Sunspot Rotation Leading to Coronal Mass Ejection

Abstract

The rotation of sunspots around their umbral center has long been considered as an important process in driving coronal mass ejections (CMEs), but the specific mechanism remains unclear. Here with numerical magnetohydrodynamic simulations of both data-inspired and data-driven approaches, we show that the rotation of a large sunspot leads to a CME actually in a way distinct from the conventional view based on ideal instabilities of twisted flux rope. It is found that through the successive rotation of the sunspot the coronal magnetic field is sheared with a vertical current sheet created progressively, and once fast reconnection sets in the current sheet, the eruption is instantly triggered, with a highly twisted flux rope originating from the eruption. The simulations also revealed a slow-rise evolution phase sandwiched between the quasi-static energy-storage phase and the impulsive eruption-acceleration phase, and it enhances building up of the current sheet.

MHD Simulation of Homologous Eruptions from Solar Active Region 10930 Caused by Sunspot Rotation

“…As a consequence, the eruption strength will decrease, because according to Bian et al (2022b), the eruption strength is highly correlated with the magnetic gradient of the main PIL. A more realistic velocity field at the photosphere, including rotational, shearing, and convergent motions, derived from observations could be applied as a boundary condition to get a more self-consistent and realistic evolution (which has been shown in Jiang et al 2021aJiang et al , 2022b. Another key point we have not considered in the current model is the flux emergence process, for which the normal velocity (i.e., velocity in the z direction) at the photosphere ought to be used to mimic the emergence process of the sunspot.…”

MHD Simulation of Homologous Eruptions from Solar Active Region 10930 Caused by Sunspot Rotation

“…As a consequence the eruption strength will decrease, because according to Bian et al (2022b), the eruption strength is highly correlated with the magnetic gradient of the main PIL. A more realistic velocity field at photosphere, including rotational, shearing and converge motions, derived from observation could be applied as the boundary condition to get a more self-consistent and realistic evolution (which has been shown in Jiang et al 2021a andJiang et al 2022b). Another key point we have not considered in the current model is the flux emergence process, for which the normal velocity (i.e.…”

“…These adjustment has potential to get a higher degree of consistence between simulated QSLs and observed flare ribbons. Also the converge motions (i.e., the collision of the two sunspots) will shorten the evolution time since it will enhance the building up of the PIL-CS and enhance the amount of the magnetic energy release by strengthening the magnetic gradient near PIL (Bian et al 2022b). Though more complex motions and settings may reproduce the flares more realistically, our result shows the key role played by sunspot rotation in leading to the eruptions and can shed light on the onset mechanism of this homologous event.…”