Temporal evolution of the transpolar potential after a sharp enhancement in solar wind dynamic pressure

Abstract

Recent studies of ionospheric convection have shown that sudden enhancements in solar wind dynamic pressure have significant effect on the transpolar potential and the coupling efficiency between the solar wind and the terrestrial magnetosphere. Super Dual Auroral Radar Network observations of the dayside convection have demonstrated that the strength of convection correlates well with solar wind dynamic pressure variations, implying an enhancement of dayside reconnection induced by changes in solar wind pressure. At the same time, dynamic pressure increases have been shown to lead to closing of the polar cap, particularly on the nightside, and thus directly drive enhanced tail reconnection. The enhanced dayside and nightside reconnection potentials can both lead to changes in the transpolar potential, but their individual contributions and the balance between the two is not known. We present a case study of the transpolar potential evolution after a long-lasting solar wind pressure step increase. We show that the potential first rises in response to the increase in pressure, then gradually subsides a few hours later despite the solar wind pressure remaining high. We interpret this behavior in terms of pressure-driven changes in dayside and nightside reconnection. Copyright 2008 by the American Geophysical Union.