Plasmapause Morphology Determined from an Empirical Ionospheric Convection Model

The steady state electric potentials derived from empirical ionospheric onvection models were mapped to the magnetospheric equatorial plane and added to the Earth's rotational field to examine the local time dependence of the plasmapause radius. The last closed equipotential line was assumed to be the plasmapause. The sensitivity of plasmapause shape and size derived in this way was studied by varying the z and y components of the interplanetary magnetic field (IMF) and the geomagnetic a tivity index Kp. Results how that the Heppner and Maynard model produces plasmasphere morphology that is broadly consistent with prior ground-based and satellite measurements of plasmapause position. Our model results show that the largest change in the characteristic shape of the plasmapause i due to the direction of IMF Bz; for IMF Bz southward, the plasmapause is circular, while a broad oval plasmapause (with a bulge at 2100 UT) is found for IMF Bz northward. The ability of our model to reproduce the Lpp-LT shape of the plasmapause as found by previous observations shows that empirical ionospheric convection models can be extended to provide a useful method to determine plasmapause location for a variety of steady geomagnetic conditions.