A statistical study of rotational sunspots in solar cycle 24: Comparing with solar flares and CMEs

The rapid rotation of sunspots is considered as one possible mechanism for triggering solar eruptions. The sunspot rotation may also contribute to the accumulation of magnetic helicity in solar active regions. Studying the sunspot rotation and the underlying mechanisms behind this motion is crucial for enhancing our understanding of solar eruptions. We aim to investigate the relationships between rotational sunspots and solar eruptions, including solar flares and coronal mass ejections (CMEs), in a larger sample. In this study, we have examined the full-disk HMI vector magnetograms with temporal resolution of one day from 2011 to 2019 and found 163 active regions that exhibit a near-bipolar configuration with single or pair of sunspots. To determine the sunspot rotation, we first employed the Differential Affine Velocity Estimator for vector magnetograms (DAVE4VM) to the HMI vector magnetogram to calculate the photospheric velocity field. We then applied the Automated Swirl Detection Algorithms (ASDA;Liu et al. 2019) to the velocity field to verify the presence of sunspot rotation. All 163 active regions were analyzed for five-days evolution to detect rotational sunspots. Some previous studies have doubted whether sunspot rotation represents an actual motion. Therefore, in this study, we only focus on the long-time rotation lasting for at least 10 hours. The results indicate that only 38 active regions are associated with rotational sunspots. We subsequently estimated the duration of rotation and the average rotational velocity for each sunspot. The rotational durations range from 16 hours to 100 hours and the average rotational velocities range from 1.00 to 4.73 deg per hour. Interestingly, not all rotational sunspots are associated with CMEs. About 16 active regions with rotational sunspots produced eruptive flares. The average rotation duration of sunspots with CMEs is approximately 10 hours longer than the sunspot without CMEs, while the average rotational velocities remain similar.