Supply of Plasma to the Inner Magnetosphere: Plasmasphere Refilling B.R. Sandel, M.H. Denton, and J.L. Green A fundamental aspect of the coupling between Earth's ionosphere and inner magnetosphere is the flow of ionospheric plasma that supplies material to the plasmasphere. Using global observations of the He+ column abundance made by the IMAGE Extreme Ultraviolet Imager (EUV), we investigate refilling of the plasmasphere after erosion events associated with geomagnetic storms. Owing to its global view, EUV can measure many radial profiles of column abundance simultaneously; such information cannot presently be obtained by other means. To minimize the confounding effects of phenomena other than refilling, we first focus on an usually quiet period of several days beginning on 27 June 2001. Just prior to this time, a moderate erosion event moved the plasmapause inward to L=3-4. During the next three days, the plasmasphere refilled so that the plasmapause moved outward past geosynchronous orbit. For this and four additional similar but less ideal periods, we follow the time history of He+ column abundances. By converting the column abundances to volume abundances, we compute refilling rates at the plane of the magnetic equator. The inferred rates are generally consistent with earlier measurements made over limited spatial ranges and with the predictions of some models. Radial profiles of our refilling rates for all five study periods are roughly proportional to L-4, and the profile given by 150 L-4 He+ cm-3 h-1 fits results from all periods to within a factor of slightly more than 2. Using nearly-contemporary measurements of plasmaspheric electron densities made by IMAGE RPI, we investigate possible inter-species differences in refilling rates, and examine temporal and spatial variations in the ratio n(He+)/n(e). We compare our measurements with the predictions of the Sheffield University Plasmasphere Ionosphere Model (SUPIM). The model solves the equations of continuity, momentum and energy balance that describe the physical and chemical processes occurring along closed field lines, and output from the model includes the He+ and electron abundances. Comparing the model results to the azimuthally-averaged measurements shows excellent agreement, both in the rates of refilling as a function of radial distance and in the final shape of the radial profile of He+ column abundance. A more detailed view, including analysis of azimuthal structure in the EUV images, suggests that the refilling rate is not always uniform in azimuth. _______________ Global Aspects of Magnetosphere-Ionosphere Coupling, 2006 Yosemite Workshop, Yosemite National Park, CA, USA, 7-10 February 2006