Influences Of Sub-Alfvénic Shear Flow On Tearing Mode Instability

Magnetic reconnection associated with the change of magnetic field topology plays an important role on which magnetic energy can be transferred into plasma kinetic energy and plasma thermal energy.Magnetic reconnection has been used to explain many natural phenomena of the sudden release of magnetic energy.Since plasma shear flow is ubiquitous in both space and laboratory plasmas,it is worth investigating an impact of the plasma shear flow in some instabilities such as the tearing mode instability.In this paper,we adopt the numerical simulation to study the sub-Alfvenic shear flow influence on tearing mode stability.Based on compressible resistive MHD model and compressible Hall MHD model,we investigate the plasma beta and Hall effects on the reconnection rate in the presence of sub-Alfvenic shear flow.We fix the asymptotic velocity of shear flow and vary the half width of shear flow.We find that the shear flow can either stabilize or destabilize the tearing mode instability.In the cases of high plasma beta(β=5.0,β=2.0),when the half width of shear flow exceeds a threshold value,the shear flow can boost the tearing mode instability,that is,the peak reconnection rate is much higher than the case in the absence of shear flow,which is in a good agreement with the results from incompressible simulation;in the cases of low plasma beta(β=0.5,β=0.2),though the shear flow can destabilize the tearing mode,the boosting effect nearly disappears,that is,when increasing the half width of shear flow,the peak reconnection rate is still close to the case without shear flow,which is associated with the presence of a pair of discontinuities in the upper and lower inflow region.We believe that the shear flow influence on reconnection rate can be explained by studying the distribution and strength of perturbed vortex at the Y direction.With the inclusion of the Hall effect,shear flow can still either stabilize or destabilize magnetic reconnection,but when the ion inertial length d is large,in other words,the Hall effect is strong,the boosting effect becomes weak since the reconnection rate is already large without considering shear flow.