Statistical distribution of current helicity in solar active regions over the magnetic cycle

TL;DR

This study analyzes over 20 years of solar active region data to examine the statistical distribution of current helicity, revealing mostly Gaussian distributions with some multi-component deviations and their relation to hemispheric sign rules.

Contribution

It provides a comprehensive statistical analysis of current helicity distributions in solar active regions over two decades, highlighting deviations from Gaussianity and their implications.

Findings

Most helicity distributions are close to Gaussian.

Some domains show multi-component distributions with zero-mean components.

Large helicity values can influence hemispheric sign rule adherence.

Abstract

The current helicity in solar active regions derived from vector magnetograph observations for more than 20 years indicates the so-called hemispheric sign rule; the helicity is predominantly negative in the northern hemisphere and positive in the southern hemisphere. In this paper we revisit this property and compare the statistical distribution of current helicity with Gaussian distribution using the method of normal probability paper. The data sample comprises 6630 independent magnetograms obtained at Huairou Solar Observing Station, China, over 1988-2005 which correspond to 983 solar active regions. We found the following. (1) For the most of cases in time-hemisphere domains the distribution of helicity is close to Gaussian. (2) At some domains (some years and hemispheres) we can clearly observe significant departure of the distribution from a single Gaussian, in the form of two- or multi-component distribution. (3) For the most non-single-Gaussian parts of the dataset we see co-existence of two or more components, one of which (often predominant) has a mean value very close to zero, which does not contribute much to the hemispheric sign rule. The other component has relatively large value of helicity that often determines agreement or disagreement with the hemispheric sign rule in accord with the global structure of helicity reported by Zhang et al. (2010).