A MHD Simulation Study Of Magnetic Reconnection Dynamics With Streaming Flows

Magnetic reconnection is a fundamental process in plasma physics, which usually occurred in the shear magnetic fields and influenced by the various parameters around the plasma. The streaming flows, which are universally detected in space and laboratory plasma, can play an important role on magnetic reconnection.Based the compressible MHD model, a series of numerical simulations is carried out to study how the streaming flows affect magnetic reconnection under various balance parameters, such as the strength and width of the streaming flow as well as plasma beta β. We also analyze the properties of the discontinuity formed in magnetic reconnection.In Chapter 1, a review on magnetic reconnection, tearing mode and shock wave is introduced. The importance of streamer shear flow on magnetic reconnection is also elucidated.In Chapter 2, the linear dynamic evolution of tearing mode is systematically investigated with sub-Alfvenic streamer flow for different flow thicknesses and plasma betas. It is found that the growth rate of the tearing mode instability is larger than that without the streaming flow. With the streaming flow, there exist two Alfvenic resonance layers near the central current sheet. These resonance layers can enhance the development of the tearing mode for a narrower streaming flow. For a broader streaming flow, a larger separation of Alfvenic resonance layers suppress the magnetic reconnection. The linear growth rate decreases with increase of the streaming flow thickness. The growth rate of the tearing instability also depends on the plasma beta (β). When the streaming flow is embedded in the current sheet, there exists a specific value βs corresponding to the maximum growth rate, which can be attributed to competition between the suppressing effect of β and the enhancing effect of the streaming flow on the magnetic reconnection. The critical value βs increases with increase of the streaming flow strength.In Chapter 3, the nonlinear dynamic evolution of the tearing mode is systematically investigated with sub-Alfvenic streamer flow for different flow thicknesses and plasma betas. It is found that the exhausting flow velocity in the outflow region mainly depends on the nonlinear convective term (-v·▽v) in MHD equations. The inflow towards the neutral current sheet is the result of competition between electromagnetic force and thermal pressure. With the increase of the streaming shear flow thickness, the time evolution of magnetic reconnection rate changes from a multi-peak profile to a single-peak profile. With combination of a streaming flow and a shear magnetic field, a bifurcation structure of the current distribution emerges in the initial current sheet, which is consistent with the results from geomagnetic tail observations. The central current density largely increases. It is also found that the maximum central current density increases with the decrease of the plasma beta.In Chapter 4, The dynamics of magnetic reconnection with sub-or super-Alfvenic streaming flow have been investigated on the basis of compressible resistive MHD model. In the nonlinear growth phase of magnetic reconnection, it is found that a pair of shocks is generated in the inflow region of magnetic reconnection. The oscillating phenomenon of magnetic reconnection with streaming flow are associated with the relative positions of the shocks generated in the inflow region.In the final Chapter, the conclusions and the future researches are discussed.