The Emergence of Magnetic Flux in Active Regions
Abstract
Over the past decade, ``thin flux tube'' models have proven successful in explaining many properties of active regions in terms of magnetic flux tube dynamics in the solar interior. Unfortunately, recent, more sophisticated two-dimensional MHD simulations of the emergence of magnetic flux have shown that many of the assumptions adopted in the thin flux tube approximation are invalid. For example, unless the flux tubes exhibit a large amount of initial field line twist --- and observations of emerging active regions suggest they do not --- they will fragment (break apart) before they are able to emerge through the surface. We attempt to resolve this paradox using a number of 3-D MHD simulations (in the anelastic approximation) that describe the rise and fragmentation of twisted magnetic flux tubes. We find that the degree of fragmentation of an evolving Omega-loop depends strongly on the three-dimensional geometry of the tube --- the greater the apex curvature, the lesser the degree of fragmentation for a fixed amount of initial twist. We also find that the Coriolis force plays a dynamically important role in the evolution and emergence of magnetic flux. We are able to infer general observational characteristics of the emerging flux, and compare our theoretical data with recent observations.
- Publication:
-
Recent Insights into the Physics of the Sun and Heliosphere: Highlights from SOHO and Other Space Missions
- Pub Date:
- 2001
- Bibcode:
- 2001IAUS..203..225A