Bibliography

Comparing and contrasting dispersionless injections at geosynchronous orbit during a substorm event

Particle injections in the magnetosphere transport electrons and ions from the magnetotail to the radiation belts. Here we consider generation mechanisms of \textquotedblleftdispersionless\textquotedblright injections, namely, those with simultaneous increase of the particle flux over a wide energy range. In this study we take advantage of multisatellite observations which simultaneously monitor Earth\textquoterights magnetospheric dynamics from the tail toward the radiation belts during a substorm event. Dispersionless injections are associated with instabilities in the plasma sheet during the growth phase of the substorm, with a dipolarization front at the onset and with magnetic flux pileup during the expansion phase. They show different spatial spread and propagation characteristics. Injection associated with the dipolarization front is the most penetrating. At geosynchronous orbit (6.6 RE), the electron distributions do not have a classic power law fit but instead a bump on tail centered on \~120 keV during dispersionless electron injections. However, electron distributions of injections associated with magnetic flux pileup in the magnetotail (13 RE) do not show such a signature. We surmise that an additional resonant acceleration occurs in between these locations. We relate the acceleration mechanism to the electron drift resonance with ultralow frequency waves localized in the inner magnetosphere.

Kronberg, E.; Grigorenko, E.; Turner, D.; Daly, P.; Khotyaintsev, Y.; Kozak, L.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 03/2017

YEAR: 2017     DOI: 10.1002/2016JA023551

Acceleration; current wedge; Dipolarization; particle injections; substorm; ULF waves; Van Allen Probes

Near-Relativistic Electron Acceleration by Landau Trapping in Time Domain Structures

Data from the Van Allen Probes have provided the first extensive evidence of nonlinear (as opposed to quasi-linear) wave-particle interactions in space with the associated rapid (less than a bounce period) electron acceleration to hundreds of keV by Landau resonance in the parallel electric field of time domain structures (TDSs) traveling at high speeds (~20,000 km/s). This observational evidence is supported by simulations and discussion of the source and spatial extent of the fast TDS. This result indicates the possibility that the electrostatic fields in TDS may generate the electron seed population for cyclotron resonance interaction with chorus waves to make higher-energy electrons.

Mozer, F.; Artemyev, A.; Agapitov, O.; Mourenas, D.; Vasko, I.;

Published by: Geophysical Research Letters      Published on: 01/2016

YEAR: 2016     DOI: 10.1002/2015GL067316

Acceleration; Van Allen Probes

Energy dependent dynamics of keV to MeV electrons in the inner zone, outer zone, and slot regions.

We present observations of the radiation belts from the HOPE and MagEIS particle detectors on the Van Allen Probes satellites that illustrate the energy-dependence and L-shell dependence of radiation belt enhancements and decays. We survey events in 2013 and analyze an event on March 1 in more detail. The observations show: (a) At all L-shells, lower-energy electrons are enhanced more often than higher energies; (b) Events that fill the slot region are more common at lower energies; (c) Enhancements of electrons in the inner zone are more common at lower energies; and (d) Even when events do not fully fill the slot region, enhancements at lower-energies tend to extend to lower L-shells than higher energies. During enhancement events the outer zone extends to lower L-shells at lower energies while being confined to higher L-shells at higher energies. The inner zone shows the opposite with an outer boundary at higher L-shells for lower energies. Both boundaries are nearly straight in log(energy) vs. L-shell space. At energies below a few hundred keV radiation belt electron penetration through the slot region into the inner zone is commonplace but the number and frequency of \textquotedblleftslot filling\textquotedblright events decreases with increasing energy. The inner zone is enhanced only at energies that penetrate through the slot. Energy- and L-shell dependent losses (that are consistent with whistler hiss interactions) return the belts to more quiescent conditions.

Reeves, Geoffrey; Friedel, Reiner; Larsen, Brian; Skoug, Ruth; Funsten, Herbert; Claudepierre, Seth; Fennell, Joseph; Turner, Drew; Denton, Mick; Spence, H.; Blake, Bernard; Baker, D.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 12/2015

YEAR: 2015     DOI: 10.1002/2015JA021569

Acceleration; energetic particles; Inner zone; Outer Zone; Radiation belts; Slot region; Van Allen Probes

Chorus-driven acceleration of radiation belt electrons in the unusual temporal/spatial regions

Cyclotron resonance with whistler-mode chorus waves is an important mechanism for the local acceleration of radiation belt energetic electrons. Such acceleration process has been widely investigated during the storm times, and its favored region is usually considered to be the low-density plasmatrough with magnetic local time (MLT) from midnight through dawn to noon. Here we present two case studies on the chorus-driven acceleration of radiation belt electrons in some \textquotedblleftunusual\textquotedblright temporal /spatial regions. (1) The first event recorded by the Van Allen Probes during the nonstorm times from 21 to 23 February 2013. Within two days, a new radiation belt centering around L=5.8 formed and gradually merged with the original outer belt. The corresponding relativistic electron fluxes increased by a factor of up to 50, accompanied by strong chorus waves. The quasi-linear STEERB model, including the local acceleration of detected chorus waves, can basically reproduce the observed 0.2\textendash5.0 MeV electron flux enhancement at the center of new belt. These results clearly illustrate the importance of chorus-driven local acceleration during the nonstorm times. (2) The second event observed by the Van Allen Probes in the duskside (MLT\~18) region on 2 October 2013. The quasi-linear diffusion analysis of STEERB code shows that, even in the duskside region with large ratio between the electron plasma frequency and the electron gyrofrequency, the detected intense (\~0.5 nT) chorus waves can still effectively accelerate radiation belt electrons. These results clearly exhibit the broader effective acceleration regions than usually estimated, at least for this one example.

Su, Zhenpeng; Xiao, Fuliang; Zheng, Huinan; Zhu, Hui;

Published by:       Published on: 08/2014

YEAR: 2014     DOI: 10.1109/URSIGASS.2014.6929875

Acceleration; Van Allen Belts; Van Allen Probes