Earth Planets Space, Vol. 53 (No. 6), pp. 453-462, 2001
Rudolf A. Treumann
Centre for Interdisciplinary Plasma Science, Max-Planck-Institute for extraterrestrial Physics, P.O.Box 1312, D-85741 Garching, Germany, and International Space Science Institute, Hallerstr. 6, CH-3012 Bern, Switzerland
(Received June 5, 2000; Revised October 10, 2000; Accepted October 16, 2000)
Abstract: Resistivity is believed to play an important role in reconnection leading to the distinction between resistive and collisionless reconnection. The former is treated in the Sweet-Parker model of long current sheets, and the Petschek model of a small resistive region. Both models in spite of their different dynamics attribute to the violation of the frozen-in condition in their diffusion regions due to the action of resistivity. In collisionless reconnection there is little consensus about the processes breaking the frozen-in condition. The question is whether anomalous processes generate sufficient resistivity or whether other processes free the particles from slavery by the magnetic field. In the present paper we review processes that may cause anomalous resistivity in collisionless current sheets. Our general conclusion is that in space plasma boundaries accessible to it in situ spacecraft, wave levels have always been found to be high enough to explain the existence of large enough local diffusivity for igniting local reconnection. However, other processes might take place as well. Non-resistive reconnection can be caused by inertia or diamagnetism.