Search for a Signature of Twist-Removal in the Magnetic Field of Sunspots in Relation with Major Flares

TL;DR

This study examines magnetic field restructuring in sunspots during major flares, using innovative methods to detect twist removal, and finds results consistent with the twist-removal model, enhancing understanding of flare-related magnetic changes.

Contribution

It introduces the azimuthal symmetry approach to analyze magnetic field changes in sunspots during flares, validating its effectiveness against full vector magnetogram data.

Findings

Changes in magnetic twist consistent with twist-removal model

Azimuthal symmetry approach agrees with vector magnetogram data

Magnetic field distribution may deviate from symmetry even in symmetric sunspots

Abstract

We investigate the restructuring of the magnetic field in sunspots associated with two flares: the X6.5 flare on 6 December 2006 and the X2.2 flare on 15 February 2011. The observed changes were evaluated with respect to the so-called twist-removal model, in which helicity (twist) is removed from the corona as the result of an eruption. Since no vector magnetograms were available for the X6.5 flare, we applied the azimuthal symmetry approach to line-of-sight magnetograms to reconstruct the pseudo-vector magnetic field and investigate the changes in average twist and inclination of magnetic field in the sunspot around the time of the flare. For the X2.2 flare, results from the full vector magnetograms were compared with the pseudo-vector field data. For both flares, the data show changes consistent with the twist-removal scenario. We also evaluate the validity of the azimuthal symmetry approach on simple isolated round sunspots. In general, the derivations based on the azimuthal symmetry approach agree with true-vector field data though we find that even for symmetric sunspots the distribution of the magnetic field may deviate from an axially symmetric distribution.