多个太阳矢量磁像仪数据计算的电流螺度对比分析

从20世纪90年代开始,太阳光球电流螺度研究已经取得了重大进展.大样本的统计结果揭示了电流螺度分布的一个重要趋势:太阳表面的活动区,在北半球的螺度符号主要为负值,在南半球的螺度符号主要为正值.虽然不同仪器观测的矢量磁场计算得到的电流螺度符号具有基本的一致性,但它们之间还存在着一些差异.本文中,利用不同矢量磁像仪观测的矢量磁场数据,我们分析了电流螺度随磁场强度的变化,探讨了不同仪器之间差异的原因.我们将纵向磁场和总磁场按强度划分成6个区间,计算了每个区间内电流螺度密度的平均值h_c.统计结果显示:当纵向磁场小于600 G时,由不同仪器数据计算的h_c具有很好的一致性,并且遵守螺度半球符号法则;当纵向磁场大于600 G时,不同仪器之间的差异增大,并且在有的磁场区间内,电流螺度不遵守半球螺度符号法则;南半球的电流螺度更好地符合半球螺度符号法则.电流螺度随总磁场的变化趋势与纵场的相似.利用同样的方法,对个别活动区进行研究,分析磁光效应对电流螺度的影响.通过上述分析,我们得出当纵向磁场小于600 G时,计算得到的电流螺度基本可信.当纵向磁场大于600 G时,造成不同仪器之间差异的真实原因需进一步研究.

Comparison analysis of current helicity inferred from several solar vector magnetographs

Since the 1990 s, great progress has been made in study of current helicity in solar photosphere. The statistical results of large samples reveal an important trend of current helicity distribution: active regions in solar surface mainly show negative sign of current helicity in northern hemisphere and positive in southern hemisphere. In this paper, using vector magnetograms from different vector magnetographs, we analyzed the variation of current helicity density h_c with magnetic field and discussed the reasons for differences among different instruments. We divided longitudinal magnetic field B_z and total magnetic field B into six intervals and calculated h_c in each interval. The statistical study show that: for B_z was less than 600 G, there was a good consistency of h_c inferred from different data sets, and h_c obeyed the hemispheric sign rule(HSR);for B_z was larger than 600 G, the discrepancy among different data sets increased and hcdisobey the HSR in some B_z intervals;the HSR was better followed in southern hemisphere. The variation trend of hcwith B was similar to that of B_z. Using the same method, we studied individual active region and analyzed the influence of magnetic optical effect on helicity calculation. Through the above analysis, we conclude that the calculated helicity parameters are basically believable when B_z is less than 600 G. The real reasons for the discrepancy among different instruments when B_z is larger than 600 G need to be further studied.