Formation of current helicity and emerging magnetic flux in solar active regions

Abstract

This paper aims to study the properties of the current helicity in solar active regions. The current helicity provides different information relative to the magnetic helicity and has a simple relationship with the magnetic energy in the approximation of the force-free field. For example, we analyse the active region (NOAA 7321) which was a newly emerging delta active region in 1992 October. It provides good evidence for the development of the magnetic chirality in the solar active regions. From a series of photospheric-vector magnetograms and corresponding soft X-ray images, it is found that the newly emerging magnetic flux associates the current helicity from the subatmosphere in the active regions with the redistribution of the current helicity density in the upper atmosphere, i.e. it provides observational evidence that flux and helicity emerge together.