Sub-Surface Meridional flow, Vorticity and the life time of Solar Active Regions

TL;DR

This study investigates sub-surface flows and vorticity in solar active regions, revealing complex flow structures and a correlation between vorticity and active region lifetime, which could aid in predicting solar activity duration.

Contribution

It uncovers the presence of steep meridional velocity gradients and sheared layers in active regions, and links vorticity patterns to the active regions' life expectancy.

Findings

Steep meridional velocity gradients at 1.5-5 Mm depth in ARs.

Identification of three sheared flow layers within 0-10 Mm depth.

Correlation between the deepest zero vorticity and AR lifetime.

Abstract

Solar sub-surface fluid topology provides an indirect approach to examine the internal characteristics of active regions (ARs). Earlier studies have revealed the prevalence of strong flows in the interior of ARs having complex magnetic fields. Using the Doppler data obtained by the Global Oscillation Network Group (GONG) project for a sample of 74 ARs, we have discovered the presence of steep gradients in meridional velocity at depths ranging from 1.5 to 5 Mm in flare productive ARs. The sample of these ARs is taken from the Carrington rotations 1980--2052 covering the period August 2001-January 2007. The gradients showed an interesting hemispheric trend of negative (positive) signs in the northern (southern) hemisphere, i.e., directed toward the equator. We have discovered three sheared layers in the depth range of 0 - 10 Mm, providing an evidence of complex flow structures in several ARs. An important inference derived from our analysis is that the location of the deepest zero vertical vorticity is correlated with the remaining life time of ARs. This new finding may be employed as a tool for predicting the life expectancy of an AR.