Generation of Near-Earth Reconnection by Divergent Flows in the Plasma Sheet

A global two-dimensional hybrid simulation is carried out to study the evolution of the near-Earth plasma sheet. The simulation domain contains the near-earth magnetotail from GSM x=0 to -40Re in the midnight meridian plane. The Earth's ionosphere is taken to be a perfect conductor. The simulation shows that reconnection X lines and plasmoids can be generated by diverging flows in the plasma sheet. These diverging flows can be caused by variations in the of the Maxwell stress due to variations of Bx and Bz components of the magnetic field outside the current sheet. In addition, the flow acceleration/deceleration in the plasma sheet can also be caused by variations in the local plasma mass density. Comparison runs have been made with a Harris model current sheet with zero Bz. We saw no evidence of reconnection. This indicates that divergent plasma flow is a sufficient condition for reconnection, even in a dissipationless plasma.