A Statistical Study on Rotating Sunspots: Polarities, Rotation Directions, and Helicities

Observations of white-light images from SOHO MDI, TRACE, Hinode, SOHO MDI magnetograms, and Hinode SP vector magnetograms show sufficient samples of rotating sunspots on the solar photosphere for a statistical study. During the period from 1996 December to 2007 December, after individually checking the active regions in detail, we found 182 measurable rotating sunspots. According to the statistics, the number of rotating sunspots in the northern hemisphere is 12% greater than the number in the southern hemisphere. The number of rotating sunspots with clockwise rotation is approximately the same as the number with counterclockwise rotation in both hemispheres. Furthermore, in the northern hemisphere the number of rotating sunspots with positive polarity is nearly twice the number of those with negative polarity, while in the southern hemisphere the situation is almost reversed. During the maximum of solar cycle 23, there were more rotating sunspots than during any other period observed. Finally, the current helicity imbalance shows a very weak hemispheric tendency. These findings may be instructive and place further constrains on the dynamo and flux emergence theories.