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Found 467 entries in the Bibliography.
Showing entries from 51 through 100
| 2021 |
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AbstractIn-situ electron density profiles obtained from Arase in the night magnetic local time (MLT) sector and from RBSP-B covering all MLTs are used to study the small-scale density irregularities present in the plasmasphere and near the plasmapause. Electron density perturbations with amplitudes > 10\% from background density and with time-scales less than 30-min are investigated here as the small-scale density irregularities. The statistical survey of the density irregularities is carried out using nearly two years of density data obtained from RBSP-B and four months of data from Arase satellites. The results show that density irregularities are present globally at all MLT sectors and L-shells both inside and outside the plasmapause, with a higher occurrence at L > 4. The occurrence of density irregularities is found to be higher during disturbed geomagnetic and interplanetary conditions. The case studies presented here revealed: 1) The plasmaspheric density irregularities observed during both quiet and disturbed conditions are found to co-exist with the hot plasma sheet population. 2) During quiet periods, the plasma waves in the whistler-mode frequency range are found to be modulated by the small-scale density irregularities, with density depletions coinciding well with the decrease in whistler intensity. Our observations suggest that different source mechanisms are responsible for the generation of density structures at different MLTs and geomagnetic conditions.This article is protected by copyright. All rights reserved. Thomas, Neethal; Shiokawa, Kazuo; Miyoshi, Yoshizumi; Kasahara, Yoshiya; Shinohara, Iku; Kumamoto, Atsushi; Tsuchiya, Fuminori; Matsuoka, Ayako; Kasahara, Satoshi; Yokota, Shoichiro; Keika, Kunihiro; Hori, Tomo; Asamura, Kazushi; Wang, Shiang-Yu; Kazama, Yoichi; Tam, Sunny; Chang, Tzu-Fang; Wang, Bo-Jhou; Wygant, John; Breneman, Aaron; Reeves, Geoff; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA027917 Electron density; small-scale density irregularities; plasmasphere; inner magnetosphere; Van Allen Probes; Arase |
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AbstractIn-situ electron density profiles obtained from Arase in the night magnetic local time (MLT) sector and from RBSP-B covering all MLTs are used to study the small-scale density irregularities present in the plasmasphere and near the plasmapause. Electron density perturbations with amplitudes > 10\% from background density and with time-scales less than 30-min are investigated here as the small-scale density irregularities. The statistical survey of the density irregularities is carried out using nearly two years of density data obtained from RBSP-B and four months of data from Arase satellites. The results show that density irregularities are present globally at all MLT sectors and L-shells both inside and outside the plasmapause, with a higher occurrence at L > 4. The occurrence of density irregularities is found to be higher during disturbed geomagnetic and interplanetary conditions. The case studies presented here revealed: 1) The plasmaspheric density irregularities observed during both quiet and disturbed conditions are found to co-exist with the hot plasma sheet population. 2) During quiet periods, the plasma waves in the whistler-mode frequency range are found to be modulated by the small-scale density irregularities, with density depletions coinciding well with the decrease in whistler intensity. Our observations suggest that different source mechanisms are responsible for the generation of density structures at different MLTs and geomagnetic conditions.This article is protected by copyright. All rights reserved. Thomas, Neethal; Shiokawa, Kazuo; Miyoshi, Yoshizumi; Kasahara, Yoshiya; Shinohara, Iku; Kumamoto, Atsushi; Tsuchiya, Fuminori; Matsuoka, Ayako; Kasahara, Satoshi; Yokota, Shoichiro; Keika, Kunihiro; Hori, Tomo; Asamura, Kazushi; Wang, Shiang-Yu; Kazama, Yoichi; Tam, Sunny; Chang, Tzu-Fang; Wang, Bo-Jhou; Wygant, John; Breneman, Aaron; Reeves, Geoff; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA027917 Electron density; small-scale density irregularities; plasmasphere; inner magnetosphere; Van Allen Probes; Arase |
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AbstractIn-situ electron density profiles obtained from Arase in the night magnetic local time (MLT) sector and from RBSP-B covering all MLTs are used to study the small-scale density irregularities present in the plasmasphere and near the plasmapause. Electron density perturbations with amplitudes > 10\% from background density and with time-scales less than 30-min are investigated here as the small-scale density irregularities. The statistical survey of the density irregularities is carried out using nearly two years of density data obtained from RBSP-B and four months of data from Arase satellites. The results show that density irregularities are present globally at all MLT sectors and L-shells both inside and outside the plasmapause, with a higher occurrence at L > 4. The occurrence of density irregularities is found to be higher during disturbed geomagnetic and interplanetary conditions. The case studies presented here revealed: 1) The plasmaspheric density irregularities observed during both quiet and disturbed conditions are found to co-exist with the hot plasma sheet population. 2) During quiet periods, the plasma waves in the whistler-mode frequency range are found to be modulated by the small-scale density irregularities, with density depletions coinciding well with the decrease in whistler intensity. Our observations suggest that different source mechanisms are responsible for the generation of density structures at different MLTs and geomagnetic conditions.This article is protected by copyright. All rights reserved. Thomas, Neethal; Shiokawa, Kazuo; Miyoshi, Yoshizumi; Kasahara, Yoshiya; Shinohara, Iku; Kumamoto, Atsushi; Tsuchiya, Fuminori; Matsuoka, Ayako; Kasahara, Satoshi; Yokota, Shoichiro; Keika, Kunihiro; Hori, Tomo; Asamura, Kazushi; Wang, Shiang-Yu; Kazama, Yoichi; Tam, Sunny; Chang, Tzu-Fang; Wang, Bo-Jhou; Wygant, John; Breneman, Aaron; Reeves, Geoff; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA027917 Electron density; small-scale density irregularities; plasmasphere; inner magnetosphere; Van Allen Probes; Arase |
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AbstractIn-situ electron density profiles obtained from Arase in the night magnetic local time (MLT) sector and from RBSP-B covering all MLTs are used to study the small-scale density irregularities present in the plasmasphere and near the plasmapause. Electron density perturbations with amplitudes > 10\% from background density and with time-scales less than 30-min are investigated here as the small-scale density irregularities. The statistical survey of the density irregularities is carried out using nearly two years of density data obtained from RBSP-B and four months of data from Arase satellites. The results show that density irregularities are present globally at all MLT sectors and L-shells both inside and outside the plasmapause, with a higher occurrence at L > 4. The occurrence of density irregularities is found to be higher during disturbed geomagnetic and interplanetary conditions. The case studies presented here revealed: 1) The plasmaspheric density irregularities observed during both quiet and disturbed conditions are found to co-exist with the hot plasma sheet population. 2) During quiet periods, the plasma waves in the whistler-mode frequency range are found to be modulated by the small-scale density irregularities, with density depletions coinciding well with the decrease in whistler intensity. Our observations suggest that different source mechanisms are responsible for the generation of density structures at different MLTs and geomagnetic conditions.This article is protected by copyright. All rights reserved. Thomas, Neethal; Shiokawa, Kazuo; Miyoshi, Yoshizumi; Kasahara, Yoshiya; Shinohara, Iku; Kumamoto, Atsushi; Tsuchiya, Fuminori; Matsuoka, Ayako; Kasahara, Satoshi; Yokota, Shoichiro; Keika, Kunihiro; Hori, Tomo; Asamura, Kazushi; Wang, Shiang-Yu; Kazama, Yoichi; Tam, Sunny; Chang, Tzu-Fang; Wang, Bo-Jhou; Wygant, John; Breneman, Aaron; Reeves, Geoff; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA027917 Electron density; small-scale density irregularities; plasmasphere; inner magnetosphere; Van Allen Probes; Arase |
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AbstractIn-situ electron density profiles obtained from Arase in the night magnetic local time (MLT) sector and from RBSP-B covering all MLTs are used to study the small-scale density irregularities present in the plasmasphere and near the plasmapause. Electron density perturbations with amplitudes > 10\% from background density and with time-scales less than 30-min are investigated here as the small-scale density irregularities. The statistical survey of the density irregularities is carried out using nearly two years of density data obtained from RBSP-B and four months of data from Arase satellites. The results show that density irregularities are present globally at all MLT sectors and L-shells both inside and outside the plasmapause, with a higher occurrence at L > 4. The occurrence of density irregularities is found to be higher during disturbed geomagnetic and interplanetary conditions. The case studies presented here revealed: 1) The plasmaspheric density irregularities observed during both quiet and disturbed conditions are found to co-exist with the hot plasma sheet population. 2) During quiet periods, the plasma waves in the whistler-mode frequency range are found to be modulated by the small-scale density irregularities, with density depletions coinciding well with the decrease in whistler intensity. Our observations suggest that different source mechanisms are responsible for the generation of density structures at different MLTs and geomagnetic conditions.This article is protected by copyright. All rights reserved. Thomas, Neethal; Shiokawa, Kazuo; Miyoshi, Yoshizumi; Kasahara, Yoshiya; Shinohara, Iku; Kumamoto, Atsushi; Tsuchiya, Fuminori; Matsuoka, Ayako; Kasahara, Satoshi; Yokota, Shoichiro; Keika, Kunihiro; Hori, Tomo; Asamura, Kazushi; Wang, Shiang-Yu; Kazama, Yoichi; Tam, Sunny; Chang, Tzu-Fang; Wang, Bo-Jhou; Wygant, John; Breneman, Aaron; Reeves, Geoff; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA027917 Electron density; small-scale density irregularities; plasmasphere; inner magnetosphere; Van Allen Probes; Arase |
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Observations of Particle Loss due to Injection-Associated EMIC Waves AbstractWe report on observations of electromagnetic ion cyclotron (EMIC) waves and their interactions with injected ring current particles and high energy radiation belt electrons. The magnetic field experiment aboard the twin Van Allen Probes spacecraft measured EMIC waves near L = 5.5 − 6. Particle data from the spacecraft show that the waves were associated with particle injections. The wave activity was also observed by a ground-based magnetometer near the spacecraft geomagnetic footprint over a more extensive temporal range. Phase space density (PSD) profiles, calculated from directional differential electron flux data from Van Allen Probes, show that there was a significant energy-dependent relativistic electron dropout over a limited L-shell range during and after the EMIC wave activity. In addition, the NOAA spacecraft observed relativistic electron precipitation associated with the EMIC waves near the footprint of the Van Allen Probes spacecraft. The observations suggest EMIC wave-induced relativistic electron loss in the radiation belt. Kim, Hyomin; Schiller, Quintin; Engebretson, Mark; Noh, Sungjun; Kuzichev, Ilya; Lanzerotti, Louis; Gerrard, Andrew; Kim, Khan-Hyuk; Lessard, Marc; Spence, Harlan; Lee, Dae-Young; Matzka, Jürgen; Fromm, Tanja; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA028503 EMIC waves; ring current; Radiation belt; wave particle interaction; injection; Particle precipitation; Van Allen Probes |
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AbstractThe two Van Allen Probes simultaneously recorded a coherently modulated quasiperiodic (QP) emission that persisted for 3 hours. The magnetic field pulsation at the locations of the two satellites showed a substantial difference, and their frequencies were close to but did not exactly match the repetition frequency of QP emissions for most of the time, suggesting that those coherent QP emissions probably originated from a common source, which then propagated over a broad area in the magnetosphere. The QP emissions were amplified by local anisotropic electron distributions, and their large-scale amplitudes were modulated by the plasma density. A novel observation of this event is that chorus waves at frequencies above QP emissions exhibit a strong correlation with QP emissions. Those chorus waves intensified when the QP emissions reach their peak frequency. This indicates that embryonic QP emissions may be critical for its own intensification as well as chorus waves under certain circumstances. The low-earth-orbit POES satellite observed enhanced energetic electron precipitation in conjunction with the Van Allen Probes, providing direct evidence that QP emissions precipitate energetic electrons into the atmosphere. This scenario is quantitatively confirmed by our quasilinear diffusion simulation results. Li, Jinxing; Bortnik, Jacob; Ma, Qianli; Li, Wen; Shen, Xiaochen; Nishimura, Yukitoshi; An, Xin; Thaller, Scott; Breneman, Aaron; Wygant, John; Kurth, William; Hospodarsky, George; Hartley, David; Reeves, Geoffrey; Funsten, Herbert; Blake, Bernard; Spence, Harlan; Baker, Daniel; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA028484 quasiperiodic emissions; electron precipitation; Radiation belt; chorus waves; Van Allen Probes; ULF wave |
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AbstractThe two Van Allen Probes simultaneously recorded a coherently modulated quasiperiodic (QP) emission that persisted for 3 hours. The magnetic field pulsation at the locations of the two satellites showed a substantial difference, and their frequencies were close to but did not exactly match the repetition frequency of QP emissions for most of the time, suggesting that those coherent QP emissions probably originated from a common source, which then propagated over a broad area in the magnetosphere. The QP emissions were amplified by local anisotropic electron distributions, and their large-scale amplitudes were modulated by the plasma density. A novel observation of this event is that chorus waves at frequencies above QP emissions exhibit a strong correlation with QP emissions. Those chorus waves intensified when the QP emissions reach their peak frequency. This indicates that embryonic QP emissions may be critical for its own intensification as well as chorus waves under certain circumstances. The low-earth-orbit POES satellite observed enhanced energetic electron precipitation in conjunction with the Van Allen Probes, providing direct evidence that QP emissions precipitate energetic electrons into the atmosphere. This scenario is quantitatively confirmed by our quasilinear diffusion simulation results. Li, Jinxing; Bortnik, Jacob; Ma, Qianli; Li, Wen; Shen, Xiaochen; Nishimura, Yukitoshi; An, Xin; Thaller, Scott; Breneman, Aaron; Wygant, John; Kurth, William; Hospodarsky, George; Hartley, David; Reeves, Geoffrey; Funsten, Herbert; Blake, Bernard; Spence, Harlan; Baker, Daniel; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA028484 quasiperiodic emissions; electron precipitation; Radiation belt; chorus waves; Van Allen Probes; ULF wave |
| 2020 |
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Using seven years of data from the HOPE instrument on the Van Allen Probes, equatorial pitch angle distributions (PADs) of 1 – 50 keV electrons in Earth s inner magnetosphere are investigated statistically. An empirical model of electron equatorial PADs as a function of radial distance, magnetic local time, geomagnetic activity, and electron energy is constructed using the method of Legendre polynomial fitting. Model results show that most equatorial PADs of 1 – 10s of keV electrons in Earth s inner magnetosphere are pancake PADs, and the lack of butterfly PADs is likely due to their relatively flat or positive flux radial gradients at higher altitudes. During geomagnetically quiet times, more anisotropic distributions of 1 – 10s of keV electrons at dayside than nightside are observed, which could be responsible for moderate chorus wave activities at dayside during quiet times as reported by previous studies. During active times, the anisotropy of 1 – 10s of keV electrons significantly enhances, consistent with the enhanced chorus wave activity during active times and suggesting the critical role of 1 – 10s of keV electrons in generating chorus waves in Earth s inner magnetosphere. Different enhanced anisotropy patterns of different energy electrons are also observed during active times: at R>∼4 RE, keV electrons are more anisotropic at dawn to noon, while 10s of keV electrons have larger anisotropy at midnight to dawn. These differences, combined with the statistical distribution of chorus waves shown in previous studies, suggest the differential roles of electrons with different energies in generating chorus waves with different properties. This article is protected by copyright. All rights reserved. Zhao, H.; Friedel, R.; Chen, Y.; Baker, D.; Li, X.; Malaspina, D.; Larsen, B.; Skoug, R.; Funsten, H.; Reeves, G.; Boyd, A.; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028322 Pitch angle distribution; energetic electrons; Earth s inner magnetosphere; Anisotropy; Chorus wave; statistical analysis; Van Allen Probes |
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Magnetospheric ELF/VLF waves have an important role in the acceleration and loss of energetic electrons in the magnetosphere through wave-particle interaction. It is necessary to understand the spatiotemporal development of magnetospheric ELF/VLF waves to quantitatively estimate this effect of wave-particle interaction, a global process not yet well understood. We investigated spatiotemporal development of magnetospheric ELF/VLF waves using 6 PWING ground-based stations at subauroral latitudes, ERG and RBSP satellites, POES/MetOp satellites, and the RAM-SCB model, focusing on the March and November 2017 storms driven by corotating interaction regions in the solar wind. Our results show that the ELF/VLF waves are enhanced over a longitudinal extent from midnight to morning and dayside associated with substorm electron injections. In the main to early storm recovery phase, we observe continuous ELF/VLF waves from ∼0 to ∼12 MLT in the dawn sector. This wide extent seems to be caused by frequent occurrence of substorms. The wave region expands eastward in association with the drift of source electrons injected by substorms from the nightside. We also observed dayside ELF/VLF wave enhancement, possibly driven by magnetospheric compression by solar wind, over an MLT extent of at least 5 hours. Ground observations tend not to observe ELF/VLF waves in the post-midnight sector, although other methods clearly show the existence of waves. This is possibly due to Landau damping of the waves, the absence of the plasma density duct structure, and/or enhanced auroral ionization of the ionosphere in the post-midnight sector. Takeshita, Yuhei; Shiokawa, Kazuo; Miyoshi, Yoshizumi; Ozaki, Mitsunori; Kasahara, Yoshiya; Oyama, Shin-Ichiro; Connors, Martin; Manninen, Jyrki; Jordanova, Vania; Baishev, Dmitry; Oinats, Alexey; Kurkin, Vladimir; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028216 ELF/VLF wave; Arase; Van Allen Probes; PWING; RAM-SCB simulation; subauroral latitudes |
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Magnetospheric ELF/VLF waves have an important role in the acceleration and loss of energetic electrons in the magnetosphere through wave-particle interaction. It is necessary to understand the spatiotemporal development of magnetospheric ELF/VLF waves to quantitatively estimate this effect of wave-particle interaction, a global process not yet well understood. We investigated spatiotemporal development of magnetospheric ELF/VLF waves using 6 PWING ground-based stations at subauroral latitudes, ERG and RBSP satellites, POES/MetOp satellites, and the RAM-SCB model, focusing on the March and November 2017 storms driven by corotating interaction regions in the solar wind. Our results show that the ELF/VLF waves are enhanced over a longitudinal extent from midnight to morning and dayside associated with substorm electron injections. In the main to early storm recovery phase, we observe continuous ELF/VLF waves from ∼0 to ∼12 MLT in the dawn sector. This wide extent seems to be caused by frequent occurrence of substorms. The wave region expands eastward in association with the drift of source electrons injected by substorms from the nightside. We also observed dayside ELF/VLF wave enhancement, possibly driven by magnetospheric compression by solar wind, over an MLT extent of at least 5 hours. Ground observations tend not to observe ELF/VLF waves in the post-midnight sector, although other methods clearly show the existence of waves. This is possibly due to Landau damping of the waves, the absence of the plasma density duct structure, and/or enhanced auroral ionization of the ionosphere in the post-midnight sector. Takeshita, Yuhei; Shiokawa, Kazuo; Miyoshi, Yoshizumi; Ozaki, Mitsunori; Kasahara, Yoshiya; Oyama, Shin-Ichiro; Connors, Martin; Manninen, Jyrki; Jordanova, Vania; Baishev, Dmitry; Oinats, Alexey; Kurkin, Vladimir; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028216 ELF/VLF wave; Arase; Van Allen Probes; PWING; RAM-SCB simulation; subauroral latitudes |
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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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We present new and previously unreported in situ observations of Hertz frequency multiharmonic mode field line resonances detected by the Electric Field and Waves instrument on-board the NASA Van Allen probes during low-L perigee passes. Spectral analysis of the spin-plane electric field data reveals the waves in numerous perigee passes, in sequential passes of probes A and B, and with harmonic frequency structures from ∼0.5 to 3.5 Hz which vary with L-shell, altitude, and from day-to-day. Comparing the observations to wave models using plasma mass density values along the field line given by empirical power laws and from the International Reference Ionosphere model, we conclude that the waves are standing Alfvén field line resonances and that only odd-mode harmonics are excited. The model eigenfrequencies are strongly controlled by the density close to the apex of the field line, suggesting a new diagnostic for equatorial ionospheric density dynamics. Lena, F.; Ozeke, L.; Wygant, J.; Tian, S.; Breneman, A.; Mann, I.; Published by: Geophysical Research Letters Published on: 12/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020GL090632 Field line resonance; Ionosphere; magneto-seismology; Magnetosphere; plasmasphere; standing Alfvén waves; Van Allen Probes |
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We present new and previously unreported in situ observations of Hertz frequency multiharmonic mode field line resonances detected by the Electric Field and Waves instrument on-board the NASA Van Allen probes during low-L perigee passes. Spectral analysis of the spin-plane electric field data reveals the waves in numerous perigee passes, in sequential passes of probes A and B, and with harmonic frequency structures from ∼0.5 to 3.5 Hz which vary with L-shell, altitude, and from day-to-day. Comparing the observations to wave models using plasma mass density values along the field line given by empirical power laws and from the International Reference Ionosphere model, we conclude that the waves are standing Alfvén field line resonances and that only odd-mode harmonics are excited. The model eigenfrequencies are strongly controlled by the density close to the apex of the field line, suggesting a new diagnostic for equatorial ionospheric density dynamics. Lena, F.; Ozeke, L.; Wygant, J.; Tian, S.; Breneman, A.; Mann, I.; Published by: Geophysical Research Letters Published on: 12/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020GL090632 Field line resonance; Ionosphere; magneto-seismology; Magnetosphere; plasmasphere; standing Alfvén waves; Van Allen Probes |
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We utilize 17 years of combined Van Allen Probes and Arase data to statistically analyze the response of the inner magnetosphere to the orientation of the interplanetary magnetic field (IMF) By component. Past studies have demonstrated that the IMF By component introduces a similarly oriented By component into the magnetosphere. However, these studies have tended to focus on field lines in the magnetotail only reaching as close to the Earth as the geosynchronous orbit. By exploiting data from these inner magnetospheric spacecraft, we have been able to investigate the response at radial distances of <7RE. When subtracting the background magnetic field values, provided by the T01 and IGRF magnetic field models, we find that the IMF By component does affect the configuration of the magnetic field lines in the inner magnetosphere. This control is observed throughout the inner magnetosphere, across both hemispheres, all radial distances, and all magnetic local time sectors. The ratio of IMF By to the observed By residual, also known as the “penetration efficiency,” is found to be ∼0.33. The IMF Bz component is found to increase, or inhibit, this control depending upon its orientation. Case, N.; Hartley, D.; Grocott, A.; Miyoshi, Y.; Matsuoka, A.; Imajo, S.; Kurita, S.; Shinohara, I.; Teramoto, M.; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028765 By; y-component; inner magnetosphere; IMF; response; Van Allen Probes |
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We utilize 17 years of combined Van Allen Probes and Arase data to statistically analyze the response of the inner magnetosphere to the orientation of the interplanetary magnetic field (IMF) By component. Past studies have demonstrated that the IMF By component introduces a similarly oriented By component into the magnetosphere. However, these studies have tended to focus on field lines in the magnetotail only reaching as close to the Earth as the geosynchronous orbit. By exploiting data from these inner magnetospheric spacecraft, we have been able to investigate the response at radial distances of <7RE. When subtracting the background magnetic field values, provided by the T01 and IGRF magnetic field models, we find that the IMF By component does affect the configuration of the magnetic field lines in the inner magnetosphere. This control is observed throughout the inner magnetosphere, across both hemispheres, all radial distances, and all magnetic local time sectors. The ratio of IMF By to the observed By residual, also known as the “penetration efficiency,” is found to be ∼0.33. The IMF Bz component is found to increase, or inhibit, this control depending upon its orientation. Case, N.; Hartley, D.; Grocott, A.; Miyoshi, Y.; Matsuoka, A.; Imajo, S.; Kurita, S.; Shinohara, I.; Teramoto, M.; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028765 By; y-component; inner magnetosphere; IMF; response; Van Allen Probes |
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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 |
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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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Precipitation Loss of Radiation Belt Electrons by Two-Band Plasmaspheric Hiss Waves A two-band plasmaspheric hiss consisting of a low-frequency band (normal hiss with the frequency below 2 kHz) and a high-frequency band (locally generated hiss with the frequency up to 10 kHz) was observed on 6 January 2014 by the Van Allen Probes (He et al., 2019, https://doi.org/10.1029/2018GL081578). The electron scattering effect driven by this kind of two-band plasmaspheric hiss is evaluated by the quasi-linear diffusion simulation for the first time. Realistic wave characteristic parameters of the two-band plasmaspheric hiss from statistics are adopted for driving our simulation. The pitch angle diffusion rates of the low-frequency band hiss present a “gap” with minimum magnitude at pitch angle αe ∼ 70°, a condition not favoring the transport of large pitch angle electrons toward the loss cone. However, the diffusion rates of the high-frequency band hiss have peak values at αe ∼ 70°, filling up for the “gap” of the low-frequency hiss diffusion rates. The realistic wave-driven electron PSD evolutions demonstrate that the collaborated effect of the low-frequency band and high-frequency band hiss can cause significant precipitation losses of energetic electrons of tens to several hundred keV within 2 days. He, Zhaoguo; Yan, Qi; Zhang, Xiaoping; Yu, Jiang; Ma, Yonghui; Cao, Yong; Cui, Jun; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028157 two-band hiss; radiation belt electron; loss; Van Allen Probes |
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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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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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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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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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Energetic electron dynamics is highly affected by plasma waves through quasilinear and/or nonlinear interactions in the Earth s inner magnetosphere. In this letter, we provide physical explanations for a previously reported intriguing event from the Van Allen Probes observations, where bursts of electron butterfly distributions at tens of keV exhibit remarkable correlations with chorus waves. Both test particle and quasilinear simulations are used to reveal the formation mechanism for the bursts of electron butterfly distribution. The test particle simulation results indicate that nonlinear phase trapping due to chorus waves is the key process to accelerate electrons to form the electron butterfly distribution within ~30 s, and reproduces the observed features. Quasilinear simulation results show that although the diffusion process alone also contributes to form the electron butterfly distribution, the timescale is slower. Our study demonstrates the importance of nonlinear interaction in rapid electron acceleration at tens of keV by chorus waves. Gan, L.; Li, W.; Ma, Q.; Artemyev, A.; Albert, J.; Published by: Geophysical Research Letters Published on: 10/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020GL090749 butterfly distribution; chorus waves; Electron acceleration; Radiation belts; nonlinear interaction; Van Allen Probes |
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Recent availability of a considerable amount of satellite and ground-based data has allowed us to analyze rare conjugated events where extremely low and very low frequency waves from the same source region are observed in different locations. Here, we report a quasiperiodic (QP) emission, showing one-to-one correspondence, observed by three satellites in space (Arase and the Van Allen Probes) and a ground station. The main event was on 29 November 2018 from 12:06 to 13:08 UT during geomagnetically quiet times. Using the position of the satellites we estimated the spatial extent of the area where the one-to-one correspondence is observed. We found this to be up to 1.21 Earth s radii by 2.26 hr MLT, in radial and longitudinal directions, respectively. Using simple ray tracing calculations, we discuss the probable source location of these waves. At ∼12:20 UT, changes in the frequency sweep rate of the QP elements are observed at all locations associated with magnetic disturbances. We also discuss temporal changes of the spectral shape of QP observed simultaneously in space and on the ground, suggesting the changes are related to properties of the source mechanisms of the waves. This could be linked to two separate sources or a larger source region with different source intensities (i.e., electron flux). At frequencies below the low hybrid resonance, waves can experience attenuation and/or reflection in the magnetosphere. This could explain the sudden end of the observations at the spacecraft, which are moving away from the area where waves can propagate. Martinez-Calderon, C.; Němec, F.; Katoh, Y.; Shiokawa, K.; Kletzing, C.; Hospodarsky, G.; Santolik, O.; Kasahara, Y.; Matsuda, S.; Kumamoto, A.; Tsuchiya, F.; Matsuoka, A.; Shoji, M.; Teramoto, M.; Kurita, S.; Miyoshi, Y.; Ozaki, M.; Nishitani, N.; Oinats, A.; Kurkin, V.; Published by: Journal of Geophysical Research: Space Physics Published on: 08/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028126 VLF/ELF; spatial extent; conjugated events; ERG; RBSP; quasiperiodic emissions; Van Allen Probes |
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Recent availability of a considerable amount of satellite and ground-based data has allowed us to analyze rare conjugated events where extremely low and very low frequency waves from the same source region are observed in different locations. Here, we report a quasiperiodic (QP) emission, showing one-to-one correspondence, observed by three satellites in space (Arase and the Van Allen Probes) and a ground station. The main event was on 29 November 2018 from 12:06 to 13:08 UT during geomagnetically quiet times. Using the position of the satellites we estimated the spatial extent of the area where the one-to-one correspondence is observed. We found this to be up to 1.21 Earth s radii by 2.26 hr MLT, in radial and longitudinal directions, respectively. Using simple ray tracing calculations, we discuss the probable source location of these waves. At ∼12:20 UT, changes in the frequency sweep rate of the QP elements are observed at all locations associated with magnetic disturbances. We also discuss temporal changes of the spectral shape of QP observed simultaneously in space and on the ground, suggesting the changes are related to properties of the source mechanisms of the waves. This could be linked to two separate sources or a larger source region with different source intensities (i.e., electron flux). At frequencies below the low hybrid resonance, waves can experience attenuation and/or reflection in the magnetosphere. This could explain the sudden end of the observations at the spacecraft, which are moving away from the area where waves can propagate. Martinez-Calderon, C.; Němec, F.; Katoh, Y.; Shiokawa, K.; Kletzing, C.; Hospodarsky, G.; Santolik, O.; Kasahara, Y.; Matsuda, S.; Kumamoto, A.; Tsuchiya, F.; Matsuoka, A.; Shoji, M.; Teramoto, M.; Kurita, S.; Miyoshi, Y.; Ozaki, M.; Nishitani, N.; Oinats, A.; Kurkin, V.; Published by: Journal of Geophysical Research: Space Physics Published on: 08/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028126 VLF/ELF; spatial extent; conjugated events; ERG; RBSP; quasiperiodic emissions; Van Allen Probes |
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Recent availability of a considerable amount of satellite and ground-based data has allowed us to analyze rare conjugated events where extremely low and very low frequency waves from the same source region are observed in different locations. Here, we report a quasiperiodic (QP) emission, showing one-to-one correspondence, observed by three satellites in space (Arase and the Van Allen Probes) and a ground station. The main event was on 29 November 2018 from 12:06 to 13:08 UT during geomagnetically quiet times. Using the position of the satellites we estimated the spatial extent of the area where the one-to-one correspondence is observed. We found this to be up to 1.21 Earth s radii by 2.26 hr MLT, in radial and longitudinal directions, respectively. Using simple ray tracing calculations, we discuss the probable source location of these waves. At ∼12:20 UT, changes in the frequency sweep rate of the QP elements are observed at all locations associated with magnetic disturbances. We also discuss temporal changes of the spectral shape of QP observed simultaneously in space and on the ground, suggesting the changes are related to properties of the source mechanisms of the waves. This could be linked to two separate sources or a larger source region with different source intensities (i.e., electron flux). At frequencies below the low hybrid resonance, waves can experience attenuation and/or reflection in the magnetosphere. This could explain the sudden end of the observations at the spacecraft, which are moving away from the area where waves can propagate. Martinez-Calderon, C.; Němec, F.; Katoh, Y.; Shiokawa, K.; Kletzing, C.; Hospodarsky, G.; Santolik, O.; Kasahara, Y.; Matsuda, S.; Kumamoto, A.; Tsuchiya, F.; Matsuoka, A.; Shoji, M.; Teramoto, M.; Kurita, S.; Miyoshi, Y.; Ozaki, M.; Nishitani, N.; Oinats, A.; Kurkin, V.; Published by: Journal of Geophysical Research: Space Physics Published on: 08/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028126 VLF/ELF; spatial extent; conjugated events; ERG; RBSP; quasiperiodic emissions; Van Allen Probes |
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Recent availability of a considerable amount of satellite and ground-based data has allowed us to analyze rare conjugated events where extremely low and very low frequency waves from the same source region are observed in different locations. Here, we report a quasiperiodic (QP) emission, showing one-to-one correspondence, observed by three satellites in space (Arase and the Van Allen Probes) and a ground station. The main event was on 29 November 2018 from 12:06 to 13:08 UT during geomagnetically quiet times. Using the position of the satellites we estimated the spatial extent of the area where the one-to-one correspondence is observed. We found this to be up to 1.21 Earth s radii by 2.26 hr MLT, in radial and longitudinal directions, respectively. Using simple ray tracing calculations, we discuss the probable source location of these waves. At ∼12:20 UT, changes in the frequency sweep rate of the QP elements are observed at all locations associated with magnetic disturbances. We also discuss temporal changes of the spectral shape of QP observed simultaneously in space and on the ground, suggesting the changes are related to properties of the source mechanisms of the waves. This could be linked to two separate sources or a larger source region with different source intensities (i.e., electron flux). At frequencies below the low hybrid resonance, waves can experience attenuation and/or reflection in the magnetosphere. This could explain the sudden end of the observations at the spacecraft, which are moving away from the area where waves can propagate. Martinez-Calderon, C.; Němec, F.; Katoh, Y.; Shiokawa, K.; Kletzing, C.; Hospodarsky, G.; Santolik, O.; Kasahara, Y.; Matsuda, S.; Kumamoto, A.; Tsuchiya, F.; Matsuoka, A.; Shoji, M.; Teramoto, M.; Kurita, S.; Miyoshi, Y.; Ozaki, M.; Nishitani, N.; Oinats, A.; Kurkin, V.; Published by: Journal of Geophysical Research: Space Physics Published on: 08/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028126 VLF/ELF; spatial extent; conjugated events; ERG; RBSP; quasiperiodic emissions; Van Allen Probes |
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Lightning generated whistlers (LGWs) play an important role in precipitating energetic electrons in the Earth s inner radiation belt and beyond. Wave burst data from the Van Allen Probes are used to unambiguously identify LGWs and analyze their properties at L < 4 by extending their frequencies down to ~100 Hz for the first time. The statistical results show that LGWs typically occur at frequencies from 100 Hz to 10 kHz with the major wave power below the equatorial lower hybrid resonance frequency, and their wave amplitudes are typically strong at L < 3 with an occurrence rate up to ~30\% on the nightside. The lifetime calculation indicates that LGWs play an important role in scattering electrons from tens of keV to several MeV at L < ~2.5. Our newly constructed LGW models are critical for evaluating the global effects of LGWs on energetic electron loss at L < 4. Green, A.; Li, W.; Ma, Q.; Shen, X.-C.; Bortnik, J.; Hospodarsky, G.; Published by: Geophysical Research Letters Published on: 08/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020GL089584 lightning generated whistlers; electron precipitation; Inner radiation belt; hiss; VLF transmitter waves; global distribution; Van Allen Probes |
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Whistler mode chorus waves can scatter plasma sheet electrons into the loss cone and produce the Earth s diffuse aurora. Van Allen Probes observed plasma sheet electron injections and intense chorus waves on 24 November 2012. We use quasilinear theory to calculate the precipitating electron fluxes, demonstrating that the chorus waves could lead to high differential energy fluxes of precipitating electrons with characteristic energies of 10–30 keV. Using this method, we calculate the precipitating electron flux from 2012 to 2019 when the Van Allen Probes were near the magnetic equator and perform global surveys of electron precipitation under different geomagnetic conditions. The most significant electron precipitation due to chorus is found from the nightside to dawn sectors over 4 < L < 6.5. The average total precipitating energy flux is enhanced during disturbed conditions, with time-averaged values reaching ~3–10 erg/cm2/s when AE ≥ 500 nT. Ma, Q.; Connor, H.; Zhang, X.-J.; Li, W.; Shen, X.-C.; Gillespie, D.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Claudepierre, S.; Reeves, G.; Spence, H.; Published by: Geophysical Research Letters Published on: 07/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020GL088798 Chorus wave; electron precipitation; plasma sheet electron; Van Allen Probes observation; Van Allen Probes |
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The background cold electron density plays an important role in plasma and wave dynamics. Here, we investigate an event with clear modulation of the particle fluxes and wave intensities by background electron density irregularities based on Van Allen Probes observations. The energies at the peak fluxes of protons and Helium ions of 100 eV to several keV are well correlated with the total electron density variation. Intense electromagnetic ion cyclotron (EMIC) and magnetosonic (MS) waves are simultaneously observed in the high-density regions and disappear in low-density regions. Based on the linear theory of wave growth, the EMIC waves are generated by the ~10 keV protons, while most MS waves are generated by the positive gradient of proton phase space density at several hundred eV in the high-density regions. Our results indicate the importance of background plasma density structures in generation of plasma waves by unstable ion distributions. Yue, Chao; Ma, Qianli; Jun, Chae-Woo; Bortnik, Jacob; Zong, Qiugang; Zhou, Xuzhi; Jang, Eunjin; Reeves, Geoffrey; Spence, Harlan; Wygant, John; Published by: Geophysical Research Letters Published on: 07/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020GL088855 electron density irregularities; electromagnetic ion cyclotron; magnetosonic waves; suprathermal particles; Wave-particle interaction; wave growth rate; Van Allen Probes |
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Whistler mode waves observed in the Earth s inner magnetosphere at frequencies between about 0.5 and 4 kHz which exhibit a nearly periodic time modulation of the wave intensity are called quasiperiodic (QP) emissions. Conjugate measurements of QP events at several different locations can be used to estimate their spatial extent and spatiotemporal variability. Results obtained using conjugate QP measurements provided by the ground-based station Kannuslehto (L≈5.5) and the Van Allen Probes spacecraft (L shells between about 1.1 and 6.5) between September 2012 and November 2017 are presented. Altogether, 26 simultaneously detected events were analyzed. The event modulation periods and frequency-time structures were generally the same at all observation points. Spatial separations of the spacecraft and the ground-based station during conjugate observations are typically within about 40° in azimuth and from about 1 to 3 in L shell. RBSP consistently observes events at lower L shells than Kannuslehto, with the event occurrence primarily inside of the plasmasphere. Ratios of Poynting fluxes observed by the spacecraft and on the ground are used to evaluate event intensity variations related to the spacecraft position. It is found that the intensity decreases considerably both at low L shells and outside of the plasmasphere. Finally, an event containing a gap in its frequency-time structure related to a sudden change of its properties is analyzed in detail. Bezděková, B.; Němec, F.; Manninen, J.; Hospodarsky, G.; Santolik, O.; Kurth, W.; Hartley, D.; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020JA027793 |
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Global ENA Imaging and In Situ Observations of Substorm Dipolarization on 10 August 2016 Abstract This paper presents the first combined use of data from Magnetospheric Multiscale (MMS), Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS), and Van Allen Probes (RBSP) to study the 10 August 2016 magnetic dipolarization. We report the first correlation of MMS tail observations with TWINS energetic neutral atom (ENA) images of the ring current (RC). We analyze 15-min, 1° TWINS 2 images in 1–50 keV energy bins. To characterize the high-altitude RC we extract peak ENA flux from L= 2.5 to 5 in the postmidnight sector. We estimate peak low-altitude ion flux from ENAs near the Earth s limb. For a local perspective, we use spin-averaged proton fluxes from the RBSP A Helium Oxygen Proton Electron (HOPE) spectrometer. We find that the 1000 UT dipolarization triggered an abrupt and significant increase in low-altitude ions and a gradual but modest increase in the high-altitude RC. The relative strength and timing of the low versus high-altitude flux indicate that the dipolarization isotropized the injected ions and initially filled the loss cone. The substorm injection brought cooler ions in from the magnetotail, reducing the peak energy at both low and high altitudes. The post-dipolarization low-altitude flux exhibited a decay rate dispersion favoring longer decay times at lower energies, possibly caused by growth of the low energy RC providing enhanced flux into the loss cone. A variety of finer scale local injection structures were observed in the high-altitude RC both before and after the dipolarization, and the average system level RC intensity increased after 1000 UT. Goldstein, J.; Valek, P.; McComas, D.; Redfern, J.; Spence, H.; Skoug, R.; Larsen, B.; Reeves, G.; Nakamura, R.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2020 YEAR: 2020 DOI: 10.1029/2019JA027733 substorm dipolarization; cross-scale physics; imaging; multipoint in situ; ring current; Van Allen Probes |
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Abstract A comprehensive numerical raytracing study of whistler mode wave power with the inclusion of finite background electron and ion temperature is performed in order to investigate wave power distribution in relation to the plasmapause. Both Landau damping and linear growth of whistler mode waves are taken into account using a bi-Maxwellian hot electron distribution as well as an isotropic hot electron distribution. Isotropic and bi-Maxwellian distributions yield similar results of statistical spatial wave power for frequencies below 500 Hz. The effect of finite background temperature of ∼1 eV for electrons and ions are secondary in terms of the spatial distribution of whistler mode waves relative to the plasmapause. Three primary equatorial source locations at L=2, Lpp and L=5, corresponding to within the plasmasphere, at the plasmapause and outside the plasmapause, are investigated for MLT values of 00, 06, 12, and 18. At each location, waves are launched with a range of initial wave normal angles (−70° to 20°). The simulated wave power distributions are compared with observations from the EMFISIS instrument on Van Allen Probe A. Correspondence between the simulated distribution and the observations requires a weighting of the source regions. Results suggest that the majority of whistler mode power in the plasmasphere is sourced from within the plasmasphere itself and near the plasmapause. Only at noon (MLT 12) is wave power sourced primarily from at and outside the plasmapause. Maxworth, A.; Gołkowski, M.; Malaspina, D.; Jaynes, A.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2020 YEAR: 2020 DOI: 10.1029/2019JA027154 hiss; plasmasphere; Warm Plasma; Raytracing; Magnetosphere; Van Allen Probes |
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Abstract A comprehensive numerical raytracing study of whistler mode wave power with the inclusion of finite background electron and ion temperature is performed in order to investigate wave power distribution in relation to the plasmapause. Both Landau damping and linear growth of whistler mode waves are taken into account using a bi-Maxwellian hot electron distribution as well as an isotropic hot electron distribution. Isotropic and bi-Maxwellian distributions yield similar results of statistical spatial wave power for frequencies below 500 Hz. The effect of finite background temperature of ∼1 eV for electrons and ions are secondary in terms of the spatial distribution of whistler mode waves relative to the plasmapause. Three primary equatorial source locations at L=2, Lpp and L=5, corresponding to within the plasmasphere, at the plasmapause and outside the plasmapause, are investigated for MLT values of 00, 06, 12, and 18. At each location, waves are launched with a range of initial wave normal angles (−70° to 20°). The simulated wave power distributions are compared with observations from the EMFISIS instrument on Van Allen Probe A. Correspondence between the simulated distribution and the observations requires a weighting of the source regions. Results suggest that the majority of whistler mode power in the plasmasphere is sourced from within the plasmasphere itself and near the plasmapause. Only at noon (MLT 12) is wave power sourced primarily from at and outside the plasmapause. Maxworth, A.; Gołkowski, M.; Malaspina, D.; Jaynes, A.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2020 YEAR: 2020 DOI: 10.1029/2019JA027154 hiss; plasmasphere; Warm Plasma; Raytracing; Magnetosphere; Van Allen Probes |
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Bayesian Inference of Quasi-Linear Radial Diffusion Parameters using Van Allen Probes Abstract The Van Allen radiation belts in the magnetosphere have been extensively studied using models based on radial diffusion theory, which is derived from a quasi-linear approach with prescribed inner and outer boundary conditions. The 1D diffusion model requires the knowledge of a diffusion coefficient and an electron loss timescale, which is typically parameterized in terms of various quantities such as the spatial (L) coordinate or a geomagnetic index (e.g., Kp). These terms are typically empirically derived, not directly measurable, and hence are not known precisely, due to the inherent nonlinearity of the process and the variable boundary conditions. In this work, we demonstrate a probabilistic approach by inferring the values of the diffusion and loss term parameters, along with their uncertainty, in a Bayesian framework, where identification is obtained using the Van Allen Probe measurements. Our results show that the probabilistic approach statistically improves the performance of the model, compared to the empirical parameterization employed in the literature. Sarma, Rakesh; Chandorkar, Mandar; Zhelavskaya, Irina; Shprits, Yuri; Drozdov, Alexander; Camporeale, Enrico; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2020 YEAR: 2020 DOI: 10.1029/2019JA027618 radial diffusion; Magnetosphere; Bayesian inference; Van Allen radiation belt; Van Allen Probes |
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Abstract We study quasiperiodic very low frequency (VLF) emissions observed simultaneously by Van Allen Probes spacecraft and Kannuslehto and Lovozero ground-based stations on 25 December 2015. Both Van Allen Probes A and B detected quasiperiodic emissions, probably originated from a common source, and observed on the ground. In order to locate possible regions of wave generation, we analyze wave-normal angles with respect to the geomagnetic field, Poynting flux direction, and cyclotron instability growth rate calculated by using the measured phase space density of energetic electrons. We demonstrate that even parallel wave propagation and proper (downward) Poynting flux direction are not sufficient for claiming observations to be in the source region. Agreement between the growth rate and emission bands was obtained for a restricted part of Van Allen Probe A trajectory corresponding to localized enhancement of plasma density with scale of 700 km. We employ spacecraft density data to build a model plasma profile and to calculate ray trajectories from the point of wave detection in space to the ionosphere and examine the possibility of their propagation toward the ground. For the considered event, the wave could propagate toward the ground in the geomagnetic flux tube with enhanced plasma density, which ensured ducted propagation. The region of wave exit was confirmed by the analysis of wave propagation direction at the ground detection point. Demekhov, A.; Titova, E.; Maninnen, J.; Pasmanik, D.; Lubchich, A.; Santolik, O.; Larchenko, A.; Nikitenko, A.; Turunen, T.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2020 YEAR: 2020 DOI: 10.1029/2020JA027776 quasiperiodic VLF emissions; Cyclotron instability; wave propagation; Magnetosphere; whistler mode waves; Van Allen Probes |
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Abstract We study quasiperiodic very low frequency (VLF) emissions observed simultaneously by Van Allen Probes spacecraft and Kannuslehto and Lovozero ground-based stations on 25 December 2015. Both Van Allen Probes A and B detected quasiperiodic emissions, probably originated from a common source, and observed on the ground. In order to locate possible regions of wave generation, we analyze wave-normal angles with respect to the geomagnetic field, Poynting flux direction, and cyclotron instability growth rate calculated by using the measured phase space density of energetic electrons. We demonstrate that even parallel wave propagation and proper (downward) Poynting flux direction are not sufficient for claiming observations to be in the source region. Agreement between the growth rate and emission bands was obtained for a restricted part of Van Allen Probe A trajectory corresponding to localized enhancement of plasma density with scale of 700 km. We employ spacecraft density data to build a model plasma profile and to calculate ray trajectories from the point of wave detection in space to the ionosphere and examine the possibility of their propagation toward the ground. For the considered event, the wave could propagate toward the ground in the geomagnetic flux tube with enhanced plasma density, which ensured ducted propagation. The region of wave exit was confirmed by the analysis of wave propagation direction at the ground detection point. Demekhov, A.; Titova, E.; Maninnen, J.; Pasmanik, D.; Lubchich, A.; Santolik, O.; Larchenko, A.; Nikitenko, A.; Turunen, T.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2020 YEAR: 2020 DOI: 10.1029/2020JA027776 quasiperiodic VLF emissions; Cyclotron instability; wave propagation; Magnetosphere; whistler mode waves; Van Allen Probes |
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Global ENA Imaging and In Situ Observations of Substorm Dipolarization on 10 August 2016 This paper presents the first combined use of data from Magnetospheric Multiscale (MMS), Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS), and Van Allen Probes (RBSP) to study the 10 August 2016 magnetic dipolarization. We report the first correlation of MMS tail observations with TWINS energetic neutral atom (ENA) images of the ring current (RC). We analyze 15-min, 1° TWINS 2 images in 1–50 keV energy bins. To characterize the high-altitude RC we extract peak ENA flux from L= 2.5 to 5 in the postmidnight sector. We estimate peak low-altitude ion flux from ENAs near the Earth s limb. For a local perspective, we use spin-averaged proton fluxes from the RBSP A Helium Oxygen Proton Electron (HOPE) spectrometer. We find that the 1000 UT dipolarization triggered an abrupt and significant increase in low-altitude ions and a gradual but modest increase in the high-altitude RC. The relative strength and timing of the low versus high-altitude flux indicate that the dipolarization isotropized the injected ions and initially filled the loss cone. The substorm injection brought cooler ions in from the magnetotail, reducing the peak energy at both low and high altitudes. The post-dipolarization low-altitude flux exhibited a decay rate dispersion favoring longer decay times at lower energies, possibly caused by growth of the low energy RC providing enhanced flux into the loss cone. A variety of finer scale local injection structures were observed in the high-altitude RC both before and after the dipolarization, and the average system level RC intensity increased after 1000 UT. Goldstein, J.; Valek, P.; McComas, D.; Redfern, J.; Spence, H.; Skoug, R.; Larsen, B.; Reeves, G.; Nakamura, R.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2019JA027733 substorm dipolarization; cross-scale physics; imaging; multipoint in situ; ring current |
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A comprehensive numerical raytracing study of whistler mode wave power with the inclusion of finite background electron and ion temperature is performed in order to investigate wave power distribution in relation to the plasmapause. Both Landau damping and linear growth of whistler mode waves are taken into account using a bi-Maxwellian hot electron distribution as well as an isotropic hot electron distribution. Isotropic and bi-Maxwellian distributions yield similar results of statistical spatial wave power for frequencies below 500 Hz. The effect of finite background temperature of ∼1 eV for electrons and ions are secondary in terms of the spatial distribution of whistler mode waves relative to the plasmapause. Three primary equatorial source locations at L=2, Lpp and L=5, corresponding to within the plasmasphere, at the plasmapause and outside the plasmapause, are investigated for MLT values of 00, 06, 12, and 18. At each location, waves are launched with a range of initial wave normal angles (−70° to 20°). The simulated wave power distributions are compared with observations from the EMFISIS instrument on Van Allen Probe A. Correspondence between the simulated distribution and the observations requires a weighting of the source regions. Results suggest that the majority of whistler mode power in the plasmasphere is sourced from within the plasmasphere itself and near the plasmapause. Only at noon (MLT 12) is wave power sourced primarily from at and outside the plasmapause. Maxworth, A.; Gołkowski, M.; Malaspina, D.; Jaynes, A.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2019JA027154 hiss; plasmasphere; Warm Plasma; Raytracing; Magnetosphere; Van Allen Probes |
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A comprehensive numerical raytracing study of whistler mode wave power with the inclusion of finite background electron and ion temperature is performed in order to investigate wave power distribution in relation to the plasmapause. Both Landau damping and linear growth of whistler mode waves are taken into account using a bi-Maxwellian hot electron distribution as well as an isotropic hot electron distribution. Isotropic and bi-Maxwellian distributions yield similar results of statistical spatial wave power for frequencies below 500 Hz. The effect of finite background temperature of ∼1 eV for electrons and ions are secondary in terms of the spatial distribution of whistler mode waves relative to the plasmapause. Three primary equatorial source locations at L=2, Lpp and L=5, corresponding to within the plasmasphere, at the plasmapause and outside the plasmapause, are investigated for MLT values of 00, 06, 12, and 18. At each location, waves are launched with a range of initial wave normal angles (−70° to 20°). The simulated wave power distributions are compared with observations from the EMFISIS instrument on Van Allen Probe A. Correspondence between the simulated distribution and the observations requires a weighting of the source regions. Results suggest that the majority of whistler mode power in the plasmasphere is sourced from within the plasmasphere itself and near the plasmapause. Only at noon (MLT 12) is wave power sourced primarily from at and outside the plasmapause. Maxworth, A.; Gołkowski, M.; Malaspina, D.; Jaynes, A.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2019JA027154 hiss; plasmasphere; Warm Plasma; Raytracing; Magnetosphere; Van Allen Probes |
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Bayesian Inference of Quasi-Linear Radial Diffusion Parameters using Van Allen Probes The Van Allen radiation belts in the magnetosphere have been extensively studied using models based on radial diffusion theory, which is derived from a quasi-linear approach with prescribed inner and outer boundary conditions. The 1D diffusion model requires the knowledge of a diffusion coefficient and an electron loss timescale, which is typically parameterized in terms of various quantities such as the spatial (L) coordinate or a geomagnetic index (e.g., Kp). These terms are typically empirically derived, not directly measurable, and hence are not known precisely, due to the inherent nonlinearity of the process and the variable boundary conditions. In this work, we demonstrate a probabilistic approach by inferring the values of the diffusion and loss term parameters, along with their uncertainty, in a Bayesian framework, where identification is obtained using the Van Allen Probe measurements. Our results show that the probabilistic approach statistically improves the performance of the model, compared to the empirical parameterization employed in the literature. Sarma, Rakesh; Chandorkar, Mandar; Zhelavskaya, Irina; Shprits, Yuri; Drozdov, Alexander; Camporeale, Enrico; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2019JA027618 radial diffusion; Magnetosphere; Bayesian inference; Van Allen radiation belt; Van Allen Probes |
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We study quasiperiodic very low frequency (VLF) emissions observed simultaneously by Van Allen Probes spacecraft and Kannuslehto and Lovozero ground-based stations on 25 December 2015. Both Van Allen Probes A and B detected quasiperiodic emissions, probably originated from a common source, and observed on the ground. In order to locate possible regions of wave generation, we analyze wave-normal angles with respect to the geomagnetic field, Poynting flux direction, and cyclotron instability growth rate calculated by using the measured phase space density of energetic electrons. We demonstrate that even parallel wave propagation and proper (downward) Poynting flux direction are not sufficient for claiming observations to be in the source region. Agreement between the growth rate and emission bands was obtained for a restricted part of Van Allen Probe A trajectory corresponding to localized enhancement of plasma density with scale of 700 km. We employ spacecraft density data to build a model plasma profile and to calculate ray trajectories from the point of wave detection in space to the ionosphere and examine the possibility of their propagation toward the ground. For the considered event, the wave could propagate toward the ground in the geomagnetic flux tube with enhanced plasma density, which ensured ducted propagation. The region of wave exit was confirmed by the analysis of wave propagation direction at the ground detection point. Demekhov, A.; Titova, E.; Maninnen, J.; Pasmanik, D.; Lubchich, A.; Santolik, O.; Larchenko, A.; Nikitenko, A.; Turunen, T.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020JA027776 quasiperiodic VLF emissions; Cyclotron instability; wave propagation; Magnetosphere; whistler mode waves; Van Allen Probes |
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We study quasiperiodic very low frequency (VLF) emissions observed simultaneously by Van Allen Probes spacecraft and Kannuslehto and Lovozero ground-based stations on 25 December 2015. Both Van Allen Probes A and B detected quasiperiodic emissions, probably originated from a common source, and observed on the ground. In order to locate possible regions of wave generation, we analyze wave-normal angles with respect to the geomagnetic field, Poynting flux direction, and cyclotron instability growth rate calculated by using the measured phase space density of energetic electrons. We demonstrate that even parallel wave propagation and proper (downward) Poynting flux direction are not sufficient for claiming observations to be in the source region. Agreement between the growth rate and emission bands was obtained for a restricted part of Van Allen Probe A trajectory corresponding to localized enhancement of plasma density with scale of 700 km. We employ spacecraft density data to build a model plasma profile and to calculate ray trajectories from the point of wave detection in space to the ionosphere and examine the possibility of their propagation toward the ground. For the considered event, the wave could propagate toward the ground in the geomagnetic flux tube with enhanced plasma density, which ensured ducted propagation. The region of wave exit was confirmed by the analysis of wave propagation direction at the ground detection point. Demekhov, A.; Titova, E.; Maninnen, J.; Pasmanik, D.; Lubchich, A.; Santolik, O.; Larchenko, A.; Nikitenko, A.; Turunen, T.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020JA027776 quasiperiodic VLF emissions; Cyclotron instability; wave propagation; Magnetosphere; whistler mode waves; Van Allen Probes |
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A Multi-Instrument Approach to Determining the Source-Region Extent of EEP-Driving EMIC Waves Abstract Recent years have seen debate regarding the ability of electromagnetic ion cyclotron (EMIC) waves to drive EEP (energetic electron precipitation) into the Earth s atmosphere. Questions still remain regarding the energies and rates at which these waves are able to interact with electrons. Many studies have attempted to characterize these interactions using simulations; however, these are limited by a lack of precise information regarding the spatial scale size of EMIC activity regions. In this study we examine a fortuitous simultaneous observation of EMIC wave activity by the RBSP-B and Arase satellites in conjunction with ground-based observations of EEP by a subionospheric VLF network. We describe a simple method for determining the longitudinal extent of the EMIC source region based on these observations, calculating a width of 0.75 hr MLT and a drift rate of 0.67 MLT/hr. We describe how this may be applied to other similar EMIC wave events. Hendry, A.; Santolik, O.; Miyoshi, Y.; Matsuoka, A.; Rodger, C.; Clilverd, M.; Kletzing, C.; Shoji, M.; Shinohara, I.; Published by: Geophysical Research Letters Published on: 03/2020 YEAR: 2020 DOI: 10.1029/2019GL086599 EMIC waves; electron precipitation; subionospheric VLF; Van Allen Probes; AARDDVARK; Arase |
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The Role of the Dynamic Plasmapause in Outer Radiation Belt Electron Flux Enhancement Abstract The plasmasphere is a highly dynamic toroidal region of cold, dense plasma around Earth. Plasma waves exist both inside and outside this region and can contribute to the loss and acceleration of high energy outer radiation belt electrons. Early observational studies found an apparent correlation on long time scales between the observed inner edge of the outer radiation belt and the modeled innermost plasmapause location. More recent work using high-resolution Van Allen Probes data has found a more complex relationship. For this study, we determine the standoff distance of the location of maximum electron flux of the outer belt MeV electrons from the plasmapause following rapid enhancement events. We find that the location of the outer radiation belt based on maximum electron flux is consistently outside the plasmapause, with a peak radial standoff distance of ∆L ~ 1. We discuss the implications this result has for acceleration mechanisms. Bruff, M.; Jaynes, A.; Zhao, H.; Goldstein, J.; Malaspina, D.; Baker, D.; Kanekal, S.; Spence, H.; Reeves, G.; Published by: Geophysical Research Letters Published on: 03/2020 YEAR: 2020 DOI: 10.1029/2020GL086991 Plasmapause; outer radiation belt; Magnetosphere; chorus waves; Van Allen Probes |
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Abstract We provide a statistical analysis of both electric and magnetic field wave amplitudes of very low frequency lightning-generated waves (LGWs) based on the equivalent of 11.5 years of observations made by the Van Allen Probes encompassing ~24.6 × 106 survey mode measurements. We complement this analysis with data from the ground-based World Wide Lightning Location Network to explore differences between satellite and ground-based measurements. LGW mean amplitudes are found to be low compared with other whistler mode waves (1 ± 1.6 pT and 19 ± 59 μV/m). Extreme events (1/5,000) can reach 100 pT and contributes strongly to the mean power below L = 2. We find excellent correlations between World Wide Lightning Location Network-based power and wave amplitudes in space at various longitudes. We reveal strong dayside ionospheric damping of the LGW electric field. LGW amplitudes drop for L < 2, contrary to the Earth s intense equatorial lightning activity. We conclude that it is difficult for equatorial LGW to propagate and remain at L < 2. Ripoll, J.-F.; Farges, T.; Malaspina, D.; Lay, E.; Cunningham, G.; Hospodarsky, G.; Kletzing, C.; Wygant, J.; Published by: Geophysical Research Letters Published on: 03/2020 YEAR: 2020 DOI: 10.1029/2020GL087503 lightning-generated waves; electric wave power; magnetic wave power; WWLLN database; Radiation belts; Van Allen Probes |
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Plasmaspheric hiss is an important whistler-mode emission shaping the Van Allen radiation belt environment. How the plasmaspheric hiss waves are generated, propagate, and dissipate remains under intense debate. With the five spacecraft of Van Allen Probes, Exploration of energization and Radiation in Geospace (Arase), and Geostationary Operational Environmental Satellites missions at widely spaced locations, we present here the first comprehensive observations of hiss waves growing from the substorm-injected electron instability, spreading within the plasmasphere, and dissipating over a large spatial scale. During substorms, hot electrons were injected energy-dispersively into the plasmasphere near the dawnside and, probably through a combination of linear and nonlinear cyclotron resonances, generated whistler-mode waves with globally drifting frequencies. These waves were able to propagate from the dawnside to the noonside, with the frequency-drifting feature retained. Approximately 5 hr of magnetic local time away from the source region in the dayside sector, the wave power was dissipated to urn:x-wiley:grl:media:grl60110:grl60110-math-0001 of its original level. Liu, Nigang; Su, Zhenpeng; Gao, Zhonglei; Zheng, Huinan; Wang, Yuming; Wang, Shui; Miyoshi, Yoshizumi; Shinohara, Iku; Kasahara, Yoshiya; Tsuchiya, Fuminori; Kumamoto, Atsushi; Matsuda, Shoya; Shoji, Masafumi; Mitani, Takefumi; Takashima, Takeshi; Kazama, Yoichi; Wang, Bo-Jhou; Wang, Shiang-Yu; Jun, Chae-Woo; Chang, Tzu-Fang; W. Y. Tam, Sunny; Kasahara, Satoshi; Yokota, Shoichiro; Keika, Kunihiro; Hori, Tomoaki; Matsuoka, Ayako; Published by: Geophysical Research Letters Published on: 01/2020 YEAR: 2020 DOI: 10.1029/2019GL086040 plasmasphere; Plasmaspheric Hiss; Radiation belt; Van Allen Probes; Wave Dissipation; wave generation; wave propagation |
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Plasmaspheric hiss is an important whistler-mode emission shaping the Van Allen radiation belt environment. How the plasmaspheric hiss waves are generated, propagate, and dissipate remains under intense debate. With the five spacecraft of Van Allen Probes, Exploration of energization and Radiation in Geospace (Arase), and Geostationary Operational Environmental Satellites missions at widely spaced locations, we present here the first comprehensive observations of hiss waves growing from the substorm-injected electron instability, spreading within the plasmasphere, and dissipating over a large spatial scale. During substorms, hot electrons were injected energy-dispersively into the plasmasphere near the dawnside and, probably through a combination of linear and nonlinear cyclotron resonances, generated whistler-mode waves with globally drifting frequencies. These waves were able to propagate from the dawnside to the noonside, with the frequency-drifting feature retained. Approximately 5 hr of magnetic local time away from the source region in the dayside sector, the wave power was dissipated to urn:x-wiley:grl:media:grl60110:grl60110-math-0001 of its original level. Liu, Nigang; Su, Zhenpeng; Gao, Zhonglei; Zheng, Huinan; Wang, Yuming; Wang, Shui; Miyoshi, Yoshizumi; Shinohara, Iku; Kasahara, Yoshiya; Tsuchiya, Fuminori; Kumamoto, Atsushi; Matsuda, Shoya; Shoji, Masafumi; Mitani, Takefumi; Takashima, Takeshi; Kazama, Yoichi; Wang, Bo-Jhou; Wang, Shiang-Yu; Jun, Chae-Woo; Chang, Tzu-Fang; W. Y. Tam, Sunny; Kasahara, Satoshi; Yokota, Shoichiro; Keika, Kunihiro; Hori, Tomoaki; Matsuoka, Ayako; Published by: Geophysical Research Letters Published on: 01/2020 YEAR: 2020 DOI: 10.1029/2019GL086040 plasmasphere; Plasmaspheric Hiss; Radiation belt; Van Allen Probes; Wave Dissipation; wave generation; wave propagation |
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Plasmaspheric hiss is an important whistler-mode emission shaping the Van Allen radiation belt environment. How the plasmaspheric hiss waves are generated, propagate, and dissipate remains under intense debate. With the five spacecraft of Van Allen Probes, Exploration of energization and Radiation in Geospace (Arase), and Geostationary Operational Environmental Satellites missions at widely spaced locations, we present here the first comprehensive observations of hiss waves growing from the substorm-injected electron instability, spreading within the plasmasphere, and dissipating over a large spatial scale. During substorms, hot electrons were injected energy-dispersively into the plasmasphere near the dawnside and, probably through a combination of linear and nonlinear cyclotron resonances, generated whistler-mode waves with globally drifting frequencies. These waves were able to propagate from the dawnside to the noonside, with the frequency-drifting feature retained. Approximately 5 hr of magnetic local time away from the source region in the dayside sector, the wave power was dissipated to urn:x-wiley:grl:media:grl60110:grl60110-math-0001 of its original level. Liu, Nigang; Su, Zhenpeng; Gao, Zhonglei; Zheng, Huinan; Wang, Yuming; Wang, Shui; Miyoshi, Yoshizumi; Shinohara, Iku; Kasahara, Yoshiya; Tsuchiya, Fuminori; Kumamoto, Atsushi; Matsuda, Shoya; Shoji, Masafumi; Mitani, Takefumi; Takashima, Takeshi; Kazama, Yoichi; Wang, Bo-Jhou; Wang, Shiang-Yu; Jun, Chae-Woo; Chang, Tzu-Fang; W. Y. Tam, Sunny; Kasahara, Satoshi; Yokota, Shoichiro; Keika, Kunihiro; Hori, Tomoaki; Matsuoka, Ayako; Published by: Geophysical Research Letters Published on: 01/2020 YEAR: 2020 DOI: 10.1029/2019GL086040 plasmasphere; Plasmaspheric Hiss; Radiation belt; Van Allen Probes; Wave Dissipation; wave generation; wave propagation |