Magnetotail reconnection: Current diversion and field‐aligned currents

We have used a three‐dimensional resistive and compressible MHD code to study reconnection in a magnetotail configuration. The initial state is a two‐dimensional equilibrium with a northward magnetic field component B z across the current sheet. Reconnection is initiated by applying a finite resistivity localized in the near‐Earth region with a finite extent in the dawn‐dusk direction. The inflow of plasma in the equatorial plane into the reconnection region from dawn and dusk and the divergence of the fast earthward and tailward flow from the reconnection region toward dawn and dusk leads to a magnetic shear. Both this shear and the dipolarization over a limited dawn‐dusk extent are responsible for region 1 field‐aligned currents earthward and tailward of the neutral line. The occurrence of the shear is independent of a particular initial equilibrium, i.e., region 1 field‐aligned currents will also occur during reconnection in a one‐dimensional current sheet when the reconnection line has a limited extent. We also obtained region 2 field‐aligned currents at lower z values near the earthward boundary.