Global MHD simulations of Flux Transfer Events under generic southward IMF conditions

Recently, Raeder [Annales Geophys., 24, 2006] proposed a FTE generation mechanism in which Earth's dipole tilt, and the associated movement of the stagnation flow line away from the magnetic separator, results in the formation of a new dayside X line. As a result, a magnetic flux rope forms at the dayside magnetopause, eventually propagating toward one of the polar cusps. In Raeder's simulations, new flux ropes were observed to form periodically at the subsolar magnetopause via this mechanism. Fedder et al. [Journal of Geophys. Res., 107, 2002] proposed an alternative mechanism in which a dayside separator line becomes twisted as intense parallel currents develop along it, eventually undergoing a topological change in which one of the separator's dayside magnetic nulls becomes detached from the separator. As the nulls then move tailward, the flux rope propagates poleward, and the process begins anew. While the Fedder mechanism seems interesting and plausible, the idea has not been quantiatively tested (via a calculation of the time- dependent "magnetic skeleton" -- the system of nulls, separatrices and separators which characterizes the magnetic field topology) with simulations. In this presentation, we use global MHD simulations (the UNH OpenGGCM code) to test the Fedder mechanism by computing the time-dependent magnetic skeleton during time intervals where FTEs are observed under generic southward IMF conditions.