ar X iv : a st ro - p h / 98 11 03 7 v 1 3 N ov 1 99 8 Preprint Reconnection in a Weakly Stochastic Field

We examine the effect of weak, small scale magnetic field structure on the rate of reconnection in a strongly magnetized plasma. We recover lower and upper limits on the reconnection rate, depending on the reaction of the magnetic field to stresses exerted from within the reconnection layer. Using Goldreich and Sridhar’s model of strong turbulence in a magnetized plasma with negligible intermittency, we find that the lower limit for the reconnection speed is ∼ VAR −3/16 B M , where VA is the Alfvén speed, RB is the magnetic Reynolds number, and M is the large scale magnetic Mach number of the turbulence. The upper limit on the reconnection speed is typically a large fraction of VAM . We argue that generic reconnection in turbulent plasmas will normally occur at close to this upper limit. The fraction of magnetic energy that goes directly into electron heating scales as R −2/5 B M , and the thickness of the current sheet scales as R −3/5 B M . A large fraction of the magnetic energy goes into high frequency Alfvén waves. The angle between adjacent field lines on the same side of the reconnection layer is ∼ R −1/5 B M 6/5 on the scale of the current sheet thickness. We claim that the qualitative sense of these conclusions, that reconnection is fast even though current sheets are narrow, is almost independent of the local physics of reconnection and the nature of the turbulent cascade. Subject headings: Magnetic fields; Galaxies: magnetic fields, ISM: molecular clouds, magnetic fields