Temporal Relation Between the Disappearance of Penumbral Fine-scale Structure and Evershed Flow

Abstract

We investigate the temporal relation between the Evershed flow, dot-like bright features (penumbral grain), the complex magnetic field structure, and dark lanes (dark core) along bright filaments in a sunspot penumbra. We use a time series of high spatial resolution photospheric intensity, vector magnetic field maps, and Doppler velocity maps obtained with the Solar Optical Telescope aboard the Hinode spacecraft. We conclude that the appearance and disappearance of the Evershed flow and penumbra grains occur at nearly the same time and are associated with changes of the inclination angle of the magnetic field from vertical to more horizontal. This supports the idea that Evershed flow is a result of thermal convection in the inclined field lines. The dark core of the bright penumbral filament also appears coincidental with the Evershed flow. However, the dark-cored bright filament survives at least for 10-20 minutes after the disappearance of the Evershed flow. The heat input into the bright filament continues even after the end of heat transfer by the Evershed flow. This suggests that local heating along the bright filament is important for maintaining its brightness, in addition to heat transfer by the Evershed flow.