An investigation of the topology and structure of constant-α force-free fields

¹ FORTH and Department of Physics, University of Crete, PO Box 2208, 710 03 Heraklion, Crete, Greece e-mail: gordonp@physics.uoc.gr
² School of Computing, The Robert Gordon University, St. Andrews Street, Aberdeen AB25 1HG, UK e-mail: rml@scms.rgu.ac.uk

Corresponding author: G. J. D. Petrie, gordonp@physics.uoc.gr

Received: 27 July 2001
Accepted: 7 October 2002

Abstract

Coronal field structures corresponding to specified normal fields on the photosphere are investigated using a force-free model. The force-free parameter is insufficient to determine the field uniquely, and so a second parameter representing the contribution of the complementary Green's function is included. For isolated loops represented by a single source-sink pair, the influence of the two parameters on field structure is comparable. Effects on the topology (as measured by field line connectivity) of multiple source configurations are also found to be comparable. It is notable that some configurations are more stable than others to variation of either parameter. The results of this study are compared with previous magnetic charge topology studies involving only the force-free parameter.