Abstract
ABSTRACT We study the relationship between the force-free parameter α ff >, indicating twist of magnetic fields, and the common parameters of bipolar magnetic regions, such as latitude, magnetic flux, polarity separation distant and tilt angle of magnetic polarity axis with solar equator. Vector magnetograms of 286 bipolar active regions were observed at Huairou Solar Observing Station from 1988 to 1996 in Beijing. We statistically find that the correlation is good between the α ff > and the magnetic flux, the polarity separation and the tilt angle. The correlation coefficients between them is larger than about 0.117 (expected value at least) with confidence level of 95% for about 285 samples. However, the correlation is bad between the α ff > and the latitude. It is found that the force-free parameter is increased with the increasing magnetic flux and polarity separation by linear least-squares fit, that are all opposite to relationship between the tilt angle and the magnetic flux, the polarity separation. We deduce that the force-free parameter is decreased with the increasing tilt angle, in agreement with observation in this paper. Because the tilt angle is believed to be produced by Coriolis force, we speculate that the origin of the twist of magnetic field is not mainly produced by large-scale Coriolis force or by small-scale turbulent convection motion acting on a rising Ω-tube through the convection zone, after we compare the model result obtained by Longcope et al. (1998).
Published Version
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