Other
Scientific paper
Jun 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006spd....37.3502t&link_type=abstract
American Astronomical Society, SPD meeting #37, #35.02; Bulletin of the American Astronomical Society, Vol. 38, p.259
Other
Scientific paper
It is a very hot topic that which one is important origin of coronal helicity between the emergence of twisted magnetic fields and horizontal motions of photospheric mass. In this paper, we selected 23 active regions with well-formed sigmoidal structure in YOHKOH soft X-ray images during 1997-2002. Considering such active regions may be developing in a mature stage, no significant emergence of magnetic fields, we can study if the role of the horizontal motion is significant. We calculate positive and negative redial magnetic flux and estimate total helicity injection flux over five days using SOHO/MDI 96 m magnetograms and local correlation tracking technique. We find that 7/23 active regions have injected total helicity flux, delta_H, larger than 10^43 Mx^2 during emerging magnetic flux larger than 10^22 Mx; Among other 16 active regions which emerged magnetic flux littler than 10^22 Mx, only 6/16 active regions have injected total helicity flux larger than 10^43 Mx^2. Comparing with force-free parameter alpha_best calculated by vector magnetograms in Huairou Solar Observatory of China, it is found that 19/23 ARs display a consistent sign of alpha_best with delta_H; 14/19 ARs have consistent sign with the sigmoidal shape, i.e. positive (negative) helicity vs S (Z)-shaped sigmoid. Considering contribution from differential rotation, our results suggest that coronal helicity predominantly originates from the emergence of twisted magnetic fields breaking through the photosphere.
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