Bibliography

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

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

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

Statistical Study on Locally Generated High-Frequency Plasmaspheric Hiss and Its Effect on Suprathermal Electrons: Van Allen Probes Observation and Quasi-linear Simulation

The local generation of high-frequency plasmaspheric hiss has recently been reported by a case study (He et al., 2019, https://doi.org/10.1029/2018GL081578). In this research, we perform statistics of global distributions of the locally generated high-frequency plasmaspheric hiss (LHFPH) for different levels of substorm activity, using 6-year observational data from Van Allen Probes. The statistics find that the LHFPH amplitude presents a strong magnetic local time (MLT) asymmetry and highly depends on substorm activity, and intense LHFPHs occur from predawn to dusk side and can penetrate into inner plasmasphere of L ∼ 3 during AE > 300 nT. The statistical LHFPH spectrum shows that its frequency increases with the ambient magnetic field, with peaked wave powers between 0.1 and 0.5 fce. Based on the statistical properties of LHFPH, we evaluate the electron diffusion coefficients using quasi-linear theory. Those results suggest that electron pitch angle scattering driven by LHFPH could be a potential mechanism for the precipitation loss of suprathermal electrons of 0.1 keV to tens of keV, which can impact the ionization and chemical changes in the upper atmosphere.

He, Zhaoguo; Yu, Jiang; Chen, Lunjin; Xia, Zhiyang; Wang, Wenrui; Li, Kun; Cui, Jun;

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

YEAR: 2020     DOI: https://doi.org/10.1029/2020JA028526

Van Allen Probes

Statistical Study on Locally Generated High-Frequency Plasmaspheric Hiss and Its Effect on Suprathermal Electrons: Van Allen Probes Observation and Quasi-linear Simulation

The local generation of high-frequency plasmaspheric hiss has recently been reported by a case study (He et al., 2019, https://doi.org/10.1029/2018GL081578). In this research, we perform statistics of global distributions of the locally generated high-frequency plasmaspheric hiss (LHFPH) for different levels of substorm activity, using 6-year observational data from Van Allen Probes. The statistics find that the LHFPH amplitude presents a strong magnetic local time (MLT) asymmetry and highly depends on substorm activity, and intense LHFPHs occur from predawn to dusk side and can penetrate into inner plasmasphere of L ∼ 3 during AE > 300 nT. The statistical LHFPH spectrum shows that its frequency increases with the ambient magnetic field, with peaked wave powers between 0.1 and 0.5 fce. Based on the statistical properties of LHFPH, we evaluate the electron diffusion coefficients using quasi-linear theory. Those results suggest that electron pitch angle scattering driven by LHFPH could be a potential mechanism for the precipitation loss of suprathermal electrons of 0.1 keV to tens of keV, which can impact the ionization and chemical changes in the upper atmosphere.

He, Zhaoguo; Yu, Jiang; Chen, Lunjin; Xia, Zhiyang; Wang, Wenrui; Li, Kun; Cui, Jun;

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

YEAR: 2020     DOI: https://doi.org/10.1029/2020JA028526

Van Allen Probes

Statistical Evidence for EMIC Wave Excitation Driven by Substorm Injection and Enhanced Solar Wind Pressure in the Earth s Magnetosphere: Two Different EMIC Wave Sources

Substorm injection and solar wind dynamic pressure have long been considered as two main drivers of electromagnetic ion cyclotron (EMIC) wave excitation, but clear observational evidence is still lacking. With Van Allen Probes data from 2012–2017, we have investigated the roles of the two EMIC wave drivers separately, by using time-modified AE+ and . Both the occurrence rate and magnetic amplitude of waves significantly increase with the enhancement of each index. During large AE+, EMIC waves are mainly generated in the dusk sector (16 ≤ MLT ≤ 20) and near the magnetic equator (|MLAT| < 10°). This is presumably due to substorm-injected protons drifting from midnight sector to the plasmaspheric bulge. While during large , EMIC waves mainly occur in the noon sector (9 ≤ MLT ≤ 15). But there exist higher-latitude (10° < |MLAT| < 20°) source regions besides equatorial source, possibly due to the minimum B regions. Our results provide strong observational support to existing generation mechanisms of EMIC waves in the Earth s magnetosphere.

Chen, Huayue; Gao, Xinliang; Lu, Quanming; Tsurutani, Bruce; Wang, Shui;

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

YEAR: 2020     DOI: https://doi.org/10.1029/2020GL090275

EMIC wave; wave excitation; source region; substorm injection; solar wind dynamic pressure; Earth s magnetosphere; Van Allen Probes

Statistical Evidence for EMIC Wave Excitation Driven by Substorm Injection and Enhanced Solar Wind Pressure in the Earth s Magnetosphere: Two Different EMIC Wave Sources

Substorm injection and solar wind dynamic pressure have long been considered as two main drivers of electromagnetic ion cyclotron (EMIC) wave excitation, but clear observational evidence is still lacking. With Van Allen Probes data from 2012–2017, we have investigated the roles of the two EMIC wave drivers separately, by using time-modified AE+ and . Both the occurrence rate and magnetic amplitude of waves significantly increase with the enhancement of each index. During large AE+, EMIC waves are mainly generated in the dusk sector (16 ≤ MLT ≤ 20) and near the magnetic equator (|MLAT| < 10°). This is presumably due to substorm-injected protons drifting from midnight sector to the plasmaspheric bulge. While during large , EMIC waves mainly occur in the noon sector (9 ≤ MLT ≤ 15). But there exist higher-latitude (10° < |MLAT| < 20°) source regions besides equatorial source, possibly due to the minimum B regions. Our results provide strong observational support to existing generation mechanisms of EMIC waves in the Earth s magnetosphere.

Chen, Huayue; Gao, Xinliang; Lu, Quanming; Tsurutani, Bruce; Wang, Shui;

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

YEAR: 2020     DOI: https://doi.org/10.1029/2020GL090275

EMIC wave; wave excitation; source region; substorm injection; solar wind dynamic pressure; Earth s magnetosphere; Van Allen Probes

Statistical Evidence for EMIC Wave Excitation Driven by Substorm Injection and Enhanced Solar Wind Pressure in the Earth s Magnetosphere: Two Different EMIC Wave Sources

Substorm injection and solar wind dynamic pressure have long been considered as two main drivers of electromagnetic ion cyclotron (EMIC) wave excitation, but clear observational evidence is still lacking. With Van Allen Probes data from 2012–2017, we have investigated the roles of the two EMIC wave drivers separately, by using time-modified AE+ and . Both the occurrence rate and magnetic amplitude of waves significantly increase with the enhancement of each index. During large AE+, EMIC waves are mainly generated in the dusk sector (16 ≤ MLT ≤ 20) and near the magnetic equator (|MLAT| < 10°). This is presumably due to substorm-injected protons drifting from midnight sector to the plasmaspheric bulge. While during large , EMIC waves mainly occur in the noon sector (9 ≤ MLT ≤ 15). But there exist higher-latitude (10° < |MLAT| < 20°) source regions besides equatorial source, possibly due to the minimum B regions. Our results provide strong observational support to existing generation mechanisms of EMIC waves in the Earth s magnetosphere.

Chen, Huayue; Gao, Xinliang; Lu, Quanming; Tsurutani, Bruce; Wang, Shui;

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

YEAR: 2020     DOI: https://doi.org/10.1029/2020GL090275

EMIC wave; wave excitation; source region; substorm injection; solar wind dynamic pressure; Earth s magnetosphere; Van Allen Probes

Storm Time Plasma Pressure Inferred From Multimission Measurements and Its Validation Using Van Allen Probes Particle Data

The k-nearest-neighbor technique is used to mine a multimission magnetometer database for a subset of data points from time intervals that are similar to the storm state of the magnetosphere for a particular moment in time. These subsets of data are then used to fit an empirical magnetic field model. Performing this for each snapshot in time reconstructs the dynamic evolution of the magnetic and electric current density distributions during storms. However, because weaker storms occur more frequently than stronger storms, the reconstructions are biased toward them. We demonstrate that distance weighting the nearest-neighbors mitigates this issue while allowing a sufficient amount of data to be included in the fitting procedure to limit overfitting. Using this technique, we reconstruct the distribution of the magnetic field and electric currents and their evolution for two storms, the intense 17–19 March 2015 “Saint Patrick s Day” storm and a moderate storm occurring on 13–15 July 2013, from which the pressure distributions can be computed assuming isotropy and by integrating the steady-state force-balance equation. As the main phase of a storm progresses in time, the westward ring current density and pressure increases in the inner magnetosphere particularly on the nightside, becoming more symmetric as the recovery phase progresses. We validate the empirical pressure by comparing it to the observed pressures from the Van Allen Probes mission by summing over particle fluxes from all available energy channels and species.

Stephens, G.; Bingham, S.; Sitnov, M.; Gkioulidou, M.; Merkin, V.; Korth, H.; Tsyganenko, N.; Ukhorskiy, A;

Published by: Space Weather      Published on: 10/2020

YEAR: 2020     DOI: https://doi.org/10.1029/2020SW002583

storms; empirical geomagnetic field; ring current; data mining; eastward current; plasma pressure; Van Allen Probes

Storm Time Plasma Pressure Inferred From Multimission Measurements and Its Validation Using Van Allen Probes Particle Data

The k-nearest-neighbor technique is used to mine a multimission magnetometer database for a subset of data points from time intervals that are similar to the storm state of the magnetosphere for a particular moment in time. These subsets of data are then used to fit an empirical magnetic field model. Performing this for each snapshot in time reconstructs the dynamic evolution of the magnetic and electric current density distributions during storms. However, because weaker storms occur more frequently than stronger storms, the reconstructions are biased toward them. We demonstrate that distance weighting the nearest-neighbors mitigates this issue while allowing a sufficient amount of data to be included in the fitting procedure to limit overfitting. Using this technique, we reconstruct the distribution of the magnetic field and electric currents and their evolution for two storms, the intense 17–19 March 2015 “Saint Patrick s Day” storm and a moderate storm occurring on 13–15 July 2013, from which the pressure distributions can be computed assuming isotropy and by integrating the steady-state force-balance equation. As the main phase of a storm progresses in time, the westward ring current density and pressure increases in the inner magnetosphere particularly on the nightside, becoming more symmetric as the recovery phase progresses. We validate the empirical pressure by comparing it to the observed pressures from the Van Allen Probes mission by summing over particle fluxes from all available energy channels and species.

Stephens, G.; Bingham, S.; Sitnov, M.; Gkioulidou, M.; Merkin, V.; Korth, H.; Tsyganenko, N.; Ukhorskiy, A;

Published by: Space Weather      Published on: 10/2020

YEAR: 2020     DOI: https://doi.org/10.1029/2020SW002583

storms; empirical geomagnetic field; ring current; data mining; eastward current; plasma pressure; Van Allen Probes

Unraveling the Formation Mechanism for the Bursts of Electron Butterfly Distributions: Test Particle and Quasilinear Simulations

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

Unraveling the Formation Mechanism for the Bursts of Electron Butterfly Distributions: Test Particle and Quasilinear Simulations

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

Unraveling the Formation Mechanism for the Bursts of Electron Butterfly Distributions: Test Particle and Quasilinear Simulations

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

Unraveling the Formation Mechanism for the Bursts of Electron Butterfly Distributions: Test Particle and Quasilinear Simulations

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

Dynamic Properties of Particle Injections Inside Geosynchronous Orbit: A Multisatellite Case Study

Four closely located satellites at and inside geosynchronous orbit (GEO) provided a great opportunity to study the dynamical evolution and spatial scale of premidnight energetic particle injections inside GEO during a moderate substorm on 23 December 2016. Just following the substorm onset, the four spacecraft, a LANL satellite at GEO, the two Van Allen Probes (also called “RBSP”) at ~5.8 RE, and a THEMIS satellite at ~5.3 RE, observed substorm-related particle injections and local dipolarizations near the central meridian (~22 MLT) of a wedge-like current system. The large-scale evolution of the electron and ion (H, He, and O) injections was almost identical at the two RBSP spacecraft with ~0.5 RE apart. However, the initial short-timescale particle injections exhibited a striking difference between RBSP-A and -B: RBSP-B observed an energy dispersionless injection which occurred concurrently with a transient, strong dipolarization front (DF) with a peak-to-peak amplitude of ~25 nT over ~25 s; RBSP-A measured a dispersed/weaker injection with no corresponding DF. The spatiotemporally localized DF was accompanied by an impulsive, westward electric field (~20 mV m−1). The fast, impulsive E × B drift caused the radial transport of the electron and ion injection regions from GEO to ~5.8 RE. The penetrating DF fields significantly altered the rapid energy- and pitch angle-dependent flux changes of the electrons and the H and He ions inside GEO. Such flux distributions could reflect the transient DF-related particle acceleration and/or transport processes occurring inside GEO. In contrast, O ions were little affected by the DF fields.

Motoba, T.; Ohtani, S.; Claudepierre, S.; Reeves, G.; Ukhorskiy, A; Lanzerotti, L.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 09/2020

YEAR: 2020     DOI: https://doi.org/10.1029/2020JA028215

deep particle injections; dipolarizations; substorms; localized DF; Van Allen Probes

Dynamic Properties of Particle Injections Inside Geosynchronous Orbit: A Multisatellite Case Study

Four closely located satellites at and inside geosynchronous orbit (GEO) provided a great opportunity to study the dynamical evolution and spatial scale of premidnight energetic particle injections inside GEO during a moderate substorm on 23 December 2016. Just following the substorm onset, the four spacecraft, a LANL satellite at GEO, the two Van Allen Probes (also called “RBSP”) at ~5.8 RE, and a THEMIS satellite at ~5.3 RE, observed substorm-related particle injections and local dipolarizations near the central meridian (~22 MLT) of a wedge-like current system. The large-scale evolution of the electron and ion (H, He, and O) injections was almost identical at the two RBSP spacecraft with ~0.5 RE apart. However, the initial short-timescale particle injections exhibited a striking difference between RBSP-A and -B: RBSP-B observed an energy dispersionless injection which occurred concurrently with a transient, strong dipolarization front (DF) with a peak-to-peak amplitude of ~25 nT over ~25 s; RBSP-A measured a dispersed/weaker injection with no corresponding DF. The spatiotemporally localized DF was accompanied by an impulsive, westward electric field (~20 mV m−1). The fast, impulsive E × B drift caused the radial transport of the electron and ion injection regions from GEO to ~5.8 RE. The penetrating DF fields significantly altered the rapid energy- and pitch angle-dependent flux changes of the electrons and the H and He ions inside GEO. Such flux distributions could reflect the transient DF-related particle acceleration and/or transport processes occurring inside GEO. In contrast, O ions were little affected by the DF fields.

Motoba, T.; Ohtani, S.; Claudepierre, S.; Reeves, G.; Ukhorskiy, A; Lanzerotti, L.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 09/2020

YEAR: 2020     DOI: https://doi.org/10.1029/2020JA028215

deep particle injections; dipolarizations; substorms; localized DF; Van Allen Probes

Dynamic Properties of Particle Injections Inside Geosynchronous Orbit: A Multisatellite Case Study

Four closely located satellites at and inside geosynchronous orbit (GEO) provided a great opportunity to study the dynamical evolution and spatial scale of premidnight energetic particle injections inside GEO during a moderate substorm on 23 December 2016. Just following the substorm onset, the four spacecraft, a LANL satellite at GEO, the two Van Allen Probes (also called “RBSP”) at ~5.8 RE, and a THEMIS satellite at ~5.3 RE, observed substorm-related particle injections and local dipolarizations near the central meridian (~22 MLT) of a wedge-like current system. The large-scale evolution of the electron and ion (H, He, and O) injections was almost identical at the two RBSP spacecraft with ~0.5 RE apart. However, the initial short-timescale particle injections exhibited a striking difference between RBSP-A and -B: RBSP-B observed an energy dispersionless injection which occurred concurrently with a transient, strong dipolarization front (DF) with a peak-to-peak amplitude of ~25 nT over ~25 s; RBSP-A measured a dispersed/weaker injection with no corresponding DF. The spatiotemporally localized DF was accompanied by an impulsive, westward electric field (~20 mV m−1). The fast, impulsive E × B drift caused the radial transport of the electron and ion injection regions from GEO to ~5.8 RE. The penetrating DF fields significantly altered the rapid energy- and pitch angle-dependent flux changes of the electrons and the H and He ions inside GEO. Such flux distributions could reflect the transient DF-related particle acceleration and/or transport processes occurring inside GEO. In contrast, O ions were little affected by the DF fields.

Motoba, T.; Ohtani, S.; Claudepierre, S.; Reeves, G.; Ukhorskiy, A; Lanzerotti, L.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 09/2020

YEAR: 2020     DOI: https://doi.org/10.1029/2020JA028215

deep particle injections; dipolarizations; substorms; localized DF; Van Allen Probes

Dynamic Properties of Particle Injections Inside Geosynchronous Orbit: A Multisatellite Case Study

Four closely located satellites at and inside geosynchronous orbit (GEO) provided a great opportunity to study the dynamical evolution and spatial scale of premidnight energetic particle injections inside GEO during a moderate substorm on 23 December 2016. Just following the substorm onset, the four spacecraft, a LANL satellite at GEO, the two Van Allen Probes (also called “RBSP”) at ~5.8 RE, and a THEMIS satellite at ~5.3 RE, observed substorm-related particle injections and local dipolarizations near the central meridian (~22 MLT) of a wedge-like current system. The large-scale evolution of the electron and ion (H, He, and O) injections was almost identical at the two RBSP spacecraft with ~0.5 RE apart. However, the initial short-timescale particle injections exhibited a striking difference between RBSP-A and -B: RBSP-B observed an energy dispersionless injection which occurred concurrently with a transient, strong dipolarization front (DF) with a peak-to-peak amplitude of ~25 nT over ~25 s; RBSP-A measured a dispersed/weaker injection with no corresponding DF. The spatiotemporally localized DF was accompanied by an impulsive, westward electric field (~20 mV m−1). The fast, impulsive E × B drift caused the radial transport of the electron and ion injection regions from GEO to ~5.8 RE. The penetrating DF fields significantly altered the rapid energy- and pitch angle-dependent flux changes of the electrons and the H and He ions inside GEO. Such flux distributions could reflect the transient DF-related particle acceleration and/or transport processes occurring inside GEO. In contrast, O ions were little affected by the DF fields.

Motoba, T.; Ohtani, S.; Claudepierre, S.; Reeves, G.; Ukhorskiy, A; Lanzerotti, L.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 09/2020

YEAR: 2020     DOI: https://doi.org/10.1029/2020JA028215

deep particle injections; dipolarizations; substorms; localized DF; Van Allen Probes

The Impenetrable Barrier: Suppression of Chorus Wave Growth by VLF Transmitters

Rapid radiation belt recovery following storm time depletion involves local acceleration of multi-MeV electrons in nonlinear interactions with VLF chorus waves. Previous studies of an apparent impenetrable barrier at L ~ 2.8 focused on diffusion and precipitation loss mechanisms for an explanation of the sharp reduction of multi-MeV electron fluxes earthward of L ~ 3. Van Allen Probes observations for cases when the plasmasphere is contracted earthward of L ~ 3 indicate that strong coherent signals from VLF transmitters can play significant roles in the suppression of nonlinear chorus wave growth earthward of L ~ 3. As a result, local nonlinear acceleration of hundreds of keV electrons to MeV energies does not occur in this region. During the recovery of the outer radiation belt when the plasmasphere is significantly contracted, the suppression of chorus wave growth and local acceleration by the action of the transmitter waves at the outer edge of the VLF bubble contributes to the sharp inner edge of the new MeV electron population and the formation of the impenetrable barrier at L ~ 2.8.

Foster, John; Erickson, Philip; Omura, Yoshiharu; Baker, Daniel;

Published by: Journal of Geophysical Research: Space Physics      Published on: 09/2020

YEAR: 2020     DOI: https://doi.org/10.1029/2020JA027913

Radiation belt; Plasmapause; VLF transmitters; wave-particle interactions; Electron acceleration; nonlinear VLF chorus; Van Allen Probes

The Impenetrable Barrier: Suppression of Chorus Wave Growth by VLF Transmitters

Rapid radiation belt recovery following storm time depletion involves local acceleration of multi-MeV electrons in nonlinear interactions with VLF chorus waves. Previous studies of an apparent impenetrable barrier at L ~ 2.8 focused on diffusion and precipitation loss mechanisms for an explanation of the sharp reduction of multi-MeV electron fluxes earthward of L ~ 3. Van Allen Probes observations for cases when the plasmasphere is contracted earthward of L ~ 3 indicate that strong coherent signals from VLF transmitters can play significant roles in the suppression of nonlinear chorus wave growth earthward of L ~ 3. As a result, local nonlinear acceleration of hundreds of keV electrons to MeV energies does not occur in this region. During the recovery of the outer radiation belt when the plasmasphere is significantly contracted, the suppression of chorus wave growth and local acceleration by the action of the transmitter waves at the outer edge of the VLF bubble contributes to the sharp inner edge of the new MeV electron population and the formation of the impenetrable barrier at L ~ 2.8.

Foster, John; Erickson, Philip; Omura, Yoshiharu; Baker, Daniel;

Published by: Journal of Geophysical Research: Space Physics      Published on: 09/2020

YEAR: 2020     DOI: https://doi.org/10.1029/2020JA027913

Radiation belt; Plasmapause; VLF transmitters; wave-particle interactions; Electron acceleration; nonlinear VLF chorus; Van Allen Probes

Suprathermal Electron Evolution Under the Competition Between Plasmaspheric Plume Hiss Wave Heating and Collisional Cooling

Suprathermal electrons are a major heat source of ionospheric plasma. How the suprathermal electrons evolve during their bounces inside the plasmasphere is a fundamental question for the magnetosphere-ionosphere coupling. On the basis of Van Allen Probes observations and quasi-linear simulations, we present here the first quantitative study on the evolution of suprathermal electrons under the competition between Landau heating by whistler mode hiss waves and Coulomb collisional cooling by background plasma inside a plasmaspheric plume. We show that the Landau heating can prevail over the collisional cooling for >50 eV electrons and cause the field-aligned suprathermal electron fluxes to increase by up to 1 order of magnitude within 1.5 hr. Our results imply that the plasmaspheric plume hiss waves could mediate energy from the ring current electrons to the ionospheric plasma.

Wang, Zhongshan; Su, Zhenpeng; Liu, Nigang; Dai, Guyue; Zheng, Huinan; Wang, Yuming; Wang, Shui;

Published by: Geophysical Research Letters      Published on: 09/2020

YEAR: 2020     DOI: https://doi.org/10.1029/2020GL089649

magnetosphere-ionosphere coupling; whistler mode hiss waves; Landau resonance; Coulomb collisions; suprathermal electrons; ring current; Van Allen Probes

Suprathermal Electron Evolution Under the Competition Between Plasmaspheric Plume Hiss Wave Heating and Collisional Cooling

Suprathermal electrons are a major heat source of ionospheric plasma. How the suprathermal electrons evolve during their bounces inside the plasmasphere is a fundamental question for the magnetosphere-ionosphere coupling. On the basis of Van Allen Probes observations and quasi-linear simulations, we present here the first quantitative study on the evolution of suprathermal electrons under the competition between Landau heating by whistler mode hiss waves and Coulomb collisional cooling by background plasma inside a plasmaspheric plume. We show that the Landau heating can prevail over the collisional cooling for >50 eV electrons and cause the field-aligned suprathermal electron fluxes to increase by up to 1 order of magnitude within 1.5 hr. Our results imply that the plasmaspheric plume hiss waves could mediate energy from the ring current electrons to the ionospheric plasma.

Wang, Zhongshan; Su, Zhenpeng; Liu, Nigang; Dai, Guyue; Zheng, Huinan; Wang, Yuming; Wang, Shui;

Published by: Geophysical Research Letters      Published on: 09/2020

YEAR: 2020     DOI: https://doi.org/10.1029/2020GL089649

magnetosphere-ionosphere coupling; whistler mode hiss waves; Landau resonance; Coulomb collisions; suprathermal electrons; ring current; Van Allen Probes

Suprathermal Electron Evolution Under the Competition Between Plasmaspheric Plume Hiss Wave Heating and Collisional Cooling

Suprathermal electrons are a major heat source of ionospheric plasma. How the suprathermal electrons evolve during their bounces inside the plasmasphere is a fundamental question for the magnetosphere-ionosphere coupling. On the basis of Van Allen Probes observations and quasi-linear simulations, we present here the first quantitative study on the evolution of suprathermal electrons under the competition between Landau heating by whistler mode hiss waves and Coulomb collisional cooling by background plasma inside a plasmaspheric plume. We show that the Landau heating can prevail over the collisional cooling for >50 eV electrons and cause the field-aligned suprathermal electron fluxes to increase by up to 1 order of magnitude within 1.5 hr. Our results imply that the plasmaspheric plume hiss waves could mediate energy from the ring current electrons to the ionospheric plasma.

Wang, Zhongshan; Su, Zhenpeng; Liu, Nigang; Dai, Guyue; Zheng, Huinan; Wang, Yuming; Wang, Shui;

Published by: Geophysical Research Letters      Published on: 09/2020

YEAR: 2020     DOI: https://doi.org/10.1029/2020GL089649

magnetosphere-ionosphere coupling; whistler mode hiss waves; Landau resonance; Coulomb collisions; suprathermal electrons; ring current; Van Allen Probes

Suprathermal Electron Evolution Under the Competition Between Plasmaspheric Plume Hiss Wave Heating and Collisional Cooling

Suprathermal electrons are a major heat source of ionospheric plasma. How the suprathermal electrons evolve during their bounces inside the plasmasphere is a fundamental question for the magnetosphere-ionosphere coupling. On the basis of Van Allen Probes observations and quasi-linear simulations, we present here the first quantitative study on the evolution of suprathermal electrons under the competition between Landau heating by whistler mode hiss waves and Coulomb collisional cooling by background plasma inside a plasmaspheric plume. We show that the Landau heating can prevail over the collisional cooling for >50 eV electrons and cause the field-aligned suprathermal electron fluxes to increase by up to 1 order of magnitude within 1.5 hr. Our results imply that the plasmaspheric plume hiss waves could mediate energy from the ring current electrons to the ionospheric plasma.

Wang, Zhongshan; Su, Zhenpeng; Liu, Nigang; Dai, Guyue; Zheng, Huinan; Wang, Yuming; Wang, Shui;

Published by: Geophysical Research Letters      Published on: 09/2020

YEAR: 2020     DOI: https://doi.org/10.1029/2020GL089649

magnetosphere-ionosphere coupling; whistler mode hiss waves; Landau resonance; Coulomb collisions; suprathermal electrons; ring current; Van Allen Probes

Lower-Band “Monochromatic” Chorus Riser Subelement/Wave Packet Observations

Three lower-band (f < 0.5 fce) chorus riser elements detected in the dayside generation region were studied in detail using the Van Allen Probe data. Two subelements/wave packets within each riser were examined for their wave “frequency” constancy within seven consecutive wave cycles. The seven wave cycles contained the maximum amplitudes of the subelements/packets. Maximum variance B1 zero crossings were used for the identification of wave cycle start and stop times. It is found that the frequency is constant to within ~3\% (one standard deviation), with no evidence of upward frequency sweeping over the seven cycles. Continuous wavelet power spectra for the duration of the seven cycles confirm this conclusion. The implication is that a chorus riser element is composed of coherent approximately “monochromatic” steps instead of a gradual sweep in frequency over the whole element. There was no upward frequency stepping where the wave amplitude was the largest, contrary to the sideband theory prediction. It is shown that a chorus riser involves instability of cyclotron resonant energetic electrons from ~6 to ~40 keV at L = 5.8, that is, essentially the whole substorm electron energy spectrum. The above findings may have important consequences for possible wave generation mechanisms. Some new ideas for mechanisms are suggested in conclusion.

Tsurutani, Bruce; Chen, Rui; Gao, Xinliang; Lu, Quanming; Pickett, Jolene; Lakhina, Gurbax; Sen, Abhijit; Hajra, Rajkumar; Park, Sang; Falkowski, Barbara;

Published by: Journal of Geophysical Research: Space Physics      Published on: 09/2020

YEAR: 2020     DOI: https://doi.org/10.1029/2020JA028090

chorus coherency; chorus subelement monochromaticity; a modified theory needed; Van Allen Probes

Lower-Band “Monochromatic” Chorus Riser Subelement/Wave Packet Observations

Three lower-band (f < 0.5 fce) chorus riser elements detected in the dayside generation region were studied in detail using the Van Allen Probe data. Two subelements/wave packets within each riser were examined for their wave “frequency” constancy within seven consecutive wave cycles. The seven wave cycles contained the maximum amplitudes of the subelements/packets. Maximum variance B1 zero crossings were used for the identification of wave cycle start and stop times. It is found that the frequency is constant to within ~3\% (one standard deviation), with no evidence of upward frequency sweeping over the seven cycles. Continuous wavelet power spectra for the duration of the seven cycles confirm this conclusion. The implication is that a chorus riser element is composed of coherent approximately “monochromatic” steps instead of a gradual sweep in frequency over the whole element. There was no upward frequency stepping where the wave amplitude was the largest, contrary to the sideband theory prediction. It is shown that a chorus riser involves instability of cyclotron resonant energetic electrons from ~6 to ~40 keV at L = 5.8, that is, essentially the whole substorm electron energy spectrum. The above findings may have important consequences for possible wave generation mechanisms. Some new ideas for mechanisms are suggested in conclusion.

Tsurutani, Bruce; Chen, Rui; Gao, Xinliang; Lu, Quanming; Pickett, Jolene; Lakhina, Gurbax; Sen, Abhijit; Hajra, Rajkumar; Park, Sang; Falkowski, Barbara;

Published by: Journal of Geophysical Research: Space Physics      Published on: 09/2020

YEAR: 2020     DOI: https://doi.org/10.1029/2020JA028090

chorus coherency; chorus subelement monochromaticity; a modified theory needed; Van Allen Probes

Lower-Band “Monochromatic” Chorus Riser Subelement/Wave Packet Observations

Three lower-band (f < 0.5 fce) chorus riser elements detected in the dayside generation region were studied in detail using the Van Allen Probe data. Two subelements/wave packets within each riser were examined for their wave “frequency” constancy within seven consecutive wave cycles. The seven wave cycles contained the maximum amplitudes of the subelements/packets. Maximum variance B1 zero crossings were used for the identification of wave cycle start and stop times. It is found that the frequency is constant to within ~3\% (one standard deviation), with no evidence of upward frequency sweeping over the seven cycles. Continuous wavelet power spectra for the duration of the seven cycles confirm this conclusion. The implication is that a chorus riser element is composed of coherent approximately “monochromatic” steps instead of a gradual sweep in frequency over the whole element. There was no upward frequency stepping where the wave amplitude was the largest, contrary to the sideband theory prediction. It is shown that a chorus riser involves instability of cyclotron resonant energetic electrons from ~6 to ~40 keV at L = 5.8, that is, essentially the whole substorm electron energy spectrum. The above findings may have important consequences for possible wave generation mechanisms. Some new ideas for mechanisms are suggested in conclusion.

Tsurutani, Bruce; Chen, Rui; Gao, Xinliang; Lu, Quanming; Pickett, Jolene; Lakhina, Gurbax; Sen, Abhijit; Hajra, Rajkumar; Park, Sang; Falkowski, Barbara;

Published by: Journal of Geophysical Research: Space Physics      Published on: 09/2020

YEAR: 2020     DOI: https://doi.org/10.1029/2020JA028090

chorus coherency; chorus subelement monochromaticity; a modified theory needed; Van Allen Probes

Lower-Band “Monochromatic” Chorus Riser Subelement/Wave Packet Observations

Three lower-band (f < 0.5 fce) chorus riser elements detected in the dayside generation region were studied in detail using the Van Allen Probe data. Two subelements/wave packets within each riser were examined for their wave “frequency” constancy within seven consecutive wave cycles. The seven wave cycles contained the maximum amplitudes of the subelements/packets. Maximum variance B1 zero crossings were used for the identification of wave cycle start and stop times. It is found that the frequency is constant to within ~3\% (one standard deviation), with no evidence of upward frequency sweeping over the seven cycles. Continuous wavelet power spectra for the duration of the seven cycles confirm this conclusion. The implication is that a chorus riser element is composed of coherent approximately “monochromatic” steps instead of a gradual sweep in frequency over the whole element. There was no upward frequency stepping where the wave amplitude was the largest, contrary to the sideband theory prediction. It is shown that a chorus riser involves instability of cyclotron resonant energetic electrons from ~6 to ~40 keV at L = 5.8, that is, essentially the whole substorm electron energy spectrum. The above findings may have important consequences for possible wave generation mechanisms. Some new ideas for mechanisms are suggested in conclusion.

Tsurutani, Bruce; Chen, Rui; Gao, Xinliang; Lu, Quanming; Pickett, Jolene; Lakhina, Gurbax; Sen, Abhijit; Hajra, Rajkumar; Park, Sang; Falkowski, Barbara;

Published by: Journal of Geophysical Research: Space Physics      Published on: 09/2020

YEAR: 2020     DOI: https://doi.org/10.1029/2020JA028090

chorus coherency; chorus subelement monochromaticity; a modified theory needed; Van Allen Probes

Lower-Band “Monochromatic” Chorus Riser Subelement/Wave Packet Observations

Three lower-band (f < 0.5 fce) chorus riser elements detected in the dayside generation region were studied in detail using the Van Allen Probe data. Two subelements/wave packets within each riser were examined for their wave “frequency” constancy within seven consecutive wave cycles. The seven wave cycles contained the maximum amplitudes of the subelements/packets. Maximum variance B1 zero crossings were used for the identification of wave cycle start and stop times. It is found that the frequency is constant to within ~3\% (one standard deviation), with no evidence of upward frequency sweeping over the seven cycles. Continuous wavelet power spectra for the duration of the seven cycles confirm this conclusion. The implication is that a chorus riser element is composed of coherent approximately “monochromatic” steps instead of a gradual sweep in frequency over the whole element. There was no upward frequency stepping where the wave amplitude was the largest, contrary to the sideband theory prediction. It is shown that a chorus riser involves instability of cyclotron resonant energetic electrons from ~6 to ~40 keV at L = 5.8, that is, essentially the whole substorm electron energy spectrum. The above findings may have important consequences for possible wave generation mechanisms. Some new ideas for mechanisms are suggested in conclusion.

Tsurutani, Bruce; Chen, Rui; Gao, Xinliang; Lu, Quanming; Pickett, Jolene; Lakhina, Gurbax; Sen, Abhijit; Hajra, Rajkumar; Park, Sang; Falkowski, Barbara;

Published by: Journal of Geophysical Research: Space Physics      Published on: 09/2020

YEAR: 2020     DOI: https://doi.org/10.1029/2020JA028090

chorus coherency; chorus subelement monochromaticity; a modified theory needed; Van Allen Probes

Lower-Band “Monochromatic” Chorus Riser Subelement/Wave Packet Observations

Three lower-band (f < 0.5 fce) chorus riser elements detected in the dayside generation region were studied in detail using the Van Allen Probe data. Two subelements/wave packets within each riser were examined for their wave “frequency” constancy within seven consecutive wave cycles. The seven wave cycles contained the maximum amplitudes of the subelements/packets. Maximum variance B1 zero crossings were used for the identification of wave cycle start and stop times. It is found that the frequency is constant to within ~3\% (one standard deviation), with no evidence of upward frequency sweeping over the seven cycles. Continuous wavelet power spectra for the duration of the seven cycles confirm this conclusion. The implication is that a chorus riser element is composed of coherent approximately “monochromatic” steps instead of a gradual sweep in frequency over the whole element. There was no upward frequency stepping where the wave amplitude was the largest, contrary to the sideband theory prediction. It is shown that a chorus riser involves instability of cyclotron resonant energetic electrons from ~6 to ~40 keV at L = 5.8, that is, essentially the whole substorm electron energy spectrum. The above findings may have important consequences for possible wave generation mechanisms. Some new ideas for mechanisms are suggested in conclusion.

Tsurutani, Bruce; Chen, Rui; Gao, Xinliang; Lu, Quanming; Pickett, Jolene; Lakhina, Gurbax; Sen, Abhijit; Hajra, Rajkumar; Park, Sang; Falkowski, Barbara;

Published by: Journal of Geophysical Research: Space Physics      Published on: 09/2020

YEAR: 2020     DOI: https://doi.org/10.1029/2020JA028090

chorus coherency; chorus subelement monochromaticity; a modified theory needed; Van Allen Probes

Quantifying the Effects of EMIC Wave Scattering and Magnetopause Shadowing in the Outer Electron Radiation Belt by Means of Data Assimilation

In this study we investigate two distinct loss mechanisms responsible for the rapid dropouts of radiation belt electrons by assimilating data from Van Allen Probes A and B and Geostationary Operational Environmental Satellites (GOES) 13 and 15 into a 3-D diffusion model. In particular, we examine the respective contribution of electromagnetic ion cyclotron (EMIC) wave scattering and magnetopause shadowing for values of the first adiabatic invariant μ ranging from 300 to 3,000 MeV G−1. We inspect the innovation vector and perform a statistical analysis to quantitatively assess the effect of both processes as a function of various geomagnetic indices, solar wind parameters, and radial distance from the Earth. Our results are in agreement with previous studies that demonstrated the energy dependence of these two mechanisms. We show that EMIC wave scattering tends to dominate loss at lower L shells, and it may amount to between 10\%/hr and 30\%/hr of the maximum value of phase space density (PSD) over all L shells for fixed first and second adiabatic invariants. On the other hand, magnetopause shadowing is found to deplete electrons across all energies, mostly at higher L shells, resulting in loss from 50\%/hr to 70\%/hr of the maximum PSD. Nevertheless, during times of enhanced geomagnetic activity, both processes can operate beyond such location and encompass the entire outer radiation belt.

Cervantes, S.; Shprits, Y; Aseev, N.; Allison, H.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 08/2020

YEAR: 2020     DOI: https://doi.org/10.1029/2020JA028208

data assimilation; EMIC waves; magnetopause shadowing; innovation vector; Kalman Filter; radiation belt losses; Van Allen Probes

Quantifying the Effects of EMIC Wave Scattering and Magnetopause Shadowing in the Outer Electron Radiation Belt by Means of Data Assimilation

In this study we investigate two distinct loss mechanisms responsible for the rapid dropouts of radiation belt electrons by assimilating data from Van Allen Probes A and B and Geostationary Operational Environmental Satellites (GOES) 13 and 15 into a 3-D diffusion model. In particular, we examine the respective contribution of electromagnetic ion cyclotron (EMIC) wave scattering and magnetopause shadowing for values of the first adiabatic invariant μ ranging from 300 to 3,000 MeV G−1. We inspect the innovation vector and perform a statistical analysis to quantitatively assess the effect of both processes as a function of various geomagnetic indices, solar wind parameters, and radial distance from the Earth. Our results are in agreement with previous studies that demonstrated the energy dependence of these two mechanisms. We show that EMIC wave scattering tends to dominate loss at lower L shells, and it may amount to between 10\%/hr and 30\%/hr of the maximum value of phase space density (PSD) over all L shells for fixed first and second adiabatic invariants. On the other hand, magnetopause shadowing is found to deplete electrons across all energies, mostly at higher L shells, resulting in loss from 50\%/hr to 70\%/hr of the maximum PSD. Nevertheless, during times of enhanced geomagnetic activity, both processes can operate beyond such location and encompass the entire outer radiation belt.

Cervantes, S.; Shprits, Y; Aseev, N.; Allison, H.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 08/2020

YEAR: 2020     DOI: https://doi.org/10.1029/2020JA028208

data assimilation; EMIC waves; magnetopause shadowing; innovation vector; Kalman Filter; radiation belt losses; Van Allen Probes

Quantifying the Effects of EMIC Wave Scattering and Magnetopause Shadowing in the Outer Electron Radiation Belt by Means of Data Assimilation

In this study we investigate two distinct loss mechanisms responsible for the rapid dropouts of radiation belt electrons by assimilating data from Van Allen Probes A and B and Geostationary Operational Environmental Satellites (GOES) 13 and 15 into a 3-D diffusion model. In particular, we examine the respective contribution of electromagnetic ion cyclotron (EMIC) wave scattering and magnetopause shadowing for values of the first adiabatic invariant μ ranging from 300 to 3,000 MeV G−1. We inspect the innovation vector and perform a statistical analysis to quantitatively assess the effect of both processes as a function of various geomagnetic indices, solar wind parameters, and radial distance from the Earth. Our results are in agreement with previous studies that demonstrated the energy dependence of these two mechanisms. We show that EMIC wave scattering tends to dominate loss at lower L shells, and it may amount to between 10\%/hr and 30\%/hr of the maximum value of phase space density (PSD) over all L shells for fixed first and second adiabatic invariants. On the other hand, magnetopause shadowing is found to deplete electrons across all energies, mostly at higher L shells, resulting in loss from 50\%/hr to 70\%/hr of the maximum PSD. Nevertheless, during times of enhanced geomagnetic activity, both processes can operate beyond such location and encompass the entire outer radiation belt.

Cervantes, S.; Shprits, Y; Aseev, N.; Allison, H.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 08/2020

YEAR: 2020     DOI: https://doi.org/10.1029/2020JA028208

data assimilation; EMIC waves; magnetopause shadowing; innovation vector; Kalman Filter; radiation belt losses; Van Allen Probes

Evidence of Nonlinear Interactions Between Magnetospheric Electron Cyclotron Harmonic Waves

Electron cyclotron harmonic (ECH) waves play an important role in the magnetosphere-ionosphere coupling. They are usually considered to be generated by the Bernstein-mode instability with electron loss cone distributions. By analyzing the Van Allen Probes wave data, we present the direct evidence of the nonlinear interactions between ECH waves in the magnetosphere. Substorm-injected electrons excite primary ECH waves in a series of structureless bands between multiples of the electron gyrofrequency. Nonlinear interactions between the primary ECH waves produce secondary waves at sum- and difference-frequencies of the primary waves. Our results suggest that the nonlinear wave-wave interactions can redistribute the primary ECH wave energy over a broader frequency range and hence potentially affect the magnetospheric electrons over a broader range of pitch angles and energies.

Gao, Zhonglei; Zuo, Pingbing; Feng, Xueshang; Wang, Yi; Jiang, Chaowei; Wei, Fengsi;

Published by: Geophysical Research Letters      Published on: 08/2020

YEAR: 2020     DOI: https://doi.org/10.1029/2020GL088452

ECH; wave-wave interaction; nonlinear interaction; frequency spectrum broadening; electron Bernstein mode; generalized Bernstein mode; Van Allen Probes

Evidence of Nonlinear Interactions Between Magnetospheric Electron Cyclotron Harmonic Waves

Electron cyclotron harmonic (ECH) waves play an important role in the magnetosphere-ionosphere coupling. They are usually considered to be generated by the Bernstein-mode instability with electron loss cone distributions. By analyzing the Van Allen Probes wave data, we present the direct evidence of the nonlinear interactions between ECH waves in the magnetosphere. Substorm-injected electrons excite primary ECH waves in a series of structureless bands between multiples of the electron gyrofrequency. Nonlinear interactions between the primary ECH waves produce secondary waves at sum- and difference-frequencies of the primary waves. Our results suggest that the nonlinear wave-wave interactions can redistribute the primary ECH wave energy over a broader frequency range and hence potentially affect the magnetospheric electrons over a broader range of pitch angles and energies.

Gao, Zhonglei; Zuo, Pingbing; Feng, Xueshang; Wang, Yi; Jiang, Chaowei; Wei, Fengsi;

Published by: Geophysical Research Letters      Published on: 08/2020

YEAR: 2020     DOI: https://doi.org/10.1029/2020GL088452

ECH; wave-wave interaction; nonlinear interaction; frequency spectrum broadening; electron Bernstein mode; generalized Bernstein mode; Van Allen Probes

Evidence of Nonlinear Interactions Between Magnetospheric Electron Cyclotron Harmonic Waves

Electron cyclotron harmonic (ECH) waves play an important role in the magnetosphere-ionosphere coupling. They are usually considered to be generated by the Bernstein-mode instability with electron loss cone distributions. By analyzing the Van Allen Probes wave data, we present the direct evidence of the nonlinear interactions between ECH waves in the magnetosphere. Substorm-injected electrons excite primary ECH waves in a series of structureless bands between multiples of the electron gyrofrequency. Nonlinear interactions between the primary ECH waves produce secondary waves at sum- and difference-frequencies of the primary waves. Our results suggest that the nonlinear wave-wave interactions can redistribute the primary ECH wave energy over a broader frequency range and hence potentially affect the magnetospheric electrons over a broader range of pitch angles and energies.

Gao, Zhonglei; Zuo, Pingbing; Feng, Xueshang; Wang, Yi; Jiang, Chaowei; Wei, Fengsi;

Published by: Geophysical Research Letters      Published on: 08/2020

YEAR: 2020     DOI: https://doi.org/10.1029/2020GL088452

ECH; wave-wave interaction; nonlinear interaction; frequency spectrum broadening; electron Bernstein mode; generalized Bernstein mode; Van Allen Probes

Ionospheric Signatures of Ring Current Ions Scattered by Magnetosonic Waves

In this letter, we present unique conjugated satellite observations of ionospheric signatures of ring current (RC) ions scattered by fast magnetosonic (MS) waves. In the plasmasphere, the Van Allen Probe in situ observed MS waves. At ionospheric altitudes, the NOAA 16 satellite at the footprint of Van Allen Probe simultaneously observed obvious enhancements of mirroring RC ions, but no obvious variations of precipitating RC ions at subauroral latitudes. Theoretical calculations of pitch angle diffusion coefficients for RC ions confirm that observed MS waves can lead to flux enhancements only for mirroring but not for precipitating RC ions, which is in agreement with the observations of NOAA 16. Our result provides a direct link between in situ inner magnetospheric observations of MS waves and conjugated ionospheric observations of flux enhancements for mirroring RC ions caused by MS waves so as to reveal the ionospheric signature of RC ions scattered by MS waves.

Yuan, Zhigang; Yao, Fei; Yu, Xiongdong; Ouyang, Zhihai; Huang, Shiyong;

Published by: Geophysical Research Letters      Published on: 08/2020

YEAR: 2020     DOI: https://doi.org/10.1029/2020GL089032

magnetosonic waves; mirroring ions; pitch angle scatter; precipitating ions; Van Allen Probes; Ring current ions

Ionospheric Signatures of Ring Current Ions Scattered by Magnetosonic Waves

In this letter, we present unique conjugated satellite observations of ionospheric signatures of ring current (RC) ions scattered by fast magnetosonic (MS) waves. In the plasmasphere, the Van Allen Probe in situ observed MS waves. At ionospheric altitudes, the NOAA 16 satellite at the footprint of Van Allen Probe simultaneously observed obvious enhancements of mirroring RC ions, but no obvious variations of precipitating RC ions at subauroral latitudes. Theoretical calculations of pitch angle diffusion coefficients for RC ions confirm that observed MS waves can lead to flux enhancements only for mirroring but not for precipitating RC ions, which is in agreement with the observations of NOAA 16. Our result provides a direct link between in situ inner magnetospheric observations of MS waves and conjugated ionospheric observations of flux enhancements for mirroring RC ions caused by MS waves so as to reveal the ionospheric signature of RC ions scattered by MS waves.

Yuan, Zhigang; Yao, Fei; Yu, Xiongdong; Ouyang, Zhihai; Huang, Shiyong;

Published by: Geophysical Research Letters      Published on: 08/2020

YEAR: 2020     DOI: https://doi.org/10.1029/2020GL089032

magnetosonic waves; mirroring ions; pitch angle scatter; precipitating ions; Van Allen Probes; Ring current ions

Ionospheric Signatures of Ring Current Ions Scattered by Magnetosonic Waves

In this letter, we present unique conjugated satellite observations of ionospheric signatures of ring current (RC) ions scattered by fast magnetosonic (MS) waves. In the plasmasphere, the Van Allen Probe in situ observed MS waves. At ionospheric altitudes, the NOAA 16 satellite at the footprint of Van Allen Probe simultaneously observed obvious enhancements of mirroring RC ions, but no obvious variations of precipitating RC ions at subauroral latitudes. Theoretical calculations of pitch angle diffusion coefficients for RC ions confirm that observed MS waves can lead to flux enhancements only for mirroring but not for precipitating RC ions, which is in agreement with the observations of NOAA 16. Our result provides a direct link between in situ inner magnetospheric observations of MS waves and conjugated ionospheric observations of flux enhancements for mirroring RC ions caused by MS waves so as to reveal the ionospheric signature of RC ions scattered by MS waves.

Yuan, Zhigang; Yao, Fei; Yu, Xiongdong; Ouyang, Zhihai; Huang, Shiyong;

Published by: Geophysical Research Letters      Published on: 08/2020

YEAR: 2020     DOI: https://doi.org/10.1029/2020GL089032

magnetosonic waves; mirroring ions; pitch angle scatter; precipitating ions; Van Allen Probes; Ring current ions

Ionospheric Signatures of Ring Current Ions Scattered by Magnetosonic Waves

In this letter, we present unique conjugated satellite observations of ionospheric signatures of ring current (RC) ions scattered by fast magnetosonic (MS) waves. In the plasmasphere, the Van Allen Probe in situ observed MS waves. At ionospheric altitudes, the NOAA 16 satellite at the footprint of Van Allen Probe simultaneously observed obvious enhancements of mirroring RC ions, but no obvious variations of precipitating RC ions at subauroral latitudes. Theoretical calculations of pitch angle diffusion coefficients for RC ions confirm that observed MS waves can lead to flux enhancements only for mirroring but not for precipitating RC ions, which is in agreement with the observations of NOAA 16. Our result provides a direct link between in situ inner magnetospheric observations of MS waves and conjugated ionospheric observations of flux enhancements for mirroring RC ions caused by MS waves so as to reveal the ionospheric signature of RC ions scattered by MS waves.

Yuan, Zhigang; Yao, Fei; Yu, Xiongdong; Ouyang, Zhihai; Huang, Shiyong;

Published by: Geophysical Research Letters      Published on: 08/2020

YEAR: 2020     DOI: https://doi.org/10.1029/2020GL089032

magnetosonic waves; mirroring ions; pitch angle scatter; precipitating ions; Van Allen Probes; Ring current ions

New Insights From Long-Term Measurements of Inner Belt Protons (10s of MeV) by SAMPEX, POES, Van Allen Probes, and Simulation Results

The Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX) mission provided long-term measurements of 10s of megaelectron volt (MeV) inner belt (L < 2) protons (1992–2009) as did the Polar-orbiting Operational Environmental Satellite-18 (POES-18, 2005 to present). These long-term measurements at low-Earth orbit (LEO) showed clear solar cycle variations which anticorrelate with sunspot number. However, the magnitude of the variation is much greater than the solar cycle variation of galactic cosmic rays (>GeV) that are regarded as a source of these trapped protons. Furthermore, the proton fluxes and their variations sensitively depend on the altitude above the South Atlantic Anomaly (SAA) region. With respect to protons (>36 MeV) mirroring near the magnetic equator, both POES measurements and simulations show no obvious solar cycle variations at L > 1.2. This is also confirmed by recent measurements from the Van Allen Probes (2012–2019), but there are clear solar cycle variations and a strong spatial gradient of the proton flux below L = 1.2. A direct comparison between measurements and simulations leads to the conclusion that energy loss of trapped protons due to collisions with free and bound electrons in the ionosphere and atmosphere is the dominant mechanism for the strong spatial gradient and solar cycle variation of the inner belt protons. This fact is also key of importance for spacecraft and instrument design and operation in near-Earth space.

Li, Xinlin; Xiang, Zheng; Zhang, Kun; Khoo, Lengying; Zhao, Hong; Baker, Daniel; Temerin, Michael;

Published by: Journal of Geophysical Research: Space Physics      Published on: 08/2020

YEAR: 2020     DOI: https://doi.org/10.1029/2020JA028198

Inner radiation belt; Inner Belt Proton; Solar cycle variation; Cosmic rays; neutron monitor; Low Earth Orbit satellite; Van Allen Probes

New Insights From Long-Term Measurements of Inner Belt Protons (10s of MeV) by SAMPEX, POES, Van Allen Probes, and Simulation Results

The Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX) mission provided long-term measurements of 10s of megaelectron volt (MeV) inner belt (L < 2) protons (1992–2009) as did the Polar-orbiting Operational Environmental Satellite-18 (POES-18, 2005 to present). These long-term measurements at low-Earth orbit (LEO) showed clear solar cycle variations which anticorrelate with sunspot number. However, the magnitude of the variation is much greater than the solar cycle variation of galactic cosmic rays (>GeV) that are regarded as a source of these trapped protons. Furthermore, the proton fluxes and their variations sensitively depend on the altitude above the South Atlantic Anomaly (SAA) region. With respect to protons (>36 MeV) mirroring near the magnetic equator, both POES measurements and simulations show no obvious solar cycle variations at L > 1.2. This is also confirmed by recent measurements from the Van Allen Probes (2012–2019), but there are clear solar cycle variations and a strong spatial gradient of the proton flux below L = 1.2. A direct comparison between measurements and simulations leads to the conclusion that energy loss of trapped protons due to collisions with free and bound electrons in the ionosphere and atmosphere is the dominant mechanism for the strong spatial gradient and solar cycle variation of the inner belt protons. This fact is also key of importance for spacecraft and instrument design and operation in near-Earth space.

Li, Xinlin; Xiang, Zheng; Zhang, Kun; Khoo, Lengying; Zhao, Hong; Baker, Daniel; Temerin, Michael;

Published by: Journal of Geophysical Research: Space Physics      Published on: 08/2020

YEAR: 2020     DOI: https://doi.org/10.1029/2020JA028198

Inner radiation belt; Inner Belt Proton; Solar cycle variation; Cosmic rays; neutron monitor; Low Earth Orbit satellite; Van Allen Probes

New Insights From Long-Term Measurements of Inner Belt Protons (10s of MeV) by SAMPEX, POES, Van Allen Probes, and Simulation Results

The Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX) mission provided long-term measurements of 10s of megaelectron volt (MeV) inner belt (L < 2) protons (1992–2009) as did the Polar-orbiting Operational Environmental Satellite-18 (POES-18, 2005 to present). These long-term measurements at low-Earth orbit (LEO) showed clear solar cycle variations which anticorrelate with sunspot number. However, the magnitude of the variation is much greater than the solar cycle variation of galactic cosmic rays (>GeV) that are regarded as a source of these trapped protons. Furthermore, the proton fluxes and their variations sensitively depend on the altitude above the South Atlantic Anomaly (SAA) region. With respect to protons (>36 MeV) mirroring near the magnetic equator, both POES measurements and simulations show no obvious solar cycle variations at L > 1.2. This is also confirmed by recent measurements from the Van Allen Probes (2012–2019), but there are clear solar cycle variations and a strong spatial gradient of the proton flux below L = 1.2. A direct comparison between measurements and simulations leads to the conclusion that energy loss of trapped protons due to collisions with free and bound electrons in the ionosphere and atmosphere is the dominant mechanism for the strong spatial gradient and solar cycle variation of the inner belt protons. This fact is also key of importance for spacecraft and instrument design and operation in near-Earth space.

Li, Xinlin; Xiang, Zheng; Zhang, Kun; Khoo, Lengying; Zhao, Hong; Baker, Daniel; Temerin, Michael;

Published by: Journal of Geophysical Research: Space Physics      Published on: 08/2020

YEAR: 2020     DOI: https://doi.org/10.1029/2020JA028198

Inner radiation belt; Inner Belt Proton; Solar cycle variation; Cosmic rays; neutron monitor; Low Earth Orbit satellite; Van Allen Probes

New Insights From Long-Term Measurements of Inner Belt Protons (10s of MeV) by SAMPEX, POES, Van Allen Probes, and Simulation Results

The Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX) mission provided long-term measurements of 10s of megaelectron volt (MeV) inner belt (L < 2) protons (1992–2009) as did the Polar-orbiting Operational Environmental Satellite-18 (POES-18, 2005 to present). These long-term measurements at low-Earth orbit (LEO) showed clear solar cycle variations which anticorrelate with sunspot number. However, the magnitude of the variation is much greater than the solar cycle variation of galactic cosmic rays (>GeV) that are regarded as a source of these trapped protons. Furthermore, the proton fluxes and their variations sensitively depend on the altitude above the South Atlantic Anomaly (SAA) region. With respect to protons (>36 MeV) mirroring near the magnetic equator, both POES measurements and simulations show no obvious solar cycle variations at L > 1.2. This is also confirmed by recent measurements from the Van Allen Probes (2012–2019), but there are clear solar cycle variations and a strong spatial gradient of the proton flux below L = 1.2. A direct comparison between measurements and simulations leads to the conclusion that energy loss of trapped protons due to collisions with free and bound electrons in the ionosphere and atmosphere is the dominant mechanism for the strong spatial gradient and solar cycle variation of the inner belt protons. This fact is also key of importance for spacecraft and instrument design and operation in near-Earth space.

Li, Xinlin; Xiang, Zheng; Zhang, Kun; Khoo, Lengying; Zhao, Hong; Baker, Daniel; Temerin, Michael;

Published by: Journal of Geophysical Research: Space Physics      Published on: 08/2020

YEAR: 2020     DOI: https://doi.org/10.1029/2020JA028198

Inner radiation belt; Inner Belt Proton; Solar cycle variation; Cosmic rays; neutron monitor; Low Earth Orbit satellite; Van Allen Probes

Dynamics of Energetic Electrons in the Slot Region During Geomagnetically Quiet Times: Losses Due to Wave-Particle Interactions Versus a Source From Cosmic Ray Albedo Neutron Decay (CRAND)

Earth s slot region, lying between the outer and inner radiation belts, has been identified as due to a balance between inward radial diffusion and pitch angle (PA) scattering induced by waves. However, recent satellite observations and modeling studies indicate that cosmic ray albedo neutron decay (CRAND) may also play a significant role in energetic electron dynamics in the slot region. In this study, using a drift-diffusion-source model, we investigate the relative contribution of all significant waves and CRAND to the dynamics of energetic electrons in the slot region during July 2014, an extended period of quiet geomagnetic activity. The bounce-averaged PA diffusion coefficients from three types of waves (hiss, lightning-generated whistlers [LGW], and very low frequency [VLF] transmitters) are calculated based on quasi-linear theory, while the CRAND source follows the results in Xiang et al. (2019, https://doi.org/10.1029/2018GL081730). The simulation results indicate that both LGW and VLF transmitter waves can enhance loss and weaken the top hat PA distribution induced by hiss waves. For 470 keV electrons at L = 2.5, simulation results without CRAND show a much quicker decrease than observations from the Van Allen Probes. After including CRAND, simulated electron flux variations reproduce satellite observations, suggesting that CRAND is an important source for hundreds of keV electrons in the slot region during quiet times. The balance between the CRAND source and loss due to wave-particle interactions provides a lower limit to relativistic electron fluxes in the slot region, which can act as an important reference point for instrument calibration when a true background level is warranted.

Xiang, Zheng; Li, Xinlin; Ni, Binbin; Temerin, M.; Zhao, Hong; Zhang, Kun; Khoo, Leng;

Published by: Journal of Geophysical Research: Space Physics      Published on: 08/2020

YEAR: 2020     DOI: https://doi.org/10.1029/2020JA028042

Slot region; Wave-particle interaction; CRAND; energetic electrons; Van Allen Probes