Evolution of twist-shear and dip-shear during X-class flare of 13 December 2006: Hinode observations

TL;DR

This study introduces and analyzes the evolution of a new magnetic shear measure, dip-shear, alongside twist-shear, during an X-class solar flare, revealing their correlated behavior and implications for flare monitoring.

Contribution

The paper presents the first analysis of dip-shear, a novel measure of magnetic shear related to inclination, in solar active regions during a flare, using high-resolution Hinode data.

Findings

Dip-shear decreases after the flare in the flaring region.

Twist-shear tends to increase after the flare.

Dip-shear and twist-shear are highly correlated, especially post-flare.

Abstract

The non-potentiality (NP) of the solar magnetic fields is measured traditionally in terms of magnetic shear angle i.e., the angle between observed and potential field azimuth. Here, we introduce another measure of shear that has not been studied earlier in solar active regions, i.e. the one that is associated with the inclination angle of the magnetic field. This form of shear, which we call as the "dip-shear", can be calculated by taking the difference between the observed and potential field inclination. In this Letter, we study the evolution of dip-shear as well as the conventional twist-shear in a $\delta$-sunspot using high-resolution vector magnetograms from {\it Hinode} space mission. We monitor these shears in a penumbral region located close to flare site during 12 and 13 December 2006. It is found that: (i) the penumbral area close to the flaring site shows high value of twist-shear and dip-shear as compared to other parts of penumbra, (ii) after the flare the value of dip-shear drops in this region while the twist-shear in this region tends to increase after the flare, (iii) the dip-shear and twist-shear are correlated such that pixels with large twist-shear also tend to exhibit large dip-shear, and (iv) the correlation between the twist-shear and dip-shear is tighter after the flare. The present study suggests that monitoring twist-shear during the flare alone is not sufficient but we need to monitor it together with dip-shear.