Flare differentially rotates sunspot on Sun's surface

TL;DR

This study reports the first clear observation of a sunspot's sudden, non-uniform rotation triggered by a solar flare, revealing direct interactions between coronal magnetic restructuring and the solar surface.

Contribution

It provides direct observational evidence of flare-induced sunspot rotation and links it to magnetic field changes and energy transfer mechanisms.

Findings

Sunspot rotation is non-uniform and correlates with flare peaks.

Flare induces a rapid, localized rotation of the sunspot.

Magnetic restructuring causes surface Lorentz-force changes and energy flux.

Abstract

Sunspots are concentrations of magnetic field visible on the solar surface (photosphere). It was considered implausible that solar flares, as resulted from magnetic reconnection in the tenuous corona, would cause a direct perturbation of the dense photosphere involving bulk motion. Here we report the sudden flare-induced rotation of a sunspot using the unprecedented spatiotemporal resolution of the 1.6 m New Solar Telescope, supplemented by magnetic data from the Solar Dynamics Observatory. It is clearly observed that the rotation is non-uniform over the sunspot: as the flare ribbon sweeps across, its different portions accelerate (up to 50 deg per hr) at different times corresponding to peaks of flare hard X-ray emission. The rotation may be driven by the surface Lorentz-force change due to the back reaction of coronal magnetic restructuring and is accompanied by a downward Poynting flux. These results have direct consequences for our understanding of energy and momentum transportation in the flare-related phenomena.