A Semi-Automatic Method to Measure the Rotation of Sunspots

Abstract Sunspots have been observed to undergo rotation about their umbral centre. This is typically a slow rotation, with even the fastest sunspot rotations only reaching angular velocities of few degrees per hour. may inject magnetic energy into Sun’s atmosphere, which can be stored in coronal field and later released eruptive events such as solar flares mass ejections. To usefully investigate rotating sunspots long periods data need analysed, often order several days, build up bulk profile for over time. article outlines semi-automated approach analysing series continuum extract it transits across disc. Moving towards an automated vital generating large, unbiased statistical samples understand contribution activity. Existing methods focus on near disc centre short time periods, neglecting much history sunspot. The method tested six from Helioseismic Magnetic Imager (HMI) instrument board Solar Dynamics Observatory (SDO). These chosen test range different types sunspots, including well-behaved shape-changing fast rotators, non-rotators, interacting sunspots. profiles are compared by eye animations acceptable visual agreement all cases, except one contains two shared penumbra. also against active region (AR) 11158 that reported literature. While results compare some degree, outlined this reports lower than those Some discrepancy attributed selection bias approaches literature, where features larger tracked exhibit non-uniform rotation. provides uncertainties calculated broken down allow principal sources error identified. For article, dominant source uncertainty resolution SDO/HMI instrument.