The response of Jupiter's coupled magnetosphere-ionosphere system to changes in the solar wind and the release of plasmoids in the magnetotail: Results from global MHD simulations

Joint observations by the HST and in situ spacecraft have shown that the brightness of Jupiter's aurora appears to be correlated with solar wind dynamic pressure enhancement, despite theoretical work predicting the opposite. In this study, we use a time-dependent global MHD model (Sarkango et al., 2019, JGR) to investigate the response of Jupiter's coupled magnetosphere-ionosphere system to different types of changes in the upstream conditions, such as IMF rotation and forward interplanetary shock. Our model solves the single fluid semi-relativistic ideal MHD equations and self-consistently includes the mass loading associated with the Io plasma torus through the addition of source and loss terms. Using our model, we show that the response of the corotation enforcement currents (which we assume are a proxy for auroral brightness) to a shock-induced compression varies significantly with local time, with currents being depleted on the dayside and moderately enhanced on the nightside. Plasmoids are frequently seen in our model due to tail reconnection and plasmoid release occurs more frequently during periods of high solar wind dynamic pressure. The release of plasmoids is often accompanied with reduction of the net open flux in the polar regions as well as decrease in the intensity of corotation enforcement currents, consistent with the idea that the magnetosphere returns to a less stressed state after plasmoid release. Plasmoids originating on closed field lines are found to temporarily create a region of closed flux deep inside the polar cap that originally only contains open magnetic field lines, which diminishes in size as the plasmoid moves tailward and interacts with the surrounding plasma. Our results together show that the polar regions of Jupiter are highly dynamic and the formation and release of plasmoids further complicates the dynamics through large-scale reconfiguration of the magnetic field topology.