Plasmasphere Refilling Rates Inferred from Polar and IMAGE Satellite Spectrogram Data Huegerich, T., J. Goldstein, and P. H. Reiff In situ measurements of electron number density, as inferred from dynamic spectrogram data recorded by the Polar Plasma Wave Instrument (PWI) (1996-97) and IMAGE Radio Plasma Imager (RPI) (2000-01), are used to calculate plasmasphere refilling rates for several refilling events. The Polar and IMAGE satellites follow polar orbits with periods of approximately 18 hours and 14 hours, respectively. Thus, in order to compare subsequent PWI/RPI measurements of electron density at the same local latitude of the corotating plasmasphere, the measurement at a given Magnetic Local Time (MLT) is compared with the corresponding measurement approximately 36/12 hours later at the opposite MLT. Temporal refilling effects are thereby isolated as much as possible from spatial effects due to irregularities in the plasmasphere. This method of observing refilling allows the calculation of refilling rates for a range of L-shells (3 RE