Patterns of current helicity for solar cycle 22

Using a 1988-1997 data set of original photospheric vector magnetograms from the Solar Magnetic Field Telescope (SMFT) of the Huairou Solar Observing Station of Beijing Astronomical Observatory, we computed the local current helicity B-z .(del x B)(z) for 422 active regions. We found that any given active region contained mixed signs of current helicity, but in most cases current helicity with a particular sign was dominant over a whole region area. In our data set, 84% of the active regions in the northern hemisphere have negative helicity, and 81% in the southern hemisphere have positive helicity. It is estimated that the noise and error in our calculation are at the 2 sigma level. In addition, we have studied the evolution of the large-scale surface current helicity during the cycle 22, which is a running mean of absolute current helicity of the active regions observed over a Carrington rotation period. By comparing with monthly mean sunspot number, we found that the average current helicity has a good correlation with solar activity.