A new type of small-scale downflow patches in sunspot penumbrae

TL;DR

This study identifies small-scale downflow patches in sunspot penumbrae, revealing their properties, magnetic configurations, and potential links to chromospheric activity, advancing understanding of sunspot dynamics.

Contribution

It reports the discovery of small-scale downflow patches with unique configurations, suggesting new mechanisms for sunspot penumbral flows and their chromospheric interactions.

Findings

Downflow patches are 0.5" or smaller with ~1 km/s velocity.

Some downflows are associated with chromospheric brightenings.

Downflows may result from magnetic reconnection or overturning magnetoconvection.

Abstract

A sunspot penumbra is observationally examined to reveal properties of small-scale flow structures and how they are related to the filamentary magnetic structures and the Evershed flow. We also study how the photospheric dynamics is related to chromospheric activities. The study is based on data analysis of spectro-polarimetric observations of photospheric Fe I lines with the Solar Optical Telescope aboard Hinode in a sunspot penumbra at different heliocentric angles. Vector magnetic fields and velocities are derived using the spectro-polarimetric data and a Stokes inversion technique. An observation with a Ca II H filtergram co-spatial and co-temporal with the spectro-polarimetric one is also used to study possible chromospheric responses. We find small patches with downflows at photospheric layers. The downflow patches have a size of 0.5" or smaller and have a geometrical configuration different from that of the Evershed flow. The downflow velocity is about 1 km/s at lower photspheric layers, and is almost zero in the upper layers. Some of the downflow patches are associated with brightenings seen in Ca II H images. The downflows are possible observational signatures of downward flows driven by magnetic reconnection in the interlaced magnetic field configuration, where upward flows make brightenings in the chromosphere. Another possibility is that they are concentrated downward flows of overturning magnetoconvection.