Friday

SMILE will be ideally positioned to observe the coupling between the solar wind and Earth’s magnetosphere during northward IMF conditions, through both high latitude in situ observations and imaging of the auroral response. Two linked phenomena that are associated with northward IMF are the presence of hot plasma populations within the lobes, and transpolar arcs (auroral features which extend from the nightside into the polar cap). Previous studies have utilised in-situ and auroral observations to show that both the hot plasma and transpolar arc are likely to form on closed field lines and are consistent with a mechanism in which magnetotail reconnection builds up closed field lines which become “stuck” in the lobe (Milan et al., 2005).

We present an MHD simulation using the Grand Unified Magnetosphere-Ionosphere Coupling Simulation (GUMICS), in which we analyse the topology changes of the field lines in the magnetotail and compare these to observation-based mechanisms for the formation of transpolar arcs and the presence of energetic plasma in the lobe regions. Preliminary analysis shows that a large closed field line region can form in a manner consistent with recent spacecraft observations, initially at low latitude plasma sheet regions but subsequently expanding into the high latitude lobes. We discuss the similarities between the structures seen as a result of these runs and the Milan et al. (2005) magnetotail reconnection model. The run we use was previously examined by Kullen & Janhunen (2004), and we also discuss our findings in the context of their interpretation.