Magnetic reconnection in the presence of sheared plasma flow: Intermediate shock formation

Abstract

Classical models of magnetic reconnection consist of a small diffusion region, which is bounded by two pairs of slow shocks. In these models, the plasma is accelerated across the shocks. It has long been postulated that violation of symmetry across the current sheet will lead to the formation of intermediate waves in the current sheet. These asymmetries are important properties of space plasma current sheets. Equally important in space plasmas is the presence of sheared flow across current sheets. In this study, the structure of steady-state reconnection is investigated in the presence of a shear flow across the current sheet with symmetric density and magnetic field strengths using two-dimensional magnetohydrodynamic (MHD) simulations. The results show that for sheared flow above the Alfvén velocity of the inflow regions no steady-state magnetic reconnection occurs. For sheared plasma flow below this critical velocity steady-state reconnection is obtained. A detailed examination of the Rankine–Hugoniot jump conditions reveals that each pair of slow shocks is replaced by a strong intermediate shock and a weak slow shock in the presence of shear flow.