A 2-DIMENSIONAL HYBRID SIMULATION OF THE MAGNETOTAIL RECONNECTION LAYER

Two-dimensional (2-D) hybrid simulations are carried out to study the structure of the reconnection layer in the distant magnetotail. In the simulation an initial current sheet separates the two lobes with anti parallel magnetic field components in the x direction. The current she et normal is along the z direction. It is found that a leading bulge-l ike magnetic configuration and a trailing, quasi-steady reconnection l ayer are formed in a magnetic reconnection. If the duration of the rec onnection is sufficiently long, the trailing reconnection layer will d ominate the plasma outflow region. For the symmetric lobes with B-y = 0, two pairs of slow shocks are present in the quasi-steady reconnecti on layer. The slow shocks are expected to be fully developed at a suff icient distance from the X line, where the separation between the two shocks is greater than a few tens of the lobe ion inertial length. The Rankine-Hugoniot jump conditions of the slow shock are found to be be tter satisfied as the distance from the X line along the x axis increa ses. For the cases with B-y not equal 0 in the two lobes, two rotation al discontinuity-like structures appear to develop in the reconnection layer. On the other hand, in the leading bulge region of a magnetic r econnection, no steady MHD discontinuities are found. Across the plasm a sheet boundary layer the increase of the how velocity appears to be much smaller than that predicted from the Rankine-Hugoniot jump condit ions for a steady discontinuity, and the increase in the ion number de nsity is much larger. In addition, a large increase in the parallel io n temperature is found in the plasma sheet boundary layer. The 2-D sim ulation results are also compared with the one-dimensional hybrid simu lations for the Riemann problem associated with the magnetotail reconn ection. It is found that the 2-D effects may lead to the presence of t he non-switch-off slow shocks and thus the lack of coherent wave train s in slow shocks.