A coordinated ground-based and IMAGE satellite study of quiet-time plasmaspheric density profiles Z.C. Dent, I.R. Mann, F.W. Menk, J. Goldstein, C.R. Wilford, M.A. Clilverd, and L.G. Ozeke Cold plasma mass density profiles in the plasmasphere have been determined for the geomagnetically quiet day of 19th August 2000 using the cross-phase technique applied to ground-based magnetometer data from the SAMNET, IMAGE, and BGS magnetometer arrays. The cross-phase derived mass densities have been compared to electron densities derived from both ground-based VLF receiver measurements, and from the IMAGE satellite RPI and EUV measurements. The cross-phase results are in excellent agreement with both the VLF and IMAGE observational results, thus validating the cross-phase technique during quiet times. This is the first such coordinated multi-instrument study, and has enabled very few heavy ions to be inferred in hte plasmasphere for L>3.45 on this day. The observational results were also compared to plasma mass densities from the SUPIM model and were found to be in excellent agreement. EUV data also verified the existence of azimuthal structure in the outer quiet-time plasmasphere. _______________ Submitted to Geophysical Research Letters, 2003