Plasmaspheric Mass Loss and Refilling as a Result of a Magnetic Storm B. W. Reinisch, X. Huang, P. Song, J. L. Green, S. F. Fung, V. M. Vasyliunas, D. L. Gallagher, and B. R. Sandel Using the sounding measurements from the radio plasma imager on IMAGE and a density inversion algorithm, we derive the plasma density profiles along the magnetic field in a few L-shells every 14 hours at local noon before, during, and after the March 31, 2001 magnetic storm. An empirical model of the plasmaspheric density distribution is derived using the measurements before the storm as a reference. During the storm, the equatorial plasma was substantially depleted in a range of L-shells. The flux tubes were refilled after the storm. The filling ratio, the equatorial density normalized by its quiet-time value before the storm, is introduced to assess the time evolution of the depletion and refilling processes. The depletion occurred rather quickly after the storm onset, as determined by the limited temporal resolution of the measurements. The refilling proceeded significantly faster than the theoretical prediction of a 3-day time scale. Dynamic structures are in situ observed and confirmed by the extreme ultraviolet imager (EUV) measurements. _______________ Submitted to Journal of Geophysical Research, 2003