On the Role of Rotating Sunspots in the Activity of Solar Active Region NOAA 11158

TL;DR

This study investigates how rotating sunspots influence the magnetic non-potentiality and eruptive activity of solar active region NOAA 11158, highlighting the correlation between sunspot rotation, energy buildup, and solar eruptions.

Contribution

It provides new insights into the role of sunspot rotation and flux motions in enhancing magnetic non-potentiality and triggering solar eruptions, using multi-wavelength and magnetic field data.

Findings

Peak sunspot rotation coincides with eruptive events.

Energy decreases at flare onset indicating energy release.

Helicity injection varies between CME and flare-prone regions.

Abstract

We study the role of rotating sunspots in relation to the evolution of various physical parameters characterizing the non-potentiality of the active region NOAA 11158 and its eruptive events using the magnetic field data from the Helioseismic and Magnetic Imager (HMI) and multi-wavelength observations from the Atmospheric Imaging Assembly (AIA) on board Solar Dynamics Observatory (SDO). From the evolutionary study of HMI intensity and AIA channels, it is observed that the AR consists of two major rotating sunspots one connected to flare-prone region and another with CME. The constructed space-time intensity maps reveal that the sunspots exhibited peak rotation rates coinciding with the occurrence of the major eruptive events. Further, temporal profiles of twist parameters, viz., average shear angle, $\alpha_{\rm av}$, $\alpha_{\rm best}$, derived from HMI vector magnetograms and the rate of helicity injection, obtained from the horizontal flux motions of HMI line-of-sight magnetograms, corresponded well with the rotational profile of the sunspot in CME-prone region, giving predominant evidence of rotational motion to cause magnetic non-potentiality. Moreover, mean value of free-energy from the Virial theorem calculated at the photospheric level shows clear step down decrease at the on set time of the flares revealing unambiguous evidence of energy release, intermittently that is stored by flux emergence and/or motions in pre-flare phases. Additionally, distribution of helicity injection is homogeneous in CME prone region while it is not and often changes sign in flare-prone region. This study provides clear picture that both proper and rotational motions of the observed fluxes played significant role to enhance the magnetic non-potentiality of the AR, leading to favorable conditions for the observed transient activity.