Radial diffusion simulations of the 20 September 2007 radiation belt dropout
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Abstract |
This is a study of a dropout of radiation belt electrons, associated with an isolated solar wind density pulse on 20 September 2007, as seen by the solid-state telescopes (SST) detectors on THEMIS (Time History of Events and Macroscale Interactions during Substorms). Omnidirectional fluxes were converted to phase space density at constant invariants M = 700 MeV G-1 and K = 0.014 RE G1/2, with the assumption of local pitch angle α ≈ 80\textdegree and using the T04 magnetic field model. The last closed drift shell, which was calculated throughout the time interval, never came within the simulation outer boundary of L* = 6. It is found, using several different models for diffusion rates, that radial diffusion alone only allows the data-driven, time-dependent boundary values at Lmax = 6 and Lmin = 3.7 to propagate a few tenths of an RE during the simulation; far too slow to account for the dropout observed over the broad range of L* = 4\textendash5.5. Pitch angle diffusion via resonant interactions with several types of waves (chorus, electromagnetic ion cyclotron waves, and plasmaspheric and plume hiss) also seems problematic, for several reasons which are discussed.
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Year of Publication |
2014
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Journal |
Annales Geophysicae
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Volume |
32
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Number of Pages |
925-934
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Date Published |
11/2014
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URL |
http://www.ann-geophys.net/32/925/2014/http://www.ann-geophys.net/32/925/2014/angeo-32-925-2014.pdf
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DOI |
10.5194/angeo-32-925-2014
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