Bibliography
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Found 92 entries in the Bibliography.
Showing entries from 1 through 50
| 2021 |
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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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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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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 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 |
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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 |
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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 |
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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 |
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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 |
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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 |
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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 |
| 2020 |
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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 |
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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 |
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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 |
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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 |
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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 |
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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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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 |
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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 |
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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 |
| 2019 |
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Baker, D.N.; Zhao, H.; Li, X.; Kanekal, S.G.; Jaynes, A.N.; Kress, B.T.; Rodriguez, J.V.; Singer, H.J.; Claudepierre, S.G.; Fennell, J.F.; Hoxie, V.; Published by: Journal of Geophysical Research: Space Physics Published on: 11/2019 YEAR: 2019 DOI: 10.1029/2019JA027331 energetic particles; Magnetosphere:Inner; Magnetospheric configuration; Radiation belts; Space weather; Van Allen Probes |
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The magnetospheric driver of strong thermal emission velocity enhancement (STEVE) is investigated using conjugate observations when Van Allen Probes\textquoteright footprint directly crossed both STEVE and stable red aurora (SAR) arc. In the ionosphere, STEVE is associated with subauroral ion drift features, including electron temperature peak, density gradient, and westward ion flow. The SAR arc at lower latitudes corresponds to regions inside the plasmapause with isotropic plasma heating, which causes redline-only SAR emission via heat conduction. STEVE corresponds to the sharp plasmapause boundary containing quasi-static subauroral ion drift electric field and parallel-accelerated electrons by kinetic Alfv\ en waves. These parallel electrons could precipitate and be accelerated via auroral acceleration processes powered by Alfv\ en waves propagating along the magnetic field with the plasmapause as a waveguide. The electron precipitation, superimposed on the heat conduction, could explain multiwavelength continuous STEVE emission. The green picket-fence emissions are likely optical manifestations of electron precipitation associated with wave structures traveling along the plasmapause. Chu, Xiangning; Malaspina, David; Gallardo-Lacourt, Bea; Liang, Jun; Andersson, Laila; Ma, Qianli; Artemyev, Anton; Liu, Jiang; Ergun, Robert; Thaller, Scott; Akbari, Hassanali; Zhao, Hong; Larsen, Brian; Reeves, Geoffrey; Wygant, John; Breneman, Aaron; Tian, Sheng; Connors, Martin; Donovan, Eric; Archer, William; MacDonald, Elizabeth; Published by: Geophysical Research Letters Published on: 11/2019 YEAR: 2019 DOI: 10.1029/2019GL082789 aurora; kinetic Alfven wave; Plasmapause; STEVE; subauroral ion drift; table red auroral arc; Van Allen Probes |
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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 |
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Statistical analysis on plasmatrough exohiss waves from the Van Allen Probes In this study using Van Allen Probe wave observations we investigate the statistical properties of exohiss waves, which are structureless whistler mode waves observed outside the plasmapause. The exohiss waves are identified based on the cold electron number density, frequency distribution, ellipticity, and wave normal angle. The statistical analysis on exohiss wave properties shows that exohiss waves prefer to occur over 3 Zhu, Hui; Gu, Wenyao; Chen, Lunjin; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2019 YEAR: 2019 DOI: 10.1029/2018JA026359 |
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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 |
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Electromagnetic ion cyclotron (EMIC) waves can drive precipitation of tens of keV protons and relativistic electrons, and are a potential candidate for causing radiation belt flux dropouts. In this study, we quantitatively analyze three cases of EMIC-driven precipitation, which occurred near the dusk sector observed by multiple Low-Earth-Orbiting (LEO) Polar Operational Environmental Satellites/Meteorological Operational satellite programme (POES/MetOp) satellites. During EMIC wave activity, the proton precipitation occurred from few tens of keV up to hundreds of keV, while the electron precipitation was mainly at relativistic energies. We compare observations of electron precipitation with calculations using quasi-linear theory. For all cases, we consider the effects of other magnetospheric waves observed simultaneously with EMIC waves, namely, plasmaspheric hiss and magnetosonic waves, and find that the electron precipitation at MeV energies was predominantly caused by EMIC-driven pitch angle scattering. Interestingly, each precipitation event observed by a LEO satellite extended over a limited L shell region (ΔL ~ 0.3 on average), suggesting that the pitch angle scattering caused by EMIC waves occurs only when favorable conditions are met, likely in a localized region. Furthermore, we take advantage of the LEO constellation to explore the occurrence of precipitation at different L shells and magnetic local time sectors, simultaneously with EMIC wave observations near the equator (detected by Van Allen Probes) or at the ground (measured by magnetometers). Our analysis shows that although EMIC waves drove precipitation only in a narrow ΔL, electron precipitation was triggered at various locations as identified by POES/MetOp over a rather broad region (up to ~4.4 hr MLT and ~1.4 L shells) with similar patterns between satellites. Capannolo, L.; Li, W.; Ma, Q.; Shen, X.-C.; Zhang, X.-J.; Redmon, R.; Rodriguez, J.; Engebretson, M.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Spence, H.; Reeves, G.; Raita, T.; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2019 YEAR: 2019 DOI: 10.1029/2018JA026291 EMIC waves; energetic electron precipitation; pitch angle scattering; quasi-linear theory; radiation belts dropouts; Van Allen Probes |
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Whistler mode waves are important for precipitating energetic electrons into Earth\textquoterights upper atmosphere, while the quantitative effect of each type of whistler mode wave on electron precipitation is not well understood. In this letter, we evaluate energetic electron precipitation driven by three types of whistler mode waves: plume whistler mode waves, plasmaspheric hiss, and exohiss observed outside the plasmapause. By quantitatively analyzing three conjunction events between Van Allen Probes and POES/MetOp satellites, together with quasi-linear calculation, we found that plume whistler mode waves are most effective in pitch angle scattering loss, particularly for the electrons from tens to hundreds of keV. Our new finding provides the first direct evidence of effective pitch angle scattering driven by plume whistler mode waves and is critical for understanding energetic electron loss process in the inner magnetosphere. We suggest the effect of plume whistler mode waves be accurately incorporated into future radiation belt modeling. Li, W.; Shen, X.-C.; Ma, Q.; Capannolo, L.; Shi, R.; Redmon, R.; Rodriguez, J.; Reeves, G.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Published by: Geophysical Research Letters Published on: 03/2019 YEAR: 2019 DOI: 10.1029/2019GL082095 electron precipitation; hiss; plasmaspheric plume; Plume wave; Van Allen Probes; whistler mode wave |
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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 |
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There has been increasing evidence for pitch angle scattering of relativistic electrons by electromagnetic ion cyclotron (EMIC) waves. Theoretical studies have predicted that the loss time scale of MeV electrons by EMIC waves can be very fast, suggesting that MeV electron fluxes rapidly decrease in association with the EMIC wave activity. This study reports on a unique event of MeV electron loss induced by EMIC waves based on Arase, Van Allen Probes, and ground-based network observations. Arase observed a signature of MeV electron loss by EMIC waves, and the satellite and ground-based observations constrained spatial-temporal variations of the EMIC wave activity during the loss event. Multi-satellite observation of MeV electron fluxes showed that ~2.5 MeV electron fluxes substantially decreased within a few tens of minutes where the EMIC waves were present. The present study provides an observational estimate of the loss time scale of MeV electrons by EMIC waves. Kurita, S.; Miyoshi, Y.; Shiokawa, K.; Higashio, N.; Mitani, T.; Takashima, T.; Matsuoka, A.; Shinohara, I.; Kletzing, C.; Blake, J.; Claudepierre, S.; Connors, M.; Oyama, S.; Nagatsuma, T.; Sakaguchi, K.; Baishev, D.; Otsuka, Y.; Published by: Geophysical Research Letters Published on: 11/2018 YEAR: 2018 DOI: 10.1029/2018GL080262 EMIC waves; loss; PWING project; Radiation belt; The Arase satellite; Van Allen Probes |
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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 |
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The Arase spacecraft is capable of observing ultralow-frequency waves in the inner magnetosphere at intermediate magnetic latitudes, a region sparsely covered by previous space craft missions. We report a series of impulsively excited fundamental toroidal mode standing Alfv\ en waves in the midnight sector observed by Arase outside the plasmasphere at magnetic latitudes 13\textendash24\textdegree . The wave onsets are concurrent with Pi2 onsets detected by the Van Allen Probe B spacecraft at the magnetic equator in the duskside plasmasphere and by ground magnetometers at low latitudes. The duration of each toroidal wave packet is \~20 min, which is much longer than that of the corresponding Pi2 wave packet. The toroidal waves cannot be the source of high-latitude Pi2 waves because they were not detected on the ground near the magnetic field footprint of Arase. Overall, the toroidal wave event lasted more than 2 h and allowed us to use the wave frequency to estimate the plasma mass density at L = 6.1\textendash8.3. The mass density (in amu cm-3) is higher than the electron density (in cm-3) by a factor of \~6, which implies that 17\textendash33\% of the ions were O+. Takahashi, Kazue; Denton, Richard; Motoba, Tetsuo; Matsuoka, Ayako; Kasaba, Yasumasa; Kasahara, Yoshiya; Teramoto, Mariko; Shoji, Masafumi; Takahashi, Naoko; Miyoshi, Yoshizumi; e, Masahito; Kumamoto, Atsushi; Tsuchiya, Fuminori; Redmon, Robert; Rodriguez, Juan; Published by: Geophysical Research Letters Published on: 07/2018 YEAR: 2018 DOI: 10.1029/2018GL078731 |
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Magnetospheric plasma waves play a significant role in ring current and radiation belt dynamics, leading to pitch angle scattering loss and/or stochastic acceleration of the particles. During a non-storm time dropout event on 24 September 2013, intense electromagnetic ion cyclotron (EMIC) waves were detected by Van Allen Probe A (Radiation Belt Storm Probes-A). We quantitatively analyze a conjunction event when Van Allen Probe A was located approximately along the same magnetic field line as MetOp-01, which detected simultaneous precipitation of >30 keV protons and energetic electrons over an unexpectedly broad energy range (>~30 keV). Multipoint observations together with quasi-linear theory provide direct evidence that the observed electron precipitation at higher energy (>~700 keV) is primarily driven by EMIC waves. However, the newly observed feature of the simultaneous electron precipitation extending down to ~30 keV is not supported by existing theories and raises an interesting question on whether EMIC waves can scatter such low-energy electrons. Capannolo, L.; Li, W.; Ma, Q.; Zhang, X.-J.; Redmon, R.; Rodriguez, J.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Engebretson, M.; Spence, H.; Reeves, G.; Published by: Geophysical Research Letters Published on: 07/2018 YEAR: 2018 DOI: 10.1029/2018GL078604 EMIC waves; energetic particle precipitation; pitch angle scattering; Radiation belts; Van Allen Probes; wave particle interactions |
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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 |
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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 |
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During the 13-14 November 2012 storm, Van Allen Probe A simultaneously observed a 10-h period of enhanced chorus (including quasi-parallel and oblique propagation components) and relativistic electron fluxes over a broad range of L = 3-6 and MLT=2 - 10 within a complete orbit cycle. By adopting a Gaussian fit to the observed wave spectra, we obtain the wave parameters and calculate the bounce-averaged diffusion coefficients. We solve the Fokker-Planck diffusion equation to simulate flux evolutions of relativistic (1.8-4.2 MeV) electrons during two intervals when Probe A passed the location L = 4.3 along its orbit. The simulating results show that chorus with combined quasi-parallel and oblique components can produce a more pronounced flux enhancement in the pitch angle range \~45o-80o, consistent well with the observation. The current results provide the first evidence on how relativistic electron fluxes vary under the drive of almost continuously distributed chorus with both quasi-parallel and oblique components within a complete orbit of Van Allen Probe. Yang, Chang; Xiao, Fuliang; He, Yihua; Liu, Si; Zhou, Qinghua; Guo, Mingyue; Zhao, Wanli; Published by: Geophysical Research Letters Published on: 02/2018 YEAR: 2018 DOI: 10.1002/2017GL075894 energetic electron; Geomagnetic storm; outer radiation belt; Van Allen Probes; Wave-particle interaction; whistler-mode chorus wave |
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Space Weather Operation at KASI with Van Allen Probes Beacon Signals The Van Allen Probes (VAPs) are the only modern NASA spacecraft broadcasting real-time data on the Earth\textquoterights radiation belts for space weather operations. Since 2012, the Korea Astronomy and Space Science Institute (KASI) has contributed to the receipt of this data via a 7-m satellite tracking antenna and used these data for space weather operations. An approximately 15-min period is required from measurement to acquisition of Level-1 data. In this paper, we demonstrate the use of VAP data for monitoring space weather conditions at geostationary orbit (GEO) by highlighting the Saint Patrick\textquoterights Day storm of 2015. During that storm, Probe-A observed a significant increase in the relativistic electron flux at 3 RE. Those electrons diffused outward resulting in a large increase of the electron flux > 2 MeV at GEO, which potentially threatened satellite operations. Based on this study, we conclude that the combination of VAP data and National Oceanic and Atmospheric Administration-Geostationary Operational Environmental Satellite (NOAA-GOES) data can provide improved space environment information to geostationary satellite operators. In addition, the findings obtained indicate that more data-receiving sites would be necessary and data connections improved if this or a similar system were to be used as an operational data service. Lee, Jongkil; Kim, Kyung-Chan; Romeo, Giuseppe; Ukhorskiy, Sasha; Sibeck, David; Kessel, Ramona; Mauk, Barry; Giles, Barbara; Gu, Bon-Jun; Lee, Hyesook; Park, Young-Deuk; Lee, Jaejin; Published by: Space Weather Published on: 01/2018 YEAR: 2018 DOI: 10.1002/2017SW001726 Electron acceleration; Radiation belt; Relativistic electron; Space weather; Van Allen Probes |
| 2017 |
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Automated Identification and Shape Analysis of Chorus Elements in the Van Allen Radiation Belts An important goal of the Van Allen Probes mission is to understand wave-particle interaction by chorus emissions in terrestrial Van Allen radiation belts. To test models, statistical characterization of chorus properties, such as amplitude variation and sweep rates, is an important scientific goal. The Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) instrumentation suite provides measurements of wave electric and magnetic fields as well as DC magnetic fields for the Van Allen Probes mission. However, manual inspection across terabytes of EMFISIS data is not feasible and as such introduces human confirmation bias. We present signal processing techniques for automated identification, shape analysis, and sweep rate characterization of high-amplitude whistler-mode chorus elements in the Van Allen radiation belts. Specifically, we develop signal processing techniques based on the radon transform that disambiguate chorus elements with a dominant sweep rate against hiss-like chorus. We present representative results validating our techniques and also provide statistical characterization of detected chorus elements across a case study of a 6 s epoch. Gupta, Ananya; Kletzing, Craig; Howk, Robin; Kurth, William; Matheny, Morgan; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2017 YEAR: 2017 DOI: 10.1002/2017JA023949 |
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Whistler-mode chorus waves are a naturally occurring electromagnetic emission observed in Earth\textquoterights magnetosphere. Here, for the first time, data from NASA\textquoterights Magnetospheric Multiscale (MMS) mission were used to analyze chorus waves in detail, including the calculation of chorus wave normal vectors, k. A case study was examined from a period of substorm activity around the time of a conjunction between the MMS constellation and NASA\textquoterights Van Allen Probes mission on 07 April 2016. Chorus wave activity was simultaneously observed by all six spacecraft over a broad range of L-shells (5.5 < L < 8.5), magnetic local time (06:00 < MLT < 09:00), and magnetic latitude (-32\textdegree < MLat < -15\textdegree), implying a large chorus active region. Eight chorus elements and their substructure were analyzed in detail with MMS. These chorus elements were all lower band and rising tone emissions, right-handed and nearly circularly polarized, and propagating away from the magnetic equator when they were observed at MMS (MLat ~ -31\textdegree). Most of the elements had \textquotedbllefthook\textquotedblright like signatures on their wave power spectra, characterized by enhanced wave power at flat or falling frequency following the peak, and all the elements exhibited complex and well organized substructure observed consistently at all four MMS spacecraft at separations up to 70 km (60 km perpendicular and 38 km parallel to the background magnetic field). The waveforms in field-aligned coordinates also demonstrated that these waves were all phase coherent allowing for the direct calculation of k. Error estimates on calculated k revealed that the plane wave approximation was valid for six of the eight elements and most of the subelements. The wave normal vectors were within 20-30\textdegree from the direction anti-parallel to the background field for all elements and changed from subelement to subelement through at least two of the eight elements. The azimuthal angle of k in the perpendicular plane was oriented earthward and was oblique to that of the Poynting vector, which has implications for the validity of cold plasma theory. Turner, D.; Lee, J.; Claudepierre, S.; Fennell, J.; Blake, J.; Jaynes, A.; Leonard, T.; Wilder, F.; Ergun, R.; Baker, D.; Cohen, I.; Mauk, B.; Strangeway, R.; Hartley, D.; Kletzing, C.; Breuillard, H.; Le Contel, O.; Khotyaintsev, Yu; Torbert, R.; Allen, R.; Burch, J.; Santolik, O.; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2017 YEAR: 2017 DOI: 10.1002/2017JA024474 chorus waves; inner magnetosphere; Magnetospheric multiscale; MMS; Radiation belts; Van Allen Probes |
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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 |
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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 |
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Observations from Magnetospheric MultiScale (~8 Re) and Van Allen Probes (~5 and 4 Re) show that the initial dayside response to a small interplanetary shock is a double-peaked dawnward electric field, which is distinctly different from the usual bipolar (dawnward and then duskward) signature reported for large shocks. The associated ExB flow is radially inward. The shock compressed the magnetopause to inside 8 Re, as observed by MMS, with a speed that is comparable to the ExB flow. The magnetopause speed and the ExB speeds were significantly less than the propagation speed of the pulse from MMS to the Van Allen Probes and GOES-13, which is consistent with the MHD fast mode. There were increased fluxes of energetic electrons up to several MeV. Signatures of drift echoes and response to ULF waves also were seen. These observations demonstrate that even very weak shocks can have significant impact on the radiation belts. Cattell, C.; Breneman, A.; Colpitts, C.; Dombeck, J.; Thaller, S.; Tian, S.; Wygant, J.; Fennell, J.; Hudson, M.; Ergun, Robert; Russell, C.; Torbert, Roy; Lindqvist, Per-Arne; Burch, J.; Published by: Geophysical Research Letters Published on: 08/2017 YEAR: 2017 DOI: 10.1002/2017GL074895 electric field response; interplanetary shock; magnetopause; Radiation belt; Van Allen Probes |
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Statistical Properties of Low Frequency Plasmaspheric Hiss Plasmaspheric hiss is an important wave mode for the dynamics of inner terrestrial magnetosphere plasma populations. It acts to scatter high energy electrons out of trapped orbits about Earth and into the atmosphere, defining the inner edge of the radiation belts over a range of energies. A low-frequency component of hiss was recently identified and is important for its ability to interact with higher energy electrons compared to typically considered hiss frequencies. This study compares the statistical properties of low and high frequency plasmaspheric hiss in the terrestrial magnetosphere, demonstrating that they are statistically distinct wave populations. Low frequency hiss shows different behavior in frequency space, different spatial localization (in magnetic local time and radial distance), and different amplitude distributions compared to high frequency hiss. The observed statistical properties of low frequency hiss are found to be consistent with recently developed theories for low frequency hiss generation. The results presented here suggest that careful consideration of low frequency hiss properties can be important for accurate inclusion of this wave population in predictive models of inner magnetosphere plasma dynamics. Malaspina, David; Jaynes, Allison; Hospodarsky, George; Bortnik, Jacob; Ergun, Robert; Wygant, John; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2017 YEAR: 2017 DOI: 10.1002/2017JA024328 inner magnetosphere; plasma waves; Plasmaspheric Hiss; Van Allen Probes; Wave Statistics |
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On the Relationship Between Electron Flux Oscillations and ULF Wave-Driven Radial Transport The objective of this study is to investigate the relationship between the levels of electron flux oscillations and radial diffusion for different Phase Space Density (PSD) gradients, through observation and particle tracing simulations under the effect of model Ultra Low Frequency (ULF) fluctuations. This investigation aims to demonstrate that electron flux oscillation is associated with and could be used as an indicator of ongoing radial diffusion. To this direction, flux oscillations are observed through the Van Allen Probes\textquoteright MagEIS energetic particle detector; subsequently, flux oscillations are produced in a particle tracing model that simulates radial diffusion by using model magnetic and electric field fluctuations that are approximating measured magnetic and electric field fluctuations as recorded by the Van Allen Probes\textquoteright EMFISIS and EFW instruments, respectively. The flux oscillation amplitudes are then correlated with Phase Space Density gradients in the magnetosphere and with the ongoing radial diffusion process. Sarris, Theodore; Li, Xinlin; Temerin, Michael; Zhao, Hong; Califf, Sam; Liu, Wenlong; Ergun, Robert; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2017 YEAR: 2017 DOI: 10.1002/2016JA023741 Flux Oscillations; MAGEis; EMFISIS; EFW; Phase space density; radial diffusion; Radiation belts; Van Allen Probes |
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Bayesian Spectral Analysis of Chorus Sub-Elements from the Van Allen Probes We develop a Bayesian spectral analysis technique that calculates the probability distribution functions of a superposition of wave-modes each described by a linear growth rate, a frequency and a chirp rate. The Bayesian framework has a number of advantages, including 1) reducing the parameter space by integrating over the amplitude and phase of the wave, 2) incorporating the data from each channel to determine the model parameters such as frequency which leads to high resolution results in frequency and time, 3) the ability to consider the superposition of waves where the wave-parameters are closely spaced, 4) the ability to directly calculate the expectation value of wave parameters without resorting to ensemble averages, 5) the ability to calculate error bars on model parameters. We examine one rising-tone chorus element in detail from a disturbed time on November 14, 2012 using burst mode waveform data of the three components of the electric and magnetic field from the EMFISIS instrument on board NASA\textquoterights Van Allen Probes. The results demonstrate that sub-elements are likely composed of almost linear waves that are nearly parallel propagating with continuously changing wave parameters such as frequency and wave-vector. Between sub-elements the wave parameters of the dominant mode undergoes a discrete change in frequency and wave-vector. Near the boundary of sub-elements multiple waves are observed such that the evolution of the waves is reminiscent of wave-wave processes such as parametric decay or nonlinear induced scattering by particles. These nonlinear processes may affect the saturation of the whistler-mode chorus instability. Crabtree, Chris; Tejero, Erik; Ganguli, Gurudas; Hospodarsky, George; Kletzing, Craig; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2017 YEAR: 2017 DOI: 10.1002/2016JA023547 |
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Zhang, Yang; Shi, Run; Ni, Binbin; Gu, Xudong; Zhang, Xianguo; Zuo, Pingbing; Fu, Song; Xiang, Zheng; Wang, Qi; Cao, Xing; Zou, Zhengyang; Published by: Advances in Space Research Published on: 03/2017 YEAR: 2017 DOI: 10.1016/j.asr.2016.12.035 |
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Whistler mode chorus is one of the most important emissions affecting the energization of the radiation belts. Recent laboratory experiments that inject energetic electron beams into a cold plasma have revealed several spectral features in the nonlinear evolution of these instabilities that have also been observed in high-time resolution in situ wave-form data. These features include (1) a sub-element structure which consists of an amplitude modulation on time-scales slower than the bounce time, (2) closely spaced discrete frequency hopping that results in a faster apparent frequency chirp rate, (3) fast frequency changes near the sub-element boundaries, and (4) harmonic generation. In this paper, we develop a finite dimensional self-consistent Hamiltonian model for the evolution of the resonant beam of electrons. We analyze a single wave case and demonstrate that the instability occurs due to a Krein collision, which manifests as a coupling between a negative and positive energy mode. This analysis revealed that the nonlinear evolution of the spectrally stable fixed-points of the self-consistent Hamiltonian develop a sub-packet structure similar to that of space observations. We then analyze the case of two whistler waves to show that the model reproduces the nonlinear harmonic generation and leads to a hypothesis for the closely spaced frequency hopping observed in laboratory experiments and space data. Crabtree, Chris; Ganguli, Gurudas; Tejero, Erik; Published by: Physics of Plasmas Published on: 03/2017 YEAR: 2017 DOI: 10.1063/1.4977539 Dispersion relations; Electron beams; SingingEigenvalues; Van Allen Probes; Whistler waves |
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An interesting form of \textquotedblleftzipper-like\textquotedblright magnetosonic waves consisting of two bands of interleaved periodic rising-tone spectra was newly observed by the Van Allen Probes, the Time History of Events and Macroscale Interactions during Substorms (THEMIS), and the Magnetospheric Multiscale (MMS) missions. The two discrete bands are distinct in frequency and intensity; however, they maintain the same periodicity which varies in space and time, suggesting that they possibly originate from one single source intrinsically. In one event, the zipper-like magnetosonic waves exhibit the same periodicity as a constant-frequency magnetosonic wave and an electrostatic emission, but the modulation comes from neither density fluctuations nor ULF waves. A statistical survey based on 3.5 years of multisatellite observations shows that zipper-like magnetosonic waves mainly occur on the dawnside to noonside, in a frequency range between 10 fcp and fLHR. The zipper-like magnetosonic waves may provide a new clue to nonlinear excitation or modulation process, while its cause still remains to be fully understood. Li, J.; Bortnik, J.; Li, W.; Ma, Q.; Thorne, R.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Wygant, J.; Breneman, A.; Thaller, S.; Funsten, H.; Mitchell, D.; Manweiler, J.; Torbert, R.; Le Contel, O.; Ergun, R.; Lindqvist, P.-A.; Torkar, K.; Nakamura, R.; Andriopoulou, M.; Russell, C.; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2017 YEAR: 2017 DOI: 10.1002/2016JA023536 magnetosonic wave; Radiation belt; rising-tone; Van Allen Probes; zipper-like |
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Van Allen Probes observations of oxygen cyclotron harmonic waves in the inner magnetosphere Waves with frequencies in the vicinity of the oxygen cyclotron frequency and its harmonics have been regularly observed on the Van Allen Probes satellites during geomagnetic storms. We focus on properties of these waves and present events from the main phase of two storms on 1 November 2012 and 17 March 2013 and associated dropouts of a few MeV electron fluxes. They are electromagnetic, in the frequency range ~0.5 to several Hz, and amplitude ~0.1 to a few nT in magnetic and ~0.1 to a few mV/m in electric field, with both the wave velocity and the Poynting vector directed almost parallel to the background magnetic field. These properties are very similar to those of electromagnetic ion cyclotron waves, which are believed to contribute to loss of ring current ions and radiation belt electrons and therefore can be also important for inner magnetosphere dynamics. Usanova, M.; Malaspina, D.; Jaynes, A.; Bruder, R.; Mann, I.; Wygant, J.; Ergun, R.; Published by: Geophysical Research Letters Published on: 09/2016 YEAR: 2016 DOI: 10.1002/grl.v43.1710.1002/2016GL070233 cyclotron harmonic waves; energetic particle loss; Geomagnetic storms; inner magnetosphere; oxygen; Van Allen Probes |
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The distribution of plasmaspheric hiss wave power with respect to plasmapause location In this work, Van Allen Probes data are used to derive terrestrial plasmaspheric hiss wave power distributions organized by (1) distance away from the plasmapause and (2) plasmapause distance from Earth. This approach is in contrast to the traditional organization of hiss wave power by L parameter and geomagnetic activity. Plasmapause-sorting reveals previously unreported and highly repeatable features of the hiss wave power distribution, including a regular spatial distribution of hiss power with respect to the plasmapause, a standoff distance between peak hiss power and the plasmapause, and frequency-dependent spatial localization of hiss. Identification and quantification of these features can provide insight into hiss generation and propagation and will facilitate improved parameterization of hiss wave power in predictive simulations of inner magnetosphere dynamics. Malaspina, David; Jaynes, Allison; e, Cory; Bortnik, Jacob; Thaller, Scott; Ergun, Robert; Kletzing, Craig; Wygant, John; Published by: Geophysical Research Letters Published on: 08/2016 YEAR: 2016 DOI: 10.1002/2016GL069982 hiss; plasma waves; plasmasphere; Radiation belts; Van Allen Probes |
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To understand the role of electromagnetic ion cyclotron (EMIC) waves in determining the temporal features of pulsating proton aurora (PPA) via wave-particle interactions at subauroral latitudes, high-time-resolution (1/8 s) images of proton-induced N2+ emissions were recorded using a new electron multiplying charge-coupled device camera, along with related Pc1 pulsations on the ground. The observed Pc1 pulsations consisted of successive rising-tone elements with a spacing for each element of 100 s and subpacket structures, which manifest as amplitude modulations with a period of a few tens of seconds. In accordance with the temporal features of the Pc1 pulsations, the auroral intensity showed a similar repetition period of 100 s and an unpredicted fast modulation of a few tens of seconds. These results indicate that PPA is generated by pitch angle scattering, nonlinearly interacting with Pc1/EMIC waves at the magnetic equator. Ozaki, M.; Shiokawa, K.; Miyoshi, Y.; Kataoka, R.; Yagitani, S.; Inoue, T.; Ebihara, Y.; Jun, C.-W; Nomura, R.; Sakaguchi, K.; Otsuka, Y.; Shoji, M.; Schofield, I.; Connors, M.; Jordanova, V.; Published by: Geophysical Research Letters Published on: 08/2016 YEAR: 2016 DOI: 10.1002/2016GL070008 fast modulation; Pc1 geomagnetic pulsations; pulsating proton aurora; subpacket structure; Van Allen Probes; wave-particle interactions |
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