Many techniques have been developed to determine a relationship between the upstream solar wind and interplanetary magnetic field (IMF) conditions and . Some of these include spacecraft measurements of the convecting plasma [Heppner, 1972; Reiff et al., 1981; Doyle and Burke, 1983; Rich and Hairston, 1994; Boyle et al., 1997; Weimer, 2001], assimilation of ground and satellite measurements such as the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) technique [Richmond and Kamide, 1988], fitting ionospheric line-of-sight (LOS) convection velocities from ground-based radars to functional forms of the electrostatic potential [Ruohoniemi and Baker, 1998], and global magnetospheric modeling codes [Fedder and Lyon, 1987; Raeder et al., 2001; Ridley, 2001].
Siscoe et al.,  has proposed a formulation of a theoretical model, the Hill model [Hill et al., 1976], which takes into account M-I coupling by Region 1 currents that act to effectively reduce the strength of the magnetic field at the magnetopause merging region as the solar wind electric field () increases. The resulting feedback limits the amount of reconnection at the dayside magnetopause thereby limiting the magnitude of , a behavior known as saturation [e.g., Russell et al., 2001]. Siscoe et al.,  compared the Hill model with results from a global magnetospheric MHD model, the Integrated Space Weather Model (ISM), and found good agreement in terms of both Region 1 currents and . In this letter we report the first test of the transpolar potential from the Hill model ( ) against direct measurements of the potential from Super Dual Auroral Radar Network (SuperDARN) observations ( ).