On the cause and extent of outer radiation belt losses during the 30 September 2012 dropout event

TitleOn the cause and extent of outer radiation belt losses during the 30 September 2012 dropout event
Publication TypeJournal Article
Year of Publication2014
AuthorsTurner, DL, Angelopoulos, V, Morley, SK, Henderson, MG, Reeves, GD, Li, W, Baker, DN, Huang, C-L, Boyd, A, Spence, HE, Claudepierre, SG, Blake, JB, Rodriguez, JV
JournalJournal of Geophysical Research: Space Physics
Pagination1530 - 1540
Date Published03/2014
Keywordsdropouts; inner magnetosphere; loss; Radiation belts; relativistic electrons; Van Allen Probes
AbstractOn 30 September 2012, a flux “dropout” occurred throughout Earth's outer electron radiation belt during the main phase of a strong geomagnetic storm. Using eight spacecraft from NASA's Time History of Events and Macroscale Interactions during Substorms (THEMIS) and Van Allen Probes missions and NOAA's Geostationary Operational Environmental Satellites constellation, we examined the full extent and timescales of the dropout based on particle energy, equatorial pitch angle, radial distance, and species. We calculated phase space densities of relativistic electrons, in adiabatic invariant coordinates, which revealed that loss processes during the dropout were > 90% effective throughout the majority of the outer belt and the plasmapause played a key role in limiting the spatial extent of the dropout. THEMIS and the Van Allen Probes observed telltale signatures of loss due to magnetopause shadowing and subsequent outward radial transport, including similar loss of energetic ring current ions. However, Van Allen Probes observations suggest that another loss process played a role for multi-MeV electrons at lower L shells (L* < ~4).
Short TitleJ. Geophys. Res. Space Physics

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