Bibliography

Fast magnetosonic (MS) waves are excited by the ring distribution of energetic protons preferably when the ring velocity (VR) is within a factor of 2 above or below the local Alfvén speed (VA). Here we examine the global distributions of MS waves and proton rings with 0.5VA ≤ VR ≤ 2VA based on 64 months (from October 25, 2012 to February 28, 2018) of Van Allen Probes observations. The statistical results show that MS waves are present over a broad region of L = 1.2–6.0 and 00–24 magnetic local time (MLT), with a higher occurrence rate at L = 2.5–5.5 on the dayside. Proton rings occur mainly on the dayside of L > 5.0. During active geomagnetic periods, both MS waves and proton rings occur more frequently and extend to low L-shells. The current results provide the further observational evidence that MS waves can be excited by proton rings at a distant region and propagate to low L-shells.

Zhou, Qinghua; Jiang, Zheng; Yang, Chang; He, Yihua; Liu, Si; Xiao, Fuliang;

Published by: Journal of Geophysical Research: Space Physics Published on: 12/2020

YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028354

Fast Magnetosonic Waves; global occurrences; proton ring distribution; Radiation belt; Van Allen Probe observation; Van Allen Probes

Statistical Study of Chorus Modulations by Background Magnetic Field and Plasma Density

In this study, we use observations of THEMIS and Van Allen Probes to statistically study the modulations of chorus emissions by variations of background magnetic field and plasma density in the ultra low frequency range. The modulation events are identified automatically and divided into three types according to whether the chorus intensity correlates to the variations of the magnetic field only (Type B), plasma density only (Type N), or both (Type NB). For the THEMIS observations, the occurrences of the Types B and N are larger than Type NB, while for the Van Allen Probes observations, most events are of Type N. The chorus intensity is mostly correlated to the magnetic field strength negatively and plasma density positively. The chorus intensity tends to increase when the magnitude of the magnetic field perturbation increases, but little dependence on plasma density perturbation amplitude is found.

Xia, Zhiyang; Chen, Lunjin; Li, Wen;

Published by: Geophysical Research Letters Published on: 11/2020

YEAR: 2020 DOI: https://doi.org/10.1029/2020GL089344

Van Allen Probes

Global Propagation of Magnetospheric Pc5 ULF Waves Driven by Foreshock Transients

Pc5 (2–7 mHz) ultralow frequency (ULF) waves play a significant role in resonating with particles and transferring energy in the coupled magnetospheric and ionospheric system. Recent studies found that Pc5 ULF waves can be triggered by foreshock transients which can perturb the magnetopause through dynamic pressure variation. However, whether foreshock transient-driven Pc5 ULF waves are geoeffective and can propagate globally is still poorly understood. In this study, we take advantage of the conjunction between in situ (by the THEMIS probes, Geotail satellite, GOES satellites, and Van Allen probes) and ground-based (by the all-sky imager at South Pole and ground-based magnetometers) observations to simultaneously analyze the waves from the foreshock region to the dayside and nightside magnetosphere. Both of our two events show that the Pc5 ULF waves are generated by foreshock transients in the dayside magnetosphere. The in situ observations by THEMIS A and D and the 2-D auroral signatures show that the compressional mode waves are likely broadband and coupled to the FLRs with different frequencies and different azimuthal phase speeds. This is the first report that foreshock transients can drive both low- and high-m FLRs, with the azimuthal wave numbers varying from ~5 to ~23. Moreover, the Pc5 ULF waves propagated antisunward to midnight, this can potentially modulate magnetospheric and ionospheric dynamics globally.

Wang, Boyi; Liu, Terry; Nishimura, Yukitoshi; Zhang, Hui; Hartinger, Michael; Shi, Xueling; Ma, Qianli; Angelopoulos, Vassilis; Frey, Harald;

Published by: Journal of Geophysical Research: Space Physics Published on: 11/2020

YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028411

ULF wave; Field line resonance; wave number; global; THEMIS; aurora; Van Allen Probes

Global Propagation of Magnetospheric Pc5 ULF Waves Driven by Foreshock Transients

Pc5 (2–7 mHz) ultralow frequency (ULF) waves play a significant role in resonating with particles and transferring energy in the coupled magnetospheric and ionospheric system. Recent studies found that Pc5 ULF waves can be triggered by foreshock transients which can perturb the magnetopause through dynamic pressure variation. However, whether foreshock transient-driven Pc5 ULF waves are geoeffective and can propagate globally is still poorly understood. In this study, we take advantage of the conjunction between in situ (by the THEMIS probes, Geotail satellite, GOES satellites, and Van Allen probes) and ground-based (by the all-sky imager at South Pole and ground-based magnetometers) observations to simultaneously analyze the waves from the foreshock region to the dayside and nightside magnetosphere. Both of our two events show that the Pc5 ULF waves are generated by foreshock transients in the dayside magnetosphere. The in situ observations by THEMIS A and D and the 2-D auroral signatures show that the compressional mode waves are likely broadband and coupled to the FLRs with different frequencies and different azimuthal phase speeds. This is the first report that foreshock transients can drive both low- and high-m FLRs, with the azimuthal wave numbers varying from ~5 to ~23. Moreover, the Pc5 ULF waves propagated antisunward to midnight, this can potentially modulate magnetospheric and ionospheric dynamics globally.

Wang, Boyi; Liu, Terry; Nishimura, Yukitoshi; Zhang, Hui; Hartinger, Michael; Shi, Xueling; Ma, Qianli; Angelopoulos, Vassilis; Frey, Harald;

Published by: Journal of Geophysical Research: Space Physics Published on: 11/2020

YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028411

ULF wave; Field line resonance; wave number; global; THEMIS; aurora; Van Allen Probes

Global Propagation of Magnetospheric Pc5 ULF Waves Driven by Foreshock Transients

Pc5 (2–7 mHz) ultralow frequency (ULF) waves play a significant role in resonating with particles and transferring energy in the coupled magnetospheric and ionospheric system. Recent studies found that Pc5 ULF waves can be triggered by foreshock transients which can perturb the magnetopause through dynamic pressure variation. However, whether foreshock transient-driven Pc5 ULF waves are geoeffective and can propagate globally is still poorly understood. In this study, we take advantage of the conjunction between in situ (by the THEMIS probes, Geotail satellite, GOES satellites, and Van Allen probes) and ground-based (by the all-sky imager at South Pole and ground-based magnetometers) observations to simultaneously analyze the waves from the foreshock region to the dayside and nightside magnetosphere. Both of our two events show that the Pc5 ULF waves are generated by foreshock transients in the dayside magnetosphere. The in situ observations by THEMIS A and D and the 2-D auroral signatures show that the compressional mode waves are likely broadband and coupled to the FLRs with different frequencies and different azimuthal phase speeds. This is the first report that foreshock transients can drive both low- and high-m FLRs, with the azimuthal wave numbers varying from ~5 to ~23. Moreover, the Pc5 ULF waves propagated antisunward to midnight, this can potentially modulate magnetospheric and ionospheric dynamics globally.

Wang, Boyi; Liu, Terry; Nishimura, Yukitoshi; Zhang, Hui; Hartinger, Michael; Shi, Xueling; Ma, Qianli; Angelopoulos, Vassilis; Frey, Harald;

Published by: Journal of Geophysical Research: Space Physics Published on: 11/2020

YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028411

ULF wave; Field line resonance; wave number; global; THEMIS; aurora; Van Allen Probes

Global Propagation of Magnetospheric Pc5 ULF Waves Driven by Foreshock Transients

Pc5 (2–7 mHz) ultralow frequency (ULF) waves play a significant role in resonating with particles and transferring energy in the coupled magnetospheric and ionospheric system. Recent studies found that Pc5 ULF waves can be triggered by foreshock transients which can perturb the magnetopause through dynamic pressure variation. However, whether foreshock transient-driven Pc5 ULF waves are geoeffective and can propagate globally is still poorly understood. In this study, we take advantage of the conjunction between in situ (by the THEMIS probes, Geotail satellite, GOES satellites, and Van Allen probes) and ground-based (by the all-sky imager at South Pole and ground-based magnetometers) observations to simultaneously analyze the waves from the foreshock region to the dayside and nightside magnetosphere. Both of our two events show that the Pc5 ULF waves are generated by foreshock transients in the dayside magnetosphere. The in situ observations by THEMIS A and D and the 2-D auroral signatures show that the compressional mode waves are likely broadband and coupled to the FLRs with different frequencies and different azimuthal phase speeds. This is the first report that foreshock transients can drive both low- and high-m FLRs, with the azimuthal wave numbers varying from ~5 to ~23. Moreover, the Pc5 ULF waves propagated antisunward to midnight, this can potentially modulate magnetospheric and ionospheric dynamics globally.

Wang, Boyi; Liu, Terry; Nishimura, Yukitoshi; Zhang, Hui; Hartinger, Michael; Shi, Xueling; Ma, Qianli; Angelopoulos, Vassilis; Frey, Harald;

Published by: Journal of Geophysical Research: Space Physics Published on: 11/2020

YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028411

ULF wave; Field line resonance; wave number; global; THEMIS; aurora; Van Allen Probes

Global Propagation of Magnetospheric Pc5 ULF Waves Driven by Foreshock Transients

Pc5 (2–7 mHz) ultralow frequency (ULF) waves play a significant role in resonating with particles and transferring energy in the coupled magnetospheric and ionospheric system. Recent studies found that Pc5 ULF waves can be triggered by foreshock transients which can perturb the magnetopause through dynamic pressure variation. However, whether foreshock transient-driven Pc5 ULF waves are geoeffective and can propagate globally is still poorly understood. In this study, we take advantage of the conjunction between in situ (by the THEMIS probes, Geotail satellite, GOES satellites, and Van Allen probes) and ground-based (by the all-sky imager at South Pole and ground-based magnetometers) observations to simultaneously analyze the waves from the foreshock region to the dayside and nightside magnetosphere. Both of our two events show that the Pc5 ULF waves are generated by foreshock transients in the dayside magnetosphere. The in situ observations by THEMIS A and D and the 2-D auroral signatures show that the compressional mode waves are likely broadband and coupled to the FLRs with different frequencies and different azimuthal phase speeds. This is the first report that foreshock transients can drive both low- and high-m FLRs, with the azimuthal wave numbers varying from ~5 to ~23. Moreover, the Pc5 ULF waves propagated antisunward to midnight, this can potentially modulate magnetospheric and ionospheric dynamics globally.

Wang, Boyi; Liu, Terry; Nishimura, Yukitoshi; Zhang, Hui; Hartinger, Michael; Shi, Xueling; Ma, Qianli; Angelopoulos, Vassilis; Frey, Harald;

Published by: Journal of Geophysical Research: Space Physics Published on: 11/2020

YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028411

ULF wave; Field line resonance; wave number; global; THEMIS; aurora; Van Allen Probes

Global Propagation of Magnetospheric Pc5 ULF Waves Driven by Foreshock Transients

Pc5 (2–7 mHz) ultralow frequency (ULF) waves play a significant role in resonating with particles and transferring energy in the coupled magnetospheric and ionospheric system. Recent studies found that Pc5 ULF waves can be triggered by foreshock transients which can perturb the magnetopause through dynamic pressure variation. However, whether foreshock transient-driven Pc5 ULF waves are geoeffective and can propagate globally is still poorly understood. In this study, we take advantage of the conjunction between in situ (by the THEMIS probes, Geotail satellite, GOES satellites, and Van Allen probes) and ground-based (by the all-sky imager at South Pole and ground-based magnetometers) observations to simultaneously analyze the waves from the foreshock region to the dayside and nightside magnetosphere. Both of our two events show that the Pc5 ULF waves are generated by foreshock transients in the dayside magnetosphere. The in situ observations by THEMIS A and D and the 2-D auroral signatures show that the compressional mode waves are likely broadband and coupled to the FLRs with different frequencies and different azimuthal phase speeds. This is the first report that foreshock transients can drive both low- and high-m FLRs, with the azimuthal wave numbers varying from ~5 to ~23. Moreover, the Pc5 ULF waves propagated antisunward to midnight, this can potentially modulate magnetospheric and ionospheric dynamics globally.

Wang, Boyi; Liu, Terry; Nishimura, Yukitoshi; Zhang, Hui; Hartinger, Michael; Shi, Xueling; Ma, Qianli; Angelopoulos, Vassilis; Frey, Harald;

Published by: Journal of Geophysical Research: Space Physics Published on: 11/2020

YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028411

ULF wave; Field line resonance; wave number; global; THEMIS; aurora; Van Allen Probes

Characteristics of Electron Precipitation During 40 Energetic Electron Injections Inferred via Subionospheric VLF Signal Propagation

Energetic electron injection events are associated with energetic electron precipitation (EEP) through possible resonant wave-particle interactions. Previous studies confirm the impacts of injection-driven precipitation on observed amplitude/phase of subionospheric VLF (very low frequency) signals transmitted from distant artificial transmitters. Currently, there are substantial uncertainties on precipitation characteristics and flux during injection events. In this work we study 40 injection events selected by Van Allen Probes particle data to investigate the changes in amplitude and phase of VLF signals at ground receivers across Canada during particle injection events. We model the ionospheric effect of the EEP flux to find its impact on VLF propagation and characterize the injection events. Typically, we find a clear phase advance of ~40° in the received VLF signal at Fort Smith (Canada, L = 8) transmitted from U.S. Navy communication transmitter NAA at Maine (USA). Comparing to other VLF transmitter-receiver paths in North America leads us to conclude that effects are only seen on paths with adequately large range ≫200 km) through L > 7. Modeling the VLF phase change indicates that in the majority of events (>90\%), less than 10\% of the strong scattering limit inferred from particle flux measurements at the Van Allen Probes is required to obtain the observed VLF phase signature. The median precipitating flux during energetic particle injections is less than 4 × 106 el/cm2 s sr (<10\% of the strong scattering rate) for electrons above ~40 keV extracted from trapped particles energy spectrum. This implies that strong scattering is not typical for these 40 selected energetic electron injection events.

Ghaffari, R.; Cully, C.; Turner, D.; Reeves, G.;

Published by: Journal of Geophysical Research: Space Physics Published on: 11/2020

YEAR: 2020 DOI: https://doi.org/10.1029/2019JA027233

Van Allen Probes

On the loss mechanisms of radiation belt electron dropouts during the 12 September 2014 geomagnetic storm

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 loss mechanisms of radiation belt electron dropouts during the 12 September 2014 geomagnetic storm

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 loss mechanisms of radiation belt electron dropouts during the 12 September 2014 geomagnetic storm

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 loss mechanisms of radiation belt electron dropouts during the 12 September 2014 geomagnetic storm

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

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

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

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

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

Formation of the Low-Energy “Finger” Ion Spectral Structure Near the Inner Edge of the Plasma Sheet

We present a case study of the H+, He+, and O+ low-energy “finger” structure observed by the Van Allen Probe A Helium, Oxygen, Proton, and Electron (HOPE) spectrometer on 26 October 2016. This structure, whose characteristic energy is from approximately tens of eV to a few keV, looks like a “finger” that is rich in O+ and He+, faint in H+ on an energy-time spectrogram. By using the Space Weather Modeling Framework (SWMF) and Weimer05 electric fields, combined with a dipole or more self-consistent magnetohydrodynamic (MHD) magnetic field, backward tracing of O+ reveals that the structure is formed by ions with a long drift time from the plasma sheet during the magnetic storm main phase to the inner region with trajectories dominated by eastward drift motion, and the formation depends on the convection electric field model. The heavy ion dominance of the feature is explained by charge exchange losses along the long slow drift paths.

Wang, Y.; Kistler, L.; Mouikis, C.; Zhang, J.; Lu, J; Welling, D.; Rastaetter, L.; Bingham, S.; Jin, Y.; Wang, L.; Miyoshi, Y.;

Published by: Geophysical Research Letters Published on: 11/2020

YEAR: 2020 DOI: https://doi.org/10.1029/2020GL089875

Van Allen Probes

Formation of the Low-Energy “Finger” Ion Spectral Structure Near the Inner Edge of the Plasma Sheet

We present a case study of the H+, He+, and O+ low-energy “finger” structure observed by the Van Allen Probe A Helium, Oxygen, Proton, and Electron (HOPE) spectrometer on 26 October 2016. This structure, whose characteristic energy is from approximately tens of eV to a few keV, looks like a “finger” that is rich in O+ and He+, faint in H+ on an energy-time spectrogram. By using the Space Weather Modeling Framework (SWMF) and Weimer05 electric fields, combined with a dipole or more self-consistent magnetohydrodynamic (MHD) magnetic field, backward tracing of O+ reveals that the structure is formed by ions with a long drift time from the plasma sheet during the magnetic storm main phase to the inner region with trajectories dominated by eastward drift motion, and the formation depends on the convection electric field model. The heavy ion dominance of the feature is explained by charge exchange losses along the long slow drift paths.

Wang, Y.; Kistler, L.; Mouikis, C.; Zhang, J.; Lu, J; Welling, D.; Rastaetter, L.; Bingham, S.; Jin, Y.; Wang, L.; Miyoshi, Y.;

Published by: Geophysical Research Letters Published on: 11/2020

YEAR: 2020 DOI: https://doi.org/10.1029/2020GL089875

Van Allen Probes

Formation of the Low-Energy “Finger” Ion Spectral Structure Near the Inner Edge of the Plasma Sheet

We present a case study of the H+, He+, and O+ low-energy “finger” structure observed by the Van Allen Probe A Helium, Oxygen, Proton, and Electron (HOPE) spectrometer on 26 October 2016. This structure, whose characteristic energy is from approximately tens of eV to a few keV, looks like a “finger” that is rich in O+ and He+, faint in H+ on an energy-time spectrogram. By using the Space Weather Modeling Framework (SWMF) and Weimer05 electric fields, combined with a dipole or more self-consistent magnetohydrodynamic (MHD) magnetic field, backward tracing of O+ reveals that the structure is formed by ions with a long drift time from the plasma sheet during the magnetic storm main phase to the inner region with trajectories dominated by eastward drift motion, and the formation depends on the convection electric field model. The heavy ion dominance of the feature is explained by charge exchange losses along the long slow drift paths.

Wang, Y.; Kistler, L.; Mouikis, C.; Zhang, J.; Lu, J; Welling, D.; Rastaetter, L.; Bingham, S.; Jin, Y.; Wang, L.; Miyoshi, Y.;

Published by: Geophysical Research Letters Published on: 11/2020

YEAR: 2020 DOI: https://doi.org/10.1029/2020GL089875

Van Allen Probes

Formation of the Low-Energy “Finger” Ion Spectral Structure Near the Inner Edge of the Plasma Sheet

We present a case study of the H+, He+, and O+ low-energy “finger” structure observed by the Van Allen Probe A Helium, Oxygen, Proton, and Electron (HOPE) spectrometer on 26 October 2016. This structure, whose characteristic energy is from approximately tens of eV to a few keV, looks like a “finger” that is rich in O+ and He+, faint in H+ on an energy-time spectrogram. By using the Space Weather Modeling Framework (SWMF) and Weimer05 electric fields, combined with a dipole or more self-consistent magnetohydrodynamic (MHD) magnetic field, backward tracing of O+ reveals that the structure is formed by ions with a long drift time from the plasma sheet during the magnetic storm main phase to the inner region with trajectories dominated by eastward drift motion, and the formation depends on the convection electric field model. The heavy ion dominance of the feature is explained by charge exchange losses along the long slow drift paths.

Wang, Y.; Kistler, L.; Mouikis, C.; Zhang, J.; Lu, J; Welling, D.; Rastaetter, L.; Bingham, S.; Jin, Y.; Wang, L.; Miyoshi, Y.;

Published by: Geophysical Research Letters Published on: 11/2020

YEAR: 2020 DOI: https://doi.org/10.1029/2020GL089875

Van Allen Probes

Formation of the Low-Energy “Finger” Ion Spectral Structure Near the Inner Edge of the Plasma Sheet

We present a case study of the H+, He+, and O+ low-energy “finger” structure observed by the Van Allen Probe A Helium, Oxygen, Proton, and Electron (HOPE) spectrometer on 26 October 2016. This structure, whose characteristic energy is from approximately tens of eV to a few keV, looks like a “finger” that is rich in O+ and He+, faint in H+ on an energy-time spectrogram. By using the Space Weather Modeling Framework (SWMF) and Weimer05 electric fields, combined with a dipole or more self-consistent magnetohydrodynamic (MHD) magnetic field, backward tracing of O+ reveals that the structure is formed by ions with a long drift time from the plasma sheet during the magnetic storm main phase to the inner region with trajectories dominated by eastward drift motion, and the formation depends on the convection electric field model. The heavy ion dominance of the feature is explained by charge exchange losses along the long slow drift paths.

Wang, Y.; Kistler, L.; Mouikis, C.; Zhang, J.; Lu, J; Welling, D.; Rastaetter, L.; Bingham, S.; Jin, Y.; Wang, L.; Miyoshi, Y.;

Published by: Geophysical Research Letters Published on: 11/2020

YEAR: 2020 DOI: https://doi.org/10.1029/2020GL089875

Van Allen Probes

Relation Between Shock-Related Impulse and Subsequent ULF Wave in the Earth s Magnetosphere

The generation of Pc4-5 ultralow frequency (ULF) waves after interplanetary shock-induced electric field impulses in the Earth s magnetosphere is studied using Van Allen Probes measurements by investigating the relationship between the first impulses and subsequent resonant ULF waves. In the dayside, the relevant time scales of the first impulse is correlated better with local Alfvén speed than with local eigenfrequency, implying that the temporal scale of the first impulse is more likely related to fast-mode wave propagation rather than local field line resonance. There are only 20 out of 51 events with narrow-band poloidal ULF waves induced after the first impulse, showing a higher chance for ULF wave generation at the locations where the impulse equivalent frequency scale matches the local eigenfrequency. It is suggested that the shock-related ULF wave can be excited in the magnetosphere on condition that shock-induced impulse has large enough amplitude with its frequency matching the local eigenfrequency.

Zhang, Dianjun; Liu, Wenlong; Li, Xinlin; Sarris, Theodore; Wang, Yongfu; Xiao, Chao; Zhang, Zhao; Wygant, John;

Published by: Geophysical Research Letters Published on: 11/2020

YEAR: 2020 DOI: https://doi.org/10.1029/2020GL090027

ULF wave; interplanetary shock; Magnetosphere; Field line resonance; electric field; wave excitation; Van Allen Probes

Relation Between Shock-Related Impulse and Subsequent ULF Wave in the Earth s Magnetosphere

The generation of Pc4-5 ultralow frequency (ULF) waves after interplanetary shock-induced electric field impulses in the Earth s magnetosphere is studied using Van Allen Probes measurements by investigating the relationship between the first impulses and subsequent resonant ULF waves. In the dayside, the relevant time scales of the first impulse is correlated better with local Alfvén speed than with local eigenfrequency, implying that the temporal scale of the first impulse is more likely related to fast-mode wave propagation rather than local field line resonance. There are only 20 out of 51 events with narrow-band poloidal ULF waves induced after the first impulse, showing a higher chance for ULF wave generation at the locations where the impulse equivalent frequency scale matches the local eigenfrequency. It is suggested that the shock-related ULF wave can be excited in the magnetosphere on condition that shock-induced impulse has large enough amplitude with its frequency matching the local eigenfrequency.

Zhang, Dianjun; Liu, Wenlong; Li, Xinlin; Sarris, Theodore; Wang, Yongfu; Xiao, Chao; Zhang, Zhao; Wygant, John;

Published by: Geophysical Research Letters Published on: 11/2020

YEAR: 2020 DOI: https://doi.org/10.1029/2020GL090027

ULF wave; interplanetary shock; Magnetosphere; Field line resonance; electric field; wave excitation; Van Allen Probes

Relation Between Shock-Related Impulse and Subsequent ULF Wave in the Earth s Magnetosphere

The generation of Pc4-5 ultralow frequency (ULF) waves after interplanetary shock-induced electric field impulses in the Earth s magnetosphere is studied using Van Allen Probes measurements by investigating the relationship between the first impulses and subsequent resonant ULF waves. In the dayside, the relevant time scales of the first impulse is correlated better with local Alfvén speed than with local eigenfrequency, implying that the temporal scale of the first impulse is more likely related to fast-mode wave propagation rather than local field line resonance. There are only 20 out of 51 events with narrow-band poloidal ULF waves induced after the first impulse, showing a higher chance for ULF wave generation at the locations where the impulse equivalent frequency scale matches the local eigenfrequency. It is suggested that the shock-related ULF wave can be excited in the magnetosphere on condition that shock-induced impulse has large enough amplitude with its frequency matching the local eigenfrequency.

Zhang, Dianjun; Liu, Wenlong; Li, Xinlin; Sarris, Theodore; Wang, Yongfu; Xiao, Chao; Zhang, Zhao; Wygant, John;

Published by: Geophysical Research Letters Published on: 11/2020

YEAR: 2020 DOI: https://doi.org/10.1029/2020GL090027

ULF wave; interplanetary shock; Magnetosphere; Field line resonance; electric field; wave excitation; Van Allen Probes

Relation Between Shock-Related Impulse and Subsequent ULF Wave in the Earth s Magnetosphere

The generation of Pc4-5 ultralow frequency (ULF) waves after interplanetary shock-induced electric field impulses in the Earth s magnetosphere is studied using Van Allen Probes measurements by investigating the relationship between the first impulses and subsequent resonant ULF waves. In the dayside, the relevant time scales of the first impulse is correlated better with local Alfvén speed than with local eigenfrequency, implying that the temporal scale of the first impulse is more likely related to fast-mode wave propagation rather than local field line resonance. There are only 20 out of 51 events with narrow-band poloidal ULF waves induced after the first impulse, showing a higher chance for ULF wave generation at the locations where the impulse equivalent frequency scale matches the local eigenfrequency. It is suggested that the shock-related ULF wave can be excited in the magnetosphere on condition that shock-induced impulse has large enough amplitude with its frequency matching the local eigenfrequency.

Zhang, Dianjun; Liu, Wenlong; Li, Xinlin; Sarris, Theodore; Wang, Yongfu; Xiao, Chao; Zhang, Zhao; Wygant, John;

Published by: Geophysical Research Letters Published on: 11/2020

YEAR: 2020 DOI: https://doi.org/10.1029/2020GL090027

ULF wave; interplanetary shock; Magnetosphere; Field line resonance; electric field; wave excitation; Van Allen Probes

Relation Between Shock-Related Impulse and Subsequent ULF Wave in the Earth s Magnetosphere

The generation of Pc4-5 ultralow frequency (ULF) waves after interplanetary shock-induced electric field impulses in the Earth s magnetosphere is studied using Van Allen Probes measurements by investigating the relationship between the first impulses and subsequent resonant ULF waves. In the dayside, the relevant time scales of the first impulse is correlated better with local Alfvén speed than with local eigenfrequency, implying that the temporal scale of the first impulse is more likely related to fast-mode wave propagation rather than local field line resonance. There are only 20 out of 51 events with narrow-band poloidal ULF waves induced after the first impulse, showing a higher chance for ULF wave generation at the locations where the impulse equivalent frequency scale matches the local eigenfrequency. It is suggested that the shock-related ULF wave can be excited in the magnetosphere on condition that shock-induced impulse has large enough amplitude with its frequency matching the local eigenfrequency.

Zhang, Dianjun; Liu, Wenlong; Li, Xinlin; Sarris, Theodore; Wang, Yongfu; Xiao, Chao; Zhang, Zhao; Wygant, John;

Published by: Geophysical Research Letters Published on: 11/2020

YEAR: 2020 DOI: https://doi.org/10.1029/2020GL090027

ULF wave; interplanetary shock; Magnetosphere; Field line resonance; electric field; wave excitation; Van Allen Probes

Relation Between Shock-Related Impulse and Subsequent ULF Wave in the Earth s Magnetosphere

The generation of Pc4-5 ultralow frequency (ULF) waves after interplanetary shock-induced electric field impulses in the Earth s magnetosphere is studied using Van Allen Probes measurements by investigating the relationship between the first impulses and subsequent resonant ULF waves. In the dayside, the relevant time scales of the first impulse is correlated better with local Alfvén speed than with local eigenfrequency, implying that the temporal scale of the first impulse is more likely related to fast-mode wave propagation rather than local field line resonance. There are only 20 out of 51 events with narrow-band poloidal ULF waves induced after the first impulse, showing a higher chance for ULF wave generation at the locations where the impulse equivalent frequency scale matches the local eigenfrequency. It is suggested that the shock-related ULF wave can be excited in the magnetosphere on condition that shock-induced impulse has large enough amplitude with its frequency matching the local eigenfrequency.

Zhang, Dianjun; Liu, Wenlong; Li, Xinlin; Sarris, Theodore; Wang, Yongfu; Xiao, Chao; Zhang, Zhao; Wygant, John;

Published by: Geophysical Research Letters Published on: 11/2020

YEAR: 2020 DOI: https://doi.org/10.1029/2020GL090027

ULF wave; interplanetary shock; Magnetosphere; Field line resonance; electric field; wave excitation; Van Allen Probes

Long-Term Dropout of Relativistic Electrons in the Outer Radiation Belt During Two Sequential Geomagnetic Storms

On 31 January 2016, the flux of >2 MeV electrons observed by Geostationary Operational Environmental Satellite (GOES)-13 dropped to the background level during a minor storm main phase (−48 nT). Then, a second storm (−53 nT) occurred on 2 February; during the 3 days after its main phase, the flux remained at background level. Using data from various instruments on the GOES, Polar Operational Environmental Satellites (POES), Radiation Belt Storm Probes (RBSP), Meteor-M2, and Fengyun-series spacecraft, we study this long-term dropout of MeV electrons during two sequential storms of similar magnitude under lightly disturbed solar wind conditions. Observations from low-altitude satellites show that the fluxes decreased first at higher L-shells and then gradually propagated inward. Moreover, the fluxes were almost completely lost and dropped to the background level at L > 5, while the fluxes at 4 < L < 5 were partly lost, as observed by RBSP and low-altitude satellites. Finally, observations show that on 5 February, only the fluxes at L > 5.5 recovered, while the fluxes at 4 < L < 5 did not return to the prestorm levels. These observations indicate that the loss and recovery processes developed first at higher L-shells. Phase space density (PSD) analysis shows that radial outward diffusion was the main reason for the dropout at higher L-shells. Regarding electron enhancement, stronger inward diffusion was accompanied by ultra-low-frequency (ULF) wave activities at higher L-shells, and chorus waves observed at outer L-shells provided conditions for relativistic electron flux recovery to the prestorm levels.

Wu, H.; Chen, T.; Kalegaev, V.; Panasyuk, M.; Vlasova, N.; Duan, S.; Zhang, X.; He, Z.; Luo, J.; Wang, C.;

Published by: Journal of Geophysical Research: Space Physics Published on: 10/2020

YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028098

Radiation belt; relativistic electron dropout; Geomagnetic storm; Van Allen Probes

Long-Term Dropout of Relativistic Electrons in the Outer Radiation Belt During Two Sequential Geomagnetic Storms

On 31 January 2016, the flux of >2 MeV electrons observed by Geostationary Operational Environmental Satellite (GOES)-13 dropped to the background level during a minor storm main phase (−48 nT). Then, a second storm (−53 nT) occurred on 2 February; during the 3 days after its main phase, the flux remained at background level. Using data from various instruments on the GOES, Polar Operational Environmental Satellites (POES), Radiation Belt Storm Probes (RBSP), Meteor-M2, and Fengyun-series spacecraft, we study this long-term dropout of MeV electrons during two sequential storms of similar magnitude under lightly disturbed solar wind conditions. Observations from low-altitude satellites show that the fluxes decreased first at higher L-shells and then gradually propagated inward. Moreover, the fluxes were almost completely lost and dropped to the background level at L > 5, while the fluxes at 4 < L < 5 were partly lost, as observed by RBSP and low-altitude satellites. Finally, observations show that on 5 February, only the fluxes at L > 5.5 recovered, while the fluxes at 4 < L < 5 did not return to the prestorm levels. These observations indicate that the loss and recovery processes developed first at higher L-shells. Phase space density (PSD) analysis shows that radial outward diffusion was the main reason for the dropout at higher L-shells. Regarding electron enhancement, stronger inward diffusion was accompanied by ultra-low-frequency (ULF) wave activities at higher L-shells, and chorus waves observed at outer L-shells provided conditions for relativistic electron flux recovery to the prestorm levels.

Wu, H.; Chen, T.; Kalegaev, V.; Panasyuk, M.; Vlasova, N.; Duan, S.; Zhang, X.; He, Z.; Luo, J.; Wang, C.;

Published by: Journal of Geophysical Research: Space Physics Published on: 10/2020

YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028098

Radiation belt; relativistic electron dropout; Geomagnetic storm; Van Allen Probes

Long-Term Dropout of Relativistic Electrons in the Outer Radiation Belt During Two Sequential Geomagnetic Storms

On 31 January 2016, the flux of >2 MeV electrons observed by Geostationary Operational Environmental Satellite (GOES)-13 dropped to the background level during a minor storm main phase (−48 nT). Then, a second storm (−53 nT) occurred on 2 February; during the 3 days after its main phase, the flux remained at background level. Using data from various instruments on the GOES, Polar Operational Environmental Satellites (POES), Radiation Belt Storm Probes (RBSP), Meteor-M2, and Fengyun-series spacecraft, we study this long-term dropout of MeV electrons during two sequential storms of similar magnitude under lightly disturbed solar wind conditions. Observations from low-altitude satellites show that the fluxes decreased first at higher L-shells and then gradually propagated inward. Moreover, the fluxes were almost completely lost and dropped to the background level at L > 5, while the fluxes at 4 < L < 5 were partly lost, as observed by RBSP and low-altitude satellites. Finally, observations show that on 5 February, only the fluxes at L > 5.5 recovered, while the fluxes at 4 < L < 5 did not return to the prestorm levels. These observations indicate that the loss and recovery processes developed first at higher L-shells. Phase space density (PSD) analysis shows that radial outward diffusion was the main reason for the dropout at higher L-shells. Regarding electron enhancement, stronger inward diffusion was accompanied by ultra-low-frequency (ULF) wave activities at higher L-shells, and chorus waves observed at outer L-shells provided conditions for relativistic electron flux recovery to the prestorm levels.

Wu, H.; Chen, T.; Kalegaev, V.; Panasyuk, M.; Vlasova, N.; Duan, S.; Zhang, X.; He, Z.; Luo, J.; Wang, C.;

Published by: Journal of Geophysical Research: Space Physics Published on: 10/2020

YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028098

Radiation belt; relativistic electron dropout; Geomagnetic storm; Van Allen Probes

Long-Term Dropout of Relativistic Electrons in the Outer Radiation Belt During Two Sequential Geomagnetic Storms

On 31 January 2016, the flux of >2 MeV electrons observed by Geostationary Operational Environmental Satellite (GOES)-13 dropped to the background level during a minor storm main phase (−48 nT). Then, a second storm (−53 nT) occurred on 2 February; during the 3 days after its main phase, the flux remained at background level. Using data from various instruments on the GOES, Polar Operational Environmental Satellites (POES), Radiation Belt Storm Probes (RBSP), Meteor-M2, and Fengyun-series spacecraft, we study this long-term dropout of MeV electrons during two sequential storms of similar magnitude under lightly disturbed solar wind conditions. Observations from low-altitude satellites show that the fluxes decreased first at higher L-shells and then gradually propagated inward. Moreover, the fluxes were almost completely lost and dropped to the background level at L > 5, while the fluxes at 4 < L < 5 were partly lost, as observed by RBSP and low-altitude satellites. Finally, observations show that on 5 February, only the fluxes at L > 5.5 recovered, while the fluxes at 4 < L < 5 did not return to the prestorm levels. These observations indicate that the loss and recovery processes developed first at higher L-shells. Phase space density (PSD) analysis shows that radial outward diffusion was the main reason for the dropout at higher L-shells. Regarding electron enhancement, stronger inward diffusion was accompanied by ultra-low-frequency (ULF) wave activities at higher L-shells, and chorus waves observed at outer L-shells provided conditions for relativistic electron flux recovery to the prestorm levels.

Wu, H.; Chen, T.; Kalegaev, V.; Panasyuk, M.; Vlasova, N.; Duan, S.; Zhang, X.; He, Z.; Luo, J.; Wang, C.;

Published by: Journal of Geophysical Research: Space Physics Published on: 10/2020

YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028098

Radiation belt; relativistic electron dropout; Geomagnetic storm; Van Allen Probes

Long-Term Dropout of Relativistic Electrons in the Outer Radiation Belt During Two Sequential Geomagnetic Storms

On 31 January 2016, the flux of >2 MeV electrons observed by Geostationary Operational Environmental Satellite (GOES)-13 dropped to the background level during a minor storm main phase (−48 nT). Then, a second storm (−53 nT) occurred on 2 February; during the 3 days after its main phase, the flux remained at background level. Using data from various instruments on the GOES, Polar Operational Environmental Satellites (POES), Radiation Belt Storm Probes (RBSP), Meteor-M2, and Fengyun-series spacecraft, we study this long-term dropout of MeV electrons during two sequential storms of similar magnitude under lightly disturbed solar wind conditions. Observations from low-altitude satellites show that the fluxes decreased first at higher L-shells and then gradually propagated inward. Moreover, the fluxes were almost completely lost and dropped to the background level at L > 5, while the fluxes at 4 < L < 5 were partly lost, as observed by RBSP and low-altitude satellites. Finally, observations show that on 5 February, only the fluxes at L > 5.5 recovered, while the fluxes at 4 < L < 5 did not return to the prestorm levels. These observations indicate that the loss and recovery processes developed first at higher L-shells. Phase space density (PSD) analysis shows that radial outward diffusion was the main reason for the dropout at higher L-shells. Regarding electron enhancement, stronger inward diffusion was accompanied by ultra-low-frequency (ULF) wave activities at higher L-shells, and chorus waves observed at outer L-shells provided conditions for relativistic electron flux recovery to the prestorm levels.

Wu, H.; Chen, T.; Kalegaev, V.; Panasyuk, M.; Vlasova, N.; Duan, S.; Zhang, X.; He, Z.; Luo, J.; Wang, C.;

Published by: Journal of Geophysical Research: Space Physics Published on: 10/2020

YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028098

Radiation belt; relativistic electron dropout; Geomagnetic storm; Van Allen Probes

Long-Term Dropout of Relativistic Electrons in the Outer Radiation Belt During Two Sequential Geomagnetic Storms

On 31 January 2016, the flux of >2 MeV electrons observed by Geostationary Operational Environmental Satellite (GOES)-13 dropped to the background level during a minor storm main phase (−48 nT). Then, a second storm (−53 nT) occurred on 2 February; during the 3 days after its main phase, the flux remained at background level. Using data from various instruments on the GOES, Polar Operational Environmental Satellites (POES), Radiation Belt Storm Probes (RBSP), Meteor-M2, and Fengyun-series spacecraft, we study this long-term dropout of MeV electrons during two sequential storms of similar magnitude under lightly disturbed solar wind conditions. Observations from low-altitude satellites show that the fluxes decreased first at higher L-shells and then gradually propagated inward. Moreover, the fluxes were almost completely lost and dropped to the background level at L > 5, while the fluxes at 4 < L < 5 were partly lost, as observed by RBSP and low-altitude satellites. Finally, observations show that on 5 February, only the fluxes at L > 5.5 recovered, while the fluxes at 4 < L < 5 did not return to the prestorm levels. These observations indicate that the loss and recovery processes developed first at higher L-shells. Phase space density (PSD) analysis shows that radial outward diffusion was the main reason for the dropout at higher L-shells. Regarding electron enhancement, stronger inward diffusion was accompanied by ultra-low-frequency (ULF) wave activities at higher L-shells, and chorus waves observed at outer L-shells provided conditions for relativistic electron flux recovery to the prestorm levels.

Wu, H.; Chen, T.; Kalegaev, V.; Panasyuk, M.; Vlasova, N.; Duan, S.; Zhang, X.; He, Z.; Luo, J.; Wang, C.;

Published by: Journal of Geophysical Research: Space Physics Published on: 10/2020

YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028098

Radiation belt; relativistic electron dropout; Geomagnetic storm; Van Allen Probes

Precipitation Loss of Radiation Belt Electrons by Two-Band Plasmaspheric Hiss Waves

A two-band plasmaspheric hiss consisting of a low-frequency band (normal hiss with the frequency below 2 kHz) and a high-frequency band (locally generated hiss with the frequency up to 10 kHz) was observed on 6 January 2014 by the Van Allen Probes (He et al., 2019, https://doi.org/10.1029/2018GL081578). The electron scattering effect driven by this kind of two-band plasmaspheric hiss is evaluated by the quasi-linear diffusion simulation for the first time. Realistic wave characteristic parameters of the two-band plasmaspheric hiss from statistics are adopted for driving our simulation. The pitch angle diffusion rates of the low-frequency band hiss present a “gap” with minimum magnitude at pitch angle αe ∼ 70°, a condition not favoring the transport of large pitch angle electrons toward the loss cone. However, the diffusion rates of the high-frequency band hiss have peak values at αe ∼ 70°, filling up for the “gap” of the low-frequency hiss diffusion rates. The realistic wave-driven electron PSD evolutions demonstrate that the collaborated effect of the low-frequency band and high-frequency band hiss can cause significant precipitation losses of energetic electrons of tens to several hundred keV within 2 days.

He, Zhaoguo; Yan, Qi; Zhang, Xiaoping; Yu, Jiang; Ma, Yonghui; Cao, Yong; Cui, Jun;

Published by: Journal of Geophysical Research: Space Physics Published on: 10/2020

YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028157

two-band hiss; radiation belt electron; loss; Van Allen Probes

Precipitation Loss of Radiation Belt Electrons by Two-Band Plasmaspheric Hiss Waves

A two-band plasmaspheric hiss consisting of a low-frequency band (normal hiss with the frequency below 2 kHz) and a high-frequency band (locally generated hiss with the frequency up to 10 kHz) was observed on 6 January 2014 by the Van Allen Probes (He et al., 2019, https://doi.org/10.1029/2018GL081578). The electron scattering effect driven by this kind of two-band plasmaspheric hiss is evaluated by the quasi-linear diffusion simulation for the first time. Realistic wave characteristic parameters of the two-band plasmaspheric hiss from statistics are adopted for driving our simulation. The pitch angle diffusion rates of the low-frequency band hiss present a “gap” with minimum magnitude at pitch angle αe ∼ 70°, a condition not favoring the transport of large pitch angle electrons toward the loss cone. However, the diffusion rates of the high-frequency band hiss have peak values at αe ∼ 70°, filling up for the “gap” of the low-frequency hiss diffusion rates. The realistic wave-driven electron PSD evolutions demonstrate that the collaborated effect of the low-frequency band and high-frequency band hiss can cause significant precipitation losses of energetic electrons of tens to several hundred keV within 2 days.

He, Zhaoguo; Yan, Qi; Zhang, Xiaoping; Yu, Jiang; Ma, Yonghui; Cao, Yong; Cui, Jun;

Published by: Journal of Geophysical Research: Space Physics Published on: 10/2020

YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028157

two-band hiss; radiation belt electron; loss; Van Allen Probes

Precipitation Loss of Radiation Belt Electrons by Two-Band Plasmaspheric Hiss Waves

A two-band plasmaspheric hiss consisting of a low-frequency band (normal hiss with the frequency below 2 kHz) and a high-frequency band (locally generated hiss with the frequency up to 10 kHz) was observed on 6 January 2014 by the Van Allen Probes (He et al., 2019, https://doi.org/10.1029/2018GL081578). The electron scattering effect driven by this kind of two-band plasmaspheric hiss is evaluated by the quasi-linear diffusion simulation for the first time. Realistic wave characteristic parameters of the two-band plasmaspheric hiss from statistics are adopted for driving our simulation. The pitch angle diffusion rates of the low-frequency band hiss present a “gap” with minimum magnitude at pitch angle αe ∼ 70°, a condition not favoring the transport of large pitch angle electrons toward the loss cone. However, the diffusion rates of the high-frequency band hiss have peak values at αe ∼ 70°, filling up for the “gap” of the low-frequency hiss diffusion rates. The realistic wave-driven electron PSD evolutions demonstrate that the collaborated effect of the low-frequency band and high-frequency band hiss can cause significant precipitation losses of energetic electrons of tens to several hundred keV within 2 days.

He, Zhaoguo; Yan, Qi; Zhang, Xiaoping; Yu, Jiang; Ma, Yonghui; Cao, Yong; Cui, Jun;

Published by: Journal of Geophysical Research: Space Physics Published on: 10/2020

YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028157

two-band hiss; radiation belt electron; loss; Van Allen Probes

Precipitation Loss of Radiation Belt Electrons by Two-Band Plasmaspheric Hiss Waves

A two-band plasmaspheric hiss consisting of a low-frequency band (normal hiss with the frequency below 2 kHz) and a high-frequency band (locally generated hiss with the frequency up to 10 kHz) was observed on 6 January 2014 by the Van Allen Probes (He et al., 2019, https://doi.org/10.1029/2018GL081578). The electron scattering effect driven by this kind of two-band plasmaspheric hiss is evaluated by the quasi-linear diffusion simulation for the first time. Realistic wave characteristic parameters of the two-band plasmaspheric hiss from statistics are adopted for driving our simulation. The pitch angle diffusion rates of the low-frequency band hiss present a “gap” with minimum magnitude at pitch angle αe ∼ 70°, a condition not favoring the transport of large pitch angle electrons toward the loss cone. However, the diffusion rates of the high-frequency band hiss have peak values at αe ∼ 70°, filling up for the “gap” of the low-frequency hiss diffusion rates. The realistic wave-driven electron PSD evolutions demonstrate that the collaborated effect of the low-frequency band and high-frequency band hiss can cause significant precipitation losses of energetic electrons of tens to several hundred keV within 2 days.

He, Zhaoguo; Yan, Qi; Zhang, Xiaoping; Yu, Jiang; Ma, Yonghui; Cao, Yong; Cui, Jun;

Published by: Journal of Geophysical Research: Space Physics Published on: 10/2020

YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028157

two-band hiss; radiation belt electron; loss; Van Allen Probes

A New Approach to Constructing Models of Electron Diffusion by EMIC Waves in the Radiation Belts

Electromagnetic ion cyclotron (EMIC) waves play an important role in relativistic electron losses in the radiation belts through diffusion via resonant wave-particle interactions. We present a new approach for calculating bounce and drift-averaged EMIC electron diffusion coefficients. We calculate bounce-averaged diffusion coefficients, using quasi-linear theory, for each individual Combined Release and Radiation Effects Satellite (CRRES) EMIC wave observation using fitted wave properties, the plasma density and the background magnetic field. These calculations are then combined into bounce-averaged diffusion coefficients. The resulting coefficients therefore capture the combined effects of individual spectra and plasma properties as opposed to previous approaches that use average spectral and plasma properties, resulting in diffusion over a wider range of energies and pitch angles. These calculations, and their role in radiation belt simulations, are then compared against existing diffusion models. The new diffusion coefficients are found to significantly improve the agreement between the calculated decay of relativistic electrons and Van Allen Probes data.

Ross, J.; Glauert, S.; Horne, R.; Watt, C.; Meredith, N.; Woodfield, E.;

Published by: Geophysical Research Letters Published on: 10/2020

YEAR: 2020 DOI: https://doi.org/10.1029/2020GL088976

Radiation belts; EMIC waves; electron diffusion; Van Allen Probes

A New Approach to Constructing Models of Electron Diffusion by EMIC Waves in the Radiation Belts

Electromagnetic ion cyclotron (EMIC) waves play an important role in relativistic electron losses in the radiation belts through diffusion via resonant wave-particle interactions. We present a new approach for calculating bounce and drift-averaged EMIC electron diffusion coefficients. We calculate bounce-averaged diffusion coefficients, using quasi-linear theory, for each individual Combined Release and Radiation Effects Satellite (CRRES) EMIC wave observation using fitted wave properties, the plasma density and the background magnetic field. These calculations are then combined into bounce-averaged diffusion coefficients. The resulting coefficients therefore capture the combined effects of individual spectra and plasma properties as opposed to previous approaches that use average spectral and plasma properties, resulting in diffusion over a wider range of energies and pitch angles. These calculations, and their role in radiation belt simulations, are then compared against existing diffusion models. The new diffusion coefficients are found to significantly improve the agreement between the calculated decay of relativistic electrons and Van Allen Probes data.

Ross, J.; Glauert, S.; Horne, R.; Watt, C.; Meredith, N.; Woodfield, E.;

Published by: Geophysical Research Letters Published on: 10/2020

YEAR: 2020 DOI: https://doi.org/10.1029/2020GL088976

Radiation belts; EMIC waves; electron diffusion; Van Allen Probes

Analytical Fast Magnetosonic Wave Model Based on Observations of Van Allen Probe

Based on observations of Van Allen Probe-A during the period from 19 September 2012 to 28 February 2016, the relations of the fast magnetosonic (MS) wave amplitude Bw with kp index, the wave normal angle (WNA), and the wave normalized frequency (norF) are presented. Then, we establish an analytical regression model for MS wave amplitude as a function of geomagnetic storm activity (presented by kp index), L-shell (L), magnetic local time (MLT), magnetic latitude (λ), and the characteristics of MS wave, that is, wave norF and WNA. From the analytical Bw models, we found MS wave amplitude Bw has a positive relation with the intensity of geomagnetic activities both inside and outside the plasmapause, while the Bw can reach higher values inside the plasmapause than it does outside the plasmapause as the kp index increases. The Bw distribution on the norF demonstrates that most of the wave energies are concentrated on the lower harmonics part, which results from the excitation mechanism of MS waves. In addition, the Bw distribution on the WNA shows that the waves with larger normal angles have higher values of wave amplitude. Our analytic MS wave model agrees with the observed distribution in 3-D space of L, MLT, and λ well with high value of determine coefficient R2. The extended λ dimension will help us to calculate the more accurate bounced averaged diffusion coefficients during particles transit time.

Yao, Fei; Yuan, Zhigang; Yu, Xiongdong; Wang, Dedong; Ouyang, Zhihai;

Published by: Journal of Geophysical Research: Space Physics Published on: 10/2020

YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028527

fast magnetosonic wave; Van Allen Probe; analytical regression model; wave normal angle; Plasmapause; Van Allen Probes

Analytical Fast Magnetosonic Wave Model Based on Observations of Van Allen Probe

Based on observations of Van Allen Probe-A during the period from 19 September 2012 to 28 February 2016, the relations of the fast magnetosonic (MS) wave amplitude Bw with kp index, the wave normal angle (WNA), and the wave normalized frequency (norF) are presented. Then, we establish an analytical regression model for MS wave amplitude as a function of geomagnetic storm activity (presented by kp index), L-shell (L), magnetic local time (MLT), magnetic latitude (λ), and the characteristics of MS wave, that is, wave norF and WNA. From the analytical Bw models, we found MS wave amplitude Bw has a positive relation with the intensity of geomagnetic activities both inside and outside the plasmapause, while the Bw can reach higher values inside the plasmapause than it does outside the plasmapause as the kp index increases. The Bw distribution on the norF demonstrates that most of the wave energies are concentrated on the lower harmonics part, which results from the excitation mechanism of MS waves. In addition, the Bw distribution on the WNA shows that the waves with larger normal angles have higher values of wave amplitude. Our analytic MS wave model agrees with the observed distribution in 3-D space of L, MLT, and λ well with high value of determine coefficient R2. The extended λ dimension will help us to calculate the more accurate bounced averaged diffusion coefficients during particles transit time.

Yao, Fei; Yuan, Zhigang; Yu, Xiongdong; Wang, Dedong; Ouyang, Zhihai;

Published by: Journal of Geophysical Research: Space Physics Published on: 10/2020

YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028527

fast magnetosonic wave; Van Allen Probe; analytical regression model; wave normal angle; Plasmapause; Van Allen Probes

Analytical Fast Magnetosonic Wave Model Based on Observations of Van Allen Probe

Based on observations of Van Allen Probe-A during the period from 19 September 2012 to 28 February 2016, the relations of the fast magnetosonic (MS) wave amplitude Bw with kp index, the wave normal angle (WNA), and the wave normalized frequency (norF) are presented. Then, we establish an analytical regression model for MS wave amplitude as a function of geomagnetic storm activity (presented by kp index), L-shell (L), magnetic local time (MLT), magnetic latitude (λ), and the characteristics of MS wave, that is, wave norF and WNA. From the analytical Bw models, we found MS wave amplitude Bw has a positive relation with the intensity of geomagnetic activities both inside and outside the plasmapause, while the Bw can reach higher values inside the plasmapause than it does outside the plasmapause as the kp index increases. The Bw distribution on the norF demonstrates that most of the wave energies are concentrated on the lower harmonics part, which results from the excitation mechanism of MS waves. In addition, the Bw distribution on the WNA shows that the waves with larger normal angles have higher values of wave amplitude. Our analytic MS wave model agrees with the observed distribution in 3-D space of L, MLT, and λ well with high value of determine coefficient R2. The extended λ dimension will help us to calculate the more accurate bounced averaged diffusion coefficients during particles transit time.

Yao, Fei; Yuan, Zhigang; Yu, Xiongdong; Wang, Dedong; Ouyang, Zhihai;

Published by: Journal of Geophysical Research: Space Physics Published on: 10/2020

YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028527

fast magnetosonic wave; Van Allen Probe; analytical regression model; wave normal angle; Plasmapause; Van Allen Probes

Analytical Fast Magnetosonic Wave Model Based on Observations of Van Allen Probe

Based on observations of Van Allen Probe-A during the period from 19 September 2012 to 28 February 2016, the relations of the fast magnetosonic (MS) wave amplitude Bw with kp index, the wave normal angle (WNA), and the wave normalized frequency (norF) are presented. Then, we establish an analytical regression model for MS wave amplitude as a function of geomagnetic storm activity (presented by kp index), L-shell (L), magnetic local time (MLT), magnetic latitude (λ), and the characteristics of MS wave, that is, wave norF and WNA. From the analytical Bw models, we found MS wave amplitude Bw has a positive relation with the intensity of geomagnetic activities both inside and outside the plasmapause, while the Bw can reach higher values inside the plasmapause than it does outside the plasmapause as the kp index increases. The Bw distribution on the norF demonstrates that most of the wave energies are concentrated on the lower harmonics part, which results from the excitation mechanism of MS waves. In addition, the Bw distribution on the WNA shows that the waves with larger normal angles have higher values of wave amplitude. Our analytic MS wave model agrees with the observed distribution in 3-D space of L, MLT, and λ well with high value of determine coefficient R2. The extended λ dimension will help us to calculate the more accurate bounced averaged diffusion coefficients during particles transit time.

Yao, Fei; Yuan, Zhigang; Yu, Xiongdong; Wang, Dedong; Ouyang, Zhihai;

Published by: Journal of Geophysical Research: Space Physics Published on: 10/2020

YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028527

fast magnetosonic wave; Van Allen Probe; analytical regression model; wave normal angle; Plasmapause; Van Allen Probes

Cross-Scale Quantification of Storm-Time Dayside Magnetospheric Magnetic Flux Content

A clear understanding of storm-time magnetospheric dynamics is essential for a reliable storm forecasting capability. The dayside magnetospheric response to an interplanetary coronal mass ejection (ICME; dynamic pressure Pdyn > 20 nPa and storm-time index SYM-H < −150 nT) is investigated using in situ OMNI, Geotail, Cluster, MMS, GOES, Van Allen Probes, and THEMIS measurements. The dayside magnetic flux content is directly quantified from in situ magnetic field measurements at different radial distances. The arrival of the ICME, consisting of shock and sheath regions preceding a magnetic cloud, initiated a storm sudden commencement (SSC) phase (SYM-H ~ +50 nT). At SSC, the magnetopause standoff distance was compressed earthward at ICME shock encounter at an average rate ~−10.8 Earth radii per hour for ~10 min, resulting in a rapid 40\% reduction in the magnetospheric volume. The “closed” magnetic flux content remained constant at 170 ± 30 kWb inside the compressed dayside magnetosphere, even in the presence of dayside reconnection, as evident by an outsized flux transfer event containing 160 MWb. During the storm main and recovery phases, the magnetosphere expanded. The dayside magnetic flux did not remain constant within the expanding magnetosphere (110 ± 30 kWb), resulting in a 35\% reduction in pre-storm flux content during the magnetic cloud encounter. At that stage, the magnetospheric magnetic flux was eroded resulting in a weakened dayside magnetospheric field strength at radial distances R ≥ 5 RE. It is concluded that the inadequate replenishment of the eroded dayside magnetospheric flux during the magnetosphere expansion phase is due to a time lag in storm-time Dungey cycle.

Akhavan-Tafti, M.; Fontaine, D.; Slavin, J.; Le Contel, O.; Turner, D.;

Published by: Journal of Geophysical Research: Space Physics Published on: 10/2020

YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028027

interplanetary coronal mass ejection; magnetic flux quantification; cross-scale observations; flux transfer event; Dungey cycle; Geomagnetic storm; Van Allen Probes

Cross-Scale Quantification of Storm-Time Dayside Magnetospheric Magnetic Flux Content

A clear understanding of storm-time magnetospheric dynamics is essential for a reliable storm forecasting capability. The dayside magnetospheric response to an interplanetary coronal mass ejection (ICME; dynamic pressure Pdyn > 20 nPa and storm-time index SYM-H < −150 nT) is investigated using in situ OMNI, Geotail, Cluster, MMS, GOES, Van Allen Probes, and THEMIS measurements. The dayside magnetic flux content is directly quantified from in situ magnetic field measurements at different radial distances. The arrival of the ICME, consisting of shock and sheath regions preceding a magnetic cloud, initiated a storm sudden commencement (SSC) phase (SYM-H ~ +50 nT). At SSC, the magnetopause standoff distance was compressed earthward at ICME shock encounter at an average rate ~−10.8 Earth radii per hour for ~10 min, resulting in a rapid 40\% reduction in the magnetospheric volume. The “closed” magnetic flux content remained constant at 170 ± 30 kWb inside the compressed dayside magnetosphere, even in the presence of dayside reconnection, as evident by an outsized flux transfer event containing 160 MWb. During the storm main and recovery phases, the magnetosphere expanded. The dayside magnetic flux did not remain constant within the expanding magnetosphere (110 ± 30 kWb), resulting in a 35\% reduction in pre-storm flux content during the magnetic cloud encounter. At that stage, the magnetospheric magnetic flux was eroded resulting in a weakened dayside magnetospheric field strength at radial distances R ≥ 5 RE. It is concluded that the inadequate replenishment of the eroded dayside magnetospheric flux during the magnetosphere expansion phase is due to a time lag in storm-time Dungey cycle.

Akhavan-Tafti, M.; Fontaine, D.; Slavin, J.; Le Contel, O.; Turner, D.;

Published by: Journal of Geophysical Research: Space Physics Published on: 10/2020

YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028027

interplanetary coronal mass ejection; magnetic flux quantification; cross-scale observations; flux transfer event; Dungey cycle; Geomagnetic storm; Van Allen Probes

Cross-Scale Quantification of Storm-Time Dayside Magnetospheric Magnetic Flux Content

A clear understanding of storm-time magnetospheric dynamics is essential for a reliable storm forecasting capability. The dayside magnetospheric response to an interplanetary coronal mass ejection (ICME; dynamic pressure Pdyn > 20 nPa and storm-time index SYM-H < −150 nT) is investigated using in situ OMNI, Geotail, Cluster, MMS, GOES, Van Allen Probes, and THEMIS measurements. The dayside magnetic flux content is directly quantified from in situ magnetic field measurements at different radial distances. The arrival of the ICME, consisting of shock and sheath regions preceding a magnetic cloud, initiated a storm sudden commencement (SSC) phase (SYM-H ~ +50 nT). At SSC, the magnetopause standoff distance was compressed earthward at ICME shock encounter at an average rate ~−10.8 Earth radii per hour for ~10 min, resulting in a rapid 40\% reduction in the magnetospheric volume. The “closed” magnetic flux content remained constant at 170 ± 30 kWb inside the compressed dayside magnetosphere, even in the presence of dayside reconnection, as evident by an outsized flux transfer event containing 160 MWb. During the storm main and recovery phases, the magnetosphere expanded. The dayside magnetic flux did not remain constant within the expanding magnetosphere (110 ± 30 kWb), resulting in a 35\% reduction in pre-storm flux content during the magnetic cloud encounter. At that stage, the magnetospheric magnetic flux was eroded resulting in a weakened dayside magnetospheric field strength at radial distances R ≥ 5 RE. It is concluded that the inadequate replenishment of the eroded dayside magnetospheric flux during the magnetosphere expansion phase is due to a time lag in storm-time Dungey cycle.

Akhavan-Tafti, M.; Fontaine, D.; Slavin, J.; Le Contel, O.; Turner, D.;

Published by: Journal of Geophysical Research: Space Physics Published on: 10/2020

YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028027

interplanetary coronal mass ejection; magnetic flux quantification; cross-scale observations; flux transfer event; Dungey cycle; Geomagnetic storm; Van Allen Probes

First Direct Observations of Propagation of Discrete Chorus Elements From the Equatorial Source to Higher Latitudes, Using the Van Allen Probes and Arase Satellites

Whistler mode chorus waves have recently been established as the most likely candidate for scattering relativistic electrons to produce the electron microbursts observed by low altitude satellites and balloons. These waves would have to propagate from the equatorial source region to significantly higher magnetic latitude in order to scatter electrons of these relativistic energies. This theoretically proposed propagation has never been directly observed. We present the first direct observations of the same discrete rising tone chorus elements propagating from a near equatorial (Van Allen Probes) to an off-equatorial (Arase) satellite. The chorus is observed first on the more equatorial satellite and is found to be more oblique and significantly attenuated at the off-equatorial satellite. This is consistent with the prevailing theory of chorus propagation and with the idea that chorus must propagate from the equatorial source region to higher latitudes. Ray tracing of chorus at the observed frequencies confirms that these elements could be generated parallel to the field at the equator, and propagate through the medium unducted to Van Allen Probes A and then to Arase with the observed time delay, and have the observed obliquity and intensity at each satellite.

Colpitts, Chris; Miyoshi, Yoshizumi; Kasahara, Yoshiya; Delzanno, Gian; Wygant, John; Cattell, Cynthia; Breneman, Aaron; Kletzing, Craig; Cunningham, Greg; Hikishima, Mitsuru; Matsuda, Shoya; Katoh, Yuto; Ripoll, Jean-Francois; Shinohara, Iku; Matsuoka, Ayako;

Published by: Journal of Geophysical Research: Space Physics Published on: 10/2020

YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028315

Chorus; wave; propagation; Simultaneous observations; Radiation belt; Van Allen Probes

First Direct Observations of Propagation of Discrete Chorus Elements From the Equatorial Source to Higher Latitudes, Using the Van Allen Probes and Arase Satellites

Whistler mode chorus waves have recently been established as the most likely candidate for scattering relativistic electrons to produce the electron microbursts observed by low altitude satellites and balloons. These waves would have to propagate from the equatorial source region to significantly higher magnetic latitude in order to scatter electrons of these relativistic energies. This theoretically proposed propagation has never been directly observed. We present the first direct observations of the same discrete rising tone chorus elements propagating from a near equatorial (Van Allen Probes) to an off-equatorial (Arase) satellite. The chorus is observed first on the more equatorial satellite and is found to be more oblique and significantly attenuated at the off-equatorial satellite. This is consistent with the prevailing theory of chorus propagation and with the idea that chorus must propagate from the equatorial source region to higher latitudes. Ray tracing of chorus at the observed frequencies confirms that these elements could be generated parallel to the field at the equator, and propagate through the medium unducted to Van Allen Probes A and then to Arase with the observed time delay, and have the observed obliquity and intensity at each satellite.

Colpitts, Chris; Miyoshi, Yoshizumi; Kasahara, Yoshiya; Delzanno, Gian; Wygant, John; Cattell, Cynthia; Breneman, Aaron; Kletzing, Craig; Cunningham, Greg; Hikishima, Mitsuru; Matsuda, Shoya; Katoh, Yuto; Ripoll, Jean-Francois; Shinohara, Iku; Matsuoka, Ayako;

Published by: Journal of Geophysical Research: Space Physics Published on: 10/2020

YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028315

Chorus; wave; propagation; Simultaneous observations; Radiation belt; Van Allen Probes

First Direct Observations of Propagation of Discrete Chorus Elements From the Equatorial Source to Higher Latitudes, Using the Van Allen Probes and Arase Satellites

Whistler mode chorus waves have recently been established as the most likely candidate for scattering relativistic electrons to produce the electron microbursts observed by low altitude satellites and balloons. These waves would have to propagate from the equatorial source region to significantly higher magnetic latitude in order to scatter electrons of these relativistic energies. This theoretically proposed propagation has never been directly observed. We present the first direct observations of the same discrete rising tone chorus elements propagating from a near equatorial (Van Allen Probes) to an off-equatorial (Arase) satellite. The chorus is observed first on the more equatorial satellite and is found to be more oblique and significantly attenuated at the off-equatorial satellite. This is consistent with the prevailing theory of chorus propagation and with the idea that chorus must propagate from the equatorial source region to higher latitudes. Ray tracing of chorus at the observed frequencies confirms that these elements could be generated parallel to the field at the equator, and propagate through the medium unducted to Van Allen Probes A and then to Arase with the observed time delay, and have the observed obliquity and intensity at each satellite.

Colpitts, Chris; Miyoshi, Yoshizumi; Kasahara, Yoshiya; Delzanno, Gian; Wygant, John; Cattell, Cynthia; Breneman, Aaron; Kletzing, Craig; Cunningham, Greg; Hikishima, Mitsuru; Matsuda, Shoya; Katoh, Yuto; Ripoll, Jean-Francois; Shinohara, Iku; Matsuoka, Ayako;

Published by: Journal of Geophysical Research: Space Physics Published on: 10/2020

YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028315

Chorus; wave; propagation; Simultaneous observations; Radiation belt; Van Allen Probes

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