4. Two-Dimensional Reconnection

(a) New Generation of Reconnection Regimes
Magnetic reconnection is a key process in astrophysics whereby magnetic field lines come together, break and rejoin. At the same time magnetic energy is converted into other forms and the global topology is changed. It is at the core of many dynamic phenomena, such as solar flares, some coronal heating events and geomagnetic substorms. We have for many years developed the basic theory in two dimensions and now the classical regimes of Sweet-Parker and Petschek reconnection have been replaced by a new generation of fast regimes, namely:

1. Almost-Uniform Reconnection (Priest and Forbes, 1986, J. Geophys. Res. 91, 5579), in which the inflow field lines are weakly curved and for which Petschek's mechanism is a special case;
2. Nonuniform Reconnection (Priest and Lee, 1990, J. Plasma Phys. 44, 337), in which the inflow field is highly curved with plasma jets expelled along the separatrices.

In a paper entitled "Does fast magnetic reconnection exist?" (Priest and Forbes, 1992, J. Geophys. Res. 97, 16757) we have shown how the analytical theories may explain the scalings and properties of the numerical experiments and how the many different regimes depend on the imposed boundary conditions, which vary from one application to another.

(b) Linear Reconnection
We have also proved an Anti-reconnection Theorem and developed a theory for linear-reconnection (Priest, Titov, Vekstein and Rickard, J. Geophys. Res. 1994, 99, 21467 and Titov et al, 1997, J. Fluid Mechs. in press).

(c) X-Point Collapse
Finally, we have set up a self-consistent theory for the nonlinear time-dependent collapse of an X-point to form a current sheet (Priest, Titov and Rickard, 1995, Phil. Trans. Roy. Soc. Lond A. 351, 1)

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