Spatial variation of Joule heating and its relationship with the motion of polar cap boundary

During geomagnetic storms and magnetospheric substorms solar wind-magnetosphere interaction plays a crucial role in determining the magnitude of the energy transferred to the magnetosphere system. Total energy transferred to the magnetosphere system dissipates mainly in four channels: ring current enhancement, auroral particle precipitation, Joule heating, and plasmoid release. Auroral particle precipitation and Joule heating constitute the part of energy deposited to the ionosphere via magnetosphere-ionosphere (MI) current systems. In this study, we examine four substorm cases that occurred during March 2008. The conditions were simulated with SWMF/BATSRUS MHD model for each substorm case and Joule heating rates were calculated. Magnetic latitude and magnetic local time (MLT) dependence of the Joule heating were inspected according to the phases of the substorms, which are growth, expansion and recovery phases respectively. As a result, we have seen that the energy was transferred to lower latitudes during substorm expansion phase and the polar cap boundary enlarged as a result of the magnetic reconnection on the dayside. With the start of the recovery phase, the polar cap region started to contract. Joule heating dissipation was found to be greater in the night sector (20-24 MLT) when the expansion phase reaches its maximum while it was greater in the dawn (06 MLT) and dusk (18 MLT) sectors just after the onset and during the recovery. In this study, the relationship between the joule heating amount in the upper atmosphere and the motion of the polar cap boundary is being investigated using SWMF/BATSRUS MHD model and the preliminary results will be presented.