Restoring process of sunspot penumbra

TL;DR

This paper investigates the dynamic process of sunspot penumbra restoration, highlighting magnetic field inclination changes, flow transitions, and the formation of uncombed magnetic configurations over approximately 72 hours.

Contribution

It provides detailed observational insights into the magnetic and flow evolution during penumbra restoration, emphasizing the role of magnetic inclination changes without flux emergence.

Findings

Penumbra sector restored in about 72 hours.

Transition from counter-Evershed to classical Evershed flow observed.

Formation of uncombed magnetic field configuration during penumbra re-establishment.

Abstract

We describe the disappearance of a sector of sunspot penumbra and its restoring process observed in the preceding sunspot of active region NOAA 12348. The evolution of the magnetic field and the plasma flows support the idea that the penumbra forms due to a change of inclination of the magnetic field of the canopy. Moving magnetic features have been observed during the disintegration phase of that sector of sunspot penumbra. During the restoring phase we have not observed any magnetic flux emergence around the sunspot. The restoring process of the penumbra sector completed in about 72 hours and it was accompanied by the transition from the counter-Evershed flow to the classical Evershed flow. The inversion of photospheric spectropolarimetric measurements taken by IBIS allowed us to reconstruct how the uncombed configuration of the magnetic field forms during the new settlement of the penumbra, i.e., the vertical component of the magnetic field seems to be progressively replaced by some horizontal field lines, corresponding to the intra-spines.