Energetic ion observations of a large scale vortex in the distant geotail

Abstract

We present first observations in the deep tail of the magnetosphere of a vortex structure in both energetic ions (E > 35 keV) and plasma. We observe a vortex, with period about 15 minutes, at X = −217 Re within the energetic ion boundary layer which marks the boundary between the plasma sheet and the southern lobe. The vortex, which was coplanar with the boundary layer, was observed between a region of tailward flow of energetic ions (i.e. the plasma sheet) and a region with no tailward flow (i.e. the southern lobe).