Computer studies on the spontaneous fast reconnection mechanism in three dimensions

The spontaneous evolution of fast reconnection is studied in three dimensions by extending (in the z direction) the previous two-dimensional model that considered only the x-y plane [M. Ugai, Phys. Fluids B 4, 2953 (1992)]. It is demonstrated that the reconnection development strongly depends on three-dimensional effects; only when the central current sheet is sufficiently long in the z direction, say more than a few times larger than the current sheet width, the fast reconnection mechanism fully develops by the self-consistent coupling between the global reconnection flow and the current-driven anomalous resistivity. In this case, the reconnection flow can grow so powerfully as to enhance the current density (the current-driven resistivity) locally near an X line; otherwise, such a vital reconnection flow cannot be caused. The resulting quasisteady fast reconnection mechanism is significantly confined in the z direction, where a strong (Alfvénic) plasma jet results from standing switch-off shocks; accordingly, a large-scale plasmoid is formed and propagates in the middle of the system. It is concluded that the well-known two-dimensional spontaneous fast reconnection model can reasonably be extended to three dimensions.