Plasma sheet motions inferred from medium-energy ion measurements

Medium-energy ions (E>25 keV) measured by the ISEE 2 satellite are used to provide information on plasma sheet motions during expansions following substorms. We show that the upward speed of the plasma sheet edge measured locally is commonly approx.50 km/s, a value high in comparison with two-satellite measurements. It is thought that waves in the form of field-aligned corrugations of the sheet boundary may be responsible for the high speeds measured in some cases. The boundary between the lobe and plasma sheet intensity fluxes is about 2 R/sub g/ thick at the ion energies looked at, or 1000--3000 km. After the passage of the plasma sheet boundary, particle fluxes drifting downward toward the neutral sheet are often encountered. This is interpreted as an E x B drift, in which case the electric field is about 1 mV//m. This could imply high cross-tail potentials. At the outer boundary of the plasma sheet, it is found that the streaming ion layer recently reported by Moebius et al. [1980] and Spjeldvik and Fritz [unpublished manuscript, 1980] shows a peaked spectrum that softens as the plasma sheet is approached. The observation of a rising plasma sheet boundary, downward-drifting flux tubes, and the behavior of the streaming ion layer are consistent with the tailward motion of a source region together with a cross-tail electric field. The data can be interpreted to show that the source region when the plasma sheet 20 R/sub E/ downtail has expanded to about 6 R/sub E/ is approx.50 R/sub E/ down the tail