Intermittency spectra of current helicity in solar active regions

TL;DR

This study analyzes the spatial distribution and intermittency of current helicity in solar active regions using multi-instrument data, revealing that increased intermittency precedes magnetic flux emergence, indicating subphotospheric activity.

Contribution

It introduces a comparative analysis of current helicity maps from different instruments and applies flatness function analysis to identify precursors of magnetic flux emergence.

Findings

High correlation between spaceborne and ground-based helicity maps.

Intermittency increases 12-20 hours before flux emergence.

Flatness exponent serves as a potential precursor indicator.

Abstract

We analyse the spatial distribution of current helicity in solar active regions. A comparison of current helicity maps derived from three different instruments (Helioseismic and Magnetc Imager on board the Solar Dynamics Observatory, SDO/HMI, Spectro-Polarimeter on board the Hinode, and Solar Magnetic Field Telescope at the Huairou Solar Observing Station, China, HSOS/SMFT) is carried out. The comparison showed an excellent correlation between the maps derived from the spaceborne instruments and moderate correlation between the maps derived from SDO/HMI and HSOS/SMFT vector magnetograms. The results suggest that the obtained maps characterize real spatial distribution of current helicity over an active region. To analyse intermittency of current helicity, we traditionally use the high-order structure functions and flatness function approach. The slope of a flatness function within some range of scales - the flatness exponent - is a measure of the degree of intermittency. SDO/HMI vector magnetograms for 3 ARs (NOAA 11158, 12494, and 12673) were used to calculate the flatness exponent time variations. All three ARs exhibited emergence of a new magnetic flux during the observational interval. The flatness exponent indicated the increase of intermittency 12-20 hours before the emergence of a new flux. We suppose that this behaviour can indicate subphotospheric fragmentation or distortion of the pre-existed electric current system by emerging magnetic flux.