The Impact of Sunspot Rotation on Solar Flares

Abstract

Solar flares are one mechanism to release stored magnetic energy in the Sun’s atmosphere. This thesis aims to determine whether sunspot rotation can inject the energy required for solar flares into the corona. This thesis investigates the relationship between sunspot rotation and solar flares, and the impact that sunspot rotation has on the strength and frequency of flare events.
A robust analysis tool is developed which uses continuum images of the Sun to determine the rotation of sunspots. This tool is used throughout the thesis, first on the active region 11158, in an in-depth case study of the rotation and flaring properties of the region as it traverses the solar disc. The case study develops analysis techniques, such as introducing sunspot selection criteria, which are used in the following statistical studies. The first statistical study involves the analysis of the rotation and flaring properties of a sample of all sunspots that meet the selection criteria within all X-class flaring regions since the launch of the Solar Dynamics Observatory. As this first statistical study is biased towards higher flare-energy active regions, a second unbiased statistical study is carried out on all sunspots that meet the sunspot selection criteria between 1 May 2013 and 31 August 2013. The results of these statistical studies are combined and analysed, concluding that sunspot rotation injects enough energy (and in the majority of cases, an excess of energy) to account for the energy output by solar flare radiation. On average, the radiated bolometric flare energy outputs 65.6% of the injected energy due to the absolute sunspot rotation for the X-class flare sample, and 59.2% for the four-month sample.