Scattering by whistler-mode waves during a quiet period perturbed by substorm activity

0541808 - ÚFA 2022 RIV GB eng J - Journal Article
Ripoll, J.-F. - Denton, M. H. - Hartley, D. P. - Reeves, G. D. - Malaspina, D. - Cunningham, G. S. - Santolík, Ondřej - Thaller, S. A. - Loridan, V. - Fennell, J.F. - Turner, D. L. - Kurth, W. S. - Kletzing, C. A. - Henderson, M. G. - Ukhorskiy, A. Y.
Scattering by whistler-mode waves during a quiet period perturbed by substorm activity.
Journal of Atmospheric and Solar-Terrestrial Physics. Roč. 215, April (2021), č. článku 105471. ISSN 1364-6826. E-ISSN 1879-1824
Grant - others:AV ČR(CZ) AP1401
Program: Akademická prémie - Praemium Academiae
Institutional support: RVO:68378289
Keywords : Electron * Wave-particle interactions * Radiation belts * Substorm * Moderate substorm activity * Whistler-mode waves
OECD category: Fluids and plasma physics (including surface physics)
Impact factor: 2.119, year: 2021
Method of publishing: Limited access
https://www.sciencedirect.com/science/article/pii/S1364682620302741

We study the dynamics of radiation belt electrons during a 10-day quiet period perturbed by substorm activity and preceding a high-speed stream (HSS), aiming at a global description of the radiation belts in L-shell, L in [2, 6], and energy [0.1, 10] MeV. We combine Van Allen Probes observations and Fokker-Planck numerical simulations of pitch-angle diffusion. The Fokker-Planck model uses event-driven pitch angle diffusion coefficients from whistler-mode waves, built from the wave properties and the ambient plasma density measurements from the Van Allen Probes. We first find this event has some similar characteristics to regular quiet times previously studied: a widely extended plasmasphere within which we observe strong and varying whistler-mode waves. These ambient conditions lead to strong pitch-angle scattering, which contributes to the creation of a wide slot region as well as a significant decay of the outer radiation belts, which are observed and qualitatively well simulated. In addition, we find the substorm activity causes short duration (within ? 4h) decay of the plasma density and a lowering amplitude of the whistler-mode waves within the plasmasphere, both causing opposite effects in terms of pitch angle diffusion. This leads to a diminution of pitch-angle diffusion at the time of the main substorm activity. Conversely, whistler-mode waves become enhanced in the time periods between the substorm injections. All effects cumulated, we find an enhancement of pitch angle diffusion by whistler-mode waves above L-4.7 during the 10-day period. This directly relates to the combination of quietness and substorm activity which allows pitch angle diffusing of up to 1 MeV electrons in the outer belt. Relativistic electrons of 1?2 MeV remain trapped in the outer belt, from L-4.7 to L-5.2, forming, in both the observations and the simulations, a distinct pocket of remnant electrons.
Permanent Link: http://hdl.handle.net/11104/0319338