On a Cyclic Variation of the Hemispheric Helicity Rule

Details On a Cyclic Variation of the Hemispheric Helicity Rule On a Cyclic Variation of the Hemispheric Helicity Rule

Jan 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005hia....13..140p&link_type=abstract

Highlights of Astronomy, Vol. 13, as presented at the XXVth General Assembly of the IAU - 2003 [Sydney, Australia, 13 - 26 July

Astronomy and Astrophysics

Astronomy

1

Scientific paper

We report the result of a study of magnetic helicity in solar active regions during 1980-2000 (cycles 21-23). Using the vector magnetograms from four different instruments (Haleakala Stokes Polarimeter Marshall Space Flight Center Mitaka Solar Flare Telescope and Okayama Observatory Solar Telescope) we calculated the force-free parameter alpha as in Pevtsov et al. (1995). We use alpha as the proxy for current helicity. For each instrument we computed a gradient dalpha/dL as the linear fit of alpha versus latitude L using annual subsets of data. The hemispheric helicity rule (negative/positive helicity in northern/southern hemisphere) can be expressed in terms of this gradient as dalpha/dL < 0. We find that each instrument exhibits change in sign of this gradient for some years which implies that the hemispheric helicity rule may not hold in some phases of a solar cycle (see Hagino and Sakurai 2002). However we do not see consistency between different instruments in regards to years disobeying the rule. The disagreement may be due to difference in observations and/or insufficient number of magnetograms in some years. We conclude that the present data sets do not allow to make statistically significant inference about possible cyclic variation of the hemispheric helicity rule.

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