Fast Magnetic Reconnection in Free Space: Self‐similar Evolution Process

We present a new model for time evolution of fast magnetic reconnection infree space, which is characterized by self-similarity. Reconnection triggeredby locally enhanced resistivity assumed at the center of the current sheet canself-similarly and unlimitedly evolve until external factors affect theevolution. The possibility and stability of this type of evolution are verifiedby numerical simulations in a very wide spatial dynamic range. Actualastrophysical reconnection in solar flares and geomagnetospheric substorms canbe treated as an evolutionary process in free space, because the resultantscale is much larger than the initial scale. In spite of this fact, most of theprevious numerical works focused on the evolutionary characters stronglyaffected by artificial boundary conditions on the simulation boundary. Our newmodel clarifies a realistic evolution for such cases. The characteristicstructure around the diffusion region is quite similar to the Petschek modelwhich is characterized by a pair of slow-mode shocks and the fast-moderarefaction-dominated inflow. However, in the outer region, a vortex-likereturn flow driven by the fast-mode compression caused by the piston effect ofthe plasmoid takes place. The entire reconnection system expandsself-similarly.Comment: 17 Pages, 17 Figure