Electrostatic potential patterns in the high-latitude ionosphere constrained by SuperDARN measurements

The recent addition of two radars to the existing network of six Super Dual Auroral Radar Network (SuperDARN) HF radars in the Northern Hemisphere has significantly extended the area in the high latitude where measurements of convecting ionospheric plasma are made. We show that the distribution of t he electrostatic potential Phi associated with the "E x B" drift of ionosph eric plasma can be reliably mapped on global scales when velocity measurmen ts provide sufficient coverage. The global convection maps, or the equivale nt electrostatic potential maps, are solved using an established technique of fitting velocity data to an expansion of Phi in terms of spherical harmo nic functions. When the measurements are extensive, and especially when the y spall the region between the extrema in the potential distribution, the s olution for the global pattern becomes insensitive to the choice of statist ical model data used to constrain the fitting. That is, the statistical mod el data then only guide the solution in regions where no measurements are a vailable, and the details of the model data have little effect on the gross features of the large-scale convection patterns. The resulting total poten tial variation across the polar cap, Phi(PC) is virtually independent of th e statistical model. The ability to accurately determine Phi(PC) and the gl obal potential Phi on the basis of direct measurements is an important step in understanding solar wind-magnetosphere-ionosphere coupling.