On the importance of separators as sites of 3D magnetic reconnection

Abstract

For 3D magnetic reconnection to occur there must exist a volume within which the electric field component parallel to the magnetic field is non-zero. In numerical experiments, locations of non-zero parallel electric field indicate sites of 3D magnetic reconnection. If these experiments contain all types of topological feature (null points, separatrix surfaces, spines and separators), then comparing topological features with the reconnection sites reveals that all the reconnection sites are threaded by separators with the local maxima/minima of the integrated parallel electric along fieldlines coinciding with these separators. However, not all separators thread a reconnection site. Furthermore, there are different types of separator. Cluster separators are short arising within an individual weak magnetic field region and have little parallel electric field along them so are not associated with much reconnection. Intercluster separators connect a positive null point lying in one weak-field region to a negative null point that lies in a different weak-field region. Intercluster separators often thread enhanced regions of parallel electric field and are long. Since separators form the boundary between four globally significant topologically distinct domains, they are important sites of reconnection, which can result in the global restructuring of the magnetic field. By considering kinematic bifurcation models in which separators form, it is possible to understand the formation of cluster and intercluster separators and explain their key properties.