To investigate the impact of current sheet motion on the reconnection process , we perform resistive magnetohydrodynamic ( MHD ) simulations of two closely located reconnection sites which move apart from each other as reconnection develops .
This simulation develops less quickly than an otherwise equivalent single perturbation simulation but eventually exhibits a higher reconnection rate .
The unobstructed outflow jets are faster and longer than the outflow jets directed towards the magnetic island that forms between the two current sheets .
The X-line and flow stagnation point are located near the trailing end of each current sheet very close to the obstructed exit .
The speed of X-line retreat ranges from \sim 0.02 – 0.06 while the speed of stagnation point retreat ranges from \sim 0.03 – 0.07 , in units of the initial upstream Alfvén velocity .
Early in time , the flow stagnation point is located closer to the center of the current sheet than the X-line , but later on the relative positions of these two points switch .
Consequently , late in time there is significant plasma flow across the X-line in the opposite direction of X-line retreat .
Throughout the simulation , the velocity at the X-line does not equal the velocity of the X-line .
Motivated by these results , an expression for the rate of X-line retreat is derived in terms of local parameters at the X-point .
This expression shows that X-line retreat is due to both advection by the bulk plasma flow and diffusion of the normal component of the magnetic field .