Structure of reconnection layer with a shear flow perpendicular to the antiparallel magnetic field component

Abstract

A one-dimensional resistive magnetohydrodynamic (MHD) simulation of the Riemann problem is carried out for the structure of reconnection layer, i.e., outflow region of quasisteady magnetic reconnection, in the presence of a sheared flow tangential to the initial current (Jy) sheet. Unlike previous studies, the shear flow is in the y direction, perpendicular to the antiparallel component of the magnetic field Bz, with a total change of flow ΔVy≠0 across the current sheet. Cases with symmetric or asymmetric current sheet and various guide magnetic fields By are investigated. The simulation shows that in the reconnection layer, the structure of MHD discontinuities changes significantly with the strength of the shear flow. The main findings are the following: (1) In the case initially with a zero guide field (By=0, for the so-called “antiparallel reconnection”), the shear flow in Vy produces a finite By in the reconnection layer and two time-dependent intermediate shocks with rotation angle of tangential magnetic field less than 180°. (2) For initial By≠0 (the “component reconnection”) the sheared Vy leads to very different magnetic field structures in the two outflow regions on the two sides of the X line. (3) In the cases with the initial By≠0, the existence of the sheared Vy can lead to the reversal of the rotation sense of tangential magnetic field through the reconnection layer. The critical value of ΔVy for the occurrence of this field reversal is discussed. The general simulation results can be applied to space and laboratory plasmas.