Secondary island induced during magnetic reconnection by an external sub-Alfvénic shear flow

Abstract

Secondary tearing instability induced associated with sub-Alfvénic shear flow during magnetic reconnection processes is investigated using a compressible resistive MHD model. Compared to the without shear flow case, it is found that a secondary island can be built up during the reconnection process with an external sub-Alfvénic shear flow. For further investigation, we also found that the built-up island is not developed so larger due to the pairs of discontinuities formed in the inflow region of the reconnection. For the fixed initial asymptotic shear flow velocity v0, there existing a critical value λvc fastest to excite the secondary island. The critical value λvc may vary with different v0. Although, there is a significant gap for reconnection rates between the simulation results and observations, it can be deduced that the discontinuities can be formed in the situations with sheared flows associated with the magnetic reconnection. The results can be applied to interpret the multiple-X lines reconnections and discontinuities observations at the Earth's dayside magnetopause and magnetotail.