DRIVEN RECONNECTION IN THE EARTHS MAGNETOTAIL

Reconnection in the magnetotail can be driven by the convective flow due to reconnection of the terrestrial and solar magnetic fields at the dayside magnetopause. In the standard reconnection model a low flow speed leads to steady reconnection at a distant-tail x-line, but a high flow speed leads to the formation of a near-earth x-line and the onset of an auroral substorm. It is difficult to understand why an enhanced flow speed should lead to the formation of a new x-line near the earth instead of an increase in the reconnection rate at the pre-existing, distant-tail x-line. Here I discuss some recent work which suggests that the near earth x-line might result from a pile-up of magnetic flux at the distant-tail x-line.