Are Solar Emerging Flux Regions Carrying Electric Current?
Abstract
Flare-productive active regions exhibit non-potential magnetic field structures, oft described as 'sheared' or 'twisted' fields. This morphology indicates that electric currents are present. In this thesis I test whether surface flows generate observed active-region currents, or whether these currents are produced prior to their appearance at the surface as sunspots, i.e., deep in the solar convection zone. To study this question I observed emerging magnetic flux in a uniquely rapidly growing active region. First I undertook an exhaustive study of the more than 50 bipoles which appeared in a sunspot group visible in August 1992. I determined the time of emergence, magnetic connectivity and patterns of overall development of this young active region. Then, four independent analysis methods were used to determine whether the emerging flux was carrying the electric current prior to its appearance, or if the observed strong currents were generated by plasma flows in the photosphere. The four approaches gave consistent results. For a few young bipoles, I show that the morphology of chromospheric and coronal loops were definitively non-potential, that those same dipoles had proper motions which reflected twisted subsurface flux bundles, that electric current existed in greater abundance than could be generated given the observed characteristics and finally that the electric current increased as the magnetic flux itself increased with no substantial delay. All evidence was also consistent with a direction of twist defined by J_ {z}/Bz < 0. This twist direction was also present in the older flux of this active region. I conclude that the electric currents observed in this solar active region were not produced by plasma motions in the photosphere. Rather, the evidence presented in this thesis supports the hypothesis that active region electric currents are generated either deep in the convection zone or are produced with solar magnetic fields in a dynamo process.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- January 1995
- Bibcode:
- 1995PhDT..........L
- Keywords:
-
- MAGNETIC FLUX;
- SUNSPOTS;
- Physics: Astronomy and Astrophysics;
- SOLAR MAGNETIC FIELD;
- SOLAR PHYSICS;
- SUNSPOTS;
- MAGNETIC FIELDS;
- CURRENTS;
- MAGNETOHYDRODYNAMICS;
- SOLAR FLARES