Fig. 6

Schematic drawing of the ionospheric plasma flows associated with a interplanetary magnetic field (IMF) B_y > 0 and b IMF B_y < 0 (based on Cowley et al. (1991)). The dashed line in each panel delineates the open-closed magnetic flux boundary and the circled symbols represent the field-aligned current flows (upward for circles with a dot and downward for circles with a cross). The bottom row shows the field-aligned current system associated with c IMF B_y > 0 and d IMF B_y < 0 (based on Trondsen et al. 1999). The IMF B_y field produces a north–south potential drop across the magnetotail that drives field-aligned currents northward or southward depending on the orientation of IMF B_y