An investigation of the topology and structure of constant- (alpha) force-free fields

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 Greenʹs 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.