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Force-Freeness of Solar Magnetic Fields in the Photosphere View all abstracts by submitter

Yong-Jae Moon   Submitted: 2002-04-05 17:47

It is widely believed that solar magnetic fields are force-free in the solar corona, but not in the solar photosphere at all. In order to examine the force-freeness of active region magnetic fields at the photospheric level, we have calculated the integrated magnetic forces for 12 vector magnetograms of three flare-productive active regions. The magnetic field vectors are derived from simultaneous Stokes profiles of the Fe I doublet 6301.5 and 6302.5 obtained by the Haleakala Stokes Polarimeter of Mees Solar Observatory, with a non-linear least square method adopted for field calibration. The resulting vertical Lorentz force normalized to the total magnetic pressure force |F_z/F_p| ranges from 0.06 to 0.36 with a median value of 0.13, which is smaller than the values (sim 0.4) obtained by Metcalf et al. who applied a weak field derivative method to the Stokes profiles of Na I 5896. Our results indicate that the photospheric magnetic fields are not so far from force-free as conventionally regarded. As a good example of a linear force-free field, AR 5747 is examined. By applying three different methods (a most probable value method, a least square fitting method, and comparison with linear force-free solutions), we have derived relatively consistent linear force-free coefficients for AR 5747. It is found that the scaled downward Lorentz force (|F_z/F_p|) in the solar photosphere decreases with increasing α . Our results also show that the force-freeness of photospheric magnetic fields depends not only on the character of the active region, but also on its evolutionary status.

Authors: Y.-J. Moon, G. S. Choe, H. S. Yun, Y. D. Park, D. L. Mickey

Publication Status: ApJ, 2002, 568, 422-431
Last Modified: 2002-04-05 17:55
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