EVOLUTION OF THE EARTH'S DISTANT MAGNETOTAIL: ISEE 3 ELECTRON PLASMA RESULTS.

Electron plasma measurements made by ISEE 3 from October 18, 1982, through April 19, 1983, were examined for signatures identifying the spatial evolution of the earth's magnetotail out to distances of approximately 225 R//E. The lobe density distribution shows two peaks near earth ( less than equivalent to 60 R//E), a narrow peak at approximately 10** minus **2 cm** minus **3 representing quiet lobe, and a second broader peak above 10** minus **1 cm** minus **3 representing boundary layer phenomena. At larger distances the lower density peak disappears and the remaining density peak becomes broader and contains a high density tail which extends well above 1 cm** minus **3. The increase in lobe density at large distances is believed to be due to plasma which crosses the magnetopause on open field lines along its flanks and drifts inward toward the plasma sheet. The plasma sheet density distribution shows only a slight decrease in density at larger radial distances. The temperature of the plasma sheet and lobe electron plasma decreases with increasing distance, with the plasma sheet temperature decreasing at a faster rate.