Measurements of early and late time plasmasphere refilling as observed from geosynchronous orbit

Measurements of the cold ion density at geosynchronous orbit obtained by Los Alamos magnetospheric plasma analyzers over the course of 7 years are used to estimate the rate of plasmaspheric refilling at early times in the refilling process (≤24 hours) and at late times (up to several days during intervals of prolonged geomagnetic quiet). While the measured refilling rates are highly variable, we find that plasmasphere refilling at geosynchronous orbit occurs as a two-step process: for early times the refilling rate is ∼0.6-12 cm^-3 d^-1, while for later times the refilling rate rises up to 10-50 cm^-3 d^-1. These results are consistent with a model of plasmasphere refilling which uses Coulomb collisions as a dominant trapping mechanism [see Wilson et al. 1992].