A Superposed Epoch Analysis of Two Stage Refilling in the Plasmasphere

Abstract The cold, dense plasma of the plasmasphere is sourced by outflows from the ionosphere, but the refilling process is still poorly understood. Refilling may occur in stages, and studying this process is important to understanding how the ionosphere couples to the magnetosphere. This study examines the two‐stage refilling process of the plasmasphere using data from 42 geomagnetic storms observed during the Van Allen Probes era. We find that two‐stage refilling is characterized by an initial stage of low density plasma which refills slowly, followed by a second stage where the density increases and shows very high variation. We observe two‐stage refilling 40% of the time in events where the plasmasphere was significantly depleted. We find that two‐stage refilling is not strongly correlated with global geomagnetic indices (DST, AE, and Kp), but it is highly dependent on local time and rarely occurs in the noon and afternoon sectors.