Current Helicity of Emerging Active Regions

Details Current Helicity of Emerging Active Regions Current Helicity of Emerging Active Regions

Dec 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufmsh52a0466p&link_type=abstract

American Geophysical Union, Fall Meeting 2002, abstract #SH52A-0466

Physics

7509 Corona, 7524 Magnetic Fields, 7529 Photosphere

Scientific paper

We employ the SOHO MDI magnetograms and EIT images to study evolution of current helicity of solar active regions during early stages of their emergence. Using longitudinal magnetograms we compute linear force-free fields ∇ x B = α B and compare extrapolated field lines with bright coronal structures to constrain the value of α. At the beginning of emergence all studied regions have small α ~eq 0. As active region grows, α gradually increases and reaches a "plateau" within approximately one day of emergence. Using change in separation between negative and positive fluxes, we divide regions on "slow" and "rapid" emergence. Three regions show "slow" (> 1 day) emergence. For these regions α increases faster than the separation. In two "rapid" (< 1 day) emerging regions α grows slower that the separation. This observed evolution of current helicity is in agreement with Longcope and Welsch (2000) model of emergence of subphotospheric twisted flux rope into the corona. škip 0.5 truecm V. Maleev is NSO 2002 Summer Research Assistant from St. Petersburg State University, Russia

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