Computer simulations on three-dimensional magnetic loop dynamics by the spontaneous fast reconnection model

Three-dimensional (3D) dynamics of a large-scale magnetic loop is studied by precise magnetohydrodynamic simulations on the basis of the spontaneous fast reconnection model. Once a (current-driven) anomalous resistivity is ignited, the fast reconnection mechanism drastically evolves by the positive feedback between the (3D) global reconnection flow and the anomalous resistivity; on the nonlinear saturation phase, the global reconnection flow has grown so that the reconnection (diffusion) region shrinks to a small extent, and the fast reconnection mechanism involving a pair of standing slow shocks is established in the finite extent. When the 3D plasmoid, formed ahead of the fast reconnection jet, collides with the mirror plane boundary, the reconnected field lines are piled up, leading to formation of a large-scale 3D magnetic loop. Since the resulting 3D fast reconnection jet becomes supersonic, a definite fast shock builds up at the interface between the magnetic loop top and the fast reconnection jet. The 3D fast reconnection jet is limited in a narrow channel between the pair of slow shocks, so that the resulting fast shock is also limited to a small extent ahead of the magnetic loop top. On the other hand, for the uniform resistivity model the 3D fast reconnection mechanism cannot be realized without any vital positive feedback between the reconnection flow and the local magnetic diffusion; hence, such an effective resistivity that can be self-consistently enhanced locally at the X reconnection point by the global reconnection flow is essential for the fast reconnection mechanism to be realized in actual systems