ON THE KINETIC STRUCTURE OF THE MAGNETOTAIL RECONNECTION LAYER

The structure of the reconnection layer in the magnetotail is studied by solving the Riemann problem of the decay of a current sheet with a normal magnetic field component using 2-D hybrid and Hall MHD simulati ons. In the first run a segment of the reconnection layer obtained fro m a hybrid simulation of reconnection is used as initial state in a pe riodic system. The thin central current sheet be comes instable in the direction parallel to the current sheet: the electrical current becom es filamentary and a warped magnetic field structure develops. In a se cond run, where the initial state is a Harris sheet with a superposed normal magnetic field component, a similar behavior is found. In both cases the boundary of the layer is not bounded by slow mode switch-off shocks and no large-amplitude rotational wave train develops within t he layer, in contrast to 1-D hybrid simulations of the same Riemann pr oblem. The corresponding 2-D Hall MHD simulation results in a stable l ayer bounded by slow-mode switch-off shocks.