Relationship in sign between tilt and twist in active region magnetic fields
National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, PR China
Corresponding author: L. R. Tian, email@example.com
Accepted: 24 April 2001
In this paper, we analyze the photospheric vector magnetograms of 286 active regions (ARs) which were observed from 1988-1996 during the 22nd solar cycle at Huairou Solar Observing Station in Beijing. Among these active regions, which are dominated by bipolar magnetic fields, 203 ARs exhibit a simple configuration of magnetic fields, while 83 ARs show a more complicated configuration of magnetic fields. When we explore the relationship between the sign of the tilt angle of magnetic polarity axis and the sign of the mean current helicity defined by , we find that: (1) There is a negative correlation between the sign of the tilt angle and the sign of the current helicity if the tilt angle is set a positive value (0-90°) in the northern hemisphere and a negative value (0--90°) in the southern hemisphere for active regions following Joy's law. In other words, about 60% of the bipolar active regions have a positive/negative tilt angle with respect to solar equator and a negative/positive current helicity in the northern/southern hemisphere. (2) In about one-third of the bipolar active regions, the tilt angle and the current helicity have the same sign in both hemispheres. They are abnormal active regions with an "abnormal chirality" . These active regions are located preferentially in some longitudinal bins. (3) Most of the 62 X-ray flares larger than M-class during the 22nd solar cycle have a tendency to locate in some longitudinal bins, where active regions with "abnormal chirality" appear frequently.
Key words: Sun: magnetic field / Sun: photosphere / Sun: interior
© ESO, 2001