Vorticity patterns of sunspot Hα whirls Original Research Article

We study vorticity patterns of 897 superpenumbral filaments (in 142 sunspots) using Hα (BBSO) observations from July 2000 – April 2001. A majority (69%) of filaments show noticeable curvature in clockwise (CW) or counter-clockwise (CCW) sense. 73% of all sunspots contain both CW and CCW filaments in their superpenumbrae. Only 27% of sunspots have all their superpenumbral filaments twisted in the same direction. The average sunspot vorticity exhibits well-known hemispheric preference, but the dependence is weaker than in the previous studies: 34 (54%) out of 63 sunspots in the northern hemisphere exhibit CCW pattern of superpenumbral whirls, and 45 (69%) of 65 sunspots in the southern hemisphere show CW pattern. We suggest that the local distribution of magnetic fields around sunspots may affect the curvature of superpenumbral filaments and, hence, weaken the hemispheric helicity rule.