A quantity characterizing variation of observed magnetic twist in solar active regions

• 来源期刊: 天文和天体物理学研究
• 年，卷（期）: 2018,（3）
• 页码范围: 37-46
• 页数: 10页
• 语种: 英文
• DOI: 10.1088/1674-4527/18/3/28

摘要

An alternative parameter RJz is introduced as the ratio of one of two kinds of opposite-sign current to the total current and is used to investigate the relationship between this quantity and the hemispheric helicity sign rule (HSR) that has been established by a series of previous statistical studies. The classification of current in each hemisphere obeys the following rule; if the product of the current and the corresponding longitudinal field component contributes a consistent sign with respect to the HSR, it is called "HSR-compliant" current, otherwise it is called "HSR-noncompliant" current. Firstly, consistency between the butterfly diagram of RJz and current helicity was obtained in a statistical study. Active regions with RJz smaller than 0.5 tend to obey the HSR whereas those with RJz greater than 0.5 tend to disobey it. The "HSR-compliant" current systems have a 60％ probability of realization compared to 40％ for "HSR-noncompliant" current systems. Overall, the HSR is violated for active regions in which the "HSR-noncompliant" current is greater than the "HSR-compliant" current. Secondly, the parameter RJz was subsequently used to study the evolution of current systems in the case analyses of flare-productive active regions NOAA AR 11158 and AR 11283. It is found that there is a "RJz -quasistationary" phase that is relatively flare quiescent and "RJz-dynamic" phase that is characterized by the occurrence of large flares.