Testing the Hill model of transpolar potential using Super Dual Auroral Radar Network observations

We use a data set consisting of periods for which the transpo-lar ionospheric potential (pc) is well-determined by Super Dual Auroral Radar Network (SuperDARN) data to test the Hill model. The Hill model, as formulated by Siscoe et al. [2002], specifies pc as a function of solar wind speed and ram pressure, the interplan-etary magnetic field, the reconnection electric field (Er), and the ionospheric conductance (). The periods used in our study were identified as times when the interplanetary electric field was quasi-stable and SuperDARN coverage was sufficient to determine pc. SuperDARN-determined pc (SDpc) is compared to pc determined using the Hill model (Hillpc) for 1317 10-min periods. A minimum in the root-mean-square difference between SDpc (Er) and Hillpc (Er) is achieved when = 23 S and a constant potential, 0 = 17 kV, are used. Some aspects of the data agree very well for these values of and 0, including the mean value of pc(Er) and that both data sets clearly indicate saturation at higher values of Er. The ram pressure dependence of Hillpc, however, is inconsistent with that of SDpc and suggests that should be lower than 23 S. There is also significantly more variability in SDpc for all values of Er than the Hill model predicts. 1