Magnetic Helicity Accumulation and Tilt Angle Evolution of Newly Emerging Simple Active Regions

Details Magnetic Helicity Accumulation and Tilt Angle Evolution of Newly Emerging Simple Active Regions Magnetic Helicity Accumulation and Tilt Angle Evolution of Newly Emerging Simple Active Regions

Sep 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008espm...12.2.55y&link_type=abstract

"12th European Solar Physics Meeting, Freiburg, Germany, held September, 8-12, 2008. Online at http://espm.kis.uni-freiburg.de/,

Physics

Scientific paper

Recently, a general dominance of negative (positive) helicity was discovered for active regions (ARs) in the northern (southern) solar hemisphere. However, the distribution of magnetic helicity accumulation in newly emerging ARs is still unclear. Also different conclusions were drawn in the past about the relationship between the accumulated helicity and the writhe of active regions.
In order to better understand the evolution of the magnetic helicity in emerging ARs, we investigate the accumulation of helicity for newly emerged simple bipolar solar active regions. We also investigate the relation between the accumulated helicity and writhe.
Methods. We obtain the accumulated helicity by applying Fourier transforms (FFT) and local correlation tracking (LCT) to MDI data. We deduce the writhe of active regions according to the evolution of the tilt angle between the connecting line of the weighting centers of opposite polarities in the ARs. We found that 72.4% of 58 selected newly emerged simple ARs take negative (positive) helicity when the above defined tilt angle rotates clockwise (counter-clockwise). Contrary to the common believe that the tilt angle of ARs provides the information on the writhe of their magnetic fields, we have found that the accumulated helicity and writhe have same sign for most of the investigated newly emerging flux. we also found that 50.0% (59.0%) of the selected active regions from the samples in the northern (southern) photosphere provide negative (positive) helicity from the sub-atmosphere into the corona with the emerging of magnetic flux.

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