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Title:
Patterns of helicity in solar active regions
Authors:
Pevtsov, Alexei A.; Canfield, Richard C.; Metcalf, Thomas R.
Affiliation:
AA(University of Hawaii, Honolulu, HI, US), AB(University of Hawaii, Honolulu, HI, US), AC(University of Hawaii, Honolulu, HI, US)
Publication:
Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X), vol. 425, no. 2, p. L117-L119 (ApJL Homepage)
Publication Date:
04/1994
Category:
Astronomy
Origin:
STI
NASA/STI Keywords:
Astronomical Polarimetry, Dynamo Theory, Polarimeters, Solar Convection (Astronomy), Solar Magnetic Field, Sunspots, Astronomical Models, Polarization, Solar Activity, Solar Physics
DOI:
10.1086/187324
Bibliographic Code:
1994ApJ...425L.117P

Abstract

Using 46 vector magnetograms from the Stokes Polarimeter of Mees Solar Observatory (MSO), we studied patterns of local helicity in three diverse solar active regions. From these magnetograms we computed maps of the local helicity parameter alpha = Jz/Bz. Although such maps are noisy, we found patterns at the level approximately 2 to 3 sigmaJ(sub z), which repeat in successive magnetograms for up to several days. Typically, the alpha maps of any given active region contain identifiable patches with both positive and negative values of alpha. Even within a single sunspot complex, several such alpha patches can often be seen. We followed 68 alpha patches that could be identified on at least two successive alpha maps. We found that the persistence fraction of such patches decrease exponentially, with a characteristic time approximately 27 hr.

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