An empirical model of radiation belt electron pitch angle distributions based on Van Allen Probes measurements

TitleAn empirical model of radiation belt electron pitch angle distributions based on Van Allen Probes measurements
Publication TypeJournal Article
Year of Publication2018
AuthorsZhao, H, Friedel, RHW, Chen, Y, Reeves, GD, Baker, DN, Li, X, Jaynes, AN, Kanekal, SG, Claudepierre, SG, Fennell, JF, Blake, JB, Spence, HE
JournalJournal of Geophysical Research: Space Physics
Date Published04/2018
KeywordsEmpirical Model; Geomagnetic storms; inner belt and slot region; Pitch angle distribution; radiation belt electrons; Van Allen Probes
AbstractBased 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 – 6), magnetic local time (MLT), electron energy (~30 keV – 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° 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°‐minimum PADs are persistently present in the inner belt and appear in the slot region during active times, and minima at 90° 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°‐minimum PADs.
URLhttps://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018JA025277
DOI10.1029/2018JA025277
Short TitleJ. Geophys. Res. Space Physics


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