New Developments in Magnetic Reconnection Theory

Abstract

Although two-dimensional reconnection is now fairly well understood, there have recently been some interesting new developments. Four distinct types of reconnection are possible, namely: viscous (or kinematic) reconnection; extra-slow (or linear) reconnection; slow (or Sweet-Parker) reconnection; and fast (Almost-uniform or Nonuniform) reconnection. An antireconnection theorem has been discovered which states that steady two-dimensional reconnection (with flow across the separatrices) is impossible for slow inviscid flow (and it has also been generalised to three dimensions). Solutions for linear reconnection have been presented and a new theory for the self-consistent time-dependent collapse of an X-point to form a reconnecting current sheet has been developed.

The new field of three-dimensional reconnection is only just beginning. Schindler et al have suggested a concept of general magnetic reconnection and Priest et al have proposed a model for “magnetic flipping” . A magnetic null in three dimensions has a skeleton consisting of a spine and a fan, which are respectively an isolated field line and a surface of field lines that pass through the null point. At such a null, reconnection may occur either by “spine reconnection” or by “fan reconnection”, in which singular resistive behaviour occurs either at the spine or the fan, respectively. When no null points are present, reconnection can still occur at so-called “quasiseparatrix surfaces”, which are regions where the mapping of field lines has extremely steep gradients and the field lines become disconnected from the plasma.