Competing X-lines During Magnetic Reconnection

Multiple X-line reconnection has been observed in the Earth's magnetotail and is thought to occur in CME current sheets. We perform and analyze resistive MHD simulations of a Harris sheet with 5 to 20 initial X-line perturbations. We confirm the two-fluid results of Nakamura et al. (2010) that the edgeward X-lines dominate when all initial X-lines are given the same initial amplitude and spacing. When all initial X-lines are evenly spaced, the interior X-lines win when they are given a large enough initial amplitude. Simulations with unevenly spaced initial X-lines show that X-line dominance depends not only on initial amplitude but also on initial X-line spacing. Force density plots show that outflows from all winning X-lines are supported early by plasma pressure gradients. When an X-line is pulled towards one end of the reconnection layer, the flow stagnation point is located between the X-line and the central local maximum of plasma pressure. The resulting single wedge shaped current sheet usually develops an additional X-line near the other exit of the current sheet. X-lines are observed to move in the direction of increasing electric field strength.