Resonant Scattering of Radiation Belt Electrons by Off-Equatorial Magnetosonic Waves

TitleResonant Scattering of Radiation Belt Electrons by Off-Equatorial Magnetosonic Waves
Publication TypeJournal Article
Year of Publication2018
AuthorsNi, B, Zou, Z, Fu, S, Cao, X, Gu, X, Xiang, Z
JournalGeophysical Research Letters
Pagination1228 - 1236
Date Published02/2018
Keywordsbutterfly pitch angle distributions; off-equatorial MS waves; radiation belt electrons; Van Allen Probes
AbstractFast magnetosonic (MS) waves are commonly regarded as electromagnetic waves that are characteristically confined within ±3° of the geomagnetic equator. We report two typical off-equatorial MS events observed by Van Allen Probes, that is, the 8 May 2014 event that occurred at the geomagnetic latitudes of 7.5°–9.2° both inside and outside the plasmasphere with the wave amplitude up to 590 pT and the 9 January 2014 event that occurred at the latitudes of—(15.7°–17.5°) outside the plasmasphere with a smaller amplitude about 81 pT. Detailed test particle simulations quantify the electron resonant scattering rates by the off-equatorial MS waves to find that they can cause the pitch angle scattering and momentum diffusion of radiation belt electrons with equatorial pitch angles < ~75° or < ~58° (depending on the wave latitudinal coverage) on timescales of a day. Subsequent two-dimensional Fokker-Planck diffusion simulations indicate that the strong off-equatorial MS waves are capable of efficiently transporting high pitch angle electrons to lower pitch angles to facilitate the formation of radiation belt electron butterfly distributions for a broad energy range from ~100 keV to >1 MeV within an hour. Our study clearly demonstrates that the presence of off-equatorial MS waves, in addition to equatorial MS waves, can contribute importantly to the dynamical variations of radiation belt electron fluxes and their pitch angle distribution.
URLhttp://onlinelibrary.wiley.com/doi/10.1002/2017GL075788/full
DOI10.1002/grl.v45.310.1002/2017GL075788
Short TitleGeophys. Res. Lett.


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