Restoring Process of Sunspot Penumbra

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 supports 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 hr 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 the Interferometric Bidimensional Spectroscopic Instrument (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 intraspines....