Bibliography
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Found 103 entries in the Bibliography.
Showing entries from 1 through 50
| 2021 |
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Abstract Simultaneous observations from Van Allen Probes (RBSP) in Earth’s outer radiation belt (∼4-6 RE) and Magnetospheric Multiscale (MMS) in the magnetotail plasma sheet at >20 RE geocentric distance are used to compare relative levels of relativistic electron phase space density (PSD) for constant values of the first adiabatic invariant, M. We present new evidence from two events showing: i) at times, there is sufficient PSD in the central plasma sheet to provide a source of >1 MeV electrons into the outer belt; ii) the most intense levels of relativistic electrons are not accelerated in the solar wind or transported from the inner magnetosphere and thus must be accelerated rapidly (within ∼minutes or less) and efficiently across a broad region of the magnetotail itself; and iii) the highest intensity relativistic electrons observed by MMS were confined within only the central plasma sheet. The answer to the title question here is: yes, it can, however whether Earth’s plasma sheet actually does provide a source of several 100s keV to >1 MeV electrons to the outer belt and how often it does so remain important outstanding questions. Turner, Drew; Cohen, Ian; Michael, Adam; Sorathia, Kareem; Merkin, Slava; Mauk, Barry; Ukhorskiy, Sasha; Murphy, Kyle; Gabrielse, Christine; Boyd, Alexander; Fennell, Joseph; Blake, Bernard; Claudepierre, Seth; Drozdov, Alexander; Jaynes, Allison; Ripoll, Jean-Francois; Reeves, Geoffrey; Published by: Geophysical Research Letters Published on: 09/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021GL095495 Radiation belts; plasma sheet; Particle acceleration; relativistic electrons; inner magnetosphere; magnetotail; Van Allen Probes |
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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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Superposed Epoch Analysis of Dispersionless Particle Injections Inside Geosynchronous Orbit AbstractDispersionless injections, involving sudden, simultaneous flux enhancements of energetic particles over some broad range of energy, are a characteristic signature of the particles that are experiencing a significant acceleration and/or rapid inward transport at the leading edge of injections. We have statistically analyzed data from Van Allen Probes (also known as RBSP ) to reveal where the proton (H+) and electron (e–) dispersionless injections occur preferentially inside geosynchronous orbit and how they develop depending on local magnetic field changes. By surveying measurements of RBSP during four tail seasons in 2012–2019, we have identified 171 dispersionless injection events. Most of the events, which are accompanied by local magnetic dipolarizations, occur in the dusk-to-midnight sector, regardless of particle species. Out of the selected 171 events, 75 events exhibit dispersionless injections of both H+ and e–, which occur within 2 minutes of each other. With only three exceptions, the both-species injection events are further divided into two main subgroups: One is the H+ preceding e– events with a time offset of tens of seconds between H+ and e–, and the other the concurrent H+ and e– events without any time offset. Our superposed epoch results raise the intriguing possibility that the presence or absence of a pronounced negative dip in the local magnetic field ahead of the concurrent sharp dipolarization determines which of the two subgroups will occur. The difference between the two subgroups may be explained in terms of the dawn-dusk asymmetry of localized diamagnetic perturbations ahead of a deeply-penetrating dipolarization front.This article is protected by copyright. All rights reserved. Motoba, T.; Ohtani, S.; Gkioulidou, M.; Ukhorskiy, A; Lanzerotti, L.; Claudepierre, S.; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021JA029546 Dispersionless injections; substorms; inner magnetosphere; Van Allen Probes |
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Observational evidence of the excitation of magnetosonic waves by an He ion ring distribution Abstract We report plasma wave observations of equatorial magnetosonic waves at integer harmonics of the local gyrofrequency of doubly-ionized helium (He). The waves were observed by Van Allen Probe A on 08 Feb 2014 when the spacecraft was in the afternoon magnetic local time sector near inside of the plasmasphere. Analysis of the complementary in-situ energetic ion measurements (1-300 keV) reveals the presence of a helium ion ring distribution centered near 30 keV. Theoretical linear growth rate calculations suggest that the local plasma and field conditions can support the excitation of the magnetosonic waves from the unstable ring distribution. This represents the first report of the generation of magnetosonic equatorial noise via a ring distribution in energetic He ions in the near-Earth space plasma environment. Claudepierre, S.; Liu, X.; Chen, L.; Takahashi, K.; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021JA029532 magnetosonic waves; ion Bernstein waves; ring distribution; alpha particles; Plasma instability; ring current; Van Allen Probes |
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Abstract Following the end of the Van Allen Probes mission, the Arase satellite offers a unique opportunity to continue in-situ radiation belt and ring current particle measurements into the next solar cycle. In this study we compare spin-averaged flux measurements from the MEPe, HEP-L, HEP-H, and XEP-SSD instruments on Arase with those from the MagEIS and REPT instruments on the Van Allen Probes, calculating Pearson correlation coefficient and the mean ratio of fluxes at L* conjunctions between the spacecraft. Arase and Van Allen Probes measurements show a close agreement over a wide range of energies, observing a similar general evolution of electron flux, as well as average, peak, and minimum values. Measurements from the two missions agree especially well in the 3.6 ≤ L* ≤ 4.4 range where Arase samples similar magnetic latitudes to Van Allen Probes. Arase tends to record higher flux for energies < 670 keV with longer decay times after flux enhancements, particularly for L* < 3.6 . Conversely, for energies > 1.4 MeV, Arase flux measurements are generally lower than those of Van Allen Probes, especially for L* > 4.4 . The correlation coefficient values show that the > 1.4 MeV flux from both missions are well correlated, indicating a similar general evolution, although flux magnitudes differ. We perform a preliminary intercalibration between the two missions using the mean ratio of the fluxes as an energy- and L*- dependent intercalibration factor. The intercalibration factor improves agreement between the fluxes in the 0.58-1 MeV range. This article is protected by copyright. All rights reserved. Szabó-Roberts, Mátyás; Shprits, Yuri; Allison, Hayley; Vasile, Ruggero; Smirnov, Artem; Aseev, Nikita; Drozdov, Alexander; Miyoshi, Yoshizumi; Claudepierre, Seth; Kasahara, Satoshi; Yokota, Shoichiro; Mitani, Takefumi; Takashima, Takeshi; Higashio, Nana; Hori, Tomo; Keika, Kunihiro; Imajo, Shun; Shinohara, Iku; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA028929 |
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Origin of Electron Boomerang Stripes: Statistical Study Abstract In the outer radiation belt, localized ULF waves can interact with energetic electrons by drift resonance, leading to quasiperiodic oscillations. The oscillations in the pitch angle spectrum can be characterized by either boomerang-shaped or straight stripes. Previous studies have shown that boomerang-shaped stripes evolve from straight ones when electrons drift away from the localized wave interaction region. Based on the time-of-flight technique on the pitch angle-dependent drift velocity, the origin can be remotely identified from the pitch angle dispersion. We report 27 straight stripe events and 86 boomerang-shaped events observed by Van Allen Probes from 2013/01/01 to 2017/12/31. Statistical study shows a good coincidence between the locations of straight ones and traceback regions from boomerang-shaped ones. These locations, mainly located in noon-to-dusk region, coincide well with the plasmaspheric plumes. Thus localized ULF waves trapped in the plume may result in the preference of localized ULF waves-electron interactions at noon-to-dusk region. Zhao, X.; Hao, Y.; Zong, Q.; Zhou, X.; Yue, Chao; Chen, X.; Liu, Y.; Liu, Z.-Y.; Blake, J.; Claudepierre, S.; Reeves, G.; Published by: Geophysical Research Letters Published on: 05/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021GL093377 Localized ULF waves; Energetic Elctrons; drift resonance; Time-of-flight Technique; source region; boomerang-shaped stripes; Van Allen Probes |
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Abstract We present, for the first time, a plasmaspheric hiss event observed by the Van Allen probes in response to two successive interplanetary shocks occurring within an interval of ∼2 hours on December 19, 2015. The first shock arrived at 16:16 UT and caused disappearance of hiss for ∼30 minutes. Combined effect of plasmapause crossing, significant Landau damping by suprathermal electrons and their gradual removal by magnetospheric compression led to the disappearance of hiss. Calculation of electron phase space density and linear wave growth rates showed that the shock did not change the growth rate of whistler waves within the core frequency range of plasmaspheric hiss (0.1 - 0.5 kHz) during this interval making conditions unfavorable for the generation of hiss. The recovery began at ∼16:45 UT which is attributed to an enhancement in local plasma instability initiated by the first shock-induced substorm and additional possible contribution from chorus waves. This time, the wave growth rate peaked within the core frequency range ( ∼350 Hz). The second shock arrived at 18:02 UT and generated patchy hiss persisting up to ∼19:00 UT. It is shown that an enhanced growth rate and additional contribution from shock-induced poloidal Pc5 mode (periodicity ∼240 sec) ULF waves resulted in the excitation of hiss waves during this period. The hiss wave amplitudes were found to be additionally modulated by background plasma density and fluctuating plasmapause location. The investigation highlights the important roles of interplanetary shocks, substorms, ULF waves and background plasma density in the variability of plasmaspheric hiss. Chakraborty, S.; Chakrabarty, D.; Reeves, G.; Baker, D.; Claudepierre, S.; Breneman, A.; Hartley, D.; Larsen, B.; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA028873 Plasmaspheric Hiss; Van Allen Probe; Interplanetary shocks; substorms; Whistlers; ULF waves; Van Allen Probes |
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RBSP-ECT Combined Pitch Angle Resolved Electron Flux Data Product Abstract We describe a new data product combining pitch angle resolved electron flux measurements from the Radiation Belt Storm Probes (RBSP) Energetic Particle Composition and Thermal Plasma (ECT) suite on the National Aeronautics and Space Administration s Van Allen Probes. We describe the methodology used to combine each of the data sets and produce a consistent set of pitch-angle-resolved spectra for the entire Van Allen Probes mission. Three-minute-averaged flux spectra are provided spanning energies from 15 eV up to 20 MeV. This new data product offers researchers a consistent cross calibrated data set to explore the particle dynamics of the inner magnetosphere across a wide range of energies. This article is protected by copyright. All rights reserved. Boyd, A.J.; Spence, H.E.; Reeves, G.D.; Funsten, H.O; Skoug, R.K.; Larsen, B.A.; Blake, J.B.; Fennell, J.F.; Claudepierre, S.G.; Baker, D.N.; Kanekal, S.K.; Jaynes, A.N.; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA028637 |
| 2020 |
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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 |
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Whistler mode chorus waves can scatter plasma sheet electrons into the loss cone and produce the Earth s diffuse aurora. Van Allen Probes observed plasma sheet electron injections and intense chorus waves on 24 November 2012. We use quasilinear theory to calculate the precipitating electron fluxes, demonstrating that the chorus waves could lead to high differential energy fluxes of precipitating electrons with characteristic energies of 10–30 keV. Using this method, we calculate the precipitating electron flux from 2012 to 2019 when the Van Allen Probes were near the magnetic equator and perform global surveys of electron precipitation under different geomagnetic conditions. The most significant electron precipitation due to chorus is found from the nightside to dawn sectors over 4 < L < 6.5. The average total precipitating energy flux is enhanced during disturbed conditions, with time-averaged values reaching ~3–10 erg/cm2/s when AE ≥ 500 nT. Ma, Q.; Connor, H.; Zhang, X.-J.; Li, W.; Shen, X.-C.; Gillespie, D.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Claudepierre, S.; Reeves, G.; Spence, H.; Published by: Geophysical Research Letters Published on: 07/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020GL088798 Chorus wave; electron precipitation; plasma sheet electron; Van Allen Probes observation; Van Allen Probes |
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Origin of Electron Boomerang Stripes: Localized ULF Wave-Particle Interactions Ultralow frequency (ULF) wave-particle interactions play a significant role in the radiation belt dynamic process, during which drift resonance can accelerate and transport energetic electrons in the outer radiation belt. Observations of wave-electron drift resonance are characterized by quasiperiodic straight or “boomerang-shaped” stripes in the pitch angle spectrogram. Here we present an ULF wave event on 1 December 2015, during which both kinds stripes were observed by Van Allen Probes A and B, respectively. Using the time-of-flight technique based on the pitch angle dependence of electron drift velocities, the “boomerang-shaped” stripes are inferred to originate from straight stripes at the time and location covered by Probe B. Given that straight stripes were indeed observed by Probe B, our observations strongly support the charged particle interacting with azimuthally localized ULF waves. A new method is provided to identify the location of ULF wave-particle interaction on the basis of remote observations of electron flux modulations. Zhao, X.; Hao, Y.; Zong, Q.-G.; Zhou, X.-Z.; Yue, Chao; Chen, X.; Liu, Y.; Blake, J.; Claudepierre, S.; Reeves, G.; Published by: Geophysical Research Letters Published on: 07/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020GL087960 boomerang-shaped stripes; ULF waves; drift resonance; time of flight; Van Allen Probes |
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In this study we focus on the radiation belt dynamics driven by the geomagnetic storms during September 2017. Besides the long-lasting three-belt structures of ultrarelativistic electrons (>2 MeV, existing for tens of days), which has been studied intensively during the Van Allen Probe era, it is found that magnetospheric electrons of hundreds of keVs can also have three-belt structures at similar L extent during storm time. Measurements of 500–800 keV electrons from MagEIS instrument onboard Van Allen Probes show double-peaked (L = 3.5 and 4.5, respectively) flux-versus-L-shell profile in the outer belt, which lasted for 2–3 days. During the time interval of such transient three-belt structure, the energy-versus-L spectrogram shows novel distributions differing from both “S-shaped” and “V-shaped” spectrograms reported previously. Such peculiar distribution also illustrates the energy-dependent occurrence of the three-belt profile. The gradual formation of “reversed energy spectrum” at L ∼ 3.5 also indicates that hiss scattering inside the plasmapause contributed to the fast decay of sub-MeV remnant belt. Hao, Y.; Zong, Q.-G.; Zhou, X.-Z.; Zou, H.; Rankin, R.; Sun, Y.; Chen, X.; Liu, Y.; Fu, S; Baker, D.; Spence, H.; Blake, J.; Reeves, G.; Claudepierre, S.; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028031 storage ring; three-belt structure; hiss wave; electron lifetime; Radial Transport; Van Allen Probes |
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Simulations of Electron Flux Oscillations as Observed by MagEIS in Response to Broadband ULF Waves Coherent electron flux oscillations of hundreds of keV are often observed by the Van Allen Probes in the magnetosphere during quiet times in association with ultralow frequency (ULF) waves. They are observed in the form of periodic flux fluctuations, with a drift frequency that is energy dependent, but are not associated with drift echoes following storm- or substorm-related energetic particle injections. Instead, they are associated with the resonant interaction of electrons with ULF waves and are an indication of ongoing electron radial diffusion. To investigate details of such flux oscillations, particle-tracing simulations are conducted under the effect of realistic, broadband ULF electric and consistent magnetic fluctuations. Virtual detectors are simulated along spacecraft orbits and the results are compared to measurements. Through a parametric study, it is found that the width of electron energy channels is a critical parameter affecting the observed amplitude of flux oscillations, with narrower energy channel widths enabling the observation of higher-amplitude flux oscillations; this potentially explains why such features were not observed regularly before the Van Allen Probes era, as previous spacecraft generally had lower energy resolution, which only enabled the observation of large-amplitude drift echoes following a storm or substorm. Results are confirmed using the Magnetic Electron Ion Spectrometer (MagEIS) ultrahigh energy resolution data. Energy width effects are quantified through a parametric simulation study that matches flux oscillation observations during a period that is characterized by extremely quiet conditions, where the Van Allen Probes observed flux oscillations over multiple days. Sarris, Theodore; Li, Xinlin; Temerin, Michael; Zhao, Hong; Khoo, Leng; Turner, Drew; Liu, Wenlong; Claudepierre, Seth; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020JA027798 electron flux oscillations; ULF waves; Magnetosphere; Radiation belts; radial diffusion; particle tracing simulations; Van Allen Probes |
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Whistler-mode hiss waves generally determine MeV electron lifetimes inside the plasmasphere. We use Van Allen Probes measurements to provide the first comprehensive statistical survey of plasmaspheric hiss-driven quasi-linear pitch-angle diffusion rates and lifetimes of MeV electrons as a function of L*, local time, and AE index, taking into account hiss power, electron plasma frequency to gyrofrequency ratio ωpe/Ωce, hiss frequency at peak power ωm, and cross correlations of these parameters. We find that during geomagnetically active periods with hiss observations, ωpe/Ωce and ωm decrease, leading to faster electron loss. We demonstrate that spatiotemporal variations of ωm and ωpe/Ωce with AE, together with wave power changes, significantly affect MeV electron loss, potentially leading to short lifetimes of less than 1 day. A parametric model of MeV electron lifetime driven by AE for L > 2.5 up to the plasmapause is developed and validated using Magnetic Electron Ion Spectrometer (MagEIS) electron flux decay database. Agapitov, O.; Mourenas, D.; Artemyev, A.; Claudepierre, S.; Hospodarsky, G.; Bonnell, J.; Published by: Geophysical Research Letters Published on: 05/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020GL088052 electron lifetimes; plasmasphere; hiss waves; wave-particle interactions; Van Allen Probes |
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Simultaneous Observations of Localized and Global Drift Resonance In this study, we present Van Allen Probe observations showing that seed (hundreds of keV) and core ( 1 MeV) electrons can resonate with ultra-low-frequency (ULF) wave modes with distinctive m values simultaneously. An unusual electron energy spectrogram with double-banded resonant structure was recorded by energetic particle, composition, and thermal plasma (ECT)-magnetic electron ion spectrometer (MagEIS) and, meanwhile, boomerang stripes in pitch angle spectrogram appeared at the lower energy band. A localized drift resonance with m = 10 wave component was responsible for the resonant band peaked at ∼200 keV while a global drift resonance with m = 3 component gave rise to the upper band resonance peaked at ∼1 MeV. Time-Of-Flight on boomerang stripes suggested that the localized drift resonance with ∼200 keV electrons was confined within the plasmaspheric plume. Electron flux modulations were reproduced by numerical simulations in good consistency with the observations, supporting the scenario that localized and global drift resonance could coexist in the outer belt electron dynamics simultaneously. Hao, Y.; Zhao, X.; Zong, Q.-G.; Zhou, X.-Z.; Rankin, R.; Chen, X.; Liu, Y.; Fu, S; Blake, J.; Reeves, G.; Claudepierre, S.; Published by: Geophysical Research Letters Published on: 05/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020GL088019 drift resonance; ULF waves; Radiation Belt Dynamics; boomerang stripes; azimuthal wave number; multiple resonances; Van Allen Probes |
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Direct evidence of the pitch angle scattering of relativistic electrons induced by EMIC waves In this study, we analyze an EMIC wave event of rising tone elements recorded by the Van Allen Probes. The pitch angle distributions of relativistic electrons exhibit a direct response to the two elements of EMIC waves: at the intermediate pitch angle the fluxes are lower and at the low pitch angle the fluxes are higher than those when no EMIC was observed. In particular, the observed changes in the pitch angle distributions are most likely to be caused by nonlinear wave particle interaction. The calculation of the minimum resonant energy and a test particle simulation based on the observed EMIC waves support the role of the nonlinear wave-particle interaction in the pitch angle scattering. This study provides direct evidence for the nonlinear pitch angle scattering of electrons by EMIC waves. Zhu, Hui; Chen, Lunjin; Claudepierre, Seth; Zheng, Liheng; Published by: Geophysical Research Letters Published on: 01/2020 YEAR: 2020 DOI: 10.1029/2019GL085637 EMIC waves; nonlinear wave-particle interaction; pitch angle scattering; Van Allen Probes |
| 2019 |
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Excitation of toroidal mode standing Alfv\ en waves in the midnight sector of the inner magnetosphere in association with substorms is well documented, but studies are sparse on dayside sources for the waves. This paper reports observation of midnight toroidal waves by the Van Allen Probe B spacecraft during a geomagnetically quiet period on 12\textemdash13 May 2013. The spacecraft detected toroidal waves excited at odd harmonics below 30 mHz as it moved within the plasmasphere from ~2100 magnetic local time (MLT) to ~0030 MLT through midnight in the dipole L range 4.2\textemdash6.1. The frequencies and the relationship between the electric and magnetic field components of the waves are consistent with theoretical toroidal waves for a reflecting ionosphere. At the time of the nightside toroidal waves, compressional waves were observed by geostationary satellites located on the dayside, and the amplitudes of both types of waves varied with the cone angle of the interplanetary magnetic field. The nightside toroidal waves were likely driven by fast mode waves that resulted from transmission of upstream ultralow frequency waves into the magnetosphere. Ground magnetometers located near the footprint of the spacecraft did not detect toroidal waves. Takahashi, Kazue; Vellante, Massimo; Del Corpo, Alfredo; Claudepierre, Seth; Kletzing, Craig; Wygant, John; Koga, Kiyokazu; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2019 YEAR: 2019 DOI: 10.1029/2019JA027370 Ion foreshock; Nightside magnetosphere; Toroidal Alfven waves; Van Allen Probe; Van Allen Probes |
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The past decade transformed our observational understanding of energetic particle processes in near-Earth space. An unprecedented suite of observational systems were in operation including the Van Allen Probes, Arase, MMS, THEMIS, Cluster, GPS, GOES, and LANL-GEO magnetospheric missions. They were supported by conjugate low-altitude measurements on spacecraft, balloons, and ground-based arrays. Together these significantly improved our ability to determine and quantify the mechanisms that control the build-up and subsequent variability of energetic particle intensities in the inner magnetosphere. The high-quality data from NASA\textquoterights Van Allen Probes are the most comprehensive in-situ measurements ever taken in the near-Earth space radiation environment. These observations, coupled with recent advances in radiation belt theory and modeling, including dramatic increases in computational power, has ushered in a new era, perhaps a \textquotedblleftgolden era,\textquotedblright in radiation belt research. We have edited a Journal of Geophysical Research: Space Science Special Collection dedicated to Particle Dynamics in the Earth\textquoterights Radiation Belts in which we gather the most recent scientific findings and understanding of this important region of geospace. This collection includes the results presented at the American Geophysical Union Chapman International Conference in Cascais, Portugal (03/2018) and many other recent and relevant contributions. The present article introduces and review the context, current research, and main questions that motivate modern radiation belt research divided into the following topics: (1) particle acceleration and transport, (2) particle loss, (3) the role of nonlinear processes, (4) new radiation belt modeling capabilities and the quantification of model uncertainties, and (5) laboratory plasma experiments. Ripoll, Jean-Francois; Claudepierre, Seth; Ukhorskiy, Sasha; Colpitts, Chris; Li, Xinlin; Fennell, Joe; Crabtree, Chris; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2019 YEAR: 2019 DOI: 10.1029/2019JA026735 inner magnetosphere; laboratory plasma experiments; Particle acceleration; particle loss; Radiation belts; Van Allen Probes |
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Baker, D.N.; Zhao, H.; Li, X.; Kanekal, S.G.; Jaynes, A.N.; Kress, B.T.; Rodriguez, J.V.; Singer, H.J.; Claudepierre, S.G.; Fennell, J.F.; Hoxie, V.; Published by: Journal of Geophysical Research: Space Physics Published on: 11/2019 YEAR: 2019 DOI: 10.1029/2019JA027331 energetic particles; Magnetosphere:Inner; Magnetospheric configuration; Radiation belts; Space weather; Van Allen Probes |
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We report the electron flux modulations without corresponding magnetic fluctuations from unique multipoint satellite observations of the Arase (Exploration of Energization and Radiation in Geospace) and the Van Allen Probe (Radiation Belt Storm Probe [RBSP])-B satellites. On 30 March 2017, both Arase and RBSP-B observed periodic fluctuations in the relativistic electron flux with energies ranging from 500 keV to 2 MeV when they were located near the magnetic equator in the morning and dusk local time sectors, respectively. Arase did not observe Pc5 pulsations, while they were observed by RBSP-B. The clear dispersion signature of the relativistic electron fluctuations observed by Arase indicates that the source region is limited to the postnoon to the dusk sector. This is confirmed by RBSP-B and ground-magnetometer observations, where Pc5 pulsations are observed to drift-resonate with relativistic electrons on the duskside. Thus, Arase observed the drift-resonance signatures \textquotedblleftremotely,\textquotedblright whereas RBSP-B observed them \textquotedblleftlocally.\textquotedblright Teramoto, M.; Hori, T.; Saito, S.; Miyoshi, Y.; Kurita, S.; Higashio, N.; Matsuoka, A.; Kasahara, Y.; Kasaba, Y.; Takashima, T.; Nomura, R.; e, Nos\; Fujimoto, A.; Tanaka, Y.-M.; Shoji, M.; Tsugawa, Y.; Shinohara, M.; Shinohara, I.; Blake, J.; Fennell, J.F.; Claudepierre, S.G.; Turner, D.; Kletzing, C.; Sormakov, D.; Troshichev, O.; Published by: Geophysical Research Letters Published on: 11/2019 YEAR: 2019 DOI: 10.1029/2019GL084379 |
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RBSP-ECT Combined Spin-Averaged Electron Flux Data Product We describe a new data product combining the spin-averaged electron flux measurements from the Radiation Belt Storm Probes (RBSP) Energetic Particle Composition and Thermal Plasma (ECT) suite on the National Aeronautics and Space Administration\textquoterights Van Allen Probes. We describe the methodology used to combine each of the data sets and produce a consistent set of spectra for September 2013 to the present. Three-minute-averaged flux spectra are provided spanning energies from 15 eV up to 20 MeV. This new data product provides additional utility to the ECT data and offers a consistent cross calibrated data set for researchers interested in examining the dynamics of the inner magnetosphere across a wide range of energies. Boyd, A.; Reeves, G.; Spence, H.; Funsten, H.; Larsen, B.; Skoug, R.; Blake, J.; Fennell, J.; Claudepierre, S.; Baker, D.; Kanekal, S.; Jaynes, A.; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2019 YEAR: 2019 DOI: 10.1029/2019JA026733 |
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Simulation of Prompt Acceleration of Radiation Belt Electrons During the 16 July 2017 Storm We investigate the prompt enhancement of radiation belt electron flux observed by the Relativistic Electron Proton Telescope instrument on board Van Allen Probes following the 16 July 2017 CME-shock compression using MHD-test particle simulations. The prompt enhancements can be explained by the source population interacting with the azimuthally directed electric field impulses induced by CME-shock compressions of the dayside magnetopause. Electrons in drift resonance with the electric field impulse were accelerated by \~ 0.6 MeV on a drift period timescale (in minutes) as the impulse propagated from the dayside to the nightside around the flanks of the magnetosphere. MHD test particle simulation of energization and drift phase bunching, due to the bipolar electric field that accompanies the dayside compression and relaxation, is found to be consistent with Van Allen Probes observations. This study reproduces the energy-dependent drift echoes integrated over pitch angle and observed change in spectra for the first time. Patel, Maulik; Li, Zhao; Hudson, Mary; Claudepierre, Seth; Wygant, John; Published by: Geophysical Research Letters Published on: 06/2019 YEAR: 2019 DOI: 10.1029/2019GL083257 |
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Based on the measurements of ~100-keV to 10-MeV electrons from the Magnetic Electron Ion Spectrometer (MagEIS) and Relativistic Electron and Proton Telescope (REPT) on the Van Allen Probes, the radiation belt electron energy spectra characterization and evolution have been investigated systematically. The results show that the majority of radiation belt electron energy spectra can be represented by one of three types of distributions: exponential, power law, and bump-on-tail (BOT). The exponential spectra are generally dominant in the outer radiation belt outside the plasmasphere, power law spectra usually appear at high L-shells during injections of lower-energy electrons, and BOT spectra commonly dominate inside the plasmasphere at L>2.5 during relatively quiet times. The main features of three types of energy spectra have also been revealed. Specifically, for the BOT energy spectrum, the energy of local flux maximum usually ranges from approximately hundreds of keV to several MeV and the energy of local flux minimum varies from ~100 keV to ~MeV, both increasing as L-shell decreases, confirming the plasmaspheric hiss wave scattering to be the main mechanism forming the BOT energy spectra. Statistical results using 4-year observations from the Van Allen Probes on the relation between energy spectra and plasmapause location also show that the plasmasphere plays a critical role in shaping radiation belt electron energy spectrum: the peak location of BOT energy spectra is ~1 L-shell inside the minimum plasmapause, where BOT energy spectra mostly form in ~1\textendash2 days as a result of hiss wave scattering. Zhao, H.; Johnston, W.R.; Baker, D.N.; Li, X.; Ni, B.; Jaynes, A.N.; Kanekal, S.G.; Blake, J.B.; Claudepierre, S.G.; Reeves, G.D.; Boyd, A.J.; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2019 YEAR: 2019 DOI: 10.1029/2019JA026697 Bump-on-tail energy spectrum; Energy spectrum; Exponential energy spectrum; Plasmapause; Power law energy spectrum; radiation belt electrons; Van Allen Probes |
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Outer Van Allen Radiation Belt Response to Interacting Interplanetary Coronal Mass Ejections We study the response of the outer Van Allen radiation belt during an intense magnetic storm on 15\textendash22 February 2014. Four interplanetary coronal mass ejections (ICMEs) arrived at Earth, of which the three last ones were interacting. Using data from the Van Allen Probes, we report the first detailed investigation of electron fluxes from source (tens of kiloelectron volts) to core (megaelectron volts) energies and possible loss and acceleration mechanisms as a response to substructures (shock, sheath and ejecta, and regions of shock-compressed ejecta) in multiple interacting ICMEs. After an initial enhancement induced by a shock compression of the magnetosphere, core fluxes strongly depleted and stayed low for 4 days. This sustained depletion can be related to a sequence of ICME substructures and their conditions that influenced the Earth\textquoterights magnetosphere. In particular, the main depletions occurred during a high-dynamic pressure sheath and shock-compressed southward ejecta fields. These structures compressed/eroded the magnetopause close to geostationary orbit and induced intense and diverse wave activity in the inner magnetosphere (ULF Pc5, electromagnetic ion cyclotron, and hiss) facilitating both effective magnetopause shadowing and precipitation losses. Seed and source electrons in turn experienced stronger variations throughout the studied interval. The core fluxes recovered during the last ICME that made a glancing blow to Earth. This period was characterized by a concurrent lack of losses and sustained acceleration by chorus and Pc5 waves. Our study highlights that the seemingly complex behavior of the outer belt during interacting ICMEs can be understood by the knowledge of electron dynamics during different substructures. Kilpua, E.; Turner, D.; Jaynes, A.; Hietala, H.; Koskinen, H.; Osmane, A.; Palmroth, M.; Pulkkinen, T.; Vainio, R.; Baker, D.; Claudepierre, S.; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2019 YEAR: 2019 DOI: 10.1029/2018JA026238 interplanetary coronal mass ejections; magnetospheric storm; magnetospheric waves; Outer Belt; Radiation belts; Solar wind; Van Allen Probes |
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Energy coupling between the solar wind and the Earth\textquoterights magnetosphere can affect the electron population in the outer radiation belt. However, the precise role of different internal and external mechanisms that leads to changes of the relativistic electron population is not entirely known. This paper describes how Ultra Low Frequency (ULF) wave activity during the passage of Alfv\ enic solar wind streams contributes to the global recovery of the relativistic electron population in the outer radiation belt. To investigate the contribution of the ULF waves, we searched the Van Allen Probes data for a period in which we can clearly distinguish the enhancement of electron fluxes from the background. We found that the global recovery that started on September 22, 2014, which coincides with the corotating interaction region preceding a high-speed stream and the occurrence of persistent substorm activity, provides an excellent scenario to explore the contribution of ULF waves. To support our analyses, we employed ground and space-based observational data, global magnetohydrodynamic (MHD) simulations, and calculated the ULF wave radial diffusion coefficients employing an empirical model. Observations show a gradual increase of electron fluxes in the outer radiation belt and a concomitant enhancement of ULF activity that spreads from higher to lower L-shells. MHD simulation results agree with observed ULF wave activity in the magnetotail, which leads to both fast and Alfv\ en modes in the magnetospheric nightside sector. The observations agree with the empirical model and are confirmed by Phase Space Density (PhSD) calculations for this global recovery period. Da Silva, L.; Sibeck, D.; Alves, L.; Souza, V.; Jauer, P.; Claudepierre, S.; Marchezi, J.; Agapitov, O.; Medeiros, C.; Vieira, L.; Wang, C.; Jiankui, S.; Liu, Z.; Gonzalez, W.; Dal Lago, A.; Rockenbach, M.; Padua, M.; Alves, M.; Barbosa, M.; Fok, M.-C.; Baker, D.; Kletzing, C.; Kanekal, S.; Georgiou, M.; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2019 YEAR: 2019 DOI: 10.1029/2018JA026184 alfv\ en fluctuations; Earth\textquoterights magnetosphere; high speed stream; Radiation belts; relativistic electron flux; ULF wave; Van Allen Probes |
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Reply to \textquoterightThe dynamics of Van Allen belts revisited\textquoteright Mann, I.; Ozeke, L.; Morley, S.; Murphy, K.; Claudepierre, S.; Turner, D.; Baker, D.; Rae, I.; Kale, A.; Milling, D.; Boyd, A.; Spence, H.; Singer, H.; Dimitrakoudis, S.; Daglis, I.; Honary, F.; Published by: Nature Physics Published on: 02/2019 YEAR: 2019 DOI: 10.1038/nphys4351 |
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We present the temporal evolution of electron Phase Space Density (PSD) in the outer radiation belt during the intense March 2015 geomagnetic storm. Comparing observed PSD profiles as a function of L* at fixed first, M, and second, K, adiabatic invariants with those produced by simulations is critical for determining the physical processes responsible for the outer radiation belt dynamics. Here we show that the bulk of the accelerated and enhanced outer radiation belt population consists of electrons with K < 0.17 G1/2Re. For these electrons, the observed PSD versus L* profiles during the recovery phase of the storm have a positive radial gradient. We compare the observed temporal evolution of the PSD profiles during the recovery phase with those produced by radial diffusion simulations driven by observed Ultralow Frequency wave power as measured on the ground. Our results indicate that the dominant flux enhancement, inside L* < 5, in the heart of the outer radiation belt during the March 2015 geomagnetic storm is consistent with that produced by fast inward radial diffusion of electrons from a dynamic outer boundary driven by enhanced Ultralow Frequency wave power. Ozeke, L.; Mann, I.; Claudepierre, S.; Henderson, M.; Morley, S.; Murphy, K.; Olifer, L.; Spence, H.; Baker, D.; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2019 YEAR: 2019 DOI: 10.1029/2018JA026326 Local Acceleration; March 2015 storm; Phase space density; radial diffusion; Radiation belt; ULF waves; Van Allen Probes |
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Properties of Whistler Mode Waves in Earth\textquoterights Plasmasphere and Plumes Whistler mode wave properties inside the plasmasphere and plumes are systematically investigated using 5-year data from Van Allen Probes. The occurrence and intensity of whistler mode waves in the plasmasphere and plumes exhibit dependences on magnetic local time, L, and AE. Based on the dependence of the wave normal angle and Poynting flux direction on L shell and normalized wave frequency to electron cyclotron frequency (fce), whistler mode waves are categorized into four types. Type I: ~0.5 fce with oblique wave normal angles mostly in plumes; Type II: 0.01\textendash0.5 fce with small wave normal angles in the outer plasmasphere or inside plumes; Type III: <0.01 fce with oblique wave normal angles mostly within the plasmasphere or plumes; Type IV: 0.05\textendash0.5 fce with oblique wave normal angles deep inside the plasmasphere. The Poynting fluxes of Type I and II waves are mostly directed away from the equator, suggesting local amplification, whereas the Poynting fluxes of Type III and IV are directed either away from or toward the equator, and may originate from other source regions. Whistler mode waves in plumes have relatively small wave normal angles with Poynting flux mostly directed away from the equator and are associated with high electron fluxes from ~30 keV to hundreds of keV, all of which support local amplification. Whistler mode wave amplitudes in plumes can be stronger than typical plasmaspheric hiss, particularly during active times. Our results provide critical insights into understanding whistler mode wave generation inside the plasmasphere and plumes. Shi, Run; Li, Wen; Ma, Qianli; Green, Alex; Kletzing, Craig; Kurth, William; Hospodarsky, George; Claudepierre, Seth; Spence, Harlan; Reeves, Geoff; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2019 YEAR: 2019 DOI: 10.1029/2018JA026041 Plasmaspheric Hiss; plasmaspheric plume; Van Allen Probes; whistler mode waves |
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A statistical study was conducted of Earth\textquoterights radiation belt electron response to geomagnetic storms using NASA\textquoterights Van Allen Probes mission. Data for electrons with energies ranging from 30 keV to 6.3 MeV were included and examined as a function of L-shell, energy, and epoch time during 110 storms with SYM-H <=-50 nT during September 2012 to September 2017 (inclusive). The radiation belt response revealed clear energy and L-shell dependencies, with tens of keV electrons enhanced at all L-shells (2.5 <= L <= 6) in all storms during the storm commencement and main phase and then quickly decaying away during the early recovery phase, low hundreds of keV electrons enhanced at lower L-shells (~3 <= L <= ~4) in upward of 90\% of all storms and then decaying gradually during the recovery phase, and relativistic electrons throughout the outer belt showing main phase dropouts with subsequent and generally unpredictable levels of replenishment during the recovery phase. Compared to prestorm levels, electrons with energies >1 MeV also revealed a marked increase in likelihood of a depletion at all L-shells through the outer belt (3.5 <= L <= 6). Additional statistics were compiled revealing the storm time morphology of the radiation belts, confirming the aforementioned qualitative behavior. Considering storm drivers in the solar wind: storms driven by coronal mass ejection (CME) shocks/sheaths and CME ejecta only are most likely to result in a depletion of >1-MeV electrons throughout the outer belt, while storms driven by full CMEs and stream interaction regions are most likely to produce an enhancement of MeV electrons at lower (L < ~5) and higher (L > ~4.5) L-shells, respectively. CME sheaths intriguingly result in a distinct enhancement of ~1-MeV electrons around L~5.5, and on average, CME sheaths and stream interaction regions result in double outer belt structures. Turner, D.; Kilpua, E.; Hietala, H.; Claudepierre, S.; O\textquoterightBrien, T.; Fennell, J.; Blake, J.; Jaynes, A.; Kanekal, S.; Baker, D.; Spence, H.; Ripoll, J.-F.; Reeves, G.; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2019 YEAR: 2019 DOI: 10.1029/2018JA026066 energetic particles; Geomagnetic storms; inner magnetosphere; Radiation belts; relativistic electrons; Van Allen Probes; wave-particle interactions |
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We describe a new, more accurate procedure for estimating and removing inner zone background contamination from Van Allen Probes Magnetic Electron Ion Spectrometer (MagEIS) radiation belt measurements. This new procedure is based on the underlying assumption that the primary source of background contamination in the electron measurements at L shells less than three, energetic inner belt protons, is relatively stable. Since a magnetic spectrometer can readily distinguish between foreground electrons and background signals, we are able to exploit the proton stability to construct a model of the background contamination in each MagEIS detector by only considering times when the measurements are known to be background dominated. We demonstrate, for relativistic electron measurements in the inner zone, that the new technique is a significant improvement upon the routine background corrections that are used in the standard MagEIS data processing, which can \textquotedblleftovercorrect\textquotedblright and therefore remove real (but small) electron fluxes. As an example, we show that the previously reported 1-MeV injection into the inner zone that occurred in June of 2015 was distributed more broadly in L and persisted in the inner zone longer than suggested by previous estimates. Such differences can have important implications for both scientific studies and spacecraft engineering applications that make use of MagEIS electron data in the inner zone at relativistic energies. We compare these new results with prior work and present more recent observations that also show a 1-MeV electron injection into the inner zone following the September 2017 interplanetary shock passage. Claudepierre, S.; O\textquoterightBrien, T.; Looper, M.; Blake, J.; Fennell, J.; Roeder, J.; Clemmons, J.; Mazur, J.; Turner, D.; Reeves, G.; Spence, H.; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2019 YEAR: 2019 DOI: 10.1029/2018JA026349 Inner zone; particle detectors; Radiation belt; relativistic electrons; Slot region; Space weather; Van Allen Probes |
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Gyroresonant wave-particle interactions with very low frequency whistler mode chorus waves can accelerate subrelativistic seed electrons (hundreds of keV) to relativistic energies in the outer radiation belt during geomagnetic storms. In this study, we conduct a superposed epoch analysis of the chorus wave activity, the seed electron development, and the outer radiation belt electron response between L* = 2.5 and 5.5, for 25 coronal mass ejection and 35 corotating interaction region storms using Van Allen Probes observations. Electron data from the Magnetic Electron Ion Spectrometer and Relativistic Electron Proton Telescope instruments are used to monitor the storm-phase development of the seed and relativistic electrons, and magnetic field measurements from the Electric and Magnetic Field Instrument Suite and Integrated Science instrument are used to identify the chorus wave activity. Our results show a deeper (lower L*), stronger (higher flux), and earlier (epoch time) average seed electron enhancement and a resulting greater average radiation belt electron enhancement in coronal mass ejection storms compared to the corotating interaction region storms despite similar levels and lifetimes of average chorus wave activity for the two storm drivers. The earlier and deeper seed electron enhancement during the coronal mass ejection storms, likely driven by greater convection and substorm activity, provides a higher probability for local acceleration. These results emphasize the importance of the timing and the level of the seed electron enhancements in radiation belt dynamics. Bingham, S.; Mouikis, C.; Kistler, L.; Boyd, A.; Paulson, K.; Farrugia, C.; Huang, C.; Spence, H.; Claudepierre, S.; Kletzing, C.; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2018 YEAR: 2018 DOI: 10.1029/2018JA025963 CIR storms; CME storms; Radiation belts; seed electrons; Van Allen Probes; VLF waves |
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There has been increasing evidence for pitch angle scattering of relativistic electrons by electromagnetic ion cyclotron (EMIC) waves. Theoretical studies have predicted that the loss time scale of MeV electrons by EMIC waves can be very fast, suggesting that MeV electron fluxes rapidly decrease in association with the EMIC wave activity. This study reports on a unique event of MeV electron loss induced by EMIC waves based on Arase, Van Allen Probes, and ground-based network observations. Arase observed a signature of MeV electron loss by EMIC waves, and the satellite and ground-based observations constrained spatial-temporal variations of the EMIC wave activity during the loss event. Multi-satellite observation of MeV electron fluxes showed that ~2.5 MeV electron fluxes substantially decreased within a few tens of minutes where the EMIC waves were present. The present study provides an observational estimate of the loss time scale of MeV electrons by EMIC waves. Kurita, S.; Miyoshi, Y.; Shiokawa, K.; Higashio, N.; Mitani, T.; Takashima, T.; Matsuoka, A.; Shinohara, I.; Kletzing, C.; Blake, J.; Claudepierre, S.; Connors, M.; Oyama, S.; Nagatsuma, T.; Sakaguchi, K.; Baishev, D.; Otsuka, Y.; Published by: Geophysical Research Letters Published on: 11/2018 YEAR: 2018 DOI: 10.1029/2018GL080262 EMIC waves; loss; PWING project; Radiation belt; The Arase satellite; Van Allen Probes |
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Electron flux measurements are an important diagnostic for interactions between ultralow-frequency (ULF) waves and relativistic (\~1 MeV) electrons. Since measurements are collected by particle detectors with finite energy channel width, they are affected by a phase mixing process that can obscure these interactions. We demonstrate that ultrahigh-resolution electron measurements from the Magnetic Electron Ion Spectrometer on the Van Allen Probes mission\textemdashobtained using a data product that improves the energy resolution by roughly an order of magnitude\textemdashare crucial for understanding ULF wave-particle interactions. In particular, the ultrahigh-resolution measurements reveal a range of complex dynamics that cannot be resolved by standard measurements. Furthermore, the standard measurements provide estimates for the ULF flux modulation amplitude, period, and phase that may not be representative of true flux modulations, potentially leading to ambiguous conclusions concerning electron dynamics. Hartinger, M.; Claudepierre, S.; Turner, D.; Reeves, G.; Breneman, A.; Mann, I.; Peek, T.; Chang, E.; Blake, J.; Fennell, J.; O\textquoterightBrien, T.; Looper, M.; Published by: Geophysical Research Letters Published on: 10/2018 YEAR: 2018 DOI: 10.1029/2018GL080291 drift resonance; particle detector; Pc5; Radiation belts; ULF wave; Van Allen Probes; Wave-particle interaction |
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In Earth\textquoterights inner magnetosphere, electromagnetic waves in the ultra-low frequency (ULF) range play an important role in accelerating and diffusing charged particles via drift resonance. In conventional drift-resonance theory, linearization is applied under the assumption of weak wave-particle energy exchange so particle trajectories are unperturbed. For ULF waves with larger amplitudes and/or durations, however, the conventional theory becomes inaccurate since particle trajectories are strongly perturbed. Here, we extend the drift-resonance theory into a nonlinear regime, to formulate nonlinear trapping of particles in a wave-carried potential well, and predict the corresponding observable signatures such as rolled-up structures in particle energy spectrum. After considering how this manifests in particle data with finite energy resolution, we compare the predicted signatures with Van Allen Probes observations. Their good agreement provides the first observational evidence for the occurrence of nonlinear drift resonance, highlighting the importance of nonlinear effects in magnetospheric particle dynamics under ULF waves. Li, Li; Zhou, Xu-Zhi; Omura, Yoshiharu; Wang, Zi-Han; Zong, Qiu-Gang; Liu, Ying; Hao, Yi-Xin; Fu, Sui-Yan; Kivelson, Margaret; Rankin, Robert; Claudepierre, Seth; Wygant, John; Published by: Geophysical Research Letters Published on: 08/2018 YEAR: 2018 DOI: 10.1029/2018GL079038 drift resonance; nonlinear process; Particle acceleration; Radiation belts; ULF waves; Van Allen Probes; wave-particle interactions |
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Evidence of Microbursts Observed Near the Equatorial Plane in the Outer Van Allen Radiation Belt We present the first evidence of electron microbursts observed near the equatorial plane in Earth\textquoterights outer radiation belt. We observed the microbursts on March 31st, 2017 with the Magnetic Electron Ion Spectrometer and RBSP Ion Composition Experiment on the Van Allen Probes. Microburst electrons with kinetic energies of 29-92 keV were scattered over a substantial range of pitch angles, and over time intervals of 150-500 ms. Furthermore, the microbursts arrived without dispersion in energy, indicating that they were recently scattered near the spacecraft. We have applied the relativistic theory of wave-particle resonant diffusion to the calculated phase space density, revealing that the observed transport of microburst electrons is not consistent with the hypothesized quasi-linear approximation. Shumko, Mykhaylo; Turner, Drew; O\textquoterightBrien, T.; Claudepierre, Seth; Sample, John; Hartley, D.; Fennell, Joseph; Blake, Bernard; Gkioulidou, Matina; Mitchell, Donald; Published by: Geophysical Research Letters Published on: 07/2018 YEAR: 2018 DOI: 10.1029/2018GL078451 |
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During geomagnetic storms the intensities of the outer radiation belt electron population can exhibit dramatic variability. Deep depletions in intensity during the main phase are followed by increases during the recovery phase, often to levels that significantly exceed their pre-storm values. To study these processes, we simulate the evolution of the outer radiation belt during the 17 March 2013 geomagnetic storm using our newly-developed radiation belt model (CHIMP) based on test particle and coupled 3D ring current and global MHD simulations, and driven solely with solar wind and F10.7 flux data. Our approach differs from previous work in that we use MHD information to identify regions of strong, bursty, and azimuthally localized Earthward convection in the magnetotail where test particles are then seeded. We validate our model using in situ Van Allen Probe electron intensities over a multi-day period and show that our model is able to reproduce meaningful qualitative and quantitative agreement. Analysis of our model enables us to study the processes that govern the transition from the pre- to post-storm outer belt. Our analysis demonstrates that during the early main phase of the storm the pre-existing outer belt is largely wiped out via magnetopause losses and subsequently a new outer belt is created during a handful of discrete, mesoscale injections. Finally, we demonstrate the potential importance of magnetic gradient trapping in the transport and energization of outer belt electrons using a controlled numerical experiment. Sorathia, K.; Ukhorskiy, A; Merkin, V.; Fennell, J.; Claudepierre, S.; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2018 YEAR: 2018 DOI: 10.1029/2018JA025506 dropout; Geomagnetic storms; magnetopause loss; Radial Transport; Radiation belt; Van Allen Probes |
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Ultra-low frequency (ULF) waves play a fundamental role in the dynamics of the inner-magnetosphere and outer radiation belt during geomagnetic storms. Broadband ULF wave power can transport energetic electrons via radial diffusion and discrete ULF wave power can energize electrons through a resonant interaction. Using observations from the Magnetospheric Multiscale (MMS) mission, we characterize the evolution of ULF waves during a high-speed solar wind stream (HSS) and moderate geomagnetic storm while there is an enhancement of the outer radiation belt. The Automated Flare Inference of Oscillations (AFINO) code is used to distinguish discrete ULF wave power from broadband wave power during the HSS. During periods of discrete wave power and utilizing the close separation of the MMS spacecraft, we estimate the toroidal mode ULF azimuthal wave number throughout the geomagnetic storm. We concentrate on the toroidal mode as the HSSs compresses the day side magnetosphere resulting in an asymmetric magnetic field topology where toroidal mode waves can interact with energetic electrons. Analysis of the mode structure and wave numbers demonstrates that the generation of the observed ULF waves is a combination of externally driven waves, via the Kelvin-Helmholtz instability, and internally driven waves, via unstable ion distributions. Further analysis of the periods and toroidal azimuthal wave numbers suggests that these waves can couple with the core electron radiation belt population via the drift resonance during the storm. The azimuthal wave number and structure of ULF wave power (broadband or discrete) have important implications for the inner-magnetospheric and radiation belt dynamics. Murphy, Kyle; Inglis, Andrew; Sibeck, David; Rae, Jonathan; Watt, Clare; Silveira, Marcos; Plaschke, Ferdinand; Claudepierre, Seth; Nakamura, Rumi; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2018 YEAR: 2018 DOI: 10.1029/2017JA024877 azimuthal wave number; Geomagnetic storms; mode structure; Radiation belts; ULF waves; Van Allen Probes |
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The Van Allen Probes-A spacecraft observed an \~9 mHz ultra-low-frequency wave on 6 October 2012, at L\~ 5.7, in the dawn sector, and very near the magnetic equator. The wave had a strong electric field that was initially stronger in the azimuthal component and later in the radial component, exhibited properties of a fundamental standing Alfv\ en wave, and was associated with giant pulsations observed on the ground near the magnetic field footprint of the spacecraft. The wave was accompanied by oscillations of the flux of energetic protons (jH+). The amplitude of urn:x-wiley:jgra:media:jgra54254:jgra54254-math-0001 oscillations was large at equatorial pitch angles away from 90\textdegree, and the energy dependence of the phase and amplitude of the oscillations exhibited features consistent with drift resonance of \~140 keV protons with a westward-propagating wave having an azimuthal wave number of \~-40. The wave was detected when the spacecraft entered a region of an earthward gradient of the proton phase space density, in support of a theoretical prediction that such a gradient can drive fundamental poloidal waves. Takahashi, Kazue; Claudepierre, S.; Rankin, Robert; Mann, Ian; Smith, C.; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2018 YEAR: 2018 DOI: 10.1029/2017JA025139 drift resonance; Fundamental standing Alfven wave; Giant pulsation; Proton flux oscillation; Van Allen Probes |
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Based on over 4 years of Van Allen Probes measurements, an empirical model of radiation belt electron equatorial pitch angle distribution (PAD) is constructed. The model, developed by fitting electron PADs with Legendre polynomials, provides the statistical PADs as a function of L-shell (L=1 \textendash 6), magnetic local time (MLT), electron energy (~30 keV \textendash 5.2 MeV), and geomagnetic activity (represented by the Dst index), and is also the first empirical PAD model in the inner belt and slot region. For MeV electrons, model results show more significant day-night PAD asymmetry of electrons with higher energies and during disturbed times, which is caused by geomagnetic field configuration and flux radial gradient changes. Steeper PADs with higher fluxes around 90\textdegree pitch angle (PA) and lower fluxes at lower PAs for higher energy electrons and during active times are also present, which could be due to EMIC wave scattering. For 100s of keV electrons, cap PADs are generally present in the slot region during quiet times and their energy-dependent features are consistent with hiss wave scattering, while during active times, cap PADs are less significant especially at outer part of slot region, which could be due to the complex energizing and transport processes. 90\textdegree-minimum PADs are persistently present in the inner belt and appear in the slot region during active times, and minima at 90\textdegree PA are more significant for electrons with higher energies, which could be a critical evidence in identifying the underlying physical processes responsible for the formation of 90\textdegree-minimum PADs. Zhao, H.; Friedel, R.; Chen, Y.; Reeves, G.; Baker, D.; Li, X.; Jaynes, A.; Kanekal, S.; Claudepierre, S.; Fennell, J.; Blake, J.; Spence, H.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2018 YEAR: 2018 DOI: 10.1029/2018JA025277 Empirical Model; Geomagnetic storms; inner belt and slot region; Pitch angle distribution; radiation belt electrons; Van Allen Probes |
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The global statistical response of the outer radiation belt during geomagnetic storms Using the total radiation belt electron content calculated from Van Allen Probe phase space density (PSD), the time-dependent and global response of the outer radiation belt during storms is statistically studied. Using PSD reduces the impacts of adiabatic changes in the main phase, allowing a separation of adiabatic and non-adiabatic effects, and revealing a clear modality and repeatable sequence of events in storm-time radiation belt electron dynamics. This sequence exhibits an important first adiabatic invariant (μ) dependent behaviour in the seed (150 MeV/G), relativistic (1000 MeV/G), and ultra-relativistic (4000 MeV/G) populations. The outer radiation belt statistically shows an initial phase dominated by loss followed by a second phase of rapid acceleration, whilst the seed population shows little loss and immediate enhancement. The time sequence of the transition to the acceleration is also strongly μ-dependent and occurs at low μ first, appearing to be repeatable from storm to storm. Murphy, Kyle; Watt, C.; Mann, Ian; Rae, Jonathan; Sibeck, David; Boyd, A.; Forsyth, C.; Turner, D.; Claudepierre, S.; Baker, D.; Spence, H.; Reeves, G.; Blake, J.; Fennell, J.; Published by: Geophysical Research Letters Published on: 04/2018 YEAR: 2018 DOI: 10.1002/2017GL076674 Geomagnetic storms; magnetospheric dynamics; Radiation belts; Solar Wind-Magnetosphere Coupling; statistical analysis; 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 |
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Van Allen Probes Observations of Second Harmonic Poloidal Standing Alfv\ en Waves Long-lasting second-harmonic poloidal standing Alfv\ en waves (P2 waves) were observed by the twin Van Allen Probes (Radiation Belt Storm Probes, or RBSP) spacecraft in the noon sector of the plasmasphere, when the spacecraft were close to the magnetic equator and had a small azimuthal separation. Oscillations of proton fluxes at the wave frequency (\~10 mHz) were also observed in the energy (W) range 50\textendash300 keV. Using the unique RBSP orbital configuration, we determined the phase delay of magnetic field perturbations between the spacecraft with a 2nπ ambiguity. We then used finite gyroradius effects seen in the proton flux oscillations to remove the ambiguity and found that the waves were propagating westward with an azimuthal wave number (m) of \~-200. The phase of the proton flux oscillations relative to the radial component of the wave magnetic field progresses with W, crossing 0 (northward moving protons) or 180\textdegree (southward moving protons) at W \~ 120 keV. This feature is explained by drift-bounce resonance (mωd \~ ωb) of \~120 keV protons with the waves, where ωd and ωb are the proton drift and bounce frequencies. At lower energies, the proton phase space density ( math formula) exhibits a bump-on-tail structure with math formula occurring in the 1\textendash10 keV energy range. This math formula is unstable and can excite P2 waves through bounce resonance (ω \~ ωb), where ω is the wave frequency. Takahashi, Kazue; Oimatsu, Satoshi; e, Masahito; Min, Kyungguk; Claudepierre, Seth; Chan, Anthony; Wygant, John; Kim, Hyomin; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2018 YEAR: 2018 DOI: 10.1002/2017JA024869 bounce and drift-bounce resonances; energetic protons; plasmasphere; poloidal ULF waves; second harmonic; Van Allen Probes |
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Using measurements from the Van Allen Probes, a penetration event of 10s \textendash 100s of keV electrons and 10s of keV protons into the low L-shells (L<4) is studied. Timing and magnetic local time (MLT) differences of energetic particle deep penetration are unveiled and underlying physical processes are examined. During this event, both proton and electron penetrations are MLT-asymmetric. The observed MLT difference of proton penetration is consistent with convection of plasma sheet protons, suggesting enhanced convection during geomagnetic active times to be the cause of energetic proton deep penetration during this event. The observed MLT difference of 10s \textendash 100s of keV electron penetration is completely different from 10s of keV protons and cannot be well explained by inward radial diffusion, convection of plasma sheet electrons, or transport of trapped electrons by enhanced convection electric field represented by the Volland-Stern model or a uniform dawn-dusk electric field model based on the electric field measurements. It suggests that the underlying physical mechanism responsible for energetic electron deep penetration, which is very important for fully understanding energetic electron dynamics in the low L-shells, should be MLT-localized. Zhao, H.; Baker, D.; Califf, S.; Li, X.; Jaynes, A.; Leonard, T.; Kanekal, S.; Blake, J.; Fennell, J.; Claudepierre, S.; Turner, D.; Reeves, G.; Spence, H.; Published by: Journal of Geophysical Research: Space Physics Published on: 11/2017 YEAR: 2017 DOI: 10.1002/2017JA024558 |
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Whistler-mode chorus waves are a naturally occurring electromagnetic emission observed in Earth\textquoterights magnetosphere. Here, for the first time, data from NASA\textquoterights Magnetospheric Multiscale (MMS) mission were used to analyze chorus waves in detail, including the calculation of chorus wave normal vectors, k. A case study was examined from a period of substorm activity around the time of a conjunction between the MMS constellation and NASA\textquoterights Van Allen Probes mission on 07 April 2016. Chorus wave activity was simultaneously observed by all six spacecraft over a broad range of L-shells (5.5 < L < 8.5), magnetic local time (06:00 < MLT < 09:00), and magnetic latitude (-32\textdegree < MLat < -15\textdegree), implying a large chorus active region. Eight chorus elements and their substructure were analyzed in detail with MMS. These chorus elements were all lower band and rising tone emissions, right-handed and nearly circularly polarized, and propagating away from the magnetic equator when they were observed at MMS (MLat ~ -31\textdegree). Most of the elements had \textquotedbllefthook\textquotedblright like signatures on their wave power spectra, characterized by enhanced wave power at flat or falling frequency following the peak, and all the elements exhibited complex and well organized substructure observed consistently at all four MMS spacecraft at separations up to 70 km (60 km perpendicular and 38 km parallel to the background magnetic field). The waveforms in field-aligned coordinates also demonstrated that these waves were all phase coherent allowing for the direct calculation of k. Error estimates on calculated k revealed that the plane wave approximation was valid for six of the eight elements and most of the subelements. The wave normal vectors were within 20-30\textdegree from the direction anti-parallel to the background field for all elements and changed from subelement to subelement through at least two of the eight elements. The azimuthal angle of k in the perpendicular plane was oriented earthward and was oblique to that of the Poynting vector, which has implications for the validity of cold plasma theory. Turner, D.; Lee, J.; Claudepierre, S.; Fennell, J.; Blake, J.; Jaynes, A.; Leonard, T.; Wilder, F.; Ergun, R.; Baker, D.; Cohen, I.; Mauk, B.; Strangeway, R.; Hartley, D.; Kletzing, C.; Breuillard, H.; Le Contel, O.; Khotyaintsev, Yu; Torbert, R.; Allen, R.; Burch, J.; Santolik, O.; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2017 YEAR: 2017 DOI: 10.1002/2017JA024474 chorus waves; inner magnetosphere; Magnetospheric multiscale; MMS; Radiation belts; Van Allen Probes |
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This study examines multipoint observations during a conjunction between MMS and Van Allen Probes on 07 April 2016 in which a series of energetic particle injections occurred. With complementary data from THEMIS, Geotail, and LANL-GEO (16 spacecraft in total), we develop new insights on the nature of energetic particle injections associated with substorm activity. Despite this case involving only weak substorm activity (max. AE < 300 nT) during quiet geomagnetic conditions in steady, below-average solar wind, a complex series of at least six different electron injections was observed throughout the system. Intriguingly, only one corresponding ion injection was clearly observed. All ion and electron injections were observed at < 600 keV only. MMS reveals detailed substructure within the largest electron injection. A relationship between injected electrons with energy < 60 keV and enhanced whistler-mode chorus wave activity is also established from Van Allen Probes and MMS. Drift mapping using a simplified magnetic field model provides estimates of the dispersionless injection boundary locations as a function of universal time, magnetic local time, and L-shell. The analysis reveals that at least five electron injections, which were localized in magnetic local time, preceded a larger injection of both electrons and ions across nearly the entire nightside of the magnetosphere near geosynchronous orbit. The larger, ion and electron injection did not penetrate to L < 6.6, but several of the smaller, electron injections penetrated to L < 6.6. Due to the discrepancy between the number, penetration depth, and complexity of electron vs. ion injections, this event presents challenges to the current conceptual models of energetic particle injections. Turner, D.; Fennell, J.; Blake, J.; Claudepierre, S.; Clemmons, J.; Jaynes, A.; Leonard, T.; Baker, D.; Cohen, I.; Gkioulidou, M.; Ukhorskiy, A; Mauk, B.; Gabrielse, C.; Angelopoulos, V.; Strangeway, R.; Kletzing, C.; Le Contel, O.; Spence, H.; Torbert, R.; Burch, J.; Reeves, G.; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2017 YEAR: 2017 DOI: 10.1002/2017JA024554 energetic particles; injections; inner magnetosphere; plasma sheet; substorms; Van Allen Probes; wave-particle interactions |
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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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CME- or CIR-driven storms can change the electron distributions in the radiation belt dramatically, which can in turn affect the spacecraft in this region or induce geomagnetic effects. The Van Allen Probes twin spacecraft, launched on 30 August 2012, orbit near the equatorial plane and across a wide range of L* with apogee at 5.8 RE and perigee at 620 km. Electron data from Van Allen Probes MagEIS and REPT instruments have been binned every six hours at L*=3 (defined as 2.5 Shen, Xiao-Chen; Hudson, Mary; Jaynes, Allison; Shi, Quanqi; Tian, Anmin; Claudepierre, Seth; Qin, Mu-Rong; Zong, Qiu-Gang; Sun, Wei-Jie; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2017 YEAR: 2017 DOI: 10.1002/2017JA024100 CIR-driven storm; CME-driven storm; outer radiation belt; Van Allen Probes |
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We investigate a quiet-time event of magnetospheric Pc5 ultra low frequency (ULF) waves and their likely external drivers using multiple spacecraft observations. Enhancements of electric and magnetic field perturbations in two narrow frequency bands, 1.5-2 mHz and 3.5-4 mHz, were observed over a large radial distance range from r ~5 to 11 RE. During the first half of this event, perturbations were mainly observed in the transverse components and only in the 3.5-4 mHz band. In comparison, enhancements were stronger during the second half in both transverse and compressional components and in both frequency bands. No indication of field line resonances was found for these magnetic field perturbations. Perturbations in these two bands were also observed in the magnetosheath, but not in the solar wind dynamic pressure perturbations. For the first interval, good correlations between the flow perturbations in the magnetosphere and magnetosheath and an indirect signature for Kelvin-Helmholtz (K-H) vortices suggest K-H surface waves as the driver. For the second interval, good correlations are found between the magnetosheath dynamic pressure perturbations, magnetopause deformation, and magnetospheric waves, all in good correspondence to IMF discontinuities. The characteristics of these perturbations can be explained by being driven by foreshock perturbations resulting from these IMF discontinuities. This event shows that even during quiet periods, KH-unstable magnetopause and ion foreshock perturbations can combine to create a highly dynamic magnetospheric ULF wave environment. Wang, Chih-Ping; Thorne, Richard; Liu, Terry; Hartinger, Michael; Nagai, Tsugunobu; Angelopoulos, Vassilis; Wygant, John; Breneman, Aaron; Kletzing, Craig; Reeves, Geoffrey; Claudepierre, Seth; Spence, Harlan; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2017 YEAR: 2017 DOI: 10.1002/2016JA023610 IMF discontinuity; inner magnetosphere; Kelvin-Helmholtz vortices; magnetosheath; Pc5 waves; plasma sheet; Van Allen Probes |
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The hidden dynamics of relativistic electrons (0.7-1.5~MeV) in the inner zone and slot region We present measurements of relativistic electrons (0.7\textendash1.5 MeV) in the inner zone and slot region obtained by the Magnetic Electron and Ion Spectrometer (MagEIS) instrument on Van Allen Probes. The data presented are corrected for background contamination, which is primarily due to inner-belt protons in these low-L regions. We find that \~1 MeV electrons were transported into the inner zone following the two largest geomagnetic storms of the Van Allen Probes era to date, the March and June 2015 events. As \~1 MeV electrons were not observed in Van Allen Probes data in the inner zone prior to these two events, the injections created a new inner belt that persisted for at least 1.5 years. In contrast, we find that electrons injected into the slot region decay on much faster timescales, approximately tens of days. Furthermore, we find no evidence of >1.5 MeV electrons in the inner zone during the entire time interval considered (April 2013 through September 2016). The energies we examine thus span a transition range in the steeply falling inner zone electron spectrum, where modest intensities are observed at 0.7 MeV, and no electrons are observed at 1.5 MeV. To validate the results obtained from the background corrected flux measurements, we also present detailed pulse-height spectra from individual MagEIS detectors. These measurements confirm our results and also reveal low-intensity inner zone and slot region electrons that are not captured in the standard background corrected data product. Finally, we briefly discuss efforts to refine the upper limit of inner zone MeV electron flux obtained in earlier work. Claudepierre, S.; O\textquoterightBrien, T.; Fennell, J.; Blake, J.; Clemmons, J.; Looper, M.; Mazur, J.; Roeder, J.; Turner, D.; Reeves, G.; Spence, H.; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2017 YEAR: 2017 DOI: 10.1002/2016JA023719 Inner zone; particle detectors; Radiation belt; relativistic electrons; Slot region; Space weather; Van Allen Probes |
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The hidden dynamics of relativistic electrons (0.7-1.5~MeV) in the inner zone and slot region We present measurements of relativistic electrons (0.7\textendash1.5 MeV) in the inner zone and slot region obtained by the Magnetic Electron and Ion Spectrometer (MagEIS) instrument on Van Allen Probes. The data presented are corrected for background contamination, which is primarily due to inner-belt protons in these low-L regions. We find that \~1 MeV electrons were transported into the inner zone following the two largest geomagnetic storms of the Van Allen Probes era to date, the March and June 2015 events. As \~1 MeV electrons were not observed in Van Allen Probes data in the inner zone prior to these two events, the injections created a new inner belt that persisted for at least 1.5 years. In contrast, we find that electrons injected into the slot region decay on much faster timescales, approximately tens of days. Furthermore, we find no evidence of >1.5 MeV electrons in the inner zone during the entire time interval considered (April 2013 through September 2016). The energies we examine thus span a transition range in the steeply falling inner zone electron spectrum, where modest intensities are observed at 0.7 MeV, and no electrons are observed at 1.5 MeV. To validate the results obtained from the background corrected flux measurements, we also present detailed pulse-height spectra from individual MagEIS detectors. These measurements confirm our results and also reveal low-intensity inner zone and slot region electrons that are not captured in the standard background corrected data product. Finally, we briefly discuss efforts to refine the upper limit of inner zone MeV electron flux obtained in earlier work. Claudepierre, S.; O\textquoterightBrien, T.; Fennell, J.; Blake, J.; Clemmons, J.; Looper, M.; Mazur, J.; Roeder, J.; Turner, D.; Reeves, G.; Spence, H.; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2017 YEAR: 2017 DOI: 10.1002/2016JA023719 Inner zone; particle detectors; Radiation belt; relativistic electrons; Slot region; Space weather; Van Allen Probes |