Hall Magnetohydrodynamics Simulations of Separator Collapse

We compare MHD and Hall MHD simulations of magnetic separator collapse in two and three dimensions. Using a newly developed Hall MHD solver, we investigate how the collapse of two-dimensional X type magnetic nulls and three-dimensional null-null separator loops depends on the ratio of the magnetic field gradient scale length to the ion inertial length. In particular, we address the question of whether extended thin current sheets (as opposed to more localized Petschek-like diffusion regions) form in very large systems. Implications for magnetic reconnection at Earth's dayside magnetopause are discussed.