The causes of the hardest electron precipitation events seen with SAMPEX. Issue 9 (22nd September 2016)

• Record Type: Journal Article
• Authors: 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.
• Is Part Of: Journal of geophysical research. Volume 121:Issue 9(2016:Sep.)
• Page Start: 8600
• Page End: 8613
• Publication Date: 2016-09-22
• Subjects: radiation belts -- particle precipitation -- wave‐particle interactions -- relativistic electrons; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1002/2016JA022346
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: 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. Key Points: Hard e‐ precipitation (folding energy >500 keV) has two populations: nearer dusk, with harder spectra, and nearer midnight, with softer spectra The harder population shows evidence of being due to EMIC wave scattering, while the softer may be due to current sheet scattering Concurrent proton precipitation does not necessarily help distinguish the two mechanisms