Dependence of SuperDARN cross polar cap potential upon the solar wind electric field and magnetopause subsolar distance

Abstract

Dependence of the cross polar cap potential (CPCP) upon the interplanetary electric field (IEF), solar wind ram pressure, and magnetopause standoff distance (RMS) are investigated by considering the Super Dual Auroral Radar Network (SuperDARN) HF radar data on the CPCP and information on the solar wind and interplanetary magnetic field from ACE satellite. Data of up to IEF ∼12 mV/m are available. The CPCP scatterplot versus IEF shows a linear increase between 0 and ∼3 mV/m. For larger IEFs, the rate of the CPCP growth decreases, and the dependence eventually saturates. If the same data are arranged in groups of RMS values, linear dependences were found for each group, but the slope of the regression line increases with RMS. The inferred linear fit lines of CPCP versus IEF for various RMS groups intersect each other at IEF ∼3 mV/m. This number is found to be unique because for the IEF above it (below it), the CPCP decreases (increases) with the solar wind ram pressure. This value also corresponds to the condition of the solar wind magnetic field at the subsolar point to be equal to the Earth's dipole magnetic field, as previously reported by Siscoe et al. (2002). Presented analysis suggests that the magnetopause standoff distance (the length of the merging X line) is an important factor in the CPCP saturation.