Three-dimensional magnetic reconnection in the solar corona

In two dimensions the notions of magnetic topology and null-point bifurcations are straightforward. In addition, the nature of magnetic reconnection is fairly well understood and can be described by a new generation of fast reconnection mechanisms known as almost-uniform reconnection and nonuniform reconnection. However, in complex three-dimensional (3-D) magnetic fields, such as exist in the solar corona, these phenomena are only just beginning to be explored and are considerably more complex. The structural properties of the magnetic field created in turn by two, three and more magnetic sources at the photosphere have been recently studied. Passing through each 3-D magnetic null there is an isolated spine field line and a flux surface known as a fan. The fans form separatrix surfaces that separate the volume into topologically distinct regions, and the fan of one null can terminate at the spine of another null, while the spine terminates either at a source or at infinity. The skeleton of complex 3-D fields in the corona, therefore, comprises the magnetic-null points and a network of spine curves and separatrix fan surfaces. Magnetic reconnection can occur in these fields by a variety of mechanisms, including spine reconnection, fan reconnection, separator reconnection, and quasiseparatrix layer reconnection. These types of reconnection and the bifurcations of null points are described and found to be much richer than in the relatively simple two-dimensional fields. (C) 1997 American Institute of Physics.