On the azimuthal variation of the equatorial plasmapause

Previous results of plasmapause position surveys have been synthesized into a comprehensive description of the plasmapause, taken to represent the boundary between diurnal near-corotation and large-scale circulation streamlines that traverse the entire magnetosphere. The result indicates a plasmapause that has a pronounced bulge in the dusk sector, that rotates sunward and shrinks markedly as geomagnetic activity (and presumably magnetospheric convection) increase. The shape of the plasmapause so determined is significantly different from that associated with the simple superposition of sunward flow and corotation, both in its detailed shape and in its varying orientation. The results imply that the magnetospheric circulation departs from a uniform flow field, having a radial dependence with respect to the Earth that is qualitatively consistent with electrostatic shielding of the convection electric field. Also, the results imply the the inner magnetospheric flow field rotates from duskward to dawnward as its intensity increases