On the Acceleration Mechanism of Ultrarelativistic Electrons in the Center of the Outer Radiation Belt: A Statistical Study

TitleOn the Acceleration Mechanism of Ultrarelativistic Electrons in the Center of the Outer Radiation Belt: A Statistical Study
Publication TypeJournal Article
Year of Publication2019
AuthorsZhao, H, Baker, DN, Li, X, Malaspina, DM, Jaynes, AN, Kanekal, SG
JournalJournal of Geophysical Research: Space Physics
Date Published10/2019
ISSN2169-9380
KeywordsAcceleration mechanism; Inward radial diffusion; Local Acceleration; Phase space density; Radiation belts; ultrarelativistic electrons; Van Allen Probes
AbstractUsing energetic particle and wave measurements from the Van Allen Probes, Polar Orbiting Environmental Satellites (POES), and Geostationary Operational Environmental Satellite (GOES), the acceleration mechanism of ultrarelativistic electrons (>3 MeV) in the center of the outer radiation belt is investigated statistically. A superposed epoch analysis is conducted using 19 storms, which caused flux enhancements of 1.8–7.7 MeV electrons. The evolution of electron phase space density radial profile suggests an energy‐dependent acceleration of ultrarelativistic electrons in the outer belt. Especially, for electrons with very high energies (~7 MeV), prevalent positive phase space density radial gradients support inward radial diffusion being responsible for electron acceleration in the center of the outer belt (L*~3–5) during most enhancement events in the Van Allen Probes era. We propose a two‐step acceleration process to explain the acceleration of ~7 MeV electrons in the outer belt: intense and sustained chorus waves locally energize core electron populations to ultrarelativistic energies at high L region beyond the Van Allen Probes' apogee, followed by inward radial diffusion which further energizes these populations to even higher energies. Statistical results of chorus wave activity inferred from POES precipitating electron measurements as well as core electron populations observed by the Van Allen Probes and GOES support this hypothesis.
URLhttps://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019JA027111
DOI10.1029/2019JA027111
Short TitleJ. Geophys. Res. Space Physics


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