Computer studies on the fast reconnection mechanism in a sheared field geometry

The development of the fast reconnection mechanism is systematically studied in a sheared (skewed) field geometry with no magnetic neutral (null) point. Initially, there are antiparallel fields (of component Bx0) with a current sheet in the middle, as well as a uniform sheared field component (Bz0). On the basis of the spontaneous fast reconnection model, a number of computations demonstrate that, initiated by a small disturbance, the fast reconnection mechanism can be fully established by releasing the energy associated with the antiparallel fields. Once the quasisteady fast reconnection mechanism is set up, the magnetic flux is drastically transferred, leading to an effective topological change of the skewed field configuration. The thin (shock) transition layer standing in the quasisteady fast reconnection region is divided into the intermediate wave region and the slow shock region. In the intermediate wave region, the magnetic field simply rotates without changing plasma quantities, whereas in the slow shock region a slow shock is combined with an intermediate wave. For the larger Bz0, the finite-amplitude intermediate wave becomes dominant so that the slow shock characteristics become obscure in the transition layer. The reconnection (flux transfer) rate is estimated to scale as E0/[1+tan2(Ω/2)], where Ω=2 tan-1(Bz0/Bx0), and E0 is the reconnection rate for the coplanar case (Bz0=0) and tends to decrease as the plasma beta becomes larger