Computer simulations of asymmetric spontaneous fast reconnection

Abstract

The spontaneous fast reconnection model is extended to the general asymmetric situations, where magnetic reconnection may take place between the field lines that are anchored in different magnetic dipole sources. It is demonstrated for a wide variety of parameters that the asymmetric fast reconnection mechanism can evolve as a nonlinear instability, so that an asymmetric plasmoid swells predominantly in the region of a weaker magnetic field and propagates along the field lines. In the central diffusion region, the secondary tearing is likely to take place and significant erosion of the stronger magnetic field occurs; accordingly, the X neutral point moves with time, where the (current-driven) anomalous resistivity is found to be always locally enhanced, allowing the fast reconnection mechanism to be sustained quasisteadily and extended outwards further. The associated shock structure standing at the boundary of the stronger magnetic field is identified with the ordinary slow shock, in general, combined with an intermediate wave in the presence of sheared field. On the other hand, the shock standing at the boundary of the weaker magnetic field has an intermediate shock-like structure near the diffusion region, which propagates along the shock layer to finally become the ordinary combination of a slow shock and a finite-amplitude rotational intermediate wave at the plasmoid boundary.