Global view of refilling of the plasmasphere

Abstract

We use observations by the IMAGE Extreme Ultraviolet Imager (EUV) to characterize the outflow of He+ from the ionosphere to the plasmasphere under quiet conditions. The view afforded by the IMAGE orbit encompasses the entire plasmasphere in a single exposure, enabling us to examine for the first time the globally- averaged properties of plasmasphere refilling. We focus on a study period that begins with a moderate erosion event, and follow refilling during multiple orbits for a period of 69 hours. The inferred volume refilling rate, averaged over azimuth and time, ranges from ∼1 He+ cm-3 h-1 at L = 3.3 to ∼7 × 10-2 He+ cm-3 h-1 at L = 6.3 and is generally consistent with earlier, more local measurements. We show that the measured radial abundance profiles match those predicted by the Sheffield University Plasmasphere Ionosphere Model (SUPIM) for 2 ≤ L ≤ 4. Copyright 2007 by the American Geophysical Union.