A New Technique For Measuring The Twist Of Photospheric Active Regions Without Recourse To The Force-Free-Field Equation: Reconfirming The Hemispheric Helicity Trend

Details A New Technique For Measuring The Twist Of Photospheric Active Regions Without Recourse To The Force-Free-Field Equation: Reconfirming The Hemispheric Helicity Trend A New Technique For Measuring The Twist Of Photospheric Active Regions Without Recourse To The Force-Free-Field Equation: Reconfirming The Hemispheric Helicity Trend

May 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...210.2402n&link_type=abstract

American Astronomical Society Meeting 210, #24.02; Bulletin of the American Astronomical Society, Vol. 39, p.128

Astronomy and Astrophysics

Astronomy

Scientific paper

The twist component of magnetic helicity in solar active regions is known to be an important indicator of sub-photospheric flux tube dynamics and solar eruptive activity. Traditionally, estimates of the parameter alpha -- appearing in the force-free-field equation -- has been used to infer the twist of photospheric active regions. However, the photosphere is not force-free and this has lead to recent concerns on the validity of using the alpha parameter for determining photospheric active region twist. We have devised a new flux-tube-fitting technique for determining the twist of active regions without recourse to the force-free-field equation. This method assumes that the underlying active region flux system is cylindrically symmetric and uniformly twisted. By using this new technique, on a statistically compelling number of photospheric active region vector magnetograms, we re-confirm the hemispheric helicity rule independent of the force-free-field assumption. This research has been supported in parts by a NASA Living With a Star grant NNG05GE47G. A.C. and J.W. were supported by a NSF Research Experience for Undergraduates grant ATM-0243923 to Montana State University. M.G.L. acknowledges support from NASA and the Office of Naval Research.

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