Observations have shown that active region flux tubes often emerge in a twisted state. They also indicate that the active region formed by such a flux tube has helicity of the same sense as the flux tube which forms it. Separate theoretical models have been developed for coronal magnetic fields with helicity and for flux tubes with twist. Here we present a model matching a twisted sub-photospheric flux tube to a force-free coronal field. With this model it is possible to explore the emergence of a flux tube into the corona. In particular, only a fraction of the tube's current will pass into the coronal field. As a consequence of this "mismatch" a torsional Alfven wave is launched downward along the flux tube at the instant of its emergence. As the flux tube continues to emerge the helicity of the coronal field increases. This would give the appearance of rotation applied at footpoints.
AAS/Solar Physics Division Meeting #31
- Pub Date:
- May 2000