Numerical modelling of 3D reconnection due to rotational footpoint motions

¹ School of Mathematics and Statistics, University of St Andrews, North Haugh, St Andrews, Fife KY16 9SS, Scotland e-mail: ineke@mcs.st-and.ac.uk
² Niels Bohr Institute, Julie Maries vej 30, 2100 Copenhagen Ø, Denmark

Received: 24 November 2005
Accepted: 30 January 2006

Abstract

The rapid dynamical evolution of the photospheric magnetic carpet provides a large energy source for the solar corona. In this context, the role of 3D magnetic reconnection is crucial in releasing the free magnetic energy, build up due to the continuous footpoint motions. To understand the processes by which this can take place, we have to obtain a better understanding of the basic reconnection process that can take place in 3D magnetic field configurations. In this paper, we investigate magnetic reconnection, driven by rotational footpoint motions, using 3D numerical MHD simulations. The model consists of two positive and two negative sources, which are placed symmetrically on opposite boundaries of the cubic domain. The initially potential fluxtubes are forced to interact by the rotational driving of the flux concentrations on the boundaries. We consider two variations of this setup, namely with and without an additional, constant, background magnetic field. In the no-background case, the magnetic connectivity is divided into independent regions by separatrix surfaces, while the case with a background field is represented by one global connectivity region. The dynamical evolution is followed and found to differ significantly from the comparable potential evolution. Strong currents are concentrated along separatrix surfaces or rapidly developing quasi-separatrix layers (QSLs). Investigating the reconnection rates of the systems shows that the stronger the background field is, the more efficient the reconnection process of the flux in the respective fluxtubes.