Space Physics Seminar Winter-2018

The dynamics of flow channels and dipolarizations complicate the expected field aligned current pattern during substorms. We have used a global magnetohydrodynamic simulation to investigate how meso-scale magnetotail structures participate in forming the substorm current configuration. We focus, for the most part, on the March 1, 2008 substorm, which was observed by THEMIS spacecraft. The simulation shows a sequence of fast flows and dipolarization events similar to what is seen in the data, though not at precisely the same times or locations. Both earthward and tailward flows were found in both the observations and the simulations. The simulation shows that the flow channels can have convoluted paths that are slowed and diverted as they reach the inner magnetosphere. We will use our simulation results combined with the observations to investigate the global convection systems and current sheet structure during this event, showing how meso-scale structures fit into the context of the overall magnetotail dynamics during this event. Rather than a single current wedge in the tail, several smaller structures are seen at which field aligned currents originate. Our study includes determining the location, timing and strength of several current wedges and expansion onsets during an 8-hour interval. A major consequence of the complex flow structure is the establishment of large scale vortices that start a turbulent cascade that affects transport and reconnection.