Magnetic reconnection with large separatrix angles

Abstract

A two‐dimensional incompressible MHD simulation model is developed to study magnetic reconnection with large magnetic separatrix angles. It is found that the normal magnetic field on the inflow boundary plays an important role in determining the reconnection configuration. When the normal magnetic field on the inflow boundary is large, steady state reconnection with large magnetic separatrix angles is obtained. When the normal magnetic field is small, a localized resistivity is required to maintain the steady state Petschek‐like reconnection configuration, which has small magnetic separatrix angles. Field‐aligned plasma jets are observed when the normal magnetic field and magnetic Reynolds number Rm are large. The plasma jets are located slightly downstream of the magnetic separatrices and each plasma jet consists of two parts: (1) a slow‐mode shock and (2) a fast‐mode compressional structure. The length and width of the diffusion region depend on the values of Me, Rm, and the normal magnetic field on the inflow boundary. For a fixed normal inflow magnetic field the diffusion region becomes longer and thinner as Me becomes larger; the width of the diffusion region decreases with an increasing Rm, while the length of the diffusion region has a minimum value at about Rm = 500. The length of the diffusion region increases with a decreasing normal magnetic field, while the width does not change remarkably. It is also found that the multiple X line bursty reconnection tends to occur with the development of tearing‐mode instability in cases with a large Me, a large Rm, or a small normal magnetic field on the inflow boundary.