Penumbral decay observed in active region NOAA 12585

TL;DR

This study investigates the physical conditions and magnetic properties associated with sunspot penumbra decay, revealing the roles of magnetic flux, MMFs, and overlying canopies in the decay process.

Contribution

It provides new insights into the magnetic and velocity changes during penumbral decay, emphasizing the interaction with MMFs and the influence of overlying magnetic canopies.

Findings

Penumbral decay is linked to magnetic flux evolution and MMFs.

Evershed flows persist even after penumbral disappearance.

Overlying canopies influence the decay process.

Abstract

The physical conditions leading the sunspot penumbra decay are poorly understood so far. We investigate the photospheric magnetic and velocity properties of a sunspot penumbra during the decay phase to advance the current knowledge of the conditions leading to this process. A penumbral decay was observed with the CRISP instrument at the Swedish 1m Solar Telescope on 2016 September 4 and 5 in active region NOAA 12585. During these days, full-Stokes spectropolarimetric scans along the Fe I 630 nm line pair were acquired over more than one hour. We inverted these observations with the VFISV code in order to obtain the evolution of the magnetic and velocity properties. We complement the study with data from instruments onboard the Solar Dynamics Observatory and Hinode space missions. The studied penumbra disappears progressively in both time and space. The magnetic flux evolution seems to be linked to the presence of Moving Magnetic Features (MMFs). Decreasing Stokes V signals are observed. Evershed flows and horizontal fields were detected even after the disappearance of the penumbral sector. The analyzed penumbral decay seems to result from the interaction between opposite polarity fields in type III MMFs and penumbra, while the presence of overlying canopies rules the evolution in the different penumbral sectors.