been supplied from the ionosphere. Many satellites fly in the equatorial plane, hence, do not provide information on the electron density along the field. The RBSP and the Arase satellites have different inclinations and sometimes they simultaneously fly near the equator and off the equator on the same magnetic field line. Using electron densities observed by these satellites during the 7 Sep 2017 storm, we successfully estimated the electron density distribution along of the field lines inside the partially refilled plasmasphere, outside of the plasmasphere and in the tail-like structure called a plume. Obana, Yuki; Miyashita, Yukinaga; Maruyama, Naomi; Shinbori, Atsuki; Nosé, Masahito; Shoji, Masafumi; Kumamoto, Atsushi; Tsuchiya, Fuminori; Matsuda, Shoya; Matsuoka, Ayako; Kasahara, Yoshiya; Miyoshi, Yoshizumi; Shinohara, Iku; Kurth, William; Smith, Charles; MacDowall, Robert; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA029073 plasmasphere; inner magnetosphere; Arase satellite; Van Allen Probes satellite; simultaneous observation; Geomagnetic storm; 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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Superposed Epoch Analysis of Dispersionless Particle Injections Inside Geosynchronous Orbit AbstractDispersionless injections, involving sudden, simultaneous flux enhancements of energetic particles over some broad range of energy, are a characteristic signature of the particles that are experiencing a significant acceleration and/or rapid inward transport at the leading edge of injections. We have statistically analyzed data from Van Allen Probes (also known as RBSP ) to reveal where the proton (H+) and electron (e–) dispersionless injections occur preferentially inside geosynchronous orbit and how they develop depending on local magnetic field changes. By surveying measurements of RBSP during four tail seasons in 2012–2019, we have identified 171 dispersionless injection events. Most of the events, which are accompanied by local magnetic dipolarizations, occur in the dusk-to-midnight sector, regardless of particle species. Out of the selected 171 events, 75 events exhibit dispersionless injections of both H+ and e–, which occur within 2 minutes of each other. With only three exceptions, the both-species injection events are further divided into two main subgroups: One is the H+ preceding e– events with a time offset of tens of seconds between H+ and e–, and the other the concurrent H+ and e– events without any time offset. Our superposed epoch results raise the intriguing possibility that the presence or absence of a pronounced negative dip in the local magnetic field ahead of the concurrent sharp dipolarization determines which of the two subgroups will occur. The difference between the two subgroups may be explained in terms of the dawn-dusk asymmetry of localized diamagnetic perturbations ahead of a deeply-penetrating dipolarization front.This article is protected by copyright. All rights reserved. Motoba, T.; Ohtani, S.; Gkioulidou, M.; Ukhorskiy, A; Lanzerotti, L.; Claudepierre, S.; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021JA029546 Dispersionless injections; substorms; inner magnetosphere; Van Allen Probes |
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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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Electromagnetic power of lightning superbolts from Earth to space Lightning superbolts are the most powerful and rare lightning events with intense optical emission, first identified from space. Superbolt events occurred in 2010-2018 could be localized by extracting the high energy tail of the lightning stroke signals measured by the very low frequency ground stations of the World-Wide Lightning Location Network. Here, we report electromagnetic observations of superbolts from space using Van Allen Probes satellite measurements, and ground measurements, and with two events measured both from ground and space. From burst-triggered measurements, we compute electric and magnetic power spectral density for very low frequency waves driven by superbolts, both on Earth and transmitted into space, demonstrating that superbolts transmit 10-1000 times more powerful very low frequency waves into space than typical strokes and revealing that their extreme nature is observed in space. We find several properties of superbolts that notably differ from most lightning flashes; a more symmetric first ground-wave peak due to a longer rise time, larger peak current, weaker decay of electromagnetic power density in space with distance, and a power mostly confined in the very low frequency range. Their signal is absent in space during day times and is received with a long-time delay on the Van Allen Probes. These results have implications for our understanding of lightning and superbolts, for ionosphere-magnetosphere wave transmission, wave propagation in space, and remote sensing of extreme events. Ripoll, J.-F.; Farges, T.; Malaspina, D.; Cunningham, G.; Lay, E.; Hospodarsky, G.; Kletzing, C.; Wygant, J.; Published by: Nature Communications Published on: 06/2021 YEAR: 2021 DOI: https://doi.org/10.1038/s41467-021-23740-6 |
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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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The Link between Wedge-like and Nose-like Ion Spectral Structures in the Inner Magnetosphere AbstractThe wedge-like and nose-like ion spectral structures, named after their characteristic shapes in the energy-time spectrograms, appear to be distinctively different structures in the Earth s inner magnetosphere. Here we present a case study with conjugate observations from the Arase spacecraft and the twin Van Allen Probes on July 1 and 2, 2017, which displayed the characteristic signatures of the wedge-like and nose-like ion structures, respectively. When the spacecraft nearly intersected at L =2.8, the two structures overlapped with enhanced ion fluxes in the energy range of 1-10 keV. These observations suggest that the wedge-like and nose-like spectral signatures are merely the manifestations of one single structure along different spacecraft trajectories. This finding is further validated by the reproduction of both structures from a particle-tracing model, which also indicates their formation processes associated with the intermittent substorm injections in the nightside magnetosphere. Ren, Jie; Zhou, Xu-Zhi; Zong, Qiu-Gang; Yue, Chao; Fu, Sui-Yan; Miyoshi, Y.; Zhang, Xiao-Xin; Asamura, K.; Shinohara, I.; Published by: Geophysical Research Letters Published on: 06/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021GL093930 |
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Evening side EMIC waves and related proton precipitation induced by a substorm Abstract We present the results of a multi-point and multi-instrument study of EMIC waves and related energetic proton precipitation during a substorm. We analyze the data from Arase (ERG) and Van Allen Probes (VAP) A and B spacecraft for an event of 16-17 UT on 01 December 2018. VAP-A detected an almost dispersionless injection of energetic protons related to the substorm onset in the night sector. Then the proton injection was detected by VAP-B and further by Arase, as a dispersive enhancement of energetic proton flux. The proton flux enhancement at every spacecraft coincided with the EMIC wave enhancement or appearance. This data shows the excitation of EMIC waves first inside an expanding substorm wedge and then by a drifting cloud of injected protons. Low-orbiting NOAA/POES and MetOp satellites observed precipitation of energetic protons nearly conjugate with the EMIC wave observations in the magnetosphere. The proton pitch-angle diffusion coefficient and the strong diffusion regime index were calculated based on the observed wave, plasma and magnetic field parameters. The diffusion coefficient reaches a maximum at energies corresponding well to the energy range of the observed proton precipitation. The diffusion coefficient values indicated the strong diffusion regime, in agreement with the equality of the trapped and precipitating proton flux at the low-Earth orbit. The growth rate calculations based on the plasma and magnetic field data from both VAP and Arase spacecraft indicated that the detected EMIC waves could be generated in the region of their observation or in its close vicinity. Yahnin, A.; Popova, T.; Demekhov, A.; Lubchich, A.; Matsuoka, A.; Asamura, K.; Miyoshi, Y.; Yokota, S.; Kasahara, S.; Keika, K.; Hori, T.; Tsuchiya, F.; Kumamoto, A.; Kasahara, Y.; Shoji, M.; Kasaba, Y.; Nakamura, S.; Shinohara, I.; Kim, H.; Noh, S.; Raita, T.; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA029091 |
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Evening side EMIC waves and related proton precipitation induced by a substorm Abstract We present the results of a multi-point and multi-instrument study of EMIC waves and related energetic proton precipitation during a substorm. We analyze the data from Arase (ERG) and Van Allen Probes (VAP) A and B spacecraft for an event of 16-17 UT on 01 December 2018. VAP-A detected an almost dispersionless injection of energetic protons related to the substorm onset in the night sector. Then the proton injection was detected by VAP-B and further by Arase, as a dispersive enhancement of energetic proton flux. The proton flux enhancement at every spacecraft coincided with the EMIC wave enhancement or appearance. This data shows the excitation of EMIC waves first inside an expanding substorm wedge and then by a drifting cloud of injected protons. Low-orbiting NOAA/POES and MetOp satellites observed precipitation of energetic protons nearly conjugate with the EMIC wave observations in the magnetosphere. The proton pitch-angle diffusion coefficient and the strong diffusion regime index were calculated based on the observed wave, plasma and magnetic field parameters. The diffusion coefficient reaches a maximum at energies corresponding well to the energy range of the observed proton precipitation. The diffusion coefficient values indicated the strong diffusion regime, in agreement with the equality of the trapped and precipitating proton flux at the low-Earth orbit. The growth rate calculations based on the plasma and magnetic field data from both VAP and Arase spacecraft indicated that the detected EMIC waves could be generated in the region of their observation or in its close vicinity. Yahnin, A.; Popova, T.; Demekhov, A.; Lubchich, A.; Matsuoka, A.; Asamura, K.; Miyoshi, Y.; Yokota, S.; Kasahara, S.; Keika, K.; Hori, T.; Tsuchiya, F.; Kumamoto, A.; Kasahara, Y.; Shoji, M.; Kasaba, Y.; Nakamura, S.; Shinohara, I.; Kim, H.; Noh, S.; Raita, T.; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA029091 |
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Evening side EMIC waves and related proton precipitation induced by a substorm Abstract We present the results of a multi-point and multi-instrument study of EMIC waves and related energetic proton precipitation during a substorm. We analyze the data from Arase (ERG) and Van Allen Probes (VAP) A and B spacecraft for an event of 16-17 UT on 01 December 2018. VAP-A detected an almost dispersionless injection of energetic protons related to the substorm onset in the night sector. Then the proton injection was detected by VAP-B and further by Arase, as a dispersive enhancement of energetic proton flux. The proton flux enhancement at every spacecraft coincided with the EMIC wave enhancement or appearance. This data shows the excitation of EMIC waves first inside an expanding substorm wedge and then by a drifting cloud of injected protons. Low-orbiting NOAA/POES and MetOp satellites observed precipitation of energetic protons nearly conjugate with the EMIC wave observations in the magnetosphere. The proton pitch-angle diffusion coefficient and the strong diffusion regime index were calculated based on the observed wave, plasma and magnetic field parameters. The diffusion coefficient reaches a maximum at energies corresponding well to the energy range of the observed proton precipitation. The diffusion coefficient values indicated the strong diffusion regime, in agreement with the equality of the trapped and precipitating proton flux at the low-Earth orbit. The growth rate calculations based on the plasma and magnetic field data from both VAP and Arase spacecraft indicated that the detected EMIC waves could be generated in the region of their observation or in its close vicinity. Yahnin, A.; Popova, T.; Demekhov, A.; Lubchich, A.; Matsuoka, A.; Asamura, K.; Miyoshi, Y.; Yokota, S.; Kasahara, S.; Keika, K.; Hori, T.; Tsuchiya, F.; Kumamoto, A.; Kasahara, Y.; Shoji, M.; Kasaba, Y.; Nakamura, S.; Shinohara, I.; Kim, H.; Noh, S.; Raita, T.; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA029091 |
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AbstractThe spatial scales of whistler-mode waves, determined by their generation process, propagation, and damping, are important for assessing the scaling and efficiency of wave-particle interactions affecting the dynamics of the radiation belts. We use multi-point wave measurements in 2013-2019 by two identically equipped Van Allen Probes spacecraft covering all MLTs at L=2-6 near the geomagnetic equator to investigate the spatial extent of active regions of chorus and hiss waves, their wave amplitude distribution in the source/generation region, and the scales of chorus wave packets, employing a time-domain correlation technique to the spacecraft approaches closer than 1000 km, which happened every 70 days in 2012-2018 and every 35 days in 2018-2019. The correlation of chorus wave power dynamics using two spacecraft measurements is found to remain significant up to inter-spacecraft separations of 400 km to 750 km transverse to the background magnetic field direction, consistent with previous estimates of the chorus wave packet extent, but indicating the likely presence of two different scales of about 400 km and 750 km. Our results further suggest that the chorus source region can be slightly asymmetrical, more elongated in either the azimuthal or radial direction, which could also explain the aforementioned two different scales. An analysis of average chorus and hiss wave amplitudes at separate locations similarly reveals different radial and azimuthal extents of the corresponding wave active regions, complementing previous results based on THEMIS spacecraft statistics mainly at larger L>6. Both the chorus source region scale and the chorus active region size appear smaller inside the outer radiation belt (at L< 6) than at higher L-shells.This article is protected by copyright. All rights reserved. Agapitov, O.; Mourenas, D.; Artemyev, A.; Breneman, A.; Bonnell, J.W.; Hospodarsky, G.; Wygant, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA028998 chorus waves; chorus genration; Radiation belts; Van Allen Probes |
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Abstract Following the end of the Van Allen Probes mission, the Arase satellite offers a unique opportunity to continue in-situ radiation belt and ring current particle measurements into the next solar cycle. In this study we compare spin-averaged flux measurements from the MEPe, HEP-L, HEP-H, and XEP-SSD instruments on Arase with those from the MagEIS and REPT instruments on the Van Allen Probes, calculating Pearson correlation coefficient and the mean ratio of fluxes at L* conjunctions between the spacecraft. Arase and Van Allen Probes measurements show a close agreement over a wide range of energies, observing a similar general evolution of electron flux, as well as average, peak, and minimum values. Measurements from the two missions agree especially well in the 3.6 ≤ L* ≤ 4.4 range where Arase samples similar magnetic latitudes to Van Allen Probes. Arase tends to record higher flux for energies < 670 keV with longer decay times after flux enhancements, particularly for L* < 3.6 . Conversely, for energies > 1.4 MeV, Arase flux measurements are generally lower than those of Van Allen Probes, especially for L* > 4.4 . The correlation coefficient values show that the > 1.4 MeV flux from both missions are well correlated, indicating a similar general evolution, although flux magnitudes differ. We perform a preliminary intercalibration between the two missions using the mean ratio of the fluxes as an energy- and L*- dependent intercalibration factor. The intercalibration factor improves agreement between the fluxes in the 0.58-1 MeV range. This article is protected by copyright. All rights reserved. Szabó-Roberts, Mátyás; Shprits, Yuri; Allison, Hayley; Vasile, Ruggero; Smirnov, Artem; Aseev, Nikita; Drozdov, Alexander; Miyoshi, Yoshizumi; Claudepierre, Seth; Kasahara, Satoshi; Yokota, Shoichiro; Mitani, Takefumi; Takashima, Takeshi; Higashio, Nana; Hori, Tomo; Keika, Kunihiro; Imajo, Shun; Shinohara, Iku; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA028929 |
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Abstract Equatorial magnetosonic waves, together with chorus and plasmaspheric hiss, play key roles in the dynamics of energetic electron fluxes in the magnetosphere. Numerical models, developed following a first principles approach, that are used to study the evolution of high energy electron fluxes are mainly based on quasilinear diffusion. The application of such numerical codes requires statistical models for the distribution of key magnetospheric wave modes to estimate the appropriate diffusion coefficients. These waves are generally statistically modelled as a function of spatial location and geomagnetic indices (e.g. AE, Kp, or Dst). This study presents a novel dynamic spatiotemporal model for equatorial magnetosonic (EMS) wave amplitude, developed using the Nonlinear AutoRegressive Moving Average eXogenous (NARMAX) machine learning approach. The EMS wave amplitude, measured by the Van Allen Probes, are modelled using the time lags of the solar wind and geomagnetic indices as inputs as well as the location at which the measurement is made. The resulting model performance is assessed on a separate Van Allen Probes dataset, where the prediction efficiency was found to be 34.0\% and the correlation coefficient was 56.9\%. With more training and validation data the performance metrics could potentially be improved, however, it is also possible that the EMS wave distribution is affected by stochastic factors and the performance metrics obtained for this model are close to the potential maximum. Boynton, R.; Walker, S.; Aryan, H.; Hobara, Y.; Balikhin, M.; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA028439 magnetosonic waves; Machine learning; NARMAX; Van Allen Probes |
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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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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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Rapid injections of MeV electrons and extremely fast step-like outer radiation belt enhancements Abstract Rapid injection of MeV electrons associated with strong substorm dipolarization has been suggested as a potential explanation for some radiation belt enhancement events. However, it has been difficult to quantify the contribution of MeV electron injections to radiation belt enhancements. This paper presents two isolated MeV electron injection events for which we quite precisely quantify how the entire outer-belt immediately changed with the injections. Tracking detailed outer-belt evolution observed by Van Allen Probes, for both events, we identify large step-like relativistic electron enhancements (roughly 1-order of magnitude increase for ∼2 MeV electron fluxes) for L ≳ 3.8 and L ≳ 4.6, respectively, that occurred on ∼30-min timescales nearly instantaneously with the injections. The enhancements occurred almost simultaneously for 10s keV to multi-MeV electrons, with the lowest-L of enhancement region located farther out for higher energy. The outer-belt stayed at these new levels for ≳ several hours without substantial subsequent enhancements. Kim, H.-J.; Lee, D.-Y.; Wolf, R.; Bortnik, J.; Kim, K.-C.; Lyons, L.; Choe, W.; Noh, S.-J.; Choi, K.-E.; Yue, C.; Li, J.; Published by: Geophysical Research Letters Published on: 05/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021GL093151 Radiation belt enhancement; Relatvistic electrons; substorm injection; Step-like; Extremely fast; Van Allen Probes |
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Rapid injections of MeV electrons and extremely fast step-like outer radiation belt enhancements Abstract Rapid injection of MeV electrons associated with strong substorm dipolarization has been suggested as a potential explanation for some radiation belt enhancement events. However, it has been difficult to quantify the contribution of MeV electron injections to radiation belt enhancements. This paper presents two isolated MeV electron injection events for which we quite precisely quantify how the entire outer-belt immediately changed with the injections. Tracking detailed outer-belt evolution observed by Van Allen Probes, for both events, we identify large step-like relativistic electron enhancements (roughly 1-order of magnitude increase for ∼2 MeV electron fluxes) for L ≳ 3.8 and L ≳ 4.6, respectively, that occurred on ∼30-min timescales nearly instantaneously with the injections. The enhancements occurred almost simultaneously for 10s keV to multi-MeV electrons, with the lowest-L of enhancement region located farther out for higher energy. The outer-belt stayed at these new levels for ≳ several hours without substantial subsequent enhancements. Kim, H.-J.; Lee, D.-Y.; Wolf, R.; Bortnik, J.; Kim, K.-C.; Lyons, L.; Choe, W.; Noh, S.-J.; Choi, K.-E.; Yue, C.; Li, J.; Published by: Geophysical Research Letters Published on: 05/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021GL093151 Radiation belt enhancement; Relatvistic electrons; substorm injection; Step-like; Extremely fast; Van Allen Probes |
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Abstract We performed a comprehensive statistical study of electromagnetic ion cyclotron (EMIC) waves observed by the Van Allen Probes and Exploration of energization and Radiation in Geospace satellite (ERG/Arase). From 2017 to 2018, we identified and categorized EMIC wave events with respect to wavebands (H+ and He+ EMIC waves) and relative locations from the plasmasphere (inside and outside the plasmasphere). We found that H+ EMIC waves in the morning sector at L>8 are predominantly observed with a mixture of linear and right-handed polarity and higher wave normal angles during quiet geomagnetic conditions. Both H+ and He+ EMIC waves observed in the noon sector at L∼4-6 have left-handed polarity and lower wave normal angles at |MLAT|< 20˚ during the recovery phase of a storm with moderate solar wind pressure. In the afternoon sector (12-18 MLT), He+ EMIC waves are dominantly observed with strongly enhanced wave power at L∼6-8 during the storm main phase, while in the dusk sector (17-21 MLT) they have lower wave normal angles with linear polarity at L>8 during geomagnetic quiet conditions. Based on distinct characteristics at different EMIC wave occurrence regions, we suggest that EMIC waves in the magnetosphere can be generated by different free energy sources. Possible sources include the freshly injected particles from the plasma sheet, adiabatic heating by dayside magnetospheric compressions, suprathermal proton heating by magnetosonic waves, and off-equatorial sources. This article is protected by copyright. All rights reserved. Jun, C.-W; Miyoshi, Y.; Kurita, S.; Yue, C.; Bortnik, J.; Lyons, L.; Nakamura, S.; Shoji, M.; Imajo, S.; Kletzing, C.; Kasahara, Y.; Kasaba, Y.; Matsuda, S.; Tsuchiya, F.; Kumamoto, A.; Matsuoka, A.; Shinohara, I.; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA029001 Spatial distributions of EMIC waves; RBSP and Arase observations; EMIC wave properties; EMIC wave dependence on geomagnetic condition; Van Allen Probes |
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Modeling the Dynamics of Radiation Belt Electrons with Source and Loss Driven by the Solar Wind Abstract A radial diffusion model directly driven by the solar wind is developed to reproduce MeV electron variations between L=2-12 (L is L* in this study) from October 2012 to April 2015. The radial diffusion coefficient, internal source rate, quick loss due to EMIC waves, and slow loss due to hiss waves are all expressed in terms of the solar wind speed, dynamic pressure, and interplanetary magnetic field (IMF). The model achieves a prediction efficiency (PE) of 0.45 at L=5 and 0.51 at L=4 after converting the electron phase space densities to differential fluxes and comparing with Van Allen Probes measurements of 2 MeV and 3 MeV electrons at L=5 and L=4, respectively. Machine learning techniques are used to tune parameters to get higher PE. By tuning parameters for every 60-day period, the model obtains PE values of 0.58 and 0.82 at L=5 and L=4, respectively. Inspired by these results, we divide the solar wind activity into three categories based on the condition of solar wind speed, IMF Bz, and dynamic pressure, and then tune these three sets of parameters to obtain the highest PE. This experiment confirms that the solar wind speed has the greatest influence on the electron flux variations, particularly at higher L, while the dynamic pressure has more influence at lower L. Also, the PE at L=4 is mostly higher than those at L=5, suggesting that the electron loss due to the magnetopause shadowing combined with the outward radial diffusion is not well captured in the model. This article is protected by copyright. All rights reserved. Xiang, Zheng; Li, Xinlin; Kapali, Sudha; Gannon, Jennifer; Ni, Binbin; Zhao, Hong; Zhang, Kun; Khoo, Leng; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA028988 Radiation belt; Solar wind; flux prediction; radial diffusion; magnetopause shadowing; wave-particle interactions; Van Allen Probes |
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Sustained oxygen spectral gaps and their dynamic evolution in the inner magnetosphere Abstract Van Allen Probes observations of ion spectra often show a sustained gap within a very narrow energy range throughout the full orbit. To understand their formation mechanism, we statistically investigate the characteristics of the narrow gaps for oxygen ions and find that they are most frequently observed near the noon sector with a peak occurrence rate of over 30\%. The magnetic moment (μ) of the oxygen ions in the gap shows a strong dependence on magnetic local time (MLT), with higher and lower μ in the morning and afternoon sectors, respectively. Moreover, we find through superposed epoch analysis that the gap formation also depends on geomagnetic conditions. Those gaps formed at lower magnetic moments (μ < 3000 keV/G) are associated with stable convection electric fields, which enable magnetospheric ions to follow a steady drift pattern that facilitates the gap formation by corotational drift resonance. On the other hand, gaps with higher μ values are statistically preceded by a gradual increase of geomagnetic activity. We suggest that ions within the gap were originally located inside the Alfven layer following closed drift paths, before they were transitioned into open drift paths as the convection electric field was enhanced. The sunward drift of these ions, with very low fluxes, forms a drainage void in the dayside magnetosphere manifested as the sustained gap in the oxygen spectrum. This scenario is supported by particle-tracing simulations, which reproduce most of the observed characteristics and therefore provide new insights into inner magnetospheric dynamics. This article is protected by copyright. All rights reserved. Yue, Chao; Zhou, Xu-Zhi; Bortnik, Jacob; Zong, Qiu-Gang; Li, Yuxuan; Ren, Jie; Reeves, Geoffrey; Spence, Harlan; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA029092 oxygen spectral gaps; corotational drift resonance; sustained gaps; drainage void; test particle simulations; Van Allen Probes |
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Energetic electron detection packages on board Chinese navigation satellites in MEO Abstract Energetic electron measurements and spacecraft charging are of great significance for theoretical research in space physics and space weather applications. In this paper, the energetic electron detection package (EEDP) deployed on three Chinese navigation satellites in medium Earth orbit (MEO) is reviewed. The instrument was developed by the space science payload team led by Peking University. The EEDP includes a pinhole medium-energy electron spectrometer (MES), a high-energy electron detector (HED) based on ΔE-E telescope technology, and a deep dielectric charging monitor (DDCM). The MES measures the energy spectra of 50−600 keV electrons from nine directions with a 180°×30° field of view (FOV). The HED measures the energy spectrum of 0.5−3.0 MeV electrons from one direction with a 30° cone-angle FOV. The ground test and calibration results indicate that these three sensors exhibit excellent performance. Preliminary observations show that the electron spectra measured by the MES and HED are in good agreement with the results from the magnetic electron-ion spectrometer (MagEIS) of the Van Allen Probes spacecraft, with an average relative deviation of 27.3\% for the energy spectra. The charging currents and voltages measured by the DDCM during storms are consistent with the high-energy electron observations of the HED, demonstrating the effectiveness of the DDCM. The observations of the EEDP on board the three MEO satellites can provide important support for theoretical research on the radiation belts and the applications related to space weather. YuGuang, Ye; Hong, Zou; Qiu-Gang, Zong; HongFei, Chen; JiQing, Zou; WeiHong, Shi; XiangQian, Yu; WeiYing, Zhong; YongFu, Wang; YiXin, Hao; ZhiYang, Liu; XiangHong, Jia; Bo, Wang; XiaoPing, Yang; XiaoYun, Hao; Published by: Earth and Planetary Physics Published on: 04/2021 YEAR: 2021 DOI: https://doi.org/10.26464/epp2021021 Radiation belts; energetic electron detection; Pin-hole technology; Chinese navigation satellites; MEO; internal charging; Van Allen Probes |
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Energetic electron detection packages on board Chinese navigation satellites in MEO Abstract Energetic electron measurements and spacecraft charging are of great significance for theoretical research in space physics and space weather applications. In this paper, the energetic electron detection package (EEDP) deployed on three Chinese navigation satellites in medium Earth orbit (MEO) is reviewed. The instrument was developed by the space science payload team led by Peking University. The EEDP includes a pinhole medium-energy electron spectrometer (MES), a high-energy electron detector (HED) based on ΔE-E telescope technology, and a deep dielectric charging monitor (DDCM). The MES measures the energy spectra of 50−600 keV electrons from nine directions with a 180°×30° field of view (FOV). The HED measures the energy spectrum of 0.5−3.0 MeV electrons from one direction with a 30° cone-angle FOV. The ground test and calibration results indicate that these three sensors exhibit excellent performance. Preliminary observations show that the electron spectra measured by the MES and HED are in good agreement with the results from the magnetic electron-ion spectrometer (MagEIS) of the Van Allen Probes spacecraft, with an average relative deviation of 27.3\% for the energy spectra. The charging currents and voltages measured by the DDCM during storms are consistent with the high-energy electron observations of the HED, demonstrating the effectiveness of the DDCM. The observations of the EEDP on board the three MEO satellites can provide important support for theoretical research on the radiation belts and the applications related to space weather. YuGuang, Ye; Hong, Zou; Qiu-Gang, Zong; HongFei, Chen; JiQing, Zou; WeiHong, Shi; XiangQian, Yu; WeiYing, Zhong; YongFu, Wang; YiXin, Hao; ZhiYang, Liu; XiangHong, Jia; Bo, Wang; XiaoPing, Yang; XiaoYun, Hao; Published by: Earth and Planetary Physics Published on: 04/2021 YEAR: 2021 DOI: https://doi.org/10.26464/epp2021021 Radiation belts; energetic electron detection; Pin-hole technology; Chinese navigation satellites; MEO; internal charging; Van Allen Probes |
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Energetic electron detection packages on board Chinese navigation satellites in MEO Abstract Energetic electron measurements and spacecraft charging are of great significance for theoretical research in space physics and space weather applications. In this paper, the energetic electron detection package (EEDP) deployed on three Chinese navigation satellites in medium Earth orbit (MEO) is reviewed. The instrument was developed by the space science payload team led by Peking University. The EEDP includes a pinhole medium-energy electron spectrometer (MES), a high-energy electron detector (HED) based on ΔE-E telescope technology, and a deep dielectric charging monitor (DDCM). The MES measures the energy spectra of 50−600 keV electrons from nine directions with a 180°×30° field of view (FOV). The HED measures the energy spectrum of 0.5−3.0 MeV electrons from one direction with a 30° cone-angle FOV. The ground test and calibration results indicate that these three sensors exhibit excellent performance. Preliminary observations show that the electron spectra measured by the MES and HED are in good agreement with the results from the magnetic electron-ion spectrometer (MagEIS) of the Van Allen Probes spacecraft, with an average relative deviation of 27.3\% for the energy spectra. The charging currents and voltages measured by the DDCM during storms are consistent with the high-energy electron observations of the HED, demonstrating the effectiveness of the DDCM. The observations of the EEDP on board the three MEO satellites can provide important support for theoretical research on the radiation belts and the applications related to space weather. YuGuang, Ye; Hong, Zou; Qiu-Gang, Zong; HongFei, Chen; JiQing, Zou; WeiHong, Shi; XiangQian, Yu; WeiYing, Zhong; YongFu, Wang; YiXin, Hao; ZhiYang, Liu; XiangHong, Jia; Bo, Wang; XiaoPing, Yang; XiaoYun, Hao; Published by: Earth and Planetary Physics Published on: 04/2021 YEAR: 2021 DOI: https://doi.org/10.26464/epp2021021 Radiation belts; energetic electron detection; Pin-hole technology; Chinese navigation satellites; MEO; internal charging; Van Allen Probes |
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Energetic electron detection packages on board Chinese navigation satellites in MEO Abstract Energetic electron measurements and spacecraft charging are of great significance for theoretical research in space physics and space weather applications. In this paper, the energetic electron detection package (EEDP) deployed on three Chinese navigation satellites in medium Earth orbit (MEO) is reviewed. The instrument was developed by the space science payload team led by Peking University. The EEDP includes a pinhole medium-energy electron spectrometer (MES), a high-energy electron detector (HED) based on ΔE-E telescope technology, and a deep dielectric charging monitor (DDCM). The MES measures the energy spectra of 50−600 keV electrons from nine directions with a 180°×30° field of view (FOV). The HED measures the energy spectrum of 0.5−3.0 MeV electrons from one direction with a 30° cone-angle FOV. The ground test and calibration results indicate that these three sensors exhibit excellent performance. Preliminary observations show that the electron spectra measured by the MES and HED are in good agreement with the results from the magnetic electron-ion spectrometer (MagEIS) of the Van Allen Probes spacecraft, with an average relative deviation of 27.3\% for the energy spectra. The charging currents and voltages measured by the DDCM during storms are consistent with the high-energy electron observations of the HED, demonstrating the effectiveness of the DDCM. The observations of the EEDP on board the three MEO satellites can provide important support for theoretical research on the radiation belts and the applications related to space weather. YuGuang, Ye; Hong, Zou; Qiu-Gang, Zong; HongFei, Chen; JiQing, Zou; WeiHong, Shi; XiangQian, Yu; WeiYing, Zhong; YongFu, Wang; YiXin, Hao; ZhiYang, Liu; XiangHong, Jia; Bo, Wang; XiaoPing, Yang; XiaoYun, Hao; Published by: Earth and Planetary Physics Published on: 04/2021 YEAR: 2021 DOI: https://doi.org/10.26464/epp2021021 Radiation belts; energetic electron detection; Pin-hole technology; Chinese navigation satellites; MEO; internal charging; Van Allen Probes |
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Abstract Drift-bounce resonance between ultra-low-frequency (ULF) waves and ring current ions has been widely studied, because of its important role in ring current acceleration and relevant geomagnetic activities. To identify drift-bounce resonance in observations, 180° phase shifts across resonant pitch angle have been proposed as diagnostic signatures. This study, however, presents observations that suggest this criterion may be invalid when phase space density (PSD) distributions vary non-monochromatically with energy. We identified 14 ULF wave-ion interaction cases from 2-year Van Allen Probes data. In these cases, 180° phase shifts across pitch angle are observed at particular energies. Near these energies, pitch angle-dependent PSD bump-on-tail distributions were also observed. As a result, at fixed energies, the sign of ion PSD energy gradient changes across pitch angle, which then can result in the observed 180° phase shift. Based on the observations, we suggest 180° phase shifts across pitch angle can also result from pitch angle-dependent bump-on-tail distributions, which should be taken into account in future ULF wave-ion interaction studies. This article is protected by copyright. All rights reserved. Li, Xing-Yu; Liu, Zhi-Yang; Zong, Qiu-Gang; Zhou, Xu-Zhi; Hao, Yi-Xin; Rankin, Robert; Zhang, Xiao-Xin; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA029025 ring current; ultra-low-frequency waves; drift-bounce resonance; Van Allen Probes |
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Abstract Stable auroral red (SAR) arcs are optical events with dominant 630.0-nm emission caused by low-energy electron heat flux into the topside ionosphere from the inner magnetosphere. SAR arcs are observed at subauroral latitudes and often occur during the recovery phase of magnetic storms and substorms. Past studies concluded that these low-energy electrons were generated in the spatial overlap region between the outer plasmasphere and ring-current ions and suggested that Coulomb collisions between plasmaspheric electrons and ring-current ions are more feasible for the SAR-arc generation mechanism rather than Landau damping by electromagnetic ion cyclotron waves or kinetic Alfvén waves. This paper studies three separate SAR-arc events with conjunctions, using all-sky imagers and inner magnetospheric satellites (Arase and RBSP) during non-storm-time substorms on 19 December 2012 (event 1), 17 January 2015 (event 2), and 4 November 2019 (event 3). We evaluated for the first time the heat flux via Coulomb collision using full-energy-range ion data obtained by the satellites. The electron heat fluxes due to Coulomb collisions reached ∼109 eV/cm2/s for events 1 and 2, indicating that Coulomb collisions could have caused the SAR arcs. RBSP-A also observed local enhancements of 7–20-mHz electromagnetic wave power above the SAR arc in event 2. The heat flux for the freshly-detached SAR arc in event 3 reached ∼108 eV/cm2/s, which is insufficient to have caused the SAR arc. In event 3, local flux enhancement of electrons (<200 eV) and various electromagnetic waves were observed, these are likely to have caused the freshly-detached SAR arc. Inaba, Yudai; Shiokawa, Kazuo; Oyama, Shin-Ichiro; Otsuka, Yuichi; Connors, Martin; Schofield, Ian; Miyoshi, Yoshizumi; Imajo, Shun; Shinbori, Atsuki; Gololobov, Artem; Kazama, Yoichi; Wang, Shiang-Yu; W. Y. Tam, Sunny; Chang, Tzu-Fang; Wang, Bo-Jhou; Asamura, Kazushi; Yokota, Shoichiro; Kasahara, Satoshi; Keika, Kunihiro; Hori, Tomoaki; Matsuoka, Ayako; Kasahara, Yoshiya; Kumamoto, Atsushi; Matsuda, Shoya; Kasaba, Yasumasa; Tsuchiya, Fuminori; Shoji, Masafumi; Kitahara, Masahiro; Nakamura, Satoko; Shinohara, Iku; Spence, Harlan; Reeves, Geoff; MacDowall, Robert; Smith, Charles; Wygant, John; Bonnell, John; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA029081 SAR arc; Arase; RBSP; ring current; Non-storm-time substorm; Plasmapause; Van Allen Probes |
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Abstract Stable auroral red (SAR) arcs are optical events with dominant 630.0-nm emission caused by low-energy electron heat flux into the topside ionosphere from the inner magnetosphere. SAR arcs are observed at subauroral latitudes and often occur during the recovery phase of magnetic storms and substorms. Past studies concluded that these low-energy electrons were generated in the spatial overlap region between the outer plasmasphere and ring-current ions and suggested that Coulomb collisions between plasmaspheric electrons and ring-current ions are more feasible for the SAR-arc generation mechanism rather than Landau damping by electromagnetic ion cyclotron waves or kinetic Alfvén waves. This paper studies three separate SAR-arc events with conjunctions, using all-sky imagers and inner magnetospheric satellites (Arase and RBSP) during non-storm-time substorms on 19 December 2012 (event 1), 17 January 2015 (event 2), and 4 November 2019 (event 3). We evaluated for the first time the heat flux via Coulomb collision using full-energy-range ion data obtained by the satellites. The electron heat fluxes due to Coulomb collisions reached ∼109 eV/cm2/s for events 1 and 2, indicating that Coulomb collisions could have caused the SAR arcs. RBSP-A also observed local enhancements of 7–20-mHz electromagnetic wave power above the SAR arc in event 2. The heat flux for the freshly-detached SAR arc in event 3 reached ∼108 eV/cm2/s, which is insufficient to have caused the SAR arc. In event 3, local flux enhancement of electrons (<200 eV) and various electromagnetic waves were observed, these are likely to have caused the freshly-detached SAR arc. Inaba, Yudai; Shiokawa, Kazuo; Oyama, Shin-Ichiro; Otsuka, Yuichi; Connors, Martin; Schofield, Ian; Miyoshi, Yoshizumi; Imajo, Shun; Shinbori, Atsuki; Gololobov, Artem; Kazama, Yoichi; Wang, Shiang-Yu; W. Y. Tam, Sunny; Chang, Tzu-Fang; Wang, Bo-Jhou; Asamura, Kazushi; Yokota, Shoichiro; Kasahara, Satoshi; Keika, Kunihiro; Hori, Tomoaki; Matsuoka, Ayako; Kasahara, Yoshiya; Kumamoto, Atsushi; Matsuda, Shoya; Kasaba, Yasumasa; Tsuchiya, Fuminori; Shoji, Masafumi; Kitahara, Masahiro; Nakamura, Satoko; Shinohara, Iku; Spence, Harlan; Reeves, Geoff; MacDowall, Robert; Smith, Charles; Wygant, John; Bonnell, John; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA029081 SAR arc; Arase; RBSP; ring current; Non-storm-time substorm; Plasmapause; Van Allen Probes |
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Abstract Stable auroral red (SAR) arcs are optical events with dominant 630.0-nm emission caused by low-energy electron heat flux into the topside ionosphere from the inner magnetosphere. SAR arcs are observed at subauroral latitudes and often occur during the recovery phase of magnetic storms and substorms. Past studies concluded that these low-energy electrons were generated in the spatial overlap region between the outer plasmasphere and ring-current ions and suggested that Coulomb collisions between plasmaspheric electrons and ring-current ions are more feasible for the SAR-arc generation mechanism rather than Landau damping by electromagnetic ion cyclotron waves or kinetic Alfvén waves. This paper studies three separate SAR-arc events with conjunctions, using all-sky imagers and inner magnetospheric satellites (Arase and RBSP) during non-storm-time substorms on 19 December 2012 (event 1), 17 January 2015 (event 2), and 4 November 2019 (event 3). We evaluated for the first time the heat flux via Coulomb collision using full-energy-range ion data obtained by the satellites. The electron heat fluxes due to Coulomb collisions reached ∼109 eV/cm2/s for events 1 and 2, indicating that Coulomb collisions could have caused the SAR arcs. RBSP-A also observed local enhancements of 7–20-mHz electromagnetic wave power above the SAR arc in event 2. The heat flux for the freshly-detached SAR arc in event 3 reached ∼108 eV/cm2/s, which is insufficient to have caused the SAR arc. In event 3, local flux enhancement of electrons (<200 eV) and various electromagnetic waves were observed, these are likely to have caused the freshly-detached SAR arc. Inaba, Yudai; Shiokawa, Kazuo; Oyama, Shin-Ichiro; Otsuka, Yuichi; Connors, Martin; Schofield, Ian; Miyoshi, Yoshizumi; Imajo, Shun; Shinbori, Atsuki; Gololobov, Artem; Kazama, Yoichi; Wang, Shiang-Yu; W. Y. Tam, Sunny; Chang, Tzu-Fang; Wang, Bo-Jhou; Asamura, Kazushi; Yokota, Shoichiro; Kasahara, Satoshi; Keika, Kunihiro; Hori, Tomoaki; Matsuoka, Ayako; Kasahara, Yoshiya; Kumamoto, Atsushi; Matsuda, Shoya; Kasaba, Yasumasa; Tsuchiya, Fuminori; Shoji, Masafumi; Kitahara, Masahiro; Nakamura, Satoko; Shinohara, Iku; Spence, Harlan; Reeves, Geoff; MacDowall, Robert; Smith, Charles; Wygant, John; Bonnell, John; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA029081 SAR arc; Arase; RBSP; ring current; Non-storm-time substorm; Plasmapause; Van Allen Probes |
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Abstract The impact of radial diffusion in storm time radiation belt dynamics is well-debated. In this study we quantify the changes and variability in radial diffusion coefficients during geomagnetic storms. A statistical analysis of Van Allen Probes data (2012 − 2019) is conducted to obtain measurements of the magnetic and electric power spectral densities for Ultra Low Frequency (ULF) waves, and corresponding radial diffusion coefficients. The results show global wave power enhancements occur during the storm main phase, and continue into the recovery phase. Local time asymmetries show sources of wave power are both external solar wind driving and internal sources from coupling with ring current ions and substorms. Wave power enhancements are also observed at low L values (L < 4). The accessibility of wave power to low L is attributed to a depression of the Alfvén continuum. The increased wave power drives enhancements in both the magnetic and electric field diffusion coefficients by more than an order of magnitude. Significant variability in diffusion coefficients is observed, with values ranging over several orders of magnitude. A comparison to the Kp parameterised empirical model of Ozeke et al. (2014) is conducted and indicates important differences during storm times. Although the electric field diffusion coefficient is relatively well described by the empirical model, the magnetic field diffusion coefficient is approximately ∼ 10 times larger than predicted. We discuss how differences could be attributed to dataset limitations and assumptions. Alternative storm-time radial diffusion coefficients are provided as a function of L* and storm phase. Sandhu, J.; Rae, I.; Wygant, J.; Breneman, A.; Tian, S.; Watt, C.; Horne, R.; Ozeke, L.; Georgiou, M.; Walach, M.-T.; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA029024 ULF waves; radial diffusion; outer radiation belt; Van Allen Probes; Geomagnetic storms |
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AbstractIn-situ electron density profiles obtained from Arase in the night magnetic local time (MLT) sector and from RBSP-B covering all MLTs are used to study the small-scale density irregularities present in the plasmasphere and near the plasmapause. Electron density perturbations with amplitudes > 10\% from background density and with time-scales less than 30-min are investigated here as the small-scale density irregularities. The statistical survey of the density irregularities is carried out using nearly two years of density data obtained from RBSP-B and four months of data from Arase satellites. The results show that density irregularities are present globally at all MLT sectors and L-shells both inside and outside the plasmapause, with a higher occurrence at L > 4. The occurrence of density irregularities is found to be higher during disturbed geomagnetic and interplanetary conditions. The case studies presented here revealed: 1) The plasmaspheric density irregularities observed during both quiet and disturbed conditions are found to co-exist with the hot plasma sheet population. 2) During quiet periods, the plasma waves in the whistler-mode frequency range are found to be modulated by the small-scale density irregularities, with density depletions coinciding well with the decrease in whistler intensity. Our observations suggest that different source mechanisms are responsible for the generation of density structures at different MLTs and geomagnetic conditions.This article is protected by copyright. All rights reserved. Thomas, Neethal; Shiokawa, Kazuo; Miyoshi, Yoshizumi; Kasahara, Yoshiya; Shinohara, Iku; Kumamoto, Atsushi; Tsuchiya, Fuminori; Matsuoka, Ayako; Kasahara, Satoshi; Yokota, Shoichiro; Keika, Kunihiro; Hori, Tomo; Asamura, Kazushi; Wang, Shiang-Yu; Kazama, Yoichi; Tam, Sunny; Chang, Tzu-Fang; Wang, Bo-Jhou; Wygant, John; Breneman, Aaron; Reeves, Geoff; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA027917 Electron density; small-scale density irregularities; plasmasphere; inner magnetosphere; Van Allen Probes; Arase |
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AbstractIn-situ electron density profiles obtained from Arase in the night magnetic local time (MLT) sector and from RBSP-B covering all MLTs are used to study the small-scale density irregularities present in the plasmasphere and near the plasmapause. Electron density perturbations with amplitudes > 10\% from background density and with time-scales less than 30-min are investigated here as the small-scale density irregularities. The statistical survey of the density irregularities is carried out using nearly two years of density data obtained from RBSP-B and four months of data from Arase satellites. The results show that density irregularities are present globally at all MLT sectors and L-shells both inside and outside the plasmapause, with a higher occurrence at L > 4. The occurrence of density irregularities is found to be higher during disturbed geomagnetic and interplanetary conditions. The case studies presented here revealed: 1) The plasmaspheric density irregularities observed during both quiet and disturbed conditions are found to co-exist with the hot plasma sheet population. 2) During quiet periods, the plasma waves in the whistler-mode frequency range are found to be modulated by the small-scale density irregularities, with density depletions coinciding well with the decrease in whistler intensity. Our observations suggest that different source mechanisms are responsible for the generation of density structures at different MLTs and geomagnetic conditions.This article is protected by copyright. All rights reserved. Thomas, Neethal; Shiokawa, Kazuo; Miyoshi, Yoshizumi; Kasahara, Yoshiya; Shinohara, Iku; Kumamoto, Atsushi; Tsuchiya, Fuminori; Matsuoka, Ayako; Kasahara, Satoshi; Yokota, Shoichiro; Keika, Kunihiro; Hori, Tomo; Asamura, Kazushi; Wang, Shiang-Yu; Kazama, Yoichi; Tam, Sunny; Chang, Tzu-Fang; Wang, Bo-Jhou; Wygant, John; Breneman, Aaron; Reeves, Geoff; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA027917 Electron density; small-scale density irregularities; plasmasphere; inner magnetosphere; Van Allen Probes; Arase |
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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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Multi-Parameter Chorus and Plasmaspheric Hiss Wave Models Abstract The resonant interaction of energetic particles with plasma waves, such as chorus and plasmaspheric hiss waves, plays a direct and crucial role in the acceleration and loss of radiation belt electrons that ultimately affect the dynamics of the radiation belts. In this study, we use the comprehensive wave data measurements made by the Electric and Magnetic Field Instrument Suite and Integrated Science instruments on board the two Van Allen probes, to develop multi-parameter statistical chorus and plasmaspheric hiss wave models. The models of chorus and plasmaspheric hiss waves are presented as a function of combined geomagnetic activity (AE), solar wind velocity (V), and southward interplanetary magnetic field (Bs). The relatively smooth wave models reveal new features. Despite, the coupling between geomagnetic and solar wind parameters, the results show that each parameter still carries a sufficient amount of unique information to more accurately constrain the chorus and plasmaspheric hiss wave intensities. The new wave models presented here highlight the importance of multi-parameter wave models, and can improve radiation belt modeling. Aryan, Homayon; Bortnik, Jacob; Meredith, Nigel; Horne, Richard; Sibeck, David; Balikhin, Michael; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028403 chorus waves; inner magnetosphere; multi parameter wave distribution; plasmaspheric hiss waves; Van Allen Probes; wave-particle interactions |
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The Implications of Temporal Variability in Wave-Particle Interactions in Earth s Radiation Belts Changes in electron flux in Earth s outer radiation belt can be modeled using a diffusion-based framework. Diffusion coefficients D for such models are often constructed from statistical averages of observed inputs. Here, we use stochastic parameterization to investigate the consequences of temporal variability in D. Variability time scales are constrained using Van Allen Probe observations. Results from stochastic parameterization experiments are compared with experiments using D constructed from averaged inputs and an average of observation-specific D. We find that the evolution and final state of the numerical experiment depends upon the variability time scale of D; experiments with longer variability time scales differ from those with shorter time scales, even when the time-integrated diffusion is the same. Short variability time scale experiments converge with solutions obtained using an averaged observation-specific D, and both exhibit greater diffusion than experiments using the averaged-input D. These experiments reveal the importance of temporal variability in radiation belt diffusion. Watt, C.; Allison, H.; Thompson, R.; Bentley, S.; Meredith, N.; Glauert, S.; Horne, R.; Rae, I.; Published by: Geophysical Research Letters Published on: 12/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020GL089962 probabilistic methods; stochastic parameterization; Van Allen Probes |
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The Implications of Temporal Variability in Wave-Particle Interactions in Earth s Radiation Belts Changes in electron flux in Earth s outer radiation belt can be modeled using a diffusion-based framework. Diffusion coefficients D for such models are often constructed from statistical averages of observed inputs. Here, we use stochastic parameterization to investigate the consequences of temporal variability in D. Variability time scales are constrained using Van Allen Probe observations. Results from stochastic parameterization experiments are compared with experiments using D constructed from averaged inputs and an average of observation-specific D. We find that the evolution and final state of the numerical experiment depends upon the variability time scale of D; experiments with longer variability time scales differ from those with shorter time scales, even when the time-integrated diffusion is the same. Short variability time scale experiments converge with solutions obtained using an averaged observation-specific D, and both exhibit greater diffusion than experiments using the averaged-input D. These experiments reveal the importance of temporal variability in radiation belt diffusion. Watt, C.; Allison, H.; Thompson, R.; Bentley, S.; Meredith, N.; Glauert, S.; Horne, R.; Rae, I.; Published by: Geophysical Research Letters Published on: 12/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020GL089962 probabilistic methods; stochastic parameterization; 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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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 the Formation of Wedge-Like Ion Spectral Structures in the Nightside Inner Magnetosphere Recent observations in the nightside inner magnetosphere have identified a series of wedge-like spectral structures in the energy-time spectrograms of oxygen, helium, and hydrogen ion fluxes. Although the shapes and distributions of these structures have been characterized by case and statistical studies, their formation mechanism remains unclear. Here we utilize a particle tracing model to reproduce the wedge-like structures successively observed by the twin Van Allen Probes. The model suggests that these structures originate from intermittent substorm injection, and it is the accessibility region of these injected ions that determines their shapes. This mechanism is similar to the formation of another kind of structures, the inner magnetospheric nose-like structures, except that the wedge-like structures are separated from the tail population by the discontinuation of ion injections. This scenario is also supported by the distribution statistics of wedge-like structures, which provides new insights into the dynamics of the magnetotail-inner magnetosphere coupled system. Zhou, Xu-Zhi; Ren, Jie; Yang, Fan; Yue, Chao; Zong, Qiu-Gang; Fu, Sui-Yan; Wang, Yongfu; Published by: Journal of Geophysical Research: Space Physics Published on: 11/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028420 wedge-like structure; inner magnetosphere; substorm injection; magnetospheric convection; ring current; magnetotail; Van Allen Probes |
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Simultaneously Formed Wedge-Like Structures of Different Ion Species Deep in the Inner Magnetosphere In this study, ion data from the Helium, Oxygen, Proton, and Electron (HOPE) spectrometers onboard Van Allen Probes reveal the existence of wedge-like structures of O+, He+, and H+ ions deep in the inner magnetosphere. The behaviors of the wedge-like structures in terms of temporal evolution, spatial distribution, upper energy limit, as well as dependence on solar wind and different geomagnetic indices are investigated from both event studies of several consecutive orbits on 3 February 2013 and the subsequent statistical analyses using 4 years of data. Unlike the dominant distribution at –8 in the dayside observed by the polar orbit satellites in previous studies, the wedge-like structures deep in the equatorial plane of the inner magnetosphere are found mostly at the Mcllwain L shells of –5 and have a preferential location in the duskside and nightside. The O+ and He+ structures can extend to smaller L shells with higher upper energy limits than the H+ structures, while the upper energy limits of all these particle species show a similar variation tendency with respect to magnetic local time (MLT) and L. Observations indicate that these wedge-like structures are probably attributed to fresh substorm injections from the outer region. Ren, Jie; Zong, Q.; Yue, C.; Zhou, X.; Fu, S; Spence, H.; Funsten, H.; Published by: Journal of Geophysical Research: Space Physics Published on: 11/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028192 wedge-like structures; Ring current ions; inner magnetosphere; Substorm Injections; Van Allen Probes |
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A New Approach to Constructing Models of Electron Diffusion by EMIC Waves in the Radiation Belts Electromagnetic ion cyclotron (EMIC) waves play an important role in relativistic electron losses in the radiation belts through diffusion via resonant wave-particle interactions. We present a new approach for calculating bounce and drift-averaged EMIC electron diffusion coefficients. We calculate bounce-averaged diffusion coefficients, using quasi-linear theory, for each individual Combined Release and Radiation Effects Satellite (CRRES) EMIC wave observation using fitted wave properties, the plasma density and the background magnetic field. These calculations are then combined into bounce-averaged diffusion coefficients. The resulting coefficients therefore capture the combined effects of individual spectra and plasma properties as opposed to previous approaches that use average spectral and plasma properties, resulting in diffusion over a wider range of energies and pitch angles. These calculations, and their role in radiation belt simulations, are then compared against existing diffusion models. The new diffusion coefficients are found to significantly improve the agreement between the calculated decay of relativistic electrons and Van Allen Probes data. Ross, J.; Glauert, S.; Horne, R.; Watt, C.; Meredith, N.; Woodfield, E.; Published by: Geophysical Research Letters Published on: 10/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020GL088976 Radiation belts; EMIC waves; electron diffusion; Van Allen Probes |
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The k-nearest-neighbor technique is used to mine a multimission magnetometer database for a subset of data points from time intervals that are similar to the storm state of the magnetosphere for a particular moment in time. These subsets of data are then used to fit an empirical magnetic field model. Performing this for each snapshot in time reconstructs the dynamic evolution of the magnetic and electric current density distributions during storms. However, because weaker storms occur more frequently than stronger storms, the reconstructions are biased toward them. We demonstrate that distance weighting the nearest-neighbors mitigates this issue while allowing a sufficient amount of data to be included in the fitting procedure to limit overfitting. Using this technique, we reconstruct the distribution of the magnetic field and electric currents and their evolution for two storms, the intense 17–19 March 2015 “Saint Patrick s Day” storm and a moderate storm occurring on 13–15 July 2013, from which the pressure distributions can be computed assuming isotropy and by integrating the steady-state force-balance equation. As the main phase of a storm progresses in time, the westward ring current density and pressure increases in the inner magnetosphere particularly on the nightside, becoming more symmetric as the recovery phase progresses. We validate the empirical pressure by comparing it to the observed pressures from the Van Allen Probes mission by summing over particle fluxes from all available energy channels and species. Stephens, G.; Bingham, S.; Sitnov, M.; Gkioulidou, M.; Merkin, V.; Korth, H.; Tsyganenko, N.; Ukhorskiy, A; Published by: Space Weather Published on: 10/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020SW002583 storms; empirical geomagnetic field; ring current; data mining; eastward current; plasma pressure; Van Allen Probes |
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Dynamic Properties of Particle Injections Inside Geosynchronous Orbit: A Multisatellite Case Study Four closely located satellites at and inside geosynchronous orbit (GEO) provided a great opportunity to study the dynamical evolution and spatial scale of premidnight energetic particle injections inside GEO during a moderate substorm on 23 December 2016. Just following the substorm onset, the four spacecraft, a LANL satellite at GEO, the two Van Allen Probes (also called “RBSP”) at ~5.8 RE, and a THEMIS satellite at ~5.3 RE, observed substorm-related particle injections and local dipolarizations near the central meridian (~22 MLT) of a wedge-like current system. The large-scale evolution of the electron and ion (H, He, and O) injections was almost identical at the two RBSP spacecraft with ~0.5 RE apart. However, the initial short-timescale particle injections exhibited a striking difference between RBSP-A and -B: RBSP-B observed an energy dispersionless injection which occurred concurrently with a transient, strong dipolarization front (DF) with a peak-to-peak amplitude of ~25 nT over ~25 s; RBSP-A measured a dispersed/weaker injection with no corresponding DF. The spatiotemporally localized DF was accompanied by an impulsive, westward electric field (~20 mV m−1). The fast, impulsive E × B drift caused the radial transport of the electron and ion injection regions from GEO to ~5.8 RE. The penetrating DF fields significantly altered the rapid energy- and pitch angle-dependent flux changes of the electrons and the H and He ions inside GEO. Such flux distributions could reflect the transient DF-related particle acceleration and/or transport processes occurring inside GEO. In contrast, O ions were little affected by the DF fields. Motoba, T.; Ohtani, S.; Claudepierre, S.; Reeves, G.; Ukhorskiy, A; Lanzerotti, L.; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028215 deep particle injections; dipolarizations; substorms; localized DF; Van Allen Probes |
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The Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX) mission provided long-term measurements of 10s of megaelectron volt (MeV) inner belt (L < 2) protons (1992–2009) as did the Polar-orbiting Operational Environmental Satellite-18 (POES-18, 2005 to present). These long-term measurements at low-Earth orbit (LEO) showed clear solar cycle variations which anticorrelate with sunspot number. However, the magnitude of the variation is much greater than the solar cycle variation of galactic cosmic rays (>GeV) that are regarded as a source of these trapped protons. Furthermore, the proton fluxes and their variations sensitively depend on the altitude above the South Atlantic Anomaly (SAA) region. With respect to protons (>36 MeV) mirroring near the magnetic equator, both POES measurements and simulations show no obvious solar cycle variations at L > 1.2. This is also confirmed by recent measurements from the Van Allen Probes (2012–2019), but there are clear solar cycle variations and a strong spatial gradient of the proton flux below L = 1.2. A direct comparison between measurements and simulations leads to the conclusion that energy loss of trapped protons due to collisions with free and bound electrons in the ionosphere and atmosphere is the dominant mechanism for the strong spatial gradient and solar cycle variation of the inner belt protons. This fact is also key of importance for spacecraft and instrument design and operation in near-Earth space. Li, Xinlin; Xiang, Zheng; Zhang, Kun; Khoo, Lengying; Zhao, Hong; Baker, Daniel; Temerin, Michael; Published by: Journal of Geophysical Research: Space Physics Published on: 08/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028198 Inner radiation belt; Inner Belt Proton; Solar cycle variation; Cosmic rays; neutron monitor; Low Earth Orbit satellite; Van Allen Probes |