Magnetic reconnection and the topology of interacting twisted flux tubes

Publisher Website
Google Scholar
Abstract
The self‐consistent evolution of a pair of initially straight and either parallel or antiparallel magnetic flux tubes with prescribed boundary twist is studied using fully compressible three‐dimensional (3‐D) resistive magnetohydrodynamics (MHD). 3‐D visualization techniques specially designed for divergence free vector fields are employed to investigate topological changes in the field lines and current lines associated with 3‐D reconnection in the system. Four cases are studied, corresponding to either parallel or antiparallel initial magnetic fields and to the same or opposite sign of footpoint twist. It is found that in the case with antiparallel field and opposite twist, so that the currents are parallel, the evolution proceeds in two phases. In the first phase, a series of topological changes involving magnetic nulls (where B=0) create an X‐type closed field line. In the second phase, the X‐type line serves as the separator for reconnection, allowing field lines from the two tubes to merge and form loops. The magnetic field lines exhibit spatial chaos and chaotic scattering. The observed reconnection involves the X‐type closed field line with evident current sheets. Later in time, the X‐type line changes to an O‐type closed field line, surrounded by a ring of toroidal flux surfaces. Reconnection continues until there emerges a final steady state having two reconnected loops and a toroidal ring of flux surfaces in between. The torus of magnetic surfaces has zero current in steady state because it is not connected by field lines to the twist imposed at the boundary. It is discussed how it is possible that such a region of zero current density can exist. The other three cases involve breaking of the ideal MHD flux constraint and changes in topology, but without localized current sheets, i.e., without reconnection. Implications for coronal loop interaction are discussed.

This publication has 34 references indexed in Scilit: