Abstract
This paper summarizes current helicity measurements in the solar active regions (ARs). There is a basic agreement with the “hemispheric sign rule (HSR)” of the current helicity among different vector magnetographs through two solar cycles, but there is a large dispersion of the fraction of ARs following the HSR. In our sample, there are 50%–78% ARs in solar cycle 22 and 44%–79% ARs in cycle 23 following the HSR. A variation is also found in the fraction of the ARs following the HSR between different instruments even when the same ARs are selected. The difference also exists for the same instrument when the selected ARs are different. There are some differences in the variation of HSR with solar cycle for the individual helicity parameter inferred from different instruments. Factors which influence the correlation of different data sets are analyzed.
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Supported by the National Natural Science Foundation of China (Grant Nos. 10611120338, 10473016, 10673016, 60673158, 10733020, and 10978015), the National Basic Research Program of China (Grant No. 2006CB806301), and the Important Directional Project of Chinese Academy of Sciences (Grant No. KLCX2-YW-T04)
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Xu, H., Gao, Y. & Zhang, H. Some basic questions on helicity inferred from vector magnetograms. Sci. China Ser. G-Phys. Mech. Astron. 52, 1749–1753 (2009). https://doi.org/10.1007/s11433-009-0246-3
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DOI: https://doi.org/10.1007/s11433-009-0246-3