Plasma regimes in the deep geomagnetic tail: ISEE 3

Using a lunar gravitation‐assisted orbit, the ISEE‐3 spacecraft remained close to and within a previously unexplored part of the distant (60‐220 R E ) geomagnetic tail nearly continuously from 1 January to 30 March 1983. An initial analysis of data obtained with the Los Alamos plasma electron analyzer onboard ISEE‐3 reveals that all of the plasma regimes identified previously with near‐earth measurements (i.e., plasma sheet, low‐latitude boundary layer, plasma mantle, lobe, and magnetosheath) remain recognizable entities in the distant tail as well. However, these regimes appear to be intermingled in a more chaotic fashion than near the earth. Typical flow velocities within the plasma sheet at ∼200 R E in this preliminary analysis are ∼500 km s −1 tailward, considerably higher than is characteristic of the near‐earth plasma sheet. Earthward flow within the plasma sheet has been observed occasionally, suggesting the temporary presence of a neutral line beyond 220 R E . Strong bi‐directional electron anisotropies are found throughout much of the distant plasma sheet, boundary layer, and magnetosheath.