Penumbral decay observed in active region NOAA 12585

Abstract

Context. The physical conditions leading the sunspot penumbra decay are poorly understood so far. Aims. 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. Methods. A penumbral decay was observed with the CRISP instrument at the Swedish 1 m Solar Telescope on 2016 September 4 and 5 in the 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 to obtain the evolution of the magnetic and velocity properties. We complement the study with data from instruments on board the Solar Dynamics Observatory and Hinode space missions. Results. The studied penumbra disappears progressively in 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. Conclusions. 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 regulates the evolution in the different penumbral sectors.