Structure of magnetic separators and separator reconnection

摘要

Magnetic separators are important locations of three-dimensional magneticreconnection. They are field lines that lie along the edges of four flux domains andrepresent the intersection of two separatrix surfaces. Since the intersection of two surfacesproduces an X-type structure, when viewed along the line of intersection, the global three-dimensional topology of the magnetic field around a separator is hyperbolic. It is thereforeusually assumed that the projection of the magnetic field lines themselves onto a two-dimensional plane perpendicular to a separator is also hyperbolic in nature. In this paper,we use the results of a three-dimensional MHD experiment of separator reconnection toshow that, in fact, the projection of the magnetic field lines in a cut perpendicular to aseparator may be either hyperbolic or elliptic and that the structure of the magnetic fieldprojection may change in space, along the separator, as well as in time, during the life ofthe separator. Furthermore, in our experiment, we find that there are both spatial andtemporal variations in the parallel component of current (and electric field) along theseparator, with all high parallel current regions (which are associated with reconnection)occurring between counterrotating flow regions. Importantly, reconnection occurs not onlyat locations where the structure of the projected perpendicular magnetic field is hyperbolicbut also where it is elliptic.