Geotail survey of ion flow in the plasma sheet:: Observations between 10 and 50 RE

One-minute samples of the velocity distributions of ions are used to compute plasma moments for the 18-month period between December 1, 1994 and Tune 1, 1996. Statistical analyses of these measurements are given for the plasma sheet and its boundary layer at radial distances from Earth between 10 and 50 R-E Analysis concentrates on examination of parallel and perpendicular components of bulk flow and is directed toward understanding processes that affect transport. On average, the perpendicular components of the bulk flow are small, less than 15 km/s. On the basis of this study, two distinct patterns emerge. First, at radial distances from Earth less than 30 R-E the mean perpendicular flow indicates a well-defined pattern of convection that is a combination of drift toward Earth and drift toward the flanks. The average electric field across the tail is inferred to be 0.1 mV/m. Second, there is a notable increase in the variability of the perpendicular flow speeds beyond 25 R-E Al relatively large bulk flows with speeds in the range 200 to 800 km/s are sometimes found in the tail at lesser radial distance, these are primarily field-aligned and thus do not contribute substantially to convection or to the transport of magnetic flux.