Photospheric Shear Flows in Solar Active Regions and Their Relation to Flare Occurrence

TL;DR

This study quantitatively links photospheric shear flows in solar active regions to flare occurrence, showing that larger shear flow parameters correlate with increased flare likelihood and shorter waiting times for major flares.

Contribution

It introduces a comprehensive analysis of shear-flow parameters derived from vector magnetograms and their relation to flare rates and timing, providing new quantitative insights.

Findings

Larger shear-flow sums (S_sum) increase the likelihood of flares within 24 hours.

Higher S_sum values are associated with shorter waiting times until the next major flare.

Active regions with strong shear flows tend to produce major flares more rapidly.

Abstract

Solar active regions (ARs) that produce major flares typically exhibit strong plasma shear flows around photospheric magnetic polarity inversion lines (MPILs). It is therefore important to quantitatively measure such photospheric shear flows in ARs for a better understanding of their relation to flare occurrence. Photospheric flow fields were determined by applying the Differential Affine Velocity Estimator for Vector Magnetograms (DAVE4VM) method to a large data set of 2,548 co-aligned pairs of AR vector magnetograms with 12-min separation over the period 2012-2016. From each AR flow-field map, three shear-flow parameters were derived corresponding to the mean (<S>), maximum (S_max) and integral (S_sum) shear-flow speeds along strong-gradient, strong-field MPIL segments. We calculated flaring rates within 24 hr as a function of each shear-flow parameter, and also investigated the relation between the parameters and the waiting time ({\tau}) until the next major flare (class M1.0 or above) after the parameter observation. In general, it is found that the larger S_sum an AR has, the more likely it is for the AR to produce flares within 24 hr. It is also found that among ARs which produce major flares, if one has a larger value of S_sum then {\tau} generally gets shorter. These results suggest that large ARs with widespread and/or strong shear flows along MPILs tend to not only be more flare productive, but also produce major flares within 24 hr or less.