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

Measurements of the cold ion density at geosynchronous orbit obtained by Lo s Alamos magnetospheric plasma analyzers over the course of 7 years are use d to estimate the rate of plasmaspheric refilling at early times in the ref illing process (less than or equal to 24 hours) and at late times (up to se veral days during intervals of prolonged geomagnetic quiet). While the meas ured refilling rates are highly variable, we find that plasmasphere refilli ng at geosynchronous orbit occurs as a two-step process: for early times th e refilling rate is similar to 0.6-12 cm(-3) d(-1), while for later times t he refilling rate rises up to 10-50 cm(-3) d(-1). These results are consist ent with a model of plasmasphere refilling which uses Coulomb collisions as a dominant trapping mechanism [see Wilson et al. 1992].