Global Topology and Convection of a Northward IMF Reconnection Event

Using a global resistive MHD simulation and ionospheric satellite data, we examine a northward IMF reconnection event at global separator length scales. This allows a full 3D interpretation of where reconnection occurs on the magnetopause for northward IMF with Bx and By components and for a significant dipole tilt. It also demonstrates that 3D separator reconnection with a northward IMF couples the reconnection electric field and field-aligned currents to the ionosphere to drive sunward convection in a manner that agrees with the satellite measurements of ionospheric sunward flows. We find antiparallel reconnection of the IMF to both open and closed field lines near global nulls in both hemispheres. The reconnection in turn produces both open and closed field lines, propelling both steady and non-steady convection. We discuss for the first time how line tying in the ionosphere and draping of open and IMF field lines over the dusk and dawn flanks of the magnetopause produce torsion within the magnetopause of the reconnected magnetic field lines. The models show that, consistent with Cluster observations, the reconnection geometry is not necessarily a simple two-dimensional hyperbolic structure.