Characteristics of high‐speed ion flows in the plasma sheet

Abstract

Using 8 months of tail data obtained with the AMPTE/IRM satellite, more than 270,000 ion moments and magnetic field measurements were analyzed with respect to the occurrence rates and typical characteristics of high‐speed ion flows with velocities in excess of 400 km/s. The occurrence rates in the plasma sheet boundary layer, the outer central plasma sheet and the neutral sheet neighborhood have a 4∶1∶2 ratio for flows of 400–600 km/s. For flows in excess of 800 km/s, there is only a minimal chance to detect them in the outer central plasma sheet but equal chances in the two other regions. For high AE the chances to detect high‐speed flows in the inner central plasma sheet are greater than to find them in the plasma sheet boundary layer. In the outer central plasma sheet the high‐speed flow occurrence rate is small and independent of AE. In all three regions the largest occurrence rates are found near the midnight meridian at the largest radial distances accessible to IRM. High‐speed flow occurrence rates and ion densities are anticorrelated. The high‐speed flows are bursty with the majority of the flows lasting less than 10s. The occurrence of the high‐speed flows is strongly peaked in the sunward direction. Virtually no tailward high‐speed ion flow could be detected. About 60–70% of all high‐speed flows near the neutral sheet have a dominant component perpendicular to the magnetic field and are associated with comparatively large northward and duskward magnetic field directions. At times, also appreciable duskward flow components appear. Overall, our results indicate that both the plasma sheet boundary layer and the inner central plasma sheet are important regions for the dynamics of the Earth's plasma sheet.