Energetic ion regimes in the deep geomagnetic tail: ISEE‐3

During the period January 1 to March 30, 1983, the ISEE‐3 spacecraft was in a previously unexplored part of the distant geomagnetic tail (60‐220 R E ). In two recent papers Slavin et al. (1983) have examined the gross morphology of the distant tail magnetic field, showing that a well‐ordered twin‐lobe structure is retained at these distances, while Bame et al. (1983) have reported plasma measurements for two 12‐hour intervals and have identified the plasma regions observed. In this paper, for the latter time intervals, the energetic ion (35 keV ‐ 1.6 MeV) and magnetic field measurements made by ISEE‐3 are reported and are related to the plasma measurements. The plasma sheet is found to be a region of enhanced fluxes of energetic ions, which are usually flowing unidirectionally tailward. These fluxes often extend outside the plasma sheet as identified in plasma data to form a plasma sheet boundary layer. A simple picture which accounts for these characteristics is given in which reconnection occurs at a neutral line lying Earthward of the spacecraft.