On the theory of steady state reconnection

This paper contains a brief overview of analytical models of steady-state reconnection and their relationship to recent computer simulations. A general definition of reconnection is given which is shown to be entirely local in nature. The Sweet-Parker and the Petschek models are then reviewed briefly along with several other analytical descriptions of reconnection, and their relevance to computer-simulation results is discussed. Particular attention is paid to the formation of the strong vortex layers along magnetic separatrix surfaces, an effect that has been observed in a number of numerical simulations of reconnection. Finally, two-fluid phenomena are discussed with emphasis on (i) the appearance of structures on the electron length scales at the reconnection site when ordinary or anomalous resistivity effects are absent and (ii) the appearance of Hall-current loops on length scales comparable to the ion inertial length or gyroradius.