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On the Tilt and Twist of Solar Active Regions View all abstracts by submitter

Richard Canfield   Submitted: 2004-02-13 11:05

Tilts and twists are two measurable characteristics of solar active regions which can give us information about subsurface physical processes associated with the creation and subsequent evolution of magnetic flux tubes inside the Sun. Using Mees Solar Observatory active-region vector magnetograms and Mt. Wilson Observatory full-disk longitudinal magnetograms we measure both the twist and tilt of the magnetic fields of 368 active regions. In addition to two well-known phenomena, Joy's law and the hemispheric helicity rule, this dataset also shows a lesser-known twist-tilt relationship - which is the focus of this study. We find that those regions that closely follow Joy's law do no show any twist-tilt dependence. The dispersion in tilt angles and the dispersion in twist are also found to be uncorrelated with each other. Both of these results are predicted consequences of convective buffeting of initially untwisted and un-writhed flux tubes through the Sigma-effect. However, we find that regions that strongly depart from Joy's law show significantly larger than average twist and very strong twist-tilt dependence - suggesting that the twist-tilt relationship in these regions is due to the kinking of flux tubes which are initially highly twisted, but not strongly writhed. This implies that some mechanism other than the Sigma-effect (e.g., the solar dynamo or buoyancy instability and flux tube formation) is responsible for imparting the initial twist (at the base of the solar convection zone) for the flux tubes that subsequently become kink-unstable.

Authors: Holder, Z. A., Canfield, R. C., McMullen, R. A., Nandy, D., Howard, R. F., & Pevtsov, A. A

Publication Status: ApJ, in press
Last Modified: 2004-04-28 15:58
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