Bibliography
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Found 83 entries in the Bibliography.
Showing entries from 1 through 50
| 2021 |
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Global Survey of Electron Precipitation due to Hiss Waves in the Earth s Plasmasphere and Plumes Abstract We present a global survey of energetic electron precipitation from the equatorial magnetosphere due to hiss waves in the plasmasphere and plumes. Using Van Allen Probes measurements, we calculate the pitch angle diffusion coefficients at the bounce loss cone, and evaluate the energy spectrum of precipitating electron flux. Our ∼6.5-year survey shows that, during disturbed times, hiss inside the plasmasphere primarily causes the electron precipitation at L > 4 over 8 h < MLT < 18 h, and hiss waves in plumes cause the precipitation at L > 5 over 8 h < MLT < 14 h and L > 4 over 14 h < MLT < 20 h. The precipitating energy flux increases with increasing geomagnetic activity, and is typically higher in the plasmaspheric plume than the plasmasphere. The characteristic energy of precipitation increases from ∼20 keV at L = 6 to ∼100 keV at L = 3, potentially causing the loss of electrons at several hundred keV. Ma, Q.; Li, W.; Zhang, X.-J.; Bortnik, J.; Shen, X.-C.; Connor, H.; Boyd, A.; Kurth, W.; Hospodarsky, G.; Claudepierre, S.; Reeves, G.; Spence, H.; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021JA029644 electron precipitation; hiss wave; plasmasphere; plasmaspheric plume; Precipitating Energy Flux; Van Allen Probes Survey; Van Allen Probes |
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Rapid injections of MeV electrons and extremely fast step-like outer radiation belt enhancements Abstract Rapid injection of MeV electrons associated with strong substorm dipolarization has been suggested as a potential explanation for some radiation belt enhancement events. However, it has been difficult to quantify the contribution of MeV electron injections to radiation belt enhancements. This paper presents two isolated MeV electron injection events for which we quite precisely quantify how the entire outer-belt immediately changed with the injections. Tracking detailed outer-belt evolution observed by Van Allen Probes, for both events, we identify large step-like relativistic electron enhancements (roughly 1-order of magnitude increase for ∼2 MeV electron fluxes) for L ≳ 3.8 and L ≳ 4.6, respectively, that occurred on ∼30-min timescales nearly instantaneously with the injections. The enhancements occurred almost simultaneously for 10s keV to multi-MeV electrons, with the lowest-L of enhancement region located farther out for higher energy. The outer-belt stayed at these new levels for ≳ several hours without substantial subsequent enhancements. Kim, H.-J.; Lee, D.-Y.; Wolf, R.; Bortnik, J.; Kim, K.-C.; Lyons, L.; Choe, W.; Noh, S.-J.; Choi, K.-E.; Yue, C.; Li, J.; Published by: Geophysical Research Letters Published on: 05/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021GL093151 Radiation belt enhancement; Relatvistic electrons; substorm injection; Step-like; Extremely fast; Van Allen Probes |
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Abstract We performed a comprehensive statistical study of electromagnetic ion cyclotron (EMIC) waves observed by the Van Allen Probes and Exploration of energization and Radiation in Geospace satellite (ERG/Arase). From 2017 to 2018, we identified and categorized EMIC wave events with respect to wavebands (H+ and He+ EMIC waves) and relative locations from the plasmasphere (inside and outside the plasmasphere). We found that H+ EMIC waves in the morning sector at L>8 are predominantly observed with a mixture of linear and right-handed polarity and higher wave normal angles during quiet geomagnetic conditions. Both H+ and He+ EMIC waves observed in the noon sector at L∼4-6 have left-handed polarity and lower wave normal angles at |MLAT|< 20˚ during the recovery phase of a storm with moderate solar wind pressure. In the afternoon sector (12-18 MLT), He+ EMIC waves are dominantly observed with strongly enhanced wave power at L∼6-8 during the storm main phase, while in the dusk sector (17-21 MLT) they have lower wave normal angles with linear polarity at L>8 during geomagnetic quiet conditions. Based on distinct characteristics at different EMIC wave occurrence regions, we suggest that EMIC waves in the magnetosphere can be generated by different free energy sources. Possible sources include the freshly injected particles from the plasma sheet, adiabatic heating by dayside magnetospheric compressions, suprathermal proton heating by magnetosonic waves, and off-equatorial sources. This article is protected by copyright. All rights reserved. Jun, C.-W; Miyoshi, Y.; Kurita, S.; Yue, C.; Bortnik, J.; Lyons, L.; Nakamura, S.; Shoji, M.; Imajo, S.; Kletzing, C.; Kasahara, Y.; Kasaba, Y.; Matsuda, S.; Tsuchiya, F.; Kumamoto, A.; Matsuoka, A.; Shinohara, I.; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA029001 Spatial distributions of EMIC waves; RBSP and Arase observations; EMIC wave properties; EMIC wave dependence on geomagnetic condition; Van Allen Probes |
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Sustained oxygen spectral gaps and their dynamic evolution in the inner magnetosphere Abstract Van Allen Probes observations of ion spectra often show a sustained gap within a very narrow energy range throughout the full orbit. To understand their formation mechanism, we statistically investigate the characteristics of the narrow gaps for oxygen ions and find that they are most frequently observed near the noon sector with a peak occurrence rate of over 30\%. The magnetic moment (μ) of the oxygen ions in the gap shows a strong dependence on magnetic local time (MLT), with higher and lower μ in the morning and afternoon sectors, respectively. Moreover, we find through superposed epoch analysis that the gap formation also depends on geomagnetic conditions. Those gaps formed at lower magnetic moments (μ < 3000 keV/G) are associated with stable convection electric fields, which enable magnetospheric ions to follow a steady drift pattern that facilitates the gap formation by corotational drift resonance. On the other hand, gaps with higher μ values are statistically preceded by a gradual increase of geomagnetic activity. We suggest that ions within the gap were originally located inside the Alfven layer following closed drift paths, before they were transitioned into open drift paths as the convection electric field was enhanced. The sunward drift of these ions, with very low fluxes, forms a drainage void in the dayside magnetosphere manifested as the sustained gap in the oxygen spectrum. This scenario is supported by particle-tracing simulations, which reproduce most of the observed characteristics and therefore provide new insights into inner magnetospheric dynamics. This article is protected by copyright. All rights reserved. Yue, Chao; Zhou, Xu-Zhi; Bortnik, Jacob; Zong, Qiu-Gang; Li, Yuxuan; Ren, Jie; Reeves, Geoffrey; Spence, Harlan; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA029092 oxygen spectral gaps; corotational drift resonance; sustained gaps; drainage void; test particle simulations; 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 |
| 2020 |
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Multi-Parameter Chorus and Plasmaspheric Hiss Wave Models Abstract The resonant interaction of energetic particles with plasma waves, such as chorus and plasmaspheric hiss waves, plays a direct and crucial role in the acceleration and loss of radiation belt electrons that ultimately affect the dynamics of the radiation belts. In this study, we use the comprehensive wave data measurements made by the Electric and Magnetic Field Instrument Suite and Integrated Science instruments on board the two Van Allen probes, to develop multi-parameter statistical chorus and plasmaspheric hiss wave models. The models of chorus and plasmaspheric hiss waves are presented as a function of combined geomagnetic activity (AE), solar wind velocity (V), and southward interplanetary magnetic field (Bs). The relatively smooth wave models reveal new features. Despite, the coupling between geomagnetic and solar wind parameters, the results show that each parameter still carries a sufficient amount of unique information to more accurately constrain the chorus and plasmaspheric hiss wave intensities. The new wave models presented here highlight the importance of multi-parameter wave models, and can improve radiation belt modeling. Aryan, Homayon; Bortnik, Jacob; Meredith, Nigel; Horne, Richard; Sibeck, David; Balikhin, Michael; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028403 chorus waves; inner magnetosphere; multi parameter wave distribution; plasmaspheric hiss waves; Van Allen Probes; wave-particle interactions |
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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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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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The flux of energetic electrons in the outer radiation belt shows a high variability. The interactions of electrons with very low frequency (VLF) chorus waves play a significant role in controlling the flux variation of these particles. Quantifying the effects of these interactions is crucially important for accurately modeling the global dynamics of the outer radiation belt and to provide a comprehensive description of electron flux variations over a wide energy range (from the source population of 30 keV electrons up to the relativistic core population of the outer radiation belt). Here, we use a synthetic chorus wave model based on a combined database compiled from the Van Allen Probes and Cluster spacecraft VLF measurements to develop a comprehensive parametric model of electron lifetimes as a function of L-shell, electron energy, and geomagnetic activity. The wave model takes into account the wave amplitude dependence on geomagnetic latitude, wave normal angle distribution, and variations of wave frequency with latitude. We provide general analytical formulas to estimate electron lifetimes as a function of L-shell (for L = 3.0 to L = 6.5), electron energy (from 30 keV to 2 MeV), and geomagnetic activity parameterized by the AE index. The present model lifetimes are compared to previous studies and analytical results and also show a good agreement with measured lifetimes of 30 to 300 keV electrons at geosynchronous orbit. Aryan, Homayon; Agapitov, Oleksiy; Artemyev, Anton; Mourenas, Didier; Balikhin, Michael; Boynton, Richard; Bortnik, Jacob; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028018 electron lifetimes; Van Allen radiation belts; chorus waves; pitch angle diffusion coefficients; Van Allen Probes; Cluster |
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Global Model of Whistler Mode Chorus in the Near-Equatorial Region (|λm|< 18°) We extend our database of whistler mode chorus, based on data from seven satellites, by including ∼3 years of data from Radiation Belt Storm Probes (RBSP)-A and RBSP-B and an additional ∼6 years of data from Time History of Events and Macroscale Interactions during Substorms (THEMIS)-A, THEMIS-D, and THEMIS-E. The new database allows us to probe the near-equatorial region in detail, revealing new features. In the equatorial source region, |λm|<6°, strong wave power is most extensive in the 0.1–0.4fce bands in the region 21–11 magnetic local time (MLT) from the plasmapause out to L∗ = 8 and beyond, especially near dawn. At higher frequencies, in the 0.4–0.6fce frequency bands, strong wave power is more tightly confined, typically being restricted to the postmidnight sector in the region 4 Meredith, Nigel; Horne, Richard; Shen, Xiao-Chen; Li, Wen; Bortnik, Jacob; Published by: Geophysical Research Letters Published on: 05/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020GL087311 whistler mode chorus; wave-particle interactions; Radiation belts; Van Allen Probes |
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Abstract Forecasting relativistic electron fluxes at geostationary Earth orbit (GEO) has been a long-term goal of the scientific community, and significant advances have been made in the past, but the relation to the interior of the radiation belts, that is, to lower L-shells, is still not clear. In this work we have identified 60 relativistic electron enhancement events at GEO to study the radial response of outer belt fluxes and the correlation between the fluxes at GEO and those at lower L-shells. The enhancement events occurred between 1 October 2012 and 31 December 2017 and were identified using Geostationary Operational Environmental Satellite (GOES) 15 >2 MeV fluxes at GEO, which we have used to characterize the radial response of the radiation belt, by comparing to fluxes measured by the Van Allen probes Energetic Particle, Composition and Thermal Plasma Suite Relativistic Electron-Proton Telescope (ECT-REPT) between 2.5 Pinto, Victor; Bortnik, Jacob; Moya, Pablo; Lyons, Larry; Sibeck, David; Kanekal, Shrikanth; Spence, Harlan; Baker, Daniel; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2020 YEAR: 2020 DOI: 10.1029/2019JA027660 Radiation belts; relativistic electrons; geosynchronous orbit; Outer Belt; flux correlation; enhancement events; Van Allen Probes |
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Episodic Occurrence of Field-Aligned Energetic Ions on the Dayside The tens of kiloelectron volt ions observed in the ring current region at L ~ 3\textendash7 generally have pancake pitch angle distributions, that is, peaked at 90\textdegree. However, in this study, by using the Van Allen Probe observations on the dayside, unexpectedly, we have found that about 5\% time, protons with energies of ~30 to 50 keV show two distinct populations, having an additional field-aligned population overlapping with the original pancake population. The newly appearing field-aligned populations have higher occurrence rates at ~12\textendash16 magnetic local time during geomagnetically active times. In particular, we have studied eight such events in detail and found that the source regions are located around 12 to 18 magnetic local time which coincides with our statistical result. Based on the ionospheric and geosynchronous observations, it is suggested that these energetic ions with field-aligned pitch angle distributions probably are accelerated near postnoon in association with ionospheric disturbances that are triggered by tail injections. Yue, Chao; Bortnik, Jacob; Zou, Shasha; Nishimura, Yukitoshi; Foster, John; Coppeans, Thomas; Ma, Qianli; Zong, Qiugang; Hull, A.; Henderson, Mike; Reeves, Geoffrey; Spence, Harlan; Published by: Geophysical Research Letters Published on: 01/2020 YEAR: 2020 DOI: 10.1029/2019GL086384 |
| 2019 |
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Decay of Ultrarelativistic Remnant Belt Electrons Through Scattering by Plasmaspheric Hiss Ultrarelativistic electron remnant belts appear frequently following geomagnetic disturbances and are located in-between the inner radiation belt and a reforming outer belt. As remnant belts are relatively stable, here we explore the importance of hiss and electromagnetic ion cyclotron waves in controlling the observed decay rates of remnant belt ultrarelativistic electrons in a statistical way. Using measurements from the Van Allen Probes inside the plasmasphere for 25 remnant belt events that occurred between 2012 and 2017 and that are located in the region 2.9 Pinto, V.; Mourenas, D.; Bortnik, J.; Zhang, X.-J.; Artemyev, A.; Moya, P.; Lyons, L.; Published by: Journal of Geophysical Research: Space Physics Published on: Dec-07-2019 YEAR: 2019 DOI: 10.1029/2019JA026509 Decay rates; EMIC waves; MeV Electron Decay; Plasmaspheric Hiss; Radiation belts; Remnant Belt; Van Allen Probes |
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We investigate the global distribution and provide empirical models of fast magnetosonic waves using the combined observations by the magnetometer and waveform receiver on board Van Allen Probes. The magnetometer measurements of magnetosonic waves indicate a significant wave power within the frequency range from the helium gyrofrequency to 20 Hz at L >= 4 in the afternoon sector, both inside and outside the plasmapause. The waveform receiver measurements indicate a significant wave power from 20 Hz to the lower hybrid resonance frequency at L <= 5.5 near the dayside outside the plasmapause or in the afternoon sector inside the plasmapause. The sum of the wave powers from the two instruments provides the wave power distribution over the complete frequency range. The most significant root-mean-square wave amplitude of magnetosonic waves is typically 100\textendash200 pT inside or outside the plasmapause with a magnetic local time coverage of 30\textendash50\% during geomagnetically active times when AE* > 500 nT. The magnetosonic wave frequency increases with decreasing L shell following the trend of the proton gyrofrequency outside the plasmapause, indicating a close relation with the local wave generation. Inside the plasmapause, the dependence of wave frequency on L shell is weaker, and the wave frequency is more stable across L shells, indicating the wave propagation effects from the source located at higher L shells. We have performed polynomial fits of the global magnetosonic wave distribution and wave frequency spectra, which are useful in future radiation belt simulations. Ma, Q.; Li, W.; Bortnik, J.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Wygant, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2019 YEAR: 2019 DOI: 10.1029/2019JA027407 Empirical Fitting; Global Survey; magnetosonic waves; Van Allen Probes; Van Allen Probes observation |
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Electromagnetic ion cyclotron (EMIC) waves and magnetosonic waves are commonly observed in the Earth\textquoterights magnetosphere associated with enhanced ring current activity. Using wave and ion measurements from the Van Allen Probes, we identify clear correlations between the hydrogen- and helium-band EMIC waves with the enhancement of trapped helium and oxygen ion fluxes, respectively. We calculate the diffusion coefficients of different ion species using quasi-linear theory to understand the effects of resonant scattering by EMIC waves. Our calculations indicate that EMIC waves can cause pitch angle scattering loss of several keV to hundreds of keV ions, and heating of tens of eV to several keV helium and oxygen ions by hydrogen- and helium-band EMIC waves, respectively. Moreover, we found that magnetosonic waves can cause the resonant heating of thermal protons. Our study indicates the importance of energy transfer from the EMIC and magnetosonic waves to ions with different species at thermal energies. Ma, Q.; Li, W.; Yue, C.; Thorne, R.; Bortnik, J.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Reeves, G.; Spence, H.; Published by: Geophysical Research Letters Published on: 06/2019 YEAR: 2019 DOI: 10.1029/2019GL083513 electromagnetic ion cyclotron waves; Ion heating; Quasilinear modeling; Resonant interaction in plasmasphere; ring current; Van Allen Probes; Van Allen Probes observation |
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Nonlinear Electron Interaction With Intense Chorus Waves: Statistics of Occurrence Rates A comprehensive statistical analysis on 8 years of lower-band chorus wave packets measured by the Van Allen Probes and THEMIS spacecraft is performed to examine whether, when, and where these waves are above the theoretical threshold for nonlinear resonant wave-particle interaction. We find that \~5\textendash30\% of all chorus waves interact nonlinearly with \~30- to 300-keV electrons possessing equatorial pitch angles of >40\textdegree in the outer radiation belt, especially during disturbed (AE>500 nT) periods with energetic particles associated with injections from the plasma sheet. Such considerable occurrence rates of nonlinear interactions imply that the evolution of energetic electron fluxes should be dominated by nonlinear effects, rather than by quasi-linear diffusion as commonly assumed. We discuss the possible consequences of such a large amount of high-amplitude chorus waves and examine their characteristics that can influence the efficiency of nonlinear wave-particle interactions. Zhang, X.-J.; Mourenas, D.; Artemyev, A.; Angelopoulos, V.; Bortnik, J.; Thorne, R.; Kurth, W.; Kletzing, C.; Hospodarsky, G.; Published by: Geophysical Research Letters Published on: 06/2019 YEAR: 2019 DOI: 10.1029/2019GL083833 chorus waves; Electron acceleration; nonlinear wave particle interaction; THEMIS; Van Allen Probes; wave packet size |
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Plasma kinetic theory predicts that sufficiently anisotropic proton distribution will excite electromagnetic ion cyclotron (EMIC) waves, which in turn relax the proton distribution to a marginally stable state creating an upper bound on the relaxed proton anisotropy. Here, using EMIC wave observations and coincident plasma measurements made by Van Allen Probes in the inner magnetosphere, we show that the proton distributions are well constrained by this instability to a marginally stable state. Near the threshold, the probability of EMIC wave occurrence is highest, having left-handed polarization and observed near the magnetic equator with relatively small wave normal angles, indicating that these waves are locally generated. In addition, EMIC waves are distributed in two magnetic local time regions with different intensity. Compared with helium band waves, hydrogen band waves behave similarly except that they are often observed in low-density regions. These results reveal several important features regarding EMIC waves excitation and propagation. Yue, Chao; Jun, Chae-Woo; Bortnik, Jacob; An, Xin; Ma, Qianli; Reeves, Geoffrey; Spence, Harlan; Gerrard, Andrew; Gkioulidou, Matina; Mitchell, Donald; Kletzing, Craig; Published by: Geophysical Research Letters Published on: 04/2019 YEAR: 2019 DOI: 10.1029/2019GL082633 EMIC waves; helium-band; hydrogen-band; plasma beta; proton temperature anisotropy; Van Allen Probes |
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To understand the relationship between generation of electromagnetic ion cyclotron (EMIC) waves and energetic particle injections, we performed a statistical study of EMIC waves associated with and without injections based on the Van Allen Probes (Radiation Belt Storm Probes) and Geostationary Operational Environmental Satellite (GOES; GOES-13 and GOES-15) observations. Using 47 months of observations, we identified wave events seen by the Van Allen Probes relative to the plasmapause and to energetic particle injections seen by GOES-13 and GOES-15 on the nightside. We separated the events into four categories: EMIC waves with (without) injections inside (outside) the plasmasphere. We found that He+ EMIC waves have higher occurrence rate inside the plasmasphere, while H+ EMIC waves predominantly occur outside the plasmasphere. Meanwhile, the time duration and peak occurrence rate of EMIC waves associated with injections are shorter and limited to a narrower magnetic local time region than those without injections, indicating that these waves have localized source regions. He+ EMIC waves inside the plasmasphere associated with injection are usually accompanied by an increase in H+ flux within energies of 1\textendash50 keV through all magnetic local time regions, while most wave events outside the plasmasphere show less relationship with H+ flux increase. From these observations, we suggest that injected hot ions are the major driver of He+ EMIC waves inside the plasmasphere during active time. Expanding plasmasphere during quiet times can provide broad wave source regions for He+ EMIC waves on the dayside. However, H+ EMIC waves outside the plasmasphere show different characteristics, suggesting that these waves are generated by other processes. Jun, C.-W.; Yue, C.; Bortnik, J.; Lyons, L.; Nishimura, Y.; Kletzing, C.; Wygant, J.; Spence, H.; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2019 YEAR: 2019 DOI: 10.1029/2018JA025886 EMIC waves associated with and without injections; Relationship between EMIC wave activity and energetic H+ flux variation; Simultaneous observations using the Van Allen Probes and GOES satellites; Spatial occurrence distributions of EMIC waves; Van Allen Probes |
| 2018 |
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Shortly after the launch of the Van Allen Probes, a new three-belt configuration of the electron radiation belts was reported. Using data between September 2012 and November 2017, we have identified 30 three-belt events and found that about 18\% of geomagnetic storms result in such configuration. Based on the identified events, we evaluated some characteristics of the remnant (intermediate) belt. We determined the energy range of occurrence and found it peaks at E = 5.2 MeV. We also determined that the magnetopause location and SYM-H value may play an important role in the outer belt losses that lead to formation and location of the remnant belt. Finally, we calculated the decay rates of the remnant belt for all events and found that their lifetime gets longer as energy increases, ranging from days at E = 1.8 MeV up to months at E = 6.3 MeV suggesting that remnant belts are extremely persistent. Pinto, V\; Bortnik, Jacob; Moya, Pablo; Lyons, Larry; Sibeck, David; Kanekal, Shrikanth; Spence, Harlan; Baker, Daniel; Published by: Geophysical Research Letters Published on: 10/2018 YEAR: 2018 DOI: 10.1029/2018GL080274 Belt Formation; MeV Electrons; Outer Belt; Radiation belts; Remnant Belt; Three Belts; Van Allen Probes |
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The composition of plasma inside geostationary orbit based on Van Allen Probes observations The composition of the inner magnetosphere is of great importance for determining the plasma pressure, and thus the currents and magnetic field configuration. In this study, we perform a statistical survey of equatorial plasma pressure distributions and investigate the relative contributions of ions and electron with different energies inside of geostationary orbit under two AE levels based on over sixty months of observations from the HOPE and RBSPICE mass spectrometers on board Van Allen Probes. We find that the total and partial pressures of different species increase significantly at high AE levels with Hydrogen (H+) pressure being dominant in the plasmasphere. The pressures of the heavy ions and electrons increase outside the plasmapause and develop a strong dawn-dusk asymmetry with ion pressures peaking at dusk and electron pressure peaking at dawn. In addition, ring current H+ with energies ranging from 50 keV up to several hundred keV is the dominant component of plasma pressure during both quiet (> 90\%) and active times (> 60\%), while Oxygen (O+) with 10 < E < 50 keV and electrons with 0.1 < E < 40 keV become important during active times contributing more than 25\% and 20\% on the nightside, respectively, while the Helium (He+) contribution is generally small. The results presented in this study provide a global picture of the equatorial plasma pressure distributions and the associated contributions from different species with different energy ranges, which advance our knowledge of wave generation and provide models with a systematic baseline of plasma composition. Yue, Chao; Bortnik, Jacob; Li, Wen; Ma, Qianli; Gkioulidou, Matina; Reeves, Geoffrey; Wang, Chih-Ping; Thorne, Richard; T. Y. Lui, Anthony; Gerrard, Andrew; Spence, Harlan; Mitchell, Donald; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2018 YEAR: 2018 DOI: 10.1029/2018JA025344 ion composition; plasma pressure; Plasmapause; Van Allen Probes |
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We use the measurements performed by the DEMETER (2004-2010) and the Van Allen Probes (2012-2016, still operating) spacecraft to investigate the longitudinal dependence of the intensity of whistler mode waves in the Earth\textquoterights inner magnetosphere. We show that a significant longitudinal dependence is observed inside the plasmasphere on the nightside, primarily in the frequency range 400 Hz\textendash2 kHz. On the other hand, almost no longitudinal dependence is observed on the dayside. The obtained results are compared to the lightning occurrence rate provided by the OTD/LIS mission normalized by a factor accounting for the ionospheric attenuation. The agreement between the two dependencies indicates that lightning generated electromagnetic waves may be responsible for the observed effect, thus substantially affecting the overall wave intensity in the given frequency range. Finally, we show that the longitudinal dependence is most pronounced for waves with oblique wave normal angles. ahlava, J.; emec, F.; ik, O.; a, I.; Hospodarskyy, G.; Parrot, M.; Kurth, W.; Bortnik, J.; Kletzing, C.; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2018 YEAR: 2018 DOI: 10.1029/2018JA025284 |
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Resonant interactions between electrons and chorus waves are responsible for a wide range of phenomena in near-Earth space (e.g., diffuse aurora, acceleration of MeV electrons, etc.). Although quasi-linear diffusion is believed to be the primary paradigm for describing such interactions, an increasing number of investigations suggest that nonlinear effects are also important in controlling the rapid dynamics of electrons. However, present models of nonlinear wave-particle interactions, which have been successfully used to describe individual short-term events, are not directly applicable for a statistical evaluation of nonlinear effects and the long-term dynamics of the outer radiation belt, because they lack information on the properties of intense (nonlinearly resonating with electrons) chorus waves. In this paper, we use the THEMIS and Van Allen Probes datasets of field-aligned chorus waveforms to study two key characteristics of these waves: effective amplitude w (nonlinear interaction can occur when w > 2) and wave-packet length β (the number of wave periods within it). While as many as 10 - 15\% of chorus wave-packets are sufficiently intense (w > 2 - 3) to interact nonlinearly with relativistic electrons, most of them are short (β < 10) reducing the efficacy of such interactions. Revised models of non-linear interactions are thus needed to account for the long-term effects of these common, intense but short chorus wave packets. We also discuss the dependence of w, β on location (MLT, L-shell) and on the properties of the suprathermal electron population. Zhang, X.-J.; Thorne, R.; Artemyev, A.; Mourenas, D.; Angelopoulos, V.; Bortnik, J.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2018 YEAR: 2018 DOI: 10.1029/2018JA025390 chorus waves; Effective amplitude; nonlinear wave-particle interaction; spatial distribution; statistics; Van Allen Probes; Wave-packet length |
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Electron nonlinear resonant interaction with short and intense parallel chorus wave-packets One of the major drivers of radiation belt dynamics, electron resonant interaction with whistler-mode chorus waves, is traditionally described using the quasi-linear diffusion approximation. Such a description satisfactorily explains many observed phenomena, but its applicability can be justified only for sufficiently low intensity, long duration waves. Recent spacecraft observations of a large number of very intense lower band chorus waves (with magnetic field amplitudes sometimes reaching \~1\% of the background) therefore challenge this traditional description, and call for an alternative approach when addressing the global, long-term effects of the nonlinear interaction of these waves with radiation belt electrons. In this paper, we first use observations from the Van Allen Probes and Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft to show that the majority of intense parallel chorus waves consists of relatively short wave-packets. Then, we construct a kinetic equation describing the nonlinear resonant interaction of radiation belt electrons with such short and intense wave-packets. We demonstrate that this peculiar type of nonlinear interaction produces similar effects as quasi-linear diffusion, i.e., a flattening of the electron velocity distribution function within a certain energy/pitch-angle range. The main difference is the much faster evolution of the electron distribution when nonlinear interaction prevails. Mourenas, D.; Zhang, X.-J.; Artemyev, A.; Angelopoulos, V.; Thorne, R.; Bortnik, J.; Neishtadt, A.; Vasiliev, A.; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2018 YEAR: 2018 DOI: 10.1029/2018JA025417 chorus waves; ; kinetic equation; nonlinear interaction; Radiation belts; short wave-packets; trapping; Van Allen Probes |
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Global model of plasmaspheric hiss from multiple satellite observations We present a global model of plasmaspheric hiss, using data from eight satellites, extending the coverage and improving the statistics of existing models. We use geomagnetic activity dependent templates to separate plasmaspheric hiss from chorus. In the region 22-14 MLT the boundary between plasmaspheric hiss and chorus moves to lower L* values with increasing geomagnetic activity. The average wave intensity of plasmaspheric hiss is largest on the dayside and increases with increasing geomagnetic activity from midnight through dawn to dusk. Plasmaspheric hiss is most intense and spatially extended in the 200-500 Hz frequency band during active conditions, 400 Meredith, Nigel; Horne, Richard; Kersten, Tobias; Li, Wen; Bortnik, Jacob; Sicard-Piet, elica; Yearby, Keith; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2018 YEAR: 2018 DOI: 10.1029/2018JA025226 plasmasphere; Plasmaspheric Hiss; Radiation belts; Van Allen Probes |
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We simulate the radiation belt electron flux enhancements during selected Geospace Environment Modeling (GEM) challenge events to quantitatively compare the major processes involved in relativistic electron acceleration under different conditions. Van Allen Probes observed significant electron flux enhancement during both the storm time of 17\textendash18 March 2013 and non\textendashstorm time of 19\textendash20 September 2013, but the distributions of plasma waves and energetic electrons for the two events were dramatically different. During 17\textendash18 March 2013, the SYM-H minimum reached -130 nT, intense chorus waves (peak Bw ~140 pT) occurred at 3.5 < L < 5.5, and several hundred keV to several MeV electron fluxes increased by ~2 orders of magnitude mostly at 3.5 < L < 5.5. During 19\textendash20 September 2013, the SYM-H remained higher than -30 nT, modestly intense chorus waves (peak Bw ~80 pT) occurred at L > 5.5, and electron fluxes at energies up to 3 MeV increased by a factor of ~5 at L > 5.5. The two electron flux enhancement events were simulated using the available wave distribution and diffusion coefficients from the GEM focus group Quantitative Assessment of Radiation Belt Modeling. By comparing the individual roles of local electron heating and radial transport, our simulation indicates that resonant interaction with chorus waves is the dominant process that accounts for the electron flux enhancement during the storm time event particularly near the flux peak locations, while radial diffusion by ultralow-frequency waves plays a dominant role in the enhancement during the non\textendashstorm time event. Incorporation of both processes reasonably reproduces the observed location and magnitude of electron flux enhancement. Ma, Q.; Li, W.; Bortnik, J.; Thorne, R.; Chu, X.; Ozeke, L.; Reeves, G.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Engebretson, M.; Spence, H.; Baker, D.; Blake, J.; Fennell, J.; Claudepierre, S.; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2018 YEAR: 2018 DOI: 10.1002/2017JA025114 electron accelerationl whistler mode waves; radial diffusion; radiation belt simulation; Van Allen Probes; Van Allen Probes observation |
| 2017 |
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Chorus Wave Modulation of Langmuir Waves in the Radiation Belts Using high-resolution waveforms measured by the Van Allen Probes, we report a novel observation in the radiation belts. Namely, we show that multiband, discrete, rising-tone whistler mode chorus emissions exhibit a one-to-one correlation with Langmuir wave bursts. Moreover, the periodic Langmuir wave bursts are generally observed at the phase location where the chorus wave E|| component is oriented opposite to its propagation direction. The electron measurements show a beam in phase space density at the particle velocity that matches the parallel phase velocity of the chorus waves. Based on this evidence, we conclude that the chorus waves accelerate the suprathermal electrons via Landau resonance and generate a localized electron beam in phase space density. Consequently, the Langmuir waves are excited locally and are modulated by the chorus wave phase. This microscale interaction between chorus waves and high-frequency electrostatic waves provides a new insight into the nonlinear wave-particle interaction process. Li, Jinxing; Bortnik, Jacob; An, Xin; Li, Wen; Thorne, Richard; Zhou, Meng; Kurth, William; Hospodarsky, George; Funsten, Herbert; Spence, Harlan; Published by: Geophysical Research Letters Published on: 12/2017 YEAR: 2017 DOI: 10.1002/2017GL075877 Chorus wave; Landau resonance; Langmuir wave; nonlinear interaction; Radiation belt; Van Allen Probes; wave modulation |
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A neural network model of three-dimensional dynamic electron density in the inner magnetosphere A plasma density model of the inner magnetosphere is important for a variety of applications including the study of wave-particle interactions, and wave excitation and propagation. Previous empirical models have been developed under many limiting assumptions and do not resolve short-term variations, which are especially important during storms. We present a three-dimensional dynamic electron density (DEN3D) model developed using a feedforward neural network with electron densities obtained from four satellite missions. The DEN3D model takes spacecraft location and time series of solar and geomagnetic indices (F10.7, SYM-H, and AL) as inputs. It can reproduce the observed density with a correlation coefficient of 0.95 and predict test data set with error less than a factor of 2. Its predictive ability on out-of-sample data is tested on field-aligned density profiles from the IMAGE satellite. DEN3D\textquoterights predictive ability provides unprecedented opportunities to gain insight into the 3-D behavior of the inner magnetospheric plasma density at any time and location. As an example, we apply DEN3D to a storm that occurred on 1 June 2013. It successfully reproduces various well-known dynamic features in three dimensions, such as plasmaspheric erosion and recovery, as well as plume formation. Storm time long-term density variations are consistent with expectations; short-term variations appear to be modulated by substorm activity or enhanced convection, an effect that requires further study together with multispacecraft in situ or imaging measurements. Investigating plasmaspheric refilling with the model, we find that it is not monotonic in time and is more complex than expected from previous studies, deserving further attention. Chu, X.; Bortnik, J.; Li, W.; Ma, Q.; Denton, R.; Yue, C.; Angelopoulos, V.; Thorne, R.; Darrouzet, F.; Ozhogin, P.; Kletzing, C.; Wang, Y.; Menietti, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2017 YEAR: 2017 DOI: 10.1002/2017JA024464 |
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The characteristic response of whistler mode waves to interplanetary shocks Magnetospheric whistler mode waves play a key role in regulating the dynamics of the electron radiation belts. Recent satellite observations indicate a significant influence of interplanetary (IP) shocks on whistler mode wave power in the inner magnetosphere. In this study, we statistically investigate the response of whistler mode chorus and plasmaspheric hiss to IP shocks based on Van Allen Probes and THEMIS satellite observations. Immediately after the IP shock arrival, chorus wave power is usually intensified, often at post-midnight to pre-noon sector, while plasmaspheric hiss wave power predominantly decreases near the dayside but intensifies near the nightside. We conclude that chorus wave intensification outside the plasmasphere is probably associated with the suprathermal electron flux enhancement caused by the IP shock. Through a simple ray tracing modeling assuming the scenario that plasmaspheric hiss is originated from chorus, we find that the solar wind dynamic pressure increase changes the magnetic field configuration to favor ray penetration in the nightside and promote ray refraction away from the dayside, potentially explaining the magnetic local time (MLT) dependent responses of plasmaspheric hiss waves following IP shock arrivals. Yue, Chao; Chen, Lunjin; Bortnik, Jacob; Ma, Qianli; Thorne, Richard; Angelopoulos, Vassilis; Li, Jinxing; An, Xin; Zhou, Chen; Kletzing, Craig; Reeves, Geoffrey; Spence, Harlan; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2017 YEAR: 2017 DOI: 10.1002/2017JA024574 IP shocks; MLT dependent; Plasmaspheric Hiss; Ray Tracing; Van Allen Probes; whistler mode chorus |
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Diffusive transport of several hundred keV electrons in the Earth\textquoterights slot region We investigate the gradual diffusion of energetic electrons from the inner edge of the outer radiation belt into the slot region. The Van Allen Probes observed slow inward diffusion and decay of ~200-600 keV electrons following the intense geomagnetic storm that occurred on 17 March 2013. During the 10-day non-disturbed period following the storm, the peak of electron fluxes gradually moved from L~2.7 to L~2.4, and the flux levels decreased by a factor of ~2-4 depending on the electron energy. We simulated the radial intrusion and decay of electrons using a 3-dimentional diffusion code, which reproduced the energy-dependent transport of electrons from ~100 keV to 1 MeV in the slot region. At energies of 100-200 keV, the electrons experience fast transport across the slot region due to the dominance of radial diffusion; at energies of 200-600 keV, the electrons gradually diffuse and decay in the slot region due to the comparable rate of radial diffusion and pitch angle scattering by plasmaspheric hiss; at energies of E > 700 keV, the electrons stopped diffusing near the inner edge of outer radiation belt due to the dominant pitch angle scattering loss. In addition to plasmaspheric hiss, magnetosonic waves and VLF transmitters can cause the loss of high pitch angle electrons, relaxing the sharp \textquotelefttop-hat\textquoteright shaped pitch angle distributions created by plasmaspheric hiss. Our simulation indicates the importance of balance between radial diffusion and loss through pitch angle scattering in forming the diffusive intrusion of energetic electrons across the slot region. Ma, Q.; Li, W.; Thorne, R.; Bortnik, J.; Reeves, G.; Spence, H.; Turner, D.; Blake, J.; Fennell, J.; Claudepierre, S.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Baker, D.; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2017 YEAR: 2017 DOI: 10.1002/2017JA024452 Electron transport; Energetic electron diffusion; pitch angle scattering; Slot region dynamics; Van Allen Probes; Van Allen Probes observation; Waves in plasmasphere |
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Understanding the source and loss processes of various plasma populations is greatly aided by having accurate knowledge of their pitch angle distributions (PADs). Here, we statistically analyze ~1 eV to 600 keV hydrogen (H+) PADs near the geomagnetic equator in the inner magnetosphere based on Van Allen Probes measurements, to comprehensively investigate how the H+ PADs vary with different energies, magnetic local times (MLTs), L-shells, and geomagnetic conditions. Our survey clearly indicates four distinct populations with different PADs: (1) a pancake distribution of the plasmaspheric H+ at low L-shells except for dawn sector; (2) a bi-directional field-aligned distribution of the warm plasma cloak; (3) pancake or isotropic distributions of ring current H+; (4) radiation belt particles show pancake, butterfly and isotropic distributions depending on their energy, MLT and L-shell. Meanwhile, the pancake distribution of ring current H+ moves to lower energies as L-shell increases which is primarily caused by adiabatic transport. Furthermore, energetic H+ (> 10 keV) PADs become more isotropic following the substorm injections, indicating wave-particle interactions. The radiation belt H+ butterfly distributions are identified in a narrow energy range of 100 < E < 400 keV at large L (L > 5), which are less significant during quiet times and extend from dusk to dawn sector through midnight during substorms. The different PADs near the equator provide clues of the underlying physical processes that produce the dynamics of these different populations. Yue, Chao; Bortnik, Jacob; Thorne, Richard; Ma, Qianli; An, Xin; Chappell, C.; Gerrard, Andrew; Lanzerotti, Louis; Shi, Quanqi; Reeves, Geoffrey; Spence, Harlan; Mitchell, Donald; Gkioulidou, Matina; Kletzing, Craig; Published by: Journal of Geophysical Research: Space Physics Published on: 08/2017 YEAR: 2017 DOI: 10.1002/2017JA024421 bi-directional field-aligned; H+ Pitch angle distributions; plasmaspheric H+; radiation belt H+; ring current; Van Allen Probes; warm Plasma cloak |
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Statistical Properties of Low Frequency Plasmaspheric Hiss Plasmaspheric hiss is an important wave mode for the dynamics of inner terrestrial magnetosphere plasma populations. It acts to scatter high energy electrons out of trapped orbits about Earth and into the atmosphere, defining the inner edge of the radiation belts over a range of energies. A low-frequency component of hiss was recently identified and is important for its ability to interact with higher energy electrons compared to typically considered hiss frequencies. This study compares the statistical properties of low and high frequency plasmaspheric hiss in the terrestrial magnetosphere, demonstrating that they are statistically distinct wave populations. Low frequency hiss shows different behavior in frequency space, different spatial localization (in magnetic local time and radial distance), and different amplitude distributions compared to high frequency hiss. The observed statistical properties of low frequency hiss are found to be consistent with recently developed theories for low frequency hiss generation. The results presented here suggest that careful consideration of low frequency hiss properties can be important for accurate inclusion of this wave population in predictive models of inner magnetosphere plasma dynamics. Malaspina, David; Jaynes, Allison; Hospodarsky, George; Bortnik, Jacob; Ergun, Robert; Wygant, John; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2017 YEAR: 2017 DOI: 10.1002/2017JA024328 inner magnetosphere; plasma waves; Plasmaspheric Hiss; Van Allen Probes; Wave Statistics |
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Utilizing simultaneous twin Van Allen Probes observations of whistler mode waves at variable separations, we are able to distinguish the temporal variations from spatial variations, determine the coherence spatial scale, and suggest the possible mechanism of wave modulation. The two probes observed coherently modulated whistler mode waves simultaneously at an unexpectedly large distance up to ~4.3 RE over 3 h during a relatively quiet period. The modulation of 150\textendash500 Hz plasmaspheric hiss was correlated with whistler mode waves measured outside the plasmasphere across 3 h in magnetic local time and 3 L shells, revealing that the modulation was temporal in nature. We suggest that the coherent modulation of whistler mode waves was associated with the coherent ULF waves measured over a large scale, which modulate the plasmaspheric density and result in the modulation of hiss waves via local amplification. In a later period, the 500\textendash1500 Hz periodic rising-tone whistler mode waves were strongly correlated when the two probes traversed large spatial regions and even across the plasmapause. These periodic rising-tone emissions recurred with roughly the same period as the ULF wave, but there was no one-to-one correspondence, and a cross-correlation analysis suggests that they possibly originated from large L shells although the actual cause needs further investigation. Li, Jinxing; Bortnik, Jacob; Li, Wen; Thorne, Richard; Ma, Qianli; Chu, Xiangning; Chen, Lunjin; Kletzing, Craig; Kurth, William; Hospodarsky, George; Wygant, John; Breneman, Aaron; Thaller, Scott; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2017 YEAR: 2017 DOI: 10.1002/2016JA023706 coherent waves; multisatellite; periodic rising tone; Van Allen Probes; whistler mode |
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Utilizing simultaneous twin Van Allen Probes observations of whistler mode waves at variable separations, we are able to distinguish the temporal variations from spatial variations, determine the coherence spatial scale, and suggest the possible mechanism of wave modulation. The two probes observed coherently modulated whistler mode waves simultaneously at an unexpectedly large distance up to ~4.3 RE over 3 h during a relatively quiet period. The modulation of 150\textendash500 Hz plasmaspheric hiss was correlated with whistler mode waves measured outside the plasmasphere across 3 h in magnetic local time and 3 L shells, revealing that the modulation was temporal in nature. We suggest that the coherent modulation of whistler mode waves was associated with the coherent ULF waves measured over a large scale, which modulate the plasmaspheric density and result in the modulation of hiss waves via local amplification. In a later period, the 500\textendash1500 Hz periodic rising-tone whistler mode waves were strongly correlated when the two probes traversed large spatial regions and even across the plasmapause. These periodic rising-tone emissions recurred with roughly the same period as the ULF wave, but there was no one-to-one correspondence, and a cross-correlation analysis suggests that they possibly originated from large L shells although the actual cause needs further investigation. Li, Jinxing; Bortnik, Jacob; Li, Wen; Thorne, Richard; Ma, Qianli; Chu, Xiangning; Chen, Lunjin; Kletzing, Craig; Kurth, William; Hospodarsky, George; Wygant, John; Breneman, Aaron; Thaller, Scott; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2017 YEAR: 2017 DOI: 10.1002/2016JA023706 coherent waves; multisatellite; periodic rising tone; Van Allen Probes; whistler mode |
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Transitional behavior of different energy protons based on Van Allen Probes observations Understanding the dynamical behavior of ~1 eV to 50 keV ions and identifying the energies at which the morphologies transit are important in that they involve the relative intensities and distributions of the large-scale electric and magnetic fields, the outflow, and recombination rates. However, there have been only few direct observational investigations of the transition in drift behaviors of different energy ions before the Van Allen Probes era. Here we statistically analyze ~1 eV to 50 keV hydrogen (H+) differential flux distributions near geomagnetic equator by using Van Allen Probes observations to investigate the H+ dynamics under the regulation of large-scale electric and magnetic fields. Our survey clearly indicates three types of H+ behaviors within different energy ranges, which is consistent with previous theory predictions. Using simple electric and magnetic field models in UBK coordinates, we have further constrained the source regions of different energy ions and their drift directions. Yue, Chao; Bortnik, Jacob; Chen, Lunjin; Ma, Qianli; Thorne, Richard; Reeves, Geoffrey; Spence, Harlan; Published by: Geophysical Research Letters Published on: 01/2017 YEAR: 2017 DOI: 10.1002/2016GL071324 |
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An interesting form of \textquotedblleftzipper-like\textquotedblright magnetosonic waves consisting of two bands of interleaved periodic rising-tone spectra was newly observed by the Van Allen Probes, the Time History of Events and Macroscale Interactions during Substorms (THEMIS), and the Magnetospheric Multiscale (MMS) missions. The two discrete bands are distinct in frequency and intensity; however, they maintain the same periodicity which varies in space and time, suggesting that they possibly originate from one single source intrinsically. In one event, the zipper-like magnetosonic waves exhibit the same periodicity as a constant-frequency magnetosonic wave and an electrostatic emission, but the modulation comes from neither density fluctuations nor ULF waves. A statistical survey based on 3.5 years of multisatellite observations shows that zipper-like magnetosonic waves mainly occur on the dawnside to noonside, in a frequency range between 10 fcp and fLHR. The zipper-like magnetosonic waves may provide a new clue to nonlinear excitation or modulation process, while its cause still remains to be fully understood. Li, J.; Bortnik, J.; Li, W.; Ma, Q.; Thorne, R.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Wygant, J.; Breneman, A.; Thaller, S.; Funsten, H.; Mitchell, D.; Manweiler, J.; Torbert, R.; Le Contel, O.; Ergun, R.; Lindqvist, P.-A.; Torkar, K.; Nakamura, R.; Andriopoulou, M.; Russell, C.; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2017 YEAR: 2017 DOI: 10.1002/2016JA023536 magnetosonic wave; Radiation belt; rising-tone; Van Allen Probes; zipper-like |
| 2016 |
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Statistical distribution of EMIC wave spectra: Observations from Van Allen Probes It has been known that electromagnetic ion cyclotron (EMIC) waves can precipitate ultrarelativistic electrons through cyclotron resonant scattering. However, the overall effectiveness of this mechanism has yet to be quantified, because it is difficult to obtain the global distribution of EMIC waves that usually exhibit limited spatial presence. We construct a statistical distribution of EMIC wave frequency spectra and their intensities based on Van Allen Probes measurements from September 2012 to December 2015. Our results show that as the ratio of plasma frequency over electron gyrofrequency increases, EMIC wave power becomes progressively dominated by the helium band. There is a pronounced dawn-dusk asymmetry in the wave amplitude and the frequency spectrum. The frequency spectrum does not follow the commonly used single-peak Gaussian function. Incorporating these realistic EMIC wave frequency spectra into radiation belt models is expected to improve the quantification of EMIC wave scattering effects in ultrarelativistic electron dynamics. Zhang, X.-J.; Li, W.; Thorne, R.; Angelopoulos, V.; Bortnik, J.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Published by: Geophysical Research Letters Published on: 12/2016 YEAR: 2016 DOI: 10.1002/2016GL071158 EMIC waves; magnetic storm; outer radiation belt; relativistic electron loss; Van Allen Probes; Wave-particle interaction |
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Transitional behavior of different energy protons based on Van Allen Probes observations Understanding the dynamical behavior of ~1 eV to 50 keV ions and identifying the energies at which the morphologies transit are important in that they involve the relative intensities and distributions of the large-scale electric and magnetic fields, the outflow and recombination rates. However, there have been only few direct observational investigations of the transition in drift behaviors of different energy ions before the Van Allen Probes era. Here, we statistically analyze ~1 eV to 50 keV Hydrogen (H+) differential flux distributions near geomagnetic equator by using Van Allen Probes observations to investigate the H+ dynamics under the regulation of large-scale electric and magnetic fields. Our survey clearly indicates three types of H+ behaviors within different energy ranges, which is consistent with previous theory predictions. Using simple electric and magnetic field models in UBK coordinates, we have further constrained the source regions of different energy ions and their drift directions. Yue, Chao; Bortnik, Jacob; Chen, Lunjin; Ma, Qianli; Thorne, Richard; Reeves, Geoffrey; Spence, Harlan; Published by: Geophysical Research Letters Published on: 12/2016 YEAR: 2016 DOI: 10.1002/2016GL071324 |
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Characteristic energy range of electron scattering due to plasmaspheric hiss We investigate the characteristic energy range of electron flux decay due to the interaction with plasmaspheric hiss in the Earth\textquoterights inner magnetosphere. The Van Allen Probes have measured the energetic electron flux decay profiles in the Earth\textquoterights outer radiation belt during a quiet period following the geomagnetic storm that occurred on 7 November 2015. The observed energy of significant electron decay increases with decreasing L shell and is well correlated with the energy band corresponding to the first adiabatic invariant μ = 4\textendash200 MeV/G. The electron diffusion coefficients due to hiss scattering are calculated at L = 2\textendash6, and the modeled energy band of effective pitch angle scattering is also well correlated with the constant μ lines and is consistent with the observed energy range of electron decay. Using the previously developed statistical plasmaspheric hiss model during modestly disturbed periods, we perform a 2-D Fokker-Planck simulation of the electron phase space density evolution at L = 3.5 and demonstrate that plasmaspheric hiss causes the significant decay of 100 keV\textendash1 MeV electrons with the largest decay rate occurring at around 340 keV, forming anisotropic pitch angle distributions at lower energies and more flattened distributions at higher energies. Our study provides reasonable estimates of the electron populations that can be most significantly affected by plasmaspheric hiss and the consequent electron decay profiles. Ma, Q.; Li, W.; Thorne, R.; Bortnik, J.; Reeves, G.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Spence, H.; Baker, D.; Blake, J.; Fennell, J.; Claudepierre, S.; Angelopoulos, V.; Published by: Journal of Geophysical Research: Space Physics Published on: 11/2016 YEAR: 2016 DOI: 10.1002/2016JA023311 electron flux decay; pitch angle scattering; Plasmaspheric Hiss; Van Allen Probes; Van Allen Probes observation |
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Three mechanisms have been proposed to explain relativistic electron flux depletions (dropouts) in the Earth\textquoterights outer radiation belt during storm times: adiabatic expansion of electron drift shells due to a decrease in magnetic field strength, magnetopause shadowing and subsequent outward radial diffusion, and precipitation into the atmosphere (driven by EMIC wave scattering). Which mechanism predominates in causing electron dropouts commonly observed in the outer radiation belt is still debatable. In the present study, we evaluate the physical mechanism that may be primarily responsible for causing the sudden change in relativistic electron pitch angle distributions during a dropout event observed by Van Allen Probes during the main phase of the 27 February 2014 storm. During this event, the phase space density of ultrarelativistic (>1 MeV) electrons was depleted by more than 1 order of magnitude over the entire radial extent of the outer radiation belt (3 < L* < 5) in less than 6 h after the passage of an interplanetary shock. We model the electron pitch angle distribution under a compressed magnetic field topology based on actual solar wind conditions. Although these ultrarelativistic electrons exhibit highly anisotropic (peaked in 90\textdegree), energy-dependent pitch angle distributions, which appear to be associated with the typical EMIC wave scattering, comparison of the modeled electron distribution to electron measurements indicates that drift shell splitting is responsible for this rapid change in electron pitch angle distributions. This further indicates that magnetopause loss is the predominant cause of the electron dropout right after the shock arrival. Zhang, X.-J.; Li, W.; Thorne, R.; Angelopoulos, V.; Ma, Q.; Li, J.; Bortnik, J.; Nishimura, Y.; Chen, L.; Baker, D.; Reeves, G.; Spence, H.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Blake, J.; Fennell, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2016 YEAR: 2016 DOI: 10.1002/2016JA022517 Drift shell splitting; dropouts; magnetic storm; magnetopause shadowing; outer radiation belt; relativistic electron loss; Van Allen Probes |
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A strongly energy-dependent ring current ion loss was measured by the RBSPICE instrument on the Van Allen Probes A spacecraft in the local evening sector during the 17 March 2015 geomagnetic storm. The ion loss is found to be energy dependent where only ions with energies measured above \~ 150 keV have a significant drop in intensity. At these energies the ion dynamics are principally controlled by variations of the geomagnetic field which, during magnetic storms, exhibits large scale variations on timescales from minutes to hours. Here we show that starting from \~ 19:10 UTC on March 17 the geomagnetic field increased from 220 to 260 nT on a time scale of about an hour as captured by RBSPICE-A close to spacecraft apogee, L = 6.1 and MLT = 21.85 hr. [GSM coordinates X=-4.89, Y=3.00, Z=-0.73)]. We demonstrate the relationship between this large geomagnetic field increase and the drop-outs of the inline image 150 keV ring current ions. Soto-Chavez, A.; Lanzerotti, L.; Gerrard, A.; Kim, H.; Bortnik, J.; Manweiler, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2016 YEAR: 2016 DOI: 10.1002/2016JA022512 inner magnetosphere; Magnetic Storms; Ring current ion.; Van Allen Probes |
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Unraveling the excitation mechanisms of highly oblique lower band chorus waves Excitation mechanisms of highly oblique, quasi-electrostatic lower band chorus waves are investigated using Van Allen Probes observations near the equator of the Earth\textquoterights magnetosphere. Linear growth rates are evaluated based on in situ, measured electron velocity distributions and plasma conditions and compared with simultaneously observed wave frequency spectra and wave normal angles. Accordingly, two distinct excitation mechanisms of highly oblique lower band chorus have been clearly identified for the first time. The first mechanism relies on cyclotron resonance with electrons possessing both a realistic temperature anisotropy at keV energies and a plateau at 100\textendash500 eV in the parallel velocity distribution. The second mechanism corresponds to Landau resonance with a 100\textendash500 eV beam. In both cases, a small low-energy beam-like component is necessary for suppressing an otherwise dominating Landau damping. Our new findings suggest that small variations in the electron distribution could have important impacts on energetic electron dynamics. Li, W.; Mourenas, D.; Artemyev, A.; Bortnik, J.; Thorne, R.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Reeves, G.; Funsten, H.; Spence, H.; Published by: Geophysical Research Letters Published on: 09/2016 YEAR: 2016 DOI: 10.1002/grl.v43.1710.1002/2016GL070386 beam instability; lower band chorus; oblique chorus excitation; temperature anisotropy; Van Allen Probes |
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The distribution of plasmaspheric hiss wave power with respect to plasmapause location In this work, Van Allen Probes data are used to derive terrestrial plasmaspheric hiss wave power distributions organized by (1) distance away from the plasmapause and (2) plasmapause distance from Earth. This approach is in contrast to the traditional organization of hiss wave power by L parameter and geomagnetic activity. Plasmapause-sorting reveals previously unreported and highly repeatable features of the hiss wave power distribution, including a regular spatial distribution of hiss power with respect to the plasmapause, a standoff distance between peak hiss power and the plasmapause, and frequency-dependent spatial localization of hiss. Identification and quantification of these features can provide insight into hiss generation and propagation and will facilitate improved parameterization of hiss wave power in predictive simulations of inner magnetosphere dynamics. Malaspina, David; Jaynes, Allison; e, Cory; Bortnik, Jacob; Thaller, Scott; Ergun, Robert; Kletzing, Craig; Wygant, John; Published by: Geophysical Research Letters Published on: 08/2016 YEAR: 2016 DOI: 10.1002/2016GL069982 hiss; plasma waves; plasmasphere; Radiation belts; Van Allen Probes |
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Plasma kinetic theory predicts that a sufficiently anisotropic electron distribution will excite whistler mode waves, which in turn relax the electron distribution in such a way as to create an upper bound on the relaxed electron anisotropy. Here using whistler mode chorus wave and plasma measurements by Van Allen Probes, we confirm that the electron distributions are well constrained by this instability to a marginally stable state in the whistler mode chorus waves generation region. Lower band chorus waves are organized by the electron β||e into two distinct groups: (i) relatively large-amplitude, quasi-parallel waves with inline image and (ii) relatively small-amplitude, oblique waves with inline image. The upper band chorus waves also have enhanced amplitudes close to the instability threshold, with large-amplitude waves being quasi-parallel whereas small-amplitude waves being oblique. These results provide important insight for studying the excitation of whistler mode chorus waves. Yue, Chao; An, Xin; Bortnik, Jacob; Ma, Qianli; Li, Wen; Thorne, Richard; Reeves, Geoffrey; Gkioulidou, Matina; Mitchell, Donald; Kletzing, Craig; Published by: Geophysical Research Letters Published on: 08/2016 YEAR: 2016 DOI: 10.1002/2016GL070084 beta parallel; electron temperature anisotropy; marginally stable state; oblique waves; quasi-parallel waves; Van Allen Probes; whistler mode chorus waves |
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Direct evidence for EMIC wave scattering of relativistic electrons in space Electromagnetic ion cyclotron (EMIC) waves have been proposed to cause efficient losses of highly relativistic (>1 MeV) electrons via gyroresonant interactions. Simultaneous observations of EMIC waves and equatorial electron pitch angle distributions, which can be used to directly quantify the EMIC wave scattering effect, are still very limited, however. In the present study, we evaluate the effect of EMIC waves on pitch angle scattering of ultrarelativistic (>1 MeV) electrons during the main phase of a geomagnetic storm, when intense EMIC wave activity was observed in situ (in the plasma plume region with high plasma density) on both Van Allen Probes. EMIC waves captured by Time History of Events and Macroscale Interactions during Substorms (THEMIS) probes and on the ground across the Canadian Array for Real-time Investigations of Magnetic Activity (CARISMA) are also used to infer their magnetic local time (MLT) coverage. From the observed EMIC wave spectra and local plasma parameters, we compute wave diffusion rates and model the evolution of electron pitch angle distributions. By comparing model results with local observations of pitch angle distributions, we show direct, quantitative evidence of EMIC wave-driven relativistic electron losses in the Earth\textquoterights outer radiation belt. Zhang, X.-J.; Li, W.; Ma, Q.; Thorne, R.; Angelopoulos, V.; Bortnik, J.; Chen, L.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Baker, D.; Reeves, G.; Spence, H.; Blake, J.; Fennell, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2016 YEAR: 2016 DOI: 10.1002/2016JA022521 electron precipitation; EMIC waves; equatorial pitch angle distribution; Fokker-Planck equation; relativistic electron loss; Van Allen Probes; Wave-particle interaction |
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Various physical processes are known to cause acceleration, loss, and transport of energetic electrons in the Earth\textquoterights radiation belts, but their quantitative roles in different time and space need further investigation. During the largest storm over the past decade (17 March 2015), relativistic electrons experienced fairly rapid acceleration up to ~7 MeV within 2 days after an initial substantial dropout, as observed by Van Allen Probes. In the present paper, we evaluate the relative roles of various physical processes during the recovery phase of this large storm using a 3-D diffusion simulation. By quantitatively comparing the observed and simulated electron evolution, we found that chorus plays a critical role in accelerating electrons up to several MeV near the developing peak location and produces characteristic flat-top pitch angle distributions. By only including radial diffusion, the simulation underestimates the observed electron acceleration, while radial diffusion plays an important role in redistributing electrons and potentially accelerates them to even higher energies. Moreover, plasmaspheric hiss is found to provide efficient pitch angle scattering losses for hundreds of keV electrons, while its scattering effect on > 1 MeV electrons is relatively slow. Although an additional loss process is required to fully explain the overestimated electron fluxes at multi-MeV, the combined physical processes of radial diffusion and pitch angle and energy diffusion by chorus and hiss reproduce the observed electron dynamics remarkably well, suggesting that quasi-linear diffusion theory is reasonable to evaluate radiation belt electron dynamics during this big storm. Li, W.; Ma, Q.; Thorne, R.; Bortnik, J.; Zhang, X.-J.; Li, J.; Baker, D.; Reeves, G.; Spence, H.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Blake, J.; Fennell, J.; Kanekal, S.; Angelopoulos, V.; Green, J.; Goldstein, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2016 YEAR: 2016 DOI: 10.1002/jgra.v121.610.1002/2016JA022400 chorus-driven local acceleration; Electron acceleration; radial diffusion; Van Allen Probes |
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Interactions between interplanetary (IP) shocks and the Earth\textquoterights magnetosphere manifest many important space physics phenomena including low-energy ion flux enhancements and particle acceleration. In order to investigate the mechanisms driving shock-induced enhancement of low-energy ion flux, we have examined two IP shock events that occurred when the Van Allen Probes were located near the equator while ionospheric and ground observations were available around the spacecraft footprints. We have found that, associated with the shock arrival, electromagnetic fields intensified, and low-energy ion fluxes, including H+, He+, and O+, were enhanced dramatically in both the parallel and perpendicular directions. During the 2 October 2013 shock event, both parallel and perpendicular flux enhancements lasted more than 20 min with larger fluxes observed in the perpendicular direction. In contrast, for the 15 March 2013 shock event, the low-energy perpendicular ion fluxes increased only in the first 5 min during an impulse of electric field, while the parallel flux enhancement lasted more than 30 min. In addition, ionospheric outflows were observed after shock arrivals. From a simple particle motion calculation, we found that the rapid response of low-energy ions is due to drifts of plasmaspheric population by the enhanced electric field. However, the fast acceleration in the perpendicular direction cannot solely be explained by E \texttimes B drift but betatron acceleration also plays a role. Adiabatic acceleration may also explain the fast response of the enhanced parallel ion fluxes, while ion outflows may contribute to the enhanced parallel fluxes that last longer than the perpendicular fluxes. Yue, Chao; Li, Wen; Nishimura, Yukitoshi; Zong, Qiugang; Ma, Qianli; Bortnik, Jacob; Thorne, Richard; Reeves, Geoffrey; Spence, Harlan; Kletzing, Craig; Wygant, John; Nicolls, Michael; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2016 YEAR: 2016 DOI: 10.1002/2016JA022808 adiabatic accelerations; enhancement of low-energy ion flux; ionospheric ion outflows; response to IP shocks; Van Allen Probes |
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New Chorus Wave Properties Near the Equator from Van Allen Probes Wave Observations The chorus wave properties are evaluated using Van Allen Probes data in the Earth\textquoterights equatorial magnetosphere. Two distinct modes of lower band chorus are identified: a quasi-parallel mode and a quasi-electrostatic mode, whose wave normal direction is close to the resonance cone. Statistical results indicate that the quasi-electrostatic (quasi-parallel) mode preferentially occurs during relatively quiet (disturbed) geomagnetic activity at lower (higher) L shells. Although the magnetic intensity of the quasi-electrostatic mode is considerably weaker than the quasi-parallel mode, their electric intensities are comparable. A newly identified feature of the quasi-electrostatic mode is that its frequency peaks at higher values compared to the quasi-parallel mode that exhibits a broad frequency spectrum. Moreover, upper band chorus wave normal directions vary between 0\textdegree and the resonance cone and become more parallel as geomagnetic activity increases. Our new findings suggest that chorus-driven energetic electron dynamics needs a careful examination by considering the properties of these two distinct modes. Li, W.; Santolik, O.; Bortnik, J.; Thorne, R.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Published by: Geophysical Research Letters Published on: 05/2016 YEAR: 2016 DOI: 10.1002/2016GL068780 Chorus wave; oblique; quasi-electrostatic; quasi-parallel; Van Allen Probes; wave normal angles |
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Using Van Allen Probes REPT pitch angle resolved electron flux data from September 2012 to March 2015, we investigate in detail the global occurrence pattern of equatorial (|λ| <= 3\textdegree) butterfly distribution of outer zone relativistic electrons and its potential correlation with the solar wind dynamic pressure. The statistical results demonstrate that these butterfly distributions occur with the highest occurrence rate ~ 80\% at ~ 20 \textendash 04 MLT and L > ~ 5.5 and with the second peak (> ~ 50 \%) at ~ 11 \textendash 15 MLT of lower L-shells ~ 4.0. They can also extend to L = 3.5 and to other MLT intervals but with the occurrence rates predominantly < ~25\%. It is further shown that outer zone relativistic electron butterfly distributions are likely to peak between 58\textdegree - 79\textdegree for L = 4.0 and 5.0 and between 37\textdegree - 58\textdegree for L = 6.0, regardless of the level of solar wind dynamic pressure. Relativistic electron butterfly distributions at L = 4.0 also exhibit a pronounced day-night asymmetry in response to the Pdynvariations. Compared to the significant L-shell and MLT dependence of the global occurrence pattern, outer zone relativistic electron butterfly distributions show much less but still discernable sensitivity to Pdyn, geomagnetic activity level, and electron energy, the full understanding of which requires future attempts of detailed simulations that combine and differentiate underlying physical mechanisms of the geomagnetic field asymmetry and scattering by various magnetospheric waves. Ni, Binbin; Zou, Zhengyang; Li, Xinlin; Bortnik, Jacob; Xie, Lun; Gu, Xudong; Published by: Geophysical Research Letters Published on: 05/2016 YEAR: 2016 DOI: 10.1002/2016GL069350 butterfly pitch angle distributions; global occurrence pattern; outer radiation belt; relativistic electrons; Van Allen Probes |
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Electron butterfly distribution modulation by magnetosonic waves The butterfly pitch angle distribution is observed as a dip in an otherwise normal distribution of electrons centered about αeq=90\textdegree. During storm times, the formation of the butterfly distribution on the nightside magnetosphere has been attributed to L shell splitting combined with magnetopause shadowing and strong positive radial flux gradients. It has been shown that this distribution can be caused by combined chorus and magnetosonic wave scattering where the two waves work together but at different local times. Presented in our study is an event on 21 August 2013, using Van Allen Probe measurements, where a butterfly distribution formation is modulated by local magnetosonic coherent magnetosonic waves intensity. Transition from normal to butterfly distributions coincides with rising magnetosonic wave intensity while an opposite transition occurs when wave intensity diminishes. We propose that bounce resonance with waves is the underlying process responsible for such rapid modulation, which is confirmed by our test particle simulation. Maldonado, Armando; Chen, Lunjin; Claudepierre, Seth; Bortnik, Jacob; Thorne, Richard; Spence, Harlan; Published by: Geophysical Research Letters Published on: 04/2016 YEAR: 2016 DOI: 10.1002/2016GL068161 butterfly; electron; magnetosonic; Magnetosphere; Van Allen Probes; wave particle interaction |
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Formation of Energetic Electron Butterfly Distributions by Magnetosonic Waves via Landau Resonance Radiation belt electrons can exhibit different types of pitch angle distributions in response to various magnetospheric processes. Butterfly distributions, characterized by flux minima at pitch angles around 90\textdegree, are broadly observed in both the outer and inner belts and the slot region. Butterfly distributions close to the outer magnetospheric boundary have been attributed to drift shell splitting and losses to the magnetopause. However, their occurrence in the inner belt and the slot region has hitherto not been resolved. By analyzing the particle and wave data collected by the Van Allen Probes during a geomagnetic storm, we combine test particle calculations and Fokker-Planck simulations to reveal that scattering by equatorial magnetosonic waves is a significant cause for the formation of energetic electron butterfly distributions in the inner magnetosphere. Another event shows that a large-amplitude magnetosonic wave in the outer belt can create electron butterfly distributions in just a few minutes. Li, Jinxing; Ni, Binbin; Ma, Qianli; Xie, Lun; Pu, Zuyin; Fu, Suiyan; Thorne, R.; Bortnik, J.; Chen, Lunjin; Li, Wen; Baker, Daniel; Kletzing, Craig; Kurth, William; Hospodarsky, George; Fennell, Joseph; Reeves, Geoffrey; Spence, Harlan; Funsten, Herbert; Summers, Danny; Published by: Geophysical Research Letters Published on: 04/2016 YEAR: 2016 DOI: 10.1002/2016GL067853 butterfly distributions; energetic electrons; Landau resonance; magnetosonic waves; Radiation belt; Van Allen Probes |
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