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The causes of the hardest electron precipitation events seen with SAMPEX
Author(s) -
Smith David M.,
Casavant Eric P.,
Comess Max D.,
Liang Xinqing,
Bowers Gregory S.,
Selesnick Richard S.,
Clausen Lasse B. N.,
Millan Robyn M.,
Sample John G.
Publication year - 2016
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/2016ja022346
Subject(s) - physics , solar wind , astrophysics , van allen radiation belt , population , proton , context (archaeology) , electron , solar energetic particles , midnight , electron precipitation , plasmasphere , earth's magnetic field , relativistic particle , van allen probes , interplanetary medium , interplanetary spaceflight , astronomy , magnetosphere , coronal mass ejection , nuclear physics , magnetic field , plasma , geology , paleontology , demography , quantum mechanics , sociology
We studied the geomagnetic, plasmaspheric, and solar wind context of relativistic electron precipitation (REP) events seen with the Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX) , Proton Electron Telescope (PET) to derive an exponential folding energy E 0 for each event. Events with E 0 < 400 keV peak near midnight, and with increasing E 0 , the peak magnetic local time (MLT) moves earlier but never peaks as early as the MLT distribution of electromagnetic ion cyclotron (EMIC) waves in the outer belt, and a distinct component near midnight remains. Events with E 0 >750 keV near dusk (1400 < MLT < 2000) show correlations with solar wind dynamic pressure and proton density, A E index, negative D s t index, and an extended plasmasphere, all supporting an EMIC wave interpretation. Events with 500 keV < E 0 < 600 keV near midnight (MLT 2200–0200) do not show these correlations. Comparing these two samples to all events with E 0 >500 keV (“hard REP”), we estimate that roughly 45% of the whole population has the distributions of geomagnetic and solar wind parameters associated with EMIC waves, while 55% does not. We hypothesize that the latter events may be caused by current sheet scattering (CSS), which can be mistaken for EMIC wave scattering in that both simultaneously precipitate MeV electrons and keV protons. Since a large number of MeV electrons are lost in the near‐midnight hard REP events, and in the large number of E 0 < 400 keV events that show no dusk‐like peak at all, we conclude that CSS should be studied further as a possibly important loss channel for MeV electrons.