GEOPHYSICAL RESEARCH LETTERS, VOL. 29, 10.1029/2002GL015426, 2002

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

S. G. Shepherd
Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire
J. M. Ruohoniemi and R. A. Greenwald
Applied Physics Laboratory, Johns Hopkins University, Laurel, Maryland
Received 3 May 2002; revised 26 June 2002; accepted 31 June 2002; published xx month 2002.

Abstract:

We use a dataset consisting of periods for which the transpolar ionospheric potential ( $\Phi_\mathsf{PC}$) is well-determined by SuperDARN data to test the Hill model. The Hill model, as formulated by Siscoe et al., [2002], specifies $\Phi_\mathsf{PC}$ as a function of solar wind speed and ram pressure, the interplanetary magnetic field, the Kan-Lee reconnection electric field ($E_\mathsf{KL}$), and the ionospheric conductance ($\Sigma$). The periods used in our study were identified as times when the interplanetary electric field was quasi-stable for $\ge$40 min and the SuperDARN coverage was sufficient to determine $\Phi_\mathsf{PC}$. The SuperDARN-determined $\Phi_\mathsf{PC}$ ( $\Phi_\mathsf{PC}^\mathsf{SD}$) is compared to $\Phi_\mathsf{PC}$ determined using the Hill model ( $\Phi_\mathsf{PC}^\mathsf{Hill}$) for 1317 10-min periods between February 1998 and December 2000. A minimum in the RMS difference between $\Phi_\mathsf{PC}^\mathsf{SD}$($E_\mathsf{KL}$) and $\Phi_\mathsf{PC}^\mathsf{Hill}$($E_\mathsf{KL}$) is achieved when $\Sigma$ = 23 S and a constant potential, $\Phi_0$ = 17 kV, are used. Some aspects of the data agree very well for these values of $\Sigma$ and $\Phi_0$, including the mean value of $\Phi_\mathsf{PC}$($E_\mathsf{KL}$) and that both datasets clearly indicate saturation at higher values of $E_\mathsf{KL}$. The ram pressure dependence of $\Phi_\mathsf{PC}^\mathsf{Hill}$, however, is inconsistent with that of $\Phi_\mathsf{PC}^\mathsf{SD}$ and suggests that $\Sigma$ should be lower than 23 S. There is also significantly more variability in $\Phi_\mathsf{PC}^\mathsf{SD}$ for all values of $E_\mathsf{KL}$ than the Hill model predicts. These comparisons to observations will be useful in assessing, and perhaps refining, the Hill model of Siscoe et al., [2002].