Analysing the Rotation of Sunspots
The Sun's surface is peridoically covered in dark patches known as sunspots. These sunspots are concentrations of magnetic field lines, which are important to the understanding of the solar atmosphere and interior. In my work I use data from the Solar Dynamics Observatory to analyse the motion of these sunspots and further our understanding of how they contribute to the dynamics of the sun. I developed a technique, known as Multi-Layer Thresholding (MLT), that allows us to track the rotation of sunspots over long periods of time and see how it is affected by solar flares. The technique is an extension of traditional methods and has the advantage of being able to track multiple regions simultaneously. MLT is built up of multiple threshold layers, which can be thought of as slices across the sunspot images at different brightness levels (temperatures). In each layer, the various sunspots and umbrae appear as different blobs. Depending on how dark the sunspots are, different parts of them will show up in different layers. In all of these layers, however, each independent blob is treated as a separate cluster. After all the clusters in all the layers have been found, they can be matched up with one another; clusters that have the same position in different layers can be stacked-up. Each of these clusters can be tracked independently, and it was because of this that we were able to observe evidence of differential rotation within a sunspot umbra. Further details can be found in Grimes et al (2020).