Data-driven MHD simulation of a sunspot-rotating active region leading to homologous CMEs

Coronal mass ejections (CMEs) are the leading driver of space weather and it is vital for space weather forecasting to benefit from a comprehensive understanding of the conditions in which CMEs are initiated. The rotation of sunspots around their umbral center has long been considered an important condition leading to CMEs. To unveil the underlying mechanisms, we carried out a data-driven MHD simulation for the event of a large sunspot with a rotation of days in a solar active region, NOAA 12158, which produced two homologous halo CMEs. Our simulation successfully follows the long-term quasi-static evolution of the active region and the eruptions, with magnetic field structure being highly consistent with the observed coronal emission. The onset time of the simulated eruption is a very good match to the observations. The simulation shows that through the successive rotation of the sunspot, the coronal magnetic field is sheared with a vertical current sheet created progressively. Once fast reconnection sets in at the current sheet, the eruption is instantly triggered, with a highly twisted flux rope originating from the eruption, forming the CME. This data-driven simulation stresses magnetic reconnection as the key mechanism in CMEs resulting from sunspot rotation.