A survey of flares and current helicity in active regions

Abstract

We examine the spatial and temporal rela- tionship between chromospheric H flares and photo- spheric current helicities in active regions. All of the data were obtained by the vector magnetograph system at Huairou Solar Observing Station of Beijing Astronomical Observatory. We focus our analysis on NOAA Active Region 6233, which was observed on 30 August 1990. The result shows that rapid and substantial changes of dis- tribution of current helicity in an area or in its vicinity are most likely to trigger flares, but no compelling cor- relation between peaks of current helicity and flare sites. Furthermore, we study the influence of flares on helicity for several other active regions. We nd that the time vari- ations of current helicity in the active regions with highly productive flares are more signicant than those of the poorly flare-productive active regions, and that the mag- nitude of current helicity does not always decrease after flares. Therefore we conclude that the rate of variation of current helicity may be considered as an indicator of flare activity. In this paper we describe the specication of the in- strumentation and data used, and we describe the meth- ods for computing helicity. The noises and errors in our data are estimated to be at the 2 3 level.