Low-latitude plasma mantle in the near-Earth magnetosphere: Geotail observations

This report provides evidence for the appearance of the plasma mantle at lo w latitudes, Z(GSM) similar to0 A detailed analysis of Geotail observations on January 20, 1996, clarifies the characteristics of the plasma now in th e low-latitude mantle. The tailward flow speed in the mantle is 200-400 km s(-1), smaller than the flow speed (greater than or similar to 400 km s(-1) ) in the adjacent magnetosheath, and flow and field perturbations satisfy t he criteria. for a rotational discontinuity. The velocity component paralle l to the mantle magnetic field line is positively correlated with the ion n umber density, consistent with a boundary layer interpretation. The compone nt of the velocity perpendicular to the magnetic field lines is predominant ly poleward at speeds up to 150 km s(-1). This poleward convection can be i nterpreted as being driven by a J x B force operating on the field lines.