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Introduction

The transpolar potential or cross polar cap potential ( $\Phi_\mathsf{PC}$) is the total variation in the high-latitude ionospheric electric potential and is an important indicator of the amount of energy flowing into and through the magnetosphere-ionosphere (M-I) system. It is a convenient parameter that is often used to compare different methods of calculating electric fields in the high-latitude ionosphere.

Many techniques have been developed to determine a relationship between the upstream solar wind and interplanetary magnetic field (IMF) conditions and $\Phi_\mathsf{PC}$. 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., [2002] 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 ($E_\mathsf{sw}$) increases. The resulting feedback limits the amount of reconnection at the dayside magnetopause thereby limiting the magnitude of $\Phi_\mathsf{PC}$, a behavior known as saturation [e.g., Russell et al., 2001]. Siscoe et al., [2002] 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 $\Phi_\mathsf{PC}$. In this letter we report the first test of the transpolar potential from the Hill model ( $\Phi_\mathsf{PC}^\mathsf{Hill}$) against direct measurements of the potential from Super Dual Auroral Radar Network (SuperDARN) observations ( $\Phi_\mathsf{PC}^\mathsf{SD}$).


next up previous
Next: Procedure Up: Testing the Hill model Previous: Testing the Hill model


Simon Shepherd 2002-06-04