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Of Tilt and Twist

Published online by Cambridge University Press:  30 March 2016

Zachary A. Holder
Affiliation:
Department of Physics, Montana State University, Bozeman, MT 59717-3840, U.S.A.
Richard C. Canfield
Affiliation:
Department of Physics, Montana State University, Bozeman, MT 59717-3840, U.S.A.
Rebecca A. McMullen
Affiliation:
Department of Physics, Montana State University, Bozeman, MT 59717-3840, U.S.A.
Robert F. Howard
Affiliation:
National Solar Observatory/Kitt Peak1, Tucson, AZ 85726, U.S.A.
Alexei A. Pevtsov
Affiliation:
National Solar Observatory/Sacramento Peak1, PO Box 62, Sunspot, NM 88349, U.S.A.

Abstract

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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. This dataset clearly shows two well-known phenomena, Joy’s law and the hemispheric helicity rule, as well as a lesser-known twist-tilt relationship, which is the point of this work. Those regions that closely follow Joy’s law show no twist-tilt relationship, which is a predicted consequence of convective buffeting of initially untwisted and unwrithed flux tubes through the Σ effect. Those regions that strongly depart from Joy’s law show significantly larger than average twist and a very strong twist-tilt relationship. These properties suggest that the twist-tilt relationship in these regions is due to kinking of flux tubes that are highly twisted but not strongly writhed.

Type
I. Joint Discussions
Copyright
Copyright © Astronomical Society of Pacific 2005