Statistical Study of the Effect of Long-duration, Solar Wind Dynamic Pressure Step Increases on the Transpolar Potential

It has long been established that the Interplanetary Magnetic Field (IMF) is the major contributor to geomagnetic activity on Earth. Recent studies have shown that the solar wind dynamic pressure can also have significant global effects on the terrestrial magnetosphere. In particular, it has been shown, using Defense Meteorological Satellite Program (DMSP) measurements, that solar wind dynamic pressure enhancements significantly increase the transpolar potential and the solar wind/magnetosphere coupling efficiency. It was previously suggested, based on the DMSP data, that solar wind dynamic pressure fronts induce enhanced magnetotail reconnection. Furthermore, Super Dual Auroral Radar Network (SuperDARN) observations show that solar wind pressure fronts induce significantly enhanced ionospheric convection in the dayside ionosphere, implying an increase in dayside reconnection. Thus both enhanced dayside and magnetotail reconnection, and an increase in polar cap convection and the cross-polar-cap potential occur after a sharp increase in solar wind dynamic pressure. Case studies of long-duration solar wind pressure steps indicate that the potential first rises in response to the increase in pressure, but gradually subsides a few hours later despite the solar wind pressure remaining high. We conduct a statistical study of the effect of long-duration solar wind dynamic pressure step increases on the transpolar potential temporal evolution. Our results, consistent with the individual case studies, show the transpolar potential increasing after the increase in pressure, reaching a maximum 2-3 hours after impact. It then falls again within one hour perhaps to slightly higher values than before the pressure front impact. The results are discussed in relation to enhancements in magnetospheric reconnection induced by a solar wind pressure front.