During storms, the plasmapause moves inward due to the enhanced solar wind driving, while a drainage plume develops in the dusk sector (Elphic et al., 1996). Within this plume, the cold plasma flows outward toward the magnetopause thus escaping from the plasmasphere. In the nightside, the inward motion of the plasmapause is of the order of 0.5 RE/h, with the changes following the interplanetary magnetic field variations with 20 – 30 min delay (Spasojević et al., 2003). After the field lines reconnect at the magnetopause, they convect over the polar cap toward the magnetotail, thus providing an additional source of plasma to the tail plasma sheet during storms (Elphic et al., 1997). As the storm driving subsides, the plasmasphere slowly recovers its quiet-time size. The recovery time scale is associated both with the recovery of the quiet-time electric field structure and with the outflow time scale of the cold plasma from the ionosphere. As discussed below, the location of the plasmapause during storms has been shown to be a significant factor in determining the fate of the relativistic electron population in the outer van Allen belt.
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