THE ROLE OF INTERMEDIATE SHOCKS IN MAGNETIC RECONNECTION

The structure of discontinuity layers associated with magnetic reconnection is studied by numerically solving the Riemann problem for the evolution of an initial current sheet, which separate two plasma regions with anti-parallel magnetic field components in the z direction and a common guide magnetic field in the y direction. In the presence of a non-zero normal component of magnetic field, B(x), the initial current sheet evolves into a system of MHD discontinuities. For the initial current sheet with a zero guide field (B(y) = 0), steady intermediate shocks, slow shocks, slow expansion waves, or contact discontinuity are observed to develop. However, for the current sheet with a non-zero guide field (B(y) not-equal 0), time-dependent intermediate shocks (TDIS), instead of steady intermediate shocks, are observed to bound the reconnection layer. The magnetic fields across the TDIS are non-coplanar and the width of the TDIS expands self-similarly as square-root t. The TDIS gradually evolves toward a rotational discontinuity.