Bibliography
|
Notice:
|
Found 124 entries in the Bibliography.
Showing entries from 1 through 50
| 2021 |
|
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 |
|
The effect of non-storm time substorms on the ring current dynamics Abstract During geomagnetically active times such as geomagnetic storms, large amounts of energy can be released into the Earth’s magnetosphere and change the ring current intensity. Previous studies showed that significant enhancement of the ring current was related to geomagnetic storms, while few studies have examined substorm effects on ring current dynamics. In this study, we examine the ring current variation during non-storm time (SYM-H > −50 nT) substorms, especially during super-substorms ( AE > 1000 nT). We perform a statistical analysis of ring current plasma pressure and number flux of various ion species under different substorm conditions, based on Van Allen Probe observations. The plasma pressure and ion fluxes of the ring current increased dramatically during super-substorms, while little change was observed for substorms with AE < 1000 nT. The results shown in this study indicate that a non-storm time super-substorm may also have a significant contribution to the ring current. Jang, Eunjin; Yue, Chao; Zong, Qiugang; Fu, Suiyan; Fu, HaoBo; Published by: Earth and Planetary Physics Published on: 06/2021 YEAR: 2021 DOI: https://doi.org/10.26464/epp2021032 |
|
The effect of non-storm time substorms on the ring current dynamics Abstract During geomagnetically active times such as geomagnetic storms, large amounts of energy can be released into the Earth’s magnetosphere and change the ring current intensity. Previous studies showed that significant enhancement of the ring current was related to geomagnetic storms, while few studies have examined substorm effects on ring current dynamics. In this study, we examine the ring current variation during non-storm time (SYM-H > −50 nT) substorms, especially during super-substorms ( AE > 1000 nT). We perform a statistical analysis of ring current plasma pressure and number flux of various ion species under different substorm conditions, based on Van Allen Probe observations. The plasma pressure and ion fluxes of the ring current increased dramatically during super-substorms, while little change was observed for substorms with AE < 1000 nT. The results shown in this study indicate that a non-storm time super-substorm may also have a significant contribution to the ring current. Jang, Eunjin; Yue, Chao; Zong, Qiugang; Fu, Suiyan; Fu, HaoBo; Published by: Earth and Planetary Physics Published on: 06/2021 YEAR: 2021 DOI: https://doi.org/10.26464/epp2021032 |
|
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 |
|
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 |
|
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 |
|
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 |
|
Abstract Based on Van Allen Probes observations, in this study we perform a statistical analysis of the spectral intensities of plasmaspheric hiss at L-shells of 1.8 – 3.0 in the slot region. Our results show that slot region hiss power intensifies with a strong day-night asymmetry as the level of substorm activity or L-shell increases. Using the statistical spectral profiles of plasmaspheric hiss, we calculate the drift- and bounce-averaged electron pitch angle diffusion coefficients and subsequently obtain the resultant electron loss timescales through 1-D Fokker-Planck simulations. We find that slot region electron loss timescales vary significantly from <1 day to several years, showing a strong dependence on electron energy, L-shell and substorm activity. We also construct an empirical model of slot region electron loss timescales due to scattering by plasmaspheric hiss, which agrees well with the 1-D simulation results and can be readily used in modeling the dynamics of slot region electrons. This article is protected by copyright. All rights reserved. Zhu, Qi; Cao, Xing; Gu, Xudong; Ni, Binbin; Xiang, Zheng; Fu, Song; Summers, Danny; Hua, Man; Lou, Yuequn; Ma, Xin; Guo, YingJie; Guo, DeYu; Zhang, Wenxun; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA029057 Plasmaspheric Hiss; Slot region; Electron loss timescales; Van Allen Probes |
|
Abstract Isolated proton auroras (IPAs) appearing at subauroral latitudes are generated by energetic protons precipitating from the magnetosphere through interaction with electromagnetic ion cyclotron (EMIC) waves. An IPA thus indicates the spatial scale and temporal variation of wave–particle interactions in the magnetosphere. In this study, a unique event of simultaneous ground and magnetospheric satellite observations of two IPAs were conducted on March 16, 2015, using an all-sky imager at Athabasca, Canada and Van Allen Probes. The Van Allen Probes observed two isolated EMIC waves with frequencies of ∼1 and 0.4 Hz at L ≈ 5.0 when the satellite footprint crossed over the two IPAs. This suggests that the IPAs were caused by localized EMIC waves. Proton flux at 5–20 keV increased locally when the EMIC waves appeared. Electron flux at energies below ∼500 eV also increased. Temperature anisotropy of the energetic protons was estimated as 1.5–2.5 over a wide L-value range of 3.0–5.2. Electron density gradually decreased from L = 3.5 to L = 5.4, suggesting that the EMIC wave at L ≈ 5.0 was located in the gradual plasmapause. From these observations, we conclude that the localized IPAs and associated EMIC waves took place because of localized enhancement of energetic proton flux and plasma density structure near the plasmapause. The magnetic field observed by the satellite showed small variation during the wave observation, indicating that the IPAs were accompanied by the weak field-aligned current. Nakmaura, Kohki; Shiokawa, Kazuo; Otsuka, Yuichi; Shinbori, Atsuki; Miyoshi, Yoshizumi; Connors, Martin; Spence, Harlan; Reeves, Geoff; Funsten, Herbert; MacDowall, Robert; Smith, Charles; Wygant, John; Bonnell, John; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA029078 |
|
Prediction of Dynamic Plasmapause Location Using a Neural Network Abstract As a common boundary layer that distinctly separates the regions of high-density plasmasphere and low-density plasmatrough, the plasmapause is essential to comprehend the dynamics and variability of the inner magnetosphere. Using the machine learning framework Pytorch and high-quality Van Allen Probes data set, we develop a neural network model to predict the global dynamic variation of the plasmapause location, along with the identification of 6537 plasmapause crossing events during the period from 2012 to 2017. To avoid the overfitting and optimize the model generalization, 5493 events during the period from September 2012 to December 2015 are adopted for division into the training set and validation set in terms of the 10-fold cross validation method, and the remaining 1044 events are used as the test set. The model parameterized by only AE or Kp index can reproduce the plasmapause locations similar to those modeled using all five considered solar wind and geomagnetic parameters. Model evaluation on the test set indicate that our neural network model is capable of predicting the plasmapause location with the lowest RMSE. Our model can also produce a smooth MLT variation of the plasmapause location with good accuracy, which can be incorporated into global radiation belt simulations and space weather forecasts under a variety of geomagnetic conditions. This article is protected by copyright. All rights reserved. Guo, DeYu; Fu, Song; Xiang, Zheng; Ni, Binbin; Guo, YingJie; Feng, Minghang; Guo, JianGuang; Hu, Zejun; Gu, Xudong; Zhu, Jianan; Cao, Xing; Wang, Qi; Published by: Space Weather Published on: 03/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020SW002622 Plasmapause; neural network; Van Allen Probes; space weather forecast |
|
RBSP-ECT Combined Pitch Angle Resolved Electron Flux Data Product Abstract We describe a new data product combining pitch angle resolved electron flux measurements from the Radiation Belt Storm Probes (RBSP) Energetic Particle Composition and Thermal Plasma (ECT) suite on the National Aeronautics and Space Administration s Van Allen Probes. We describe the methodology used to combine each of the data sets and produce a consistent set of pitch-angle-resolved spectra for the entire Van Allen Probes mission. Three-minute-averaged flux spectra are provided spanning energies from 15 eV up to 20 MeV. This new data product offers researchers a consistent cross calibrated data set to explore the particle dynamics of the inner magnetosphere across a wide range of energies. This article is protected by copyright. All rights reserved. Boyd, A.J.; Spence, H.E.; Reeves, G.D.; Funsten, H.O; Skoug, R.K.; Larsen, B.A.; Blake, J.B.; Fennell, J.F.; Claudepierre, S.G.; Baker, D.N.; Kanekal, S.K.; Jaynes, A.N.; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA028637 |
|
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 |
| 2020 |
|
Using seven years of data from the HOPE instrument on the Van Allen Probes, equatorial pitch angle distributions (PADs) of 1 – 50 keV electrons in Earth s inner magnetosphere are investigated statistically. An empirical model of electron equatorial PADs as a function of radial distance, magnetic local time, geomagnetic activity, and electron energy is constructed using the method of Legendre polynomial fitting. Model results show that most equatorial PADs of 1 – 10s of keV electrons in Earth s inner magnetosphere are pancake PADs, and the lack of butterfly PADs is likely due to their relatively flat or positive flux radial gradients at higher altitudes. During geomagnetically quiet times, more anisotropic distributions of 1 – 10s of keV electrons at dayside than nightside are observed, which could be responsible for moderate chorus wave activities at dayside during quiet times as reported by previous studies. During active times, the anisotropy of 1 – 10s of keV electrons significantly enhances, consistent with the enhanced chorus wave activity during active times and suggesting the critical role of 1 – 10s of keV electrons in generating chorus waves in Earth s inner magnetosphere. Different enhanced anisotropy patterns of different energy electrons are also observed during active times: at R>∼4 RE, keV electrons are more anisotropic at dawn to noon, while 10s of keV electrons have larger anisotropy at midnight to dawn. These differences, combined with the statistical distribution of chorus waves shown in previous studies, suggest the differential roles of electrons with different energies in generating chorus waves with different properties. This article is protected by copyright. All rights reserved. Zhao, H.; Friedel, R.; Chen, Y.; Baker, D.; Li, X.; Malaspina, D.; Larsen, B.; Skoug, R.; Funsten, H.; Reeves, G.; Boyd, A.; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028322 Pitch angle distribution; energetic electrons; Earth s inner magnetosphere; Anisotropy; Chorus wave; statistical analysis; Van Allen Probes |
|
Statistical Distribution of Bifurcation of Earth s Inner Energetic Electron Belt at tens of keV We present a survey of the bifurcation of the Earth s energetic electron belt (tens of keV) using 6-year measurements from Van Allen Probes. The inner energetic electron belt usually presents one-peak radial structure with high flux intensity at L < ∼2.5, which however can be bifurcated to exhibit a double-peak radial structure. By automatically identifying the events of bifurcation based on RBSPICE data, we find that the bifurcation is mostly observed at ∼30–100 keV with a local flux minimum at L=∼2.0–∼2.3 under relatively quiet geomagnetic conditions, typically after a significant flux enhancement due to radial diffusion or injections to L<∼2.5. The bifurcation typically lasts for a few days during quiet periods until interrupted by injections or radial diffusion. The L-shell, energy and seasonal dependences of the occurrence of bifurcated inner electron belt support the important role of electron scattering by very-low-frequency transmitter waves in the bifurcation formation. Hua, Man; Ni, Binbin; Li, Wen; Ma, Qianli; Gu, Xudong; Fu, Song; Cao, Xing; Guo, YingJie; Liu, Yangxizi; Published by: Geophysical Research Letters Published on: 12/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020GL091242 Inner electron radiation belt; Flux bifurcation; VLF transmitter waves; Statistical distribution; Van Allen Probes |
|
Ring current decay during storm recovery phase may be affected by different loss processes. In this study, we have investigated the lifetimes of ring current ions (H+ and O+) of energies from 1 keV to several hundred keV at L shell from 3 to 6 during the storm recovery phase through a statistical survey. The observational data of 48 geomagnetic storms from March 2013 to May 2019 are collected based on Van Allen Probe observations. We find that (1) the observed lifetimes of H+ and O+ in general increase with L shell and (2) the lifetimes of H+ is short than that of O+ when E < ∼50 keV while the situation is reversed when E > ∼50 keV. In addition, we have made use of the charge exchange theory, combined with previous experimental results on the charge exchange cross section and two distribution models of neutral hydrogen atoms in the exosphere, so as to directly estimate the ring current ions decay caused by charge exchange mechanism only. Through the comparison between the model predictions of charge exchange lifetime and the observed lifetimes, we find that (3) the observed lifetimes are in general consistent with model results, which confirms that charge exchange is a dominant loss mechanism of ring current ions during storm recovery phase. Chen, Ao; Yue, Chao; Chen, HongFei; Zong, Qiugang; Fu, Suiyan; Wang, Yongfu; Ren, Jie; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028500 charge exchange; lifetime; ring current decay; Van Allen Probes |
|
Radiation belt electron dropouts indicate electron flux decay to the background level during geomagnetic storms, which is commonly attributed to the effects of wave-induced pitch angle scattering and magnetopause shadowing. To investigate the loss mechanisms of radiation belt electron dropouts triggered by a solar wind dynamic pressure pulse event on 12 September 2014, we comprehensively analyzed the particle and wave measurements from Van Allen Probes. The dropout event was divided into three periods: before the storm, the initial phase of the storm, and the main phase of the storm. The electron pitch angle distributions (PADs) and electron flux dropouts during the initial and main phases of this storm were investigated, and the evolution of the radial profile of electron phase space density (PSD) and the (μ, K) dependence of electron PSD dropouts (where μ, K, and L* are the three adiabatic invariants) were analyzed. The energy-independent decay of electrons at L > 4.5 was accompanied by butterfly PADs, suggesting that the magnetopause shadowing process may be the major loss mechanism during the initial phase of the storm at L > 4.5. The features of electron dropouts and 90°-peaked PADs were observed only for >1 MeV electrons at L < 4, indicating that the wave-induced scattering effect may dominate the electron loss processes at the lower L-shell during the main phase of the storm. Evaluations of the (μ, K) dependence of electron PSD drops and calculations of the minimum electron resonant energies of H+-band electromagnetic ion cyclotron (EMIC) waves support the scenario that the observed PSD drop peaks around L* = 3.9 may be caused mainly by the scattering of EMIC waves, whereas the drop peaks around L* = 4.6 may result from a combination of EMIC wave scattering and outward radial diffusion. Ma, Xin; Xiang, Zheng; Ni, Binbin; Fu, Song; Cao, Xing; Hua, Man; Guo, DeYu; Guo, YingJie; Gu, Xudong; Liu, ZeYuan; Zhu, Qi; Published by: Earth and Planetary Physics Published on: 11/2020 YEAR: 2020 DOI: https://doi.org/10.26464/epp2020060 radiation belt electron flux dropouts; Geomagnetic storm; electron phase space density; magnetopause shadowing; wave–particle interactions; Van Allen Probes |
|
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 |
|
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 |
|
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 |
|
In this study we focus on the radiation belt dynamics driven by the geomagnetic storms during September 2017. Besides the long-lasting three-belt structures of ultrarelativistic electrons (>2 MeV, existing for tens of days), which has been studied intensively during the Van Allen Probe era, it is found that magnetospheric electrons of hundreds of keVs can also have three-belt structures at similar L extent during storm time. Measurements of 500–800 keV electrons from MagEIS instrument onboard Van Allen Probes show double-peaked (L = 3.5 and 4.5, respectively) flux-versus-L-shell profile in the outer belt, which lasted for 2–3 days. During the time interval of such transient three-belt structure, the energy-versus-L spectrogram shows novel distributions differing from both “S-shaped” and “V-shaped” spectrograms reported previously. Such peculiar distribution also illustrates the energy-dependent occurrence of the three-belt profile. The gradual formation of “reversed energy spectrum” at L ∼ 3.5 also indicates that hiss scattering inside the plasmapause contributed to the fast decay of sub-MeV remnant belt. Hao, Y.; Zong, Q.-G.; Zhou, X.-Z.; Zou, H.; Rankin, R.; Sun, Y.; Chen, X.; Liu, Y.; Fu, S; Baker, D.; Spence, H.; Blake, J.; Reeves, G.; Claudepierre, S.; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028031 storage ring; three-belt structure; hiss wave; electron lifetime; Radial Transport; Van Allen Probes |
|
Using wave measurements from the EMFISIS instrument onboard Van Allen Probes, we investigate statistically the spatial distributions of the intensity of plasmaspheric hiss waves. To reproduce these empirical results, we establish a fitting model that is a third-order polynomial function of L-shell, magnetic local time (MLT), magnetic latitude (MLAT), and AE*. Quantitative comparisons indicate that the model s fitting functions can reflect favorably the major empirical features of the global distribution of hiss wave intensity, including substorm dependence and the MLT asymmetry. Our results therefore provide a useful analytic model that can be readily employed in future simulations of global radiation belt electron dynamics under the impact of plasmaspheric hiss waves in geospace. Wang, JingZhi; Zhu, Qi; Gu, Xudong; Fu, Song; Guo, JianGuang; Zhang, Xiaoxin; Yi, Juan; Guo, YingJie; Ni, Binbin; Xiang, Zheng; Published by: Earth and Planetary Physics Published on: 06/2020 YEAR: 2020 DOI: https://doi.org/10.26464/epp2020034 |
|
Simultaneous Observations of Localized and Global Drift Resonance In this study, we present Van Allen Probe observations showing that seed (hundreds of keV) and core ( 1 MeV) electrons can resonate with ultra-low-frequency (ULF) wave modes with distinctive m values simultaneously. An unusual electron energy spectrogram with double-banded resonant structure was recorded by energetic particle, composition, and thermal plasma (ECT)-magnetic electron ion spectrometer (MagEIS) and, meanwhile, boomerang stripes in pitch angle spectrogram appeared at the lower energy band. A localized drift resonance with m = 10 wave component was responsible for the resonant band peaked at ∼200 keV while a global drift resonance with m = 3 component gave rise to the upper band resonance peaked at ∼1 MeV. Time-Of-Flight on boomerang stripes suggested that the localized drift resonance with ∼200 keV electrons was confined within the plasmaspheric plume. Electron flux modulations were reproduced by numerical simulations in good consistency with the observations, supporting the scenario that localized and global drift resonance could coexist in the outer belt electron dynamics simultaneously. Hao, Y.; Zhao, X.; Zong, Q.-G.; Zhou, X.-Z.; Rankin, R.; Chen, X.; Liu, Y.; Fu, S; Blake, J.; Reeves, G.; Claudepierre, S.; Published by: Geophysical Research Letters Published on: 05/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020GL088019 drift resonance; ULF waves; Radiation Belt Dynamics; boomerang stripes; azimuthal wave number; multiple resonances; Van Allen Probes |
| 2019 |
|
We report the electron flux modulations without corresponding magnetic fluctuations from unique multipoint satellite observations of the Arase (Exploration of Energization and Radiation in Geospace) and the Van Allen Probe (Radiation Belt Storm Probe [RBSP])-B satellites. On 30 March 2017, both Arase and RBSP-B observed periodic fluctuations in the relativistic electron flux with energies ranging from 500 keV to 2 MeV when they were located near the magnetic equator in the morning and dusk local time sectors, respectively. Arase did not observe Pc5 pulsations, while they were observed by RBSP-B. The clear dispersion signature of the relativistic electron fluctuations observed by Arase indicates that the source region is limited to the postnoon to the dusk sector. This is confirmed by RBSP-B and ground-magnetometer observations, where Pc5 pulsations are observed to drift-resonate with relativistic electrons on the duskside. Thus, Arase observed the drift-resonance signatures \textquotedblleftremotely,\textquotedblright whereas RBSP-B observed them \textquotedblleftlocally.\textquotedblright Teramoto, M.; Hori, T.; Saito, S.; Miyoshi, Y.; Kurita, S.; Higashio, N.; Matsuoka, A.; Kasahara, Y.; Kasaba, Y.; Takashima, T.; Nomura, R.; e, Nos\; Fujimoto, A.; Tanaka, Y.-M.; Shoji, M.; Tsugawa, Y.; Shinohara, M.; Shinohara, I.; Blake, J.; Fennell, J.F.; Claudepierre, S.G.; Turner, D.; Kletzing, C.; Sormakov, D.; Troshichev, O.; Published by: Geophysical Research Letters Published on: 11/2019 YEAR: 2019 DOI: 10.1029/2019GL084379 |
|
Six years of Van Allen Probes data are used to investigate cold plasmaspheric electrons affected by ultralow-frequency (ULF) waves in the inner magnetosphere (L<7) including spatial distributions, occurrence conditions, and resonant energy range. Events exhibit a global distribution within L= 4\textendash7 but preferentially occur at L\~5.5\textendash7 in the dayside, while there is higher occurrence rate in the duskside than dawnside. They can occur under different geomagnetic activities and solar wind velocities (VS), but the occurrence rates are increasing with larger AE, |SYMH|, and VS. These features are closely associated with the generation and propagation of ULF waves in Pc4 (45\textendash150 s) and Pc5 (150\textendash600 s) bands. Combined with electron observations from HOPE instrument, the resonant energies inferred from wave power indicate that cold electrons at ones to hundreds of electron volts can be affected by ULF waves. This study may shed new light on further investigations on the acceleration and transportation of cold plasmaspheric particles that would affect plasmaspheric material release to the Earth\textquoterights magnetosphere and instabilities for exciting various waves. Ren, Jie; Zong, Q.; Zhou, X.; Spence, H.; Funsten, H.; Wygant, J.; Rankin, R.; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2019 YEAR: 2019 DOI: 10.1029/2019JA027009 Cold plasmaspheric electrons; drift-bounce resonance; ULF waves; Van Allen Probes; Wave-particle interaction |
|
RBSP-ECT Combined Spin-Averaged Electron Flux Data Product We describe a new data product combining the spin-averaged electron flux measurements from the Radiation Belt Storm Probes (RBSP) Energetic Particle Composition and Thermal Plasma (ECT) suite on the National Aeronautics and Space Administration\textquoterights Van Allen Probes. We describe the methodology used to combine each of the data sets and produce a consistent set of spectra for September 2013 to the present. Three-minute-averaged flux spectra are provided spanning energies from 15 eV up to 20 MeV. This new data product provides additional utility to the ECT data and offers a consistent cross calibrated data set for researchers interested in examining the dynamics of the inner magnetosphere across a wide range of energies. Boyd, A.; Reeves, G.; Spence, H.; Funsten, H.; Larsen, B.; Skoug, R.; Blake, J.; Fennell, J.; Claudepierre, S.; Baker, D.; Kanekal, S.; Jaynes, A.; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2019 YEAR: 2019 DOI: 10.1029/2019JA026733 |
|
Using Van Allen Probe Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) wave observations from September 2012 to May 2018, we statistically investigate the distributions of power-weighted wave normal angle (WNA) of fast magnetosonic (MS) waves from L = 2\textendash6 within \textpm15\textdegree geomagnetic latitudes. The spatial distributions show that the MS WNAs are mainly confined within 87\textendash89\textdegree near the geomagnetic equator and decrease with increasing magnetic latitude. Further quantitative investigation demonstrates that the WNAs normally distribute as a mixture of two Gaussian distributions ranging from 85\textdegree to 88\textdegree, and the tangent of it can decrease as a Kappa distribution function when the waves propagate to higher latitudes. Our study completes the survey of spatial distributions of MS WNAs and provides quantitative dependence of the WNA distribution on the magnetic latitude in the inner magnetosphere, which can be readily useful in future global simulations of radiation belt particle dynamics. Zou, Zhengyang; Zuo, Pingbing; Ni, Binbin; Wei, Fengsi; Zhao, Zhengyu; Cao, Xing; Fu, Song; Gu, Xudong; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2019 YEAR: 2019 DOI: 10.1029/2019JA026556 Empirical Model; Fast Magnetosonic Waves; latitudinal dependence; power-weighted wave normal angles; spatial distributions; Van Allen Probes |
|
Whistler mode hiss acts as an important loss mechanism contributing to the radiation belt electron dynamics inside the plasmasphere and plasmaspheric plumes. Based on Van Allen Probes observations from September 2012 to December 2015, we conduct a detailed analysis of hiss properties in plasmaspheric plumes and illustrate that corresponding to the highest occurrence probability of plumes at L = 5.0\textendash6.0 and MLT = 18\textendash21, hiss emissions occur concurrently with a rate of >~80\%. Plume hiss can efficiently scatter ~10- to 100-keV electrons at rates up to ~10-4 s-1 near the loss cone, and the resultant electron loss timescales vary largely with energy, that is, from less than an hour for tens of kiloelectron volt electrons to several days for hundreds of kiloelectron volt electrons and to >100 days for >5-MeV electrons. These newly obtained statistical properties of plume hiss and associated electron scattering effects are useful to future modeling efforts of radiation belt electron dynamics. Zhang, Wenxun; Ni, Binbin; Huang, He; Summers, Danny; Fu, Song; Xiang, Zheng; Gu, Xudong; Cao, Xing; Lou, Yuequn; Hua, Man; Published by: Geophysical Research Letters Published on: 05/2019 YEAR: 2019 DOI: 10.1029/2018GL081863 Electron scattering; plasmaspheric plumes; plume hiss; Van Allen Probes |
|
Excitation of extremely low-frequency chorus emissions: The role of background plasma density Low-frequency chorus emissions have recently attracted much attention due to the suggestion that they may play important roles in the dynamics of the Van Allen Belts. However, the mechanism (s) generating these low-frequency chorus emissions have not been well understood. . In this letter, we report an interesting case in which background plasma density lowered the lower cutoff frequency of chorus emissions from above 0.1 f ce (typical ordinary chorus) to 0.02 f ce (extremely low-frequency chorus). Those extremely low-frequency chorus waves were observed in a rather dense plasma, where the number density N e was found to be several times larger than has been associated with observations of ordinary chorus waves. For suprathermal electrons whose free energy is supplied by anisotropic temperatures, linear growth rates (calculated using in-situ plasma parameters measured by the Van Allen Probes) show that whistler mode instability can occur at frequencies below 0.1 f ce when the background plasma density N e increases. Especially when N e reaches 90 cm\textendash3 or more, the lowest unstable frequency can extend to 0.02 f ce or even less, which is consistent with satellite observations. Therefore, our results demonstrate that a dense background plasma could play an essential role in the excitation of extremely low-frequency chorus waves by controlling the wave growth rates. Yu, Xiongdong; Yuan, Zhigang; Huang, Shiyong; Yao, Fei; Qiao, Zheng; Wygant, John; Funsten, Herbert; Published by: Earth and Planetary Physics Published on: 02/2019 YEAR: 2019 DOI: 10.26464/epp2019001 anisotropic temperature instability; linear growth rate; low-frequency chorus emissions; Van Allen Probes; whistler mode |
|
This work designs a new model called PreMevE to predict storm-time distributions of relativistic electrons within Earth\textquoterights outer radiation belt. This model takes advantage of the cross-energy, -L-shell, and \textendashpitch-angle coherence associated with wave-electron resonant interactions, ingests observations from belt boundaries\textemdashmainly by NOAA POES in low-Earth-orbits (LEOs), and provides high-fidelity nowcast (multiple-hour prediction) and forecast (> ~1 day) of MeV electron fluxes over L-shells between 2.8-7 through linear prediction filters. PreMevE can not only reliably anticipate incoming enhancements of MeV electrons during storms with at least 1-day forewarning time, but also accurately specify the evolving event-specific electron spatial distributions afterwards. The performance of PreMevE is assessed against long-term in situ data from one Van Allen Probe and a LANL geosynchronous satellite. This new model enhances our preparedness for severe MeV electron events in the future, and further adds new science utility to existing and next-generation LEO space infrastructure. Chen, Yue; Reeves, Geoffrey; Fu, Xiangrong; Henderson, Michael; Published by: Space Weather Published on: 02/2019 YEAR: 2019 DOI: 10.1029/2018SW002095 event-specific predictions; LANL GEO observations; linear predictive filters; MeV electron events; outer radiation belt; precipitation at low-earth-orbits (LEO); Van Allen Probes |
|
Simultaneous trapping of EMIC and MS waves by background plasmas Electromagnetic ion cyclotron waves and fast magnetosonic waves are found to be simultaneously modulated by background plasma density: both kinds of waves were observed in high plasma density regions but vanished in low density regions. Theoretical analysis based on Snell\textquoterights law and linear growth theory have been utilized to investigate the physical mechanisms driving such modulation. It is suggested that the modulation of fast magnetosonic waves might be due to trapping by plasma density structures, which results from a conservation of the parameter Q during their propagation. Here Q = nrsinψ, with n the refractive index, r the radial distance, and ψ the wave azimuthal angle. As for electromagnetic ion cyclotron waves, the modulation might be owed to the ion composition difference between different plasma density regions. Our results indicate the alternative mechanism for simultaneous appearance of electromagnetic ion cyclotron waves and fast magnetosonic waves (rather than wave excitations of both two wave emissions), which might take combined effects on the evolution of radiation belt electrons. Yuan, Zhigang; Yu, Xiongdong; Ouyang, Zhihai; Yao, Fei; Huang, Shiyong; Funsten, H.; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2019 YEAR: 2019 DOI: 10.1029/2018JA026149 EMIC waves; MS waves; Ring current ions; Van Allen Probes; Wave trapping |
|
Electromagnetic ion cyclotron waves have long been recognized to play a crucial role in the dynamic loss of ring current protons. While the field-aligned propagation approximation of electromagnetic ion cyclotron waves was widely used to quantify the scattering loss of ring current protons, in this study, we find that the wave normal distribution strongly affects the pitch angle scattering efficiency of protons. Increase of peak normal angle or angular width can considerably reduce the scattering rates of <=10 keV protons. For >10 keV protons, the field-aligned propagation approximation results in a pronounced underestimate of the scattering of intermediate equatorial pitch angle protons and overestimates the scattering of high equatorial pitch angle protons by orders of magnitude. Our results suggest that the wave normal distribution of electromagnetic ion cyclotron waves plays an important role in the pitch angle evolution and scattering loss of ring current protons and should be incorporated in future global modeling of ring current dynamics. Cao, Xing; Ni, Binbin; Summers, Danny; Shprits, Yuri; Gu, Xudong; Fu, Song; Lou, Yuequn; Zhang, Yang; Ma, Xin; Zhang, Wenxun; Huang, He; Yi, Juan; Published by: Geophysical Research Letters Published on: 01/2019 YEAR: 2019 DOI: 10.1029/2018GL081550 EMIC waves; Quasi-linear diffusion; Ring current protons; Van Allen Probes; wave-particle interactions |
| 2018 |
|
With observations of Van Allen Probe A, in this letter we display a typical event where banded whistler waves shifted up their frequencies with frequency bands broadening as a response to the enhancement of solar wind dynamic pressure. Meanwhile, the anisotropy of electrons with energies about several tens of keV was observed to increase. Through the comparison of the calculated wave growth rates and observed wave spectral intensity, we suggest that those banded whistler waves observed with frequencies shifted up and frequency bands broadening could be locally excited by these hot electrons with increased anisotropy. The current study provides a great in situ evidence for the influence on frequencies of banded whistler waves by the enhancement of solar wind dynamic pressures, which reveals the important role of solar wind dynamic pressures playing in the frequency properties of banded whistler waves. Yu, Xiongdong; Yuan, Zhigang; Li, Haimeng; Huang, Shiyong; Wang, Dedong; Yao, Fei; Funsten, H.; Wygant, J.; Published by: Geophysical Research Letters Published on: Mar-08-2020 YEAR: 2018 DOI: 10.1029/2018GL078849 Banded whistler-mode waves; Frequency properties; inner magnetosphere; solar wind dynamic pressure; Van Allen Probes |
|
Simultaneous observations of the magnetic field and plasma waves made by the Arase and Van Allen Probe A satellites at different magnetic local time (MLT) enable us to deduce the longitudinal structure of an oxygen torus for the first time. During 04:00\textendash07:10 UT on 24 April 2017, Arase flew from L = 6.2 to 2.0 in the morning sector and detected an enhancement of the average plasma mass up to ~3.5 amu around L = 4.9\textendash5.2 and MLT = 5.0 hr, implying that the plasma consists of approximately 15\% O+ ions. Probe A moved outbound from L = 2.0 to 6.2 in the afternoon sector during 04:10\textendash07:30 UT and observed no clear enhancements in the average plasma mass. For this event, the O+ density enhancement in the inner magnetosphere (i.e., oxygen torus) does not extend over all MLT but is skewed toward the dawn, being described more precisely as a crescent-shaped torus or a pinched torus. e, M.; Matsuoka, A.; Kumamoto, A.; Kasahara, Y.; Goldstein, J.; Teramoto, M.; Tsuchiya, F.; Matsuda, S.; Shoji, M.; Imajo, S.; Oimatsu, S.; Yamamoto, K.; Obana, Y.; Nomura, R.; Fujimoto, A.; Shinohara, I.; Miyoshi, Y.; Kurth, W.; Kletzing, C.; Smith, C.; MacDowall, R.; Published by: Geophysical Research Letters Published on: 10/2018 YEAR: 2018 DOI: 10.1029/2018GL080122 Arase satellite; Geomagnetic storm; inner magnetosphere; oxygen torus; simultaneous observation; Van Allen Probes; Van Allen Probes satellite |
|
We report a typical event that fast magnetosonic (MS) waves, exohiss, and two-band chorus waves occurred simultaneously on the dayside observed by Van Allen Probes on 25 December 2013. By combining calculations of electron diffusion coefficients and 2-D Fokker-Planck diffusion simulations, we quantitatively analyze the combined scattering effect of multiple waves to demonstrate that the net impact of combined scattering does not simply depend on the wave intensity dominance of various plasma waves. Although the observed MS waves are most intense, the electron butterfly distribution is inhibited by exohiss and chorus, and electrons are considerably accelerated by combined scattering of MS and chorus waves. The simulated electron pitch angle distributions exhibit the variation trend consistent with the observations. Our results strongly suggest that competition and cooperation between resonant interactions with concurrently occurring magnetospheric waves need to be carefully treated in modeling and comprehending the radiation belt electron dynamics. Hua, Man; Ni, Binbin; Fu, Song; Gu, Xudong; Xiang, Zheng; Cao, Xing; Zhang, Wenxun; He, Ying; Huang, He; Lou, Yuequn; Zhang, Yang; Published by: Geophysical Research Letters Published on: 09/2018 YEAR: 2018 DOI: 10.1029/2018GL079533 Combined scattering effect; diffusion simulations; Exohiss; magnetosonic waves; resonant wave-particle interactions; two-band chorus waves; Van Allen Probes |
|
Using the Van Allen Probe A observations, we obtained the global distribution of proton rings and calculated the linear wave growth rate of fast magnetosonic (MS) waves in the region L ~ 3-6. Our statistical and calculated results demonstrate that MS waves can be locally excited on the dayside outside the plasmapause, as well as in the dusk sector inside the plasmapause. The frequency range of unstable MS waves is strongly modulated by the ratio of the proton ring velocity (Vr) to the local Alfv\ en speed (VA). High harmonic MS waves (ω>20ΩH+) can be excited outside the plasmapause where Vr/VA<1 while low harmonic MS waves (ω<10ΩH+) with frequencies less than ~30 Hz are found to be excited both outside and inside the plasmapause where 1 Yuan, Zhigang; Ouyang, Zhihai; Yu, Xiongdong; Huang, Shiyong; Yao, Fei; Funsten, H.; Published by: Geophysical Research Letters Published on: 09/2018 YEAR: 2018 DOI: 10.1029/2018GL079999 Fast Magnetosonic Waves; linear growth rates; locally excited; low harmonic magnetosonic waves; Proton rings; Van Allen Probes |
|
The stimulation of EMIC waves by a magnetospheric compression is perhaps the closest thing to a controlled experiment that is currently possible in magnetospheric physics, in that one prominent factor that can increase wave growth acts at a well-defined time. We present a detailed analysis of EMIC waves observed in the outer dayside magnetosphere by the four Magnetosphere Multiscale (MMS) spacecraft, Van Allen Probe A, and GOES 13, and by four very high latitude ground magnetometer stations in the western hemisphere before, during, and after a modest interplanetary shock on December 14, 2015. Analysis shows several features consistent with current theory, as well as some unexpected features. During the most intense MMS wave burst, which began ~ 1 min after the end of a brief magnetosheath incursion, independent transverse EMIC waves with orthogonal linear polarizations appeared simultaneously at all four spacecraft. He++ band EMIC waves were observed by MMS inside the magnetosphere, whereas almost all previous studies of He++ band EMIC waves observed them only in the magnetosheath and magnetopause boundary layers. Transverse EMIC waves also appeared at Van Allen Probe A and GOES 13 very near the times when the magnetic field compression reached their locations, indicating that the compression lowered the instability threshold to allow for EMIC wave generation throughout the outer dayside magnetosphere. The timing of the EMIC waves at both MMS and Van Allen Probe A was consistent with theoretical expectations for EMIC instabilities based on characteristics of the proton distributions observed by instruments on these spacecraft. Engebretson, M.; Posch, J.; Capman, N.; Campuzano, N.; elik, P.; Allen, R.; Vines, S.; Anderson, B.; Tian, S.; Cattell, C.; Wygant, J.; Fuselier, S.; Argall, M.; Lessard, M.; Torbert, R.; Moldwin, M.; Hartinger, M.; Kim, H.; Russell, C.; Kletzing, C.; Reeves, G.; Singer, H.; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2018 YEAR: 2018 DOI: 10.1029/2018JA025984 |
|
The Response of the Energy Content of the Outer Electron Radiation Belt to Geomagnetic Storms Using the data from the Van Allen Probe-A spacecraft, the variability of the total outer radiation belt (2.5 Xiong, Ying; Xie, Lun; Chen, Lunjin; Ni, Binbin; Fu, Suiyan; Pu, Zuyin; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2018 YEAR: 2018 DOI: 10.1029/2018JA025475 Chorus wave; energetic particles; energy content; magnetic storm; outer radiation belt; Van Allen Probes |
|
In Earth\textquoterights inner magnetosphere, electromagnetic waves in the ultra-low frequency (ULF) range play an important role in accelerating and diffusing charged particles via drift resonance. In conventional drift-resonance theory, linearization is applied under the assumption of weak wave-particle energy exchange so particle trajectories are unperturbed. For ULF waves with larger amplitudes and/or durations, however, the conventional theory becomes inaccurate since particle trajectories are strongly perturbed. Here, we extend the drift-resonance theory into a nonlinear regime, to formulate nonlinear trapping of particles in a wave-carried potential well, and predict the corresponding observable signatures such as rolled-up structures in particle energy spectrum. After considering how this manifests in particle data with finite energy resolution, we compare the predicted signatures with Van Allen Probes observations. Their good agreement provides the first observational evidence for the occurrence of nonlinear drift resonance, highlighting the importance of nonlinear effects in magnetospheric particle dynamics under ULF waves. Li, Li; Zhou, Xu-Zhi; Omura, Yoshiharu; Wang, Zi-Han; Zong, Qiu-Gang; Liu, Ying; Hao, Yi-Xin; Fu, Sui-Yan; Kivelson, Margaret; Rankin, Robert; Claudepierre, Seth; Wygant, John; Published by: Geophysical Research Letters Published on: 08/2018 YEAR: 2018 DOI: 10.1029/2018GL079038 drift resonance; nonlinear process; Particle acceleration; Radiation belts; ULF waves; Van Allen Probes; wave-particle interactions |
|
By analyzing observations from Van Allen Probes in its inbound and outbound orbits, we present evidence of coherent enhancement of cold plasmaspheric electrons and ions due to drift-bounce resonance with ULF waves. From 18:00 UT on 28 May 2017 to 10:00 UT on 29 May 2017, newly formed poloidal mode standing ULF waves with significant electric field oscillations were observed in two consecutive orbits when Probe B was travelling inbound. In contrast to observations during outbound orbits, the cold (< 150 eV) electorns measured by the HOPE instrument were characterized by flux enhancements several times larger and bi-directional pitch angle distributions during inbound orbits. The electron number density inferred from upper hybrid waves is twice as larger as during inbound orbits, which were also confirmed by an increase of spacecraft potential. The observed ULF waves are identified as second harmonic modes that satisfy the drift-bounce resonant condition of N=1 with cold electrons. An enhancement of the plasmaspheric ion number density to restore charge neutrality of plasmas in inbound orbits is observed, which is associated with an increase of ULF wave periods. The observations suggest that the dynamics of plasmaspheric electrons is modified by ULF waves through drift-bounce resonance, and that plasmaspheric ions are indirectly impacted. Ren, Jie; Zong, Qiu-Gang; Miyoshi, Yoshizumi; Rankin, Robert; Spence, Harlan; Funsten, Herbert; Wygant, John; Kletzing, Craig; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2018 YEAR: 2018 DOI: 10.1029/2018JA025255 Cold plasmaspheric electrons acceleration; Drfit-bounce resonance; Modification of electron and ion density profile; Substorm activities; ULF waves; Van Allen Probes |
|
To better understand rapid enhancements of the seed populations (hundreds of keV electrons) in the heart of the Earth\textquoterights outer radiation belt (L* ~ 3.5\textendash5.0) during different geomagnetic activities, we investigate three enhancement events measured by Van Allen Probes in detail. Observations of the fluxes and the pitch angle distributions of energetic electrons are analyzed to determine rapid enhancements of the seed populations. Our study shows that three specified processes associated with substorm electron injections can lead to rapid enhancements of the seed populations, and the electron energy increases up to 342 keV. In the first process, substorm electron injections accompanied by the transient and intense substorm electric fields can directly lead to rapid enhancements of the seed populations in the heart of the outer radiation belt. In the second process, the substorm injected electrons are first trapped in the outer radiation belt and subsequently transported into L* < 4.5 by the convection electric field. In the third process, the lower energy electrons are first injected at L* ~ 5.3 and then undergo drift resonance with ultralow-frequency waves. These accelerated electrons by ultralow-frequency waves are further transported into L* < 4.5 due to the convection electric field. This process is consistent with the radial diffusion. Our results suggest that these specified processes are important for understanding the dynamics of the seed populations in the heart of the outer radiation belt. Tang, C.; Xie, X.; Ni, B.; Su, Z.; Reeves, G.; Zhang, J.-C.; Baker, D.; Spence, H.; Funsten, H.; Blake, J.; Wygant, J.; Dai, G; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2018 YEAR: 2018 DOI: 10.1029/2017JA025142 enhanced convection; Substorm Injections; the outer radiation belt; the seed population; ULF waves; Van Allen Probes |
|
Electron Scattering by Plasmaspheric Hiss in a Nightside Plume Plasmaspheric hiss is known to play an important role in radiation belt electron dynamics in high plasma density regions. We present observations of two crossings of a plasmaspheric plume by the Van Allen Probes on 26 December 2012, which occurred unusually at the post-midnight-to-dawn sector between L ~ 4\textendash6 during a geomagnetically quiet period. This plume exhibited pronounced electron densities higher than those of the average plume level. Moderate hiss emissions accompanied the two plume crossings with the peak power at about 100 Hz. Quantification of quasi-linear bounce-averaged electron scattering rates by hiss in the plume demonstrates that the waves are efficient to pitch angle scatter ~10\textendash100 keV electrons at rates up to ~10-4 s-1 near the loss cone but become gradually insignificant to scatter the higher energy electron population. The resultant timescales of electron loss due to hiss in the nightside plume vary largely with electron kinetic energy over 3 orders of magnitude, that is, from several hours for tens of keV electrons to a few days for hundreds of keV electrons to well above 100 days for >1 MeV electrons. Changing slightly with L-shell and the multiquartile profile of hiss spectral intensity, these electron loss timescales suggest that hiss emissions in the nightside plume act as a viable candidate for the fast loss of the ≲100 keV electrons and the slow decay of higher energy electrons. Zhang, Wenxun; Fu, Song; Gu, Xudong; Ni, Binbin; Xiang, Zheng; Summers, Danny; Zou, Zhengyang; Cao, Xing; Lou, Yuequn; Hua, Man; Published by: Geophysical Research Letters Published on: 05/2018 YEAR: 2018 DOI: 10.1029/2018GL077212 Electron scattering; nightside plumes; Plasmaspheric Hiss; Van Allen Probes |
|
Cold Ion Heating by Magnetosonic Waves in a Density Cavity of the Plasmasphere Fast magnetosonic (MS) waves play an important role in the dynamics of the inner magnetosphere. Theoretical prediction and simulation have demonstrated that MS waves can heat cold ions. However, direct observational evidence of cold ion heating by MS waves has so far remained elusive. In this paper, we show a typical event of cold ion heating by magnetosonic waves in a density cavity of the plasmasphere with observations of the Van Allen Probe mission on 22 August 2013. During enhancements of the MS wave intensity in the density cavity, the fluxes of trapped H+ and He+ ions with energies of 10\textendash100 eV were observed to increase, implying that cold plasmaspheric ions were heated through high-order resonances with the MS waves. Based on simultaneous observations of ring current protons, we have calculated local linear growth rates, which demonstrate that magnetosonic waves can be locally generated in the density cavity. Our results provide a direct observational proof of the energy coupling process between the ring current and plasmasphere; that is, through exciting MS waves, the free energy stored in the ring current protons with ring distributions is released. In the density cavity of the plasmasphere, both cold H+ and He+ ions are heated by MS waves. As a result, the energy of the ring current can be transferred into the plasmasphere Yuan, Zhigang; Yu, Xiongdong; Huang, Shiyong; Qiao, Zheng; Yao, Fei; Funsten, Herbert; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2018 YEAR: 2018 DOI: 10.1002/2017JA024919 cold ion heating; Density cavities; local linear growth rates; magnetosonic waves; Ring current ions; Van Allen Probes; \textquoteleftring\textquoteright distributions |
|
A typical case of electromagnetic ion cyclotron (EMIC) emissions with both He+ band and O+ band waves was observed by Van Allen Probe A on 14 July 2014. These emissions occurred in the morning sector on the equator inside the plasmasphere, in which region O+ band EMIC waves prefer to appear. Through property analysis of these emissions, it is found that the He+ band EMIC waves are linearly polarized and propagating quasi-parallelly along the background magnetic field, while the O+ band ones are of linear and left-hand polarization and propagating obliquely with respect to the background magnetic field. Using the in situ observations of plasma environment and particle data, excitation of these O+ band EMIC waves has been investigated with the linear growth theory. The calculated linear growth rate shows that these O+ band EMIC waves can be locally excited by ring current protons with ring velocity distributions. The comparison of the observed wave spectral intensity and the calculated growth rate suggests that the density of H+ rings providing the free energy for the instability has decreased after the wave grows. Therefore, this paper provides a direct observational evidence to the excitation mechanism of O+ band EMIC waves: ring current protons with ring distributions provide the free energy supporting the instability in the presence of rich O+ in the plasmasphere. Yu, Xiongdong; Yuan, Zhigang; Huang, Shiyong; Yao, Fei; Wang, Dedong; Funsten, Herbert; Wygant, John; Published by: Geophysical Research Letters Published on: 02/2018 YEAR: 2018 DOI: 10.1002/grl.v45.310.1002/2018GL077109 linear wave growth; O+ band EMIC waves; ring distributions; Van Allen Probes |
|
Resonant Scattering of Radiation Belt Electrons by Off-Equatorial Magnetosonic Waves Fast magnetosonic (MS) waves are commonly regarded as electromagnetic waves that are characteristically confined within \textpm3\textdegree of the geomagnetic equator. We report two typical off-equatorial MS events observed by Van Allen Probes, that is, the 8 May 2014 event that occurred at the geomagnetic latitudes of 7.5\textdegree\textendash9.2\textdegree both inside and outside the plasmasphere with the wave amplitude up to 590 pT and the 9 January 2014 event that occurred at the latitudes of\textemdash(15.7\textdegree\textendash17.5\textdegree) outside the plasmasphere with a smaller amplitude about 81 pT. Detailed test particle simulations quantify the electron resonant scattering rates by the off-equatorial MS waves to find that they can cause the pitch angle scattering and momentum diffusion of radiation belt electrons with equatorial pitch angles < ~75\textdegree or < ~58\textdegree (depending on the wave latitudinal coverage) on timescales of a day. Subsequent two-dimensional Fokker-Planck diffusion simulations indicate that the strong off-equatorial MS waves are capable of efficiently transporting high pitch angle electrons to lower pitch angles to facilitate the formation of radiation belt electron butterfly distributions for a broad energy range from ~100 keV to >1 MeV within an hour. Our study clearly demonstrates that the presence of off-equatorial MS waves, in addition to equatorial MS waves, can contribute importantly to the dynamical variations of radiation belt electron fluxes and their pitch angle distribution. Ni, Binbin; Zou, Zhengyang; Fu, Song; Cao, Xing; Gu, Xudong; Xiang, Zheng; Published by: Geophysical Research Letters Published on: 02/2018 YEAR: 2018 DOI: 10.1002/grl.v45.310.1002/2017GL075788 butterfly pitch angle distributions; off-equatorial MS waves; radiation belt electrons; Van Allen Probes |
| 2017 |
|
The Radiation Belt Electron Scattering by Magnetosonic Wave: Dependence on Key Parameters Magnetosonic (MS) waves have been found capable of creating radiation belt electron butterfly distributions in the inner magnetosphere. To investigate the physical nature of the interactions between radiation belt electrons and MS waves, and to explore a preferential condition for MS waves to scatter electrons efficiently, we performed a comprehensive parametric study of MS wave-electron interactions using test particle simulations. The diffusion coefficients simulated by varying the MS wave frequency show that the scattering effect of MS waves is frequency insensitive at low harmonics (f < 20 fcp), which has great implications on modeling the electron scattering caused by MS waves with harmonic structures. The electron scattering caused by MS waves is very sensitive to wave normal angles, and MS waves with off 90\textdegree wave normal angles scatter electrons more efficiently. By simulating the diffusion coefficients and the electron phase space density evolution at different L shells under different plasma environment circumstances, we find that MS waves can readily produce electron butterfly distributions in the inner part of the plasmasphere where the ratio of electron plasma-to-gyrofrequency (fpe/fce) is large, while they may essentially form a two-peak distribution outside the plasmapause and in the inner radiation belt where fpe/fce is small. Lei, Mingda; Xie, Lun; Li, Jinxing; Pu, Zuyin; Fu, Suiyan; Ni, Binbin; Hua, Man; Chen, Lunjin; Li, Wen; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2017 YEAR: 2017 DOI: 10.1002/2016JA023801 magnetosonic wave; parametric study; Radiation belt; Van Allen Probes; Wave-particle interaction |
|
Temporal evolution of ion spectral structures during a geomagnetic storm: Observations and modeling Using the Van Allen Probes/Helium, Oxygen, Proton, and Electron (HOPE) mass spectrometer, we perform a case study of the temporal evolution of ion spectral structures observed in the energy range of 1-~50 keV throughout the geomagnetic storm of 2 October 2013. The ion spectral features are observed near the inner edge of the plasma sheet and are signatures of fresh transport from the plasma sheet into the inner magnetosphere. We find that the characteristics of the ion structures are determined by the intensity of the convection electric field. Prior to the beginning of the storm, the plasma sheet inner edge exhibits narrow nose spectral structures that vary little in energy across L values. Ion access to the inner magnetosphere during these times is limited to the nose energy bands. As convection is enhanced and large amounts of plasma are injected from the plasma sheet during the main phase of the storm, ion access occurs at a wide energy range, as no nose structures are observed. As the magnetosphere recovers from the storm, single noses and then multiple noses are observed once again. We use a model of ion drift and losses due to charge exchange to simulate the ion spectra and gain insight into the main observed features. Ferradas, C.; Zhang, J.-C.; Spence, H.; Kistler, L.; Larsen, B.; Reeves, G.; Skoug, R.; Funsten, H.; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2017 YEAR: 2017 DOI: 10.1002/2017JA024702 Geomagnetic storm; ion injection; ion nose structure; numerical modeling; Van Allen Probes; Weimer electric field model |
|
Chorus Wave Modulation of Langmuir Waves in the Radiation Belts Using high-resolution waveforms measured by the Van Allen Probes, we report a novel observation in the radiation belts. Namely, we show that multiband, discrete, rising-tone whistler mode chorus emissions exhibit a one-to-one correlation with Langmuir wave bursts. Moreover, the periodic Langmuir wave bursts are generally observed at the phase location where the chorus wave E|| component is oriented opposite to its propagation direction. The electron measurements show a beam in phase space density at the particle velocity that matches the parallel phase velocity of the chorus waves. Based on this evidence, we conclude that the chorus waves accelerate the suprathermal electrons via Landau resonance and generate a localized electron beam in phase space density. Consequently, the Langmuir waves are excited locally and are modulated by the chorus wave phase. This microscale interaction between chorus waves and high-frequency electrostatic waves provides a new insight into the nonlinear wave-particle interaction process. Li, Jinxing; Bortnik, Jacob; An, Xin; Li, Wen; Thorne, Richard; Zhou, Meng; Kurth, William; Hospodarsky, George; Funsten, Herbert; Spence, Harlan; Published by: Geophysical Research Letters Published on: 12/2017 YEAR: 2017 DOI: 10.1002/2017GL075877 Chorus wave; Landau resonance; Langmuir wave; nonlinear interaction; Radiation belt; Van Allen Probes; wave modulation |
|
The Evolution of the Plasma Sheet Ion Composition: Storms and Recoveries The ion plasma sheet (~few hundred eV to ~few 10s keV) is usually dominated by H+ ions. Here, changes in ion composition within the plasma sheet are explored both during individual events, and statistically during 54 calm-to-storm events and during 21 active-to-calm events. Ion composition data from the HOPE (Helium, Oxygen, Proton, Electron) instruments onboard Van Allen Probes satellites provide exceptional spatial and temporal resolution of the H+, O+, and He+ ion fluxes in the plasma sheet. H+ shown to be the dominant ion in the plasma sheet in the calm-to-storm transition. However, the energy-flux of each ion changes in a quasi-linear manner during extended calm intervals. Heavy ions (O+ and He+) become increasingly important during such periods as charge-exchange reactions result in faster loss for H+ than for O+ or He+. Results confirm previous investigations showing that the ion composition of the plasma sheet can be largely understood (and predicted) during calm intervals from knowledge of: (a) the composition of previously injected plasma at the onset of calm conditions, and (b) use of simple drift-physics models combined with calculations of charge-exchange losses. Denton, M.; Thomsen, M.; Reeves, G.; Larsen, B.; Henderson, M.; Jordanova, V.; Fernandes, P.; Friedel, R.; Skoug, R.; Funsten, H.; MacDonald, E.; Spence, H.; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2017 YEAR: 2017 DOI: 10.1002/2017JA024475 |
|
We analyse two ion scale dipolarization fronts associated with field-aligned currents detected by the Magnetospheric Multiscale mission during a large substorm on August 10, 2016. The first event corresponds to a fast dawnward flow with an anti-parallel current and could be generated by the wake of a previous fast earthward flow. It is associated with intense lower-hybrid drift waves detected at the front and propagating dawnward with a perpendicular phase speed close to the electric drift and the ion thermal velocity. The second event corresponds to a flow reversal: from southwward/dawnward to northward/duskward associated with a parallel current consistent with a brief expansion of the plasma sheet before the front crossing, and with a smaller lower-hybrid drift wave activity. Electromagnetic electron phase-space holes are detected near these low-frequency drift waves during both events. The drift waves could accelerate electrons parallel to the magnetic field and produce the parallel electron drift needed to generate the electron holes. Yet, we cannot rule out the possibility that the drift waves are produced by the anti-parallel current associated with the fast flows, leaving the source for the electron holes unexplained. Contel, O.; Nakamura, R.; Breuillard, H.; Argall, M.; Graham, D.; Fischer, D.; o, A.; Berthomier, M.; Pottelette, R.; Mirioni, L.; Chust, T.; Wilder, F.; Gershman, D.; Varsani, A.; Lindqvist, P.-A.; Khotyaintsev, Yu.; Norgren, C.; Ergun, R.; Goodrich, K.; Burch, J.; Torbert, R.; Needell, J.; Chutter, M.; Rau, D.; Dors, I.; Russell, C.; Magnes, W.; Strangeway, R.; Bromund, K.; Wei, H; Plaschke, F.; Anderson, B.; Le, G.; Moore, T.; Giles, B.; Paterson, W.; Pollock, C.; Dorelli, J.; Avanov, L.; Saito, Y.; Lavraud, B.; Fuselier, S.; Mauk, B.; Cohen, I.; Turner, D.; Fennell, J.; Leonard, T.; Jaynes, A.; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2017 YEAR: 2017 DOI: 10.1002/2017JA024550 dipolarization front; electron hole; fast flow:Van allen Probes; Field-Aligned Current; lower-hybrid drift wave; substorm |
|
Relativistic electron increase during chorus wave activities on the 6-8 March 2016 geomagnetic storm There was a geomagnetic storm on 6\textendash8 March 2016, in which Van Allen Probes A and B separated by \~2.5 h measured increase of relativistic electrons with energies \~ several hundred keV to 1 MeV. Simultaneously, chorus waves were measured by both Van Allen Probes and Magnetospheric Multiscale (MMS) mission. Some of the chorus elements were rising-tones, possibly due to nonlinear effects. These measurements are compared with a nonlinear theory of chorus waves incorporating the inhomogeneity ratio and the field equation. From this theory, a chorus wave profile in time and one-dimensional space is simulated. Test particle calculations are then performed in order to examine the energization rate of electrons. Some electrons are accelerated, although more electrons are decelerated. The measured time scale of the electron increase is inferred to be consistent with this nonlinear theory. Matsui, H.; Torbert, R.; Spence, H.; Argall, M.; Alm, L.; Farrugia, C.; Kurth, W.; Baker, D.; Blake, J.; Funsten, H.; Reeves, G.; Ergun, R.; Khotyaintsev, Yu.; Lindqvist, P.-A.; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2017 YEAR: 2017 DOI: 10.1002/2017JA024540 chorus waves; Geomagnetic storm; relativistic electrons; Van Allen Probes |