Thermal ion temperatures from the retarding ion mass spectrometer on DE 1

Data from the retarding ion mass spectrometer (RIMS) on Dynamics Explorer 1 are analyzed by means of a thin sheath model to determine ion temperatures. A number of characteristic features of ion temperatures in and near the plasmasphere are presented. Typical H(+) temperatures in the plasmasphere are found to be 4000 K to 6000 K on the morningside and 2000 K to 4000 K on the eveningside, increasing with L throughout. In the plasma trough, typical temperatures observed are a few times 10,000 K. In the outer plasmasphere, multiple temperature components are frequently observed. H(+) and He(+) ions are found to be very close to thermal equilibrium with each other in all but perhaps the outer part of the plasmasphere. Within the plasmasphere, temperature profiles observed by DE 1/RIMS rarely show small-scale variation. During geomagnetically active times, high-altitude temperatures between L = 2 and 3 appear to be depressed over quiet time values, to the extent that they may be cooler than temperatures at low altitudes along approximately the same field line.