Temporal Relation between Disappearance of Penumbral Fine-Scale Structure and Evershed Flow

TL;DR

This study examines the temporal relationship between the Evershed flow, penumbral grains, magnetic field inclination, and dark lanes in a sunspot penumbra, revealing that flow and features are closely linked to magnetic inclination and local heating.

Contribution

It provides new observational evidence linking Evershed flow, penumbral grains, and dark lanes to magnetic field inclination and local heating, enhancing understanding of penumbral dynamics.

Findings

Evershed flow and penumbral grains appear/disappear simultaneously with magnetic inclination changes.

Dark core features persist after Evershed flow ceases, indicating ongoing local heating.

Evershed flow is likely driven by thermal convection along inclined magnetic field lines.

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 \textit{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 after the end of heat transfer by the Evershed flow. This suggests that local heating along the bright filament is important to maintain the brightness of the bright filament in addition to the heat transfer by the Evershed flow.