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Twist and writhe of δ active region magnetic fields

Published online by Cambridge University Press:  30 March 2016

Lirong Tian  and
Jing Yang
Lirong Tian
Affiliation:
National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China (tlr@ns.bao.ac.cn)
Jing Yang
Affiliation:
Astronomical Department, Beijing Normal University, Beijing 100875, China

Extract

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Twist is a parameter to measure turning of the field lines around axis of the flux tube. Observations show that each active region (AR) has a pronounced overall twist, following hemispheric helicity rule (Pevtsov et al. 1995; Bao & Zhang 1998). αbest, best-fit single value for a whole AR, is used to characterize the overall twist. Writhe is a measure of the spatial turning of the axis of the flux tube. It is described by systematic tilt angle of an AR, an angle of joined line of opposite main polarities with respect to the equator. Observations show that most ARs follow Joy’s Law. The relationship between the twist and writhe is important to studying origin of the twist and solar activities. Canfield & Pevtsov (1998) found the same handedness of the twist as that of writhe, using 99 ARs observed at MSO. However, Tian et al. (2001) found opposite handedness of them for 286 ARs taken at HSOS, among which only 19% have δ magnetic configuration. López Fuentes et al. (2003) also obtained opposite handedness for 22 ARs measured again at MSO, among which 41% have δ magnetic class. Most recently, Tian & Liu (2003) found that the twist and the writhe have same handedness for major flare-producing ARs.

Type
I. Joint Discussions
Information
Highlights of Astronomy , Volume 13 , 2005 , pp. 120 - 121
Copyright
Copyright © Astronomical Society of Pacific 2005

References

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