Electron loss rates from the outer radiation belt caused by the filling of the outer plasmasphere: the calm before the storm Page: 15 of 31
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5. Discussion
The discussion in this section focuses on three topics: (A) the interpretation of the
observed decay in the number density of the outer electron radiation belt at geosynchronous
orbit, (B) the effect of the fluxes of radiation-belt electrons into the atmosphere, and (C) the
relativistic-electron dropouts at the onset of high-speed-stream-driven storms which follow in
time the slow decay during calms.
5.A Interpretation of Loss: Waves in the Plasmasphere
The greatly enhanced loss of electrons from the outer radiation belt during calms
before storms is believed to be caused by the build up of the outer plasmasphere during the
calms [Borovsky and Steinberg, 2005,2006] leading to pitch-angle scattering of the radiation-
belt electrons by plasma waves in the plasmasphere [Smith et al., 1974; Kelley et al., 1975;
Albert, 2004; Summers et al., 2004; Shprits and Thorne, 2004]. The specific plasma-wave
candidates to pitch-angle scatter the electrons of the outer radiation belt are (whistler-mode)
plasmaspheric hiss [cf. Lyons et al, 1972; Meredith et al., 2006; Lam et al., 2007], lightning-
generated whistlers [cf. Voss et al., 1998; Lauben et a!., 2001; Rodger et al., 2003; Botnik et
al,, 2006], and electromagnetic ion-cyclotron waves [cf. Summers and Thorne, 2003; Albert,
2003].
To clarify the role of the outer plasmasphere, a set of high-speed-stream-driven storms
with outer plasmaspheres is compared to a set of high-speed-stream-driven storms without
outer plasmaspheres. In Figure 5 the temporal profile of the superposed number density of the
outer electron radiation belt is plotted as a function of time for 24 storms with calms
beforehand and for 11 of those storms with calms that also have built-up outer plasmaspheres
at geosynchronous orbit for 2 or more days prior to storm onset. The presence of a built-up
outer plasmasphere is determined by an examination of the Magnetospheric Plasma Analyzer
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Borovsky, Joseph E & Denton, Michael H. Electron loss rates from the outer radiation belt caused by the filling of the outer plasmasphere: the calm before the storm, article, January 1, 2009; [New Mexico]. (https://digital.library.unt.edu/ark:/67531/metadc927261/m1/15/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.