Disintegration of Magnetic Flux in Decaying Sunspots as Observed with the Hinode SOT

TL;DR

This study uses Hinode SOT observations to explore how magnetic flux disintegrates in decaying sunspots, revealing the roles of granules, dark filaments, and Evershed flows in flux separation and sunspot decay.

Contribution

It provides new insights into the magnetic flux disintegration process, highlighting the relationship between convective motions, dark filaments, and MMF formation in sunspot decay.

Findings

Granules appear in the outer penumbra and are linked to boundary fluctuations.

Dark penumbral filaments elongate into the moat region, indicating horizontal magnetic fields.

Pairs of MMFs with opposite polarities are observed along dark filaments, supporting a sea serpent magnetic structure.

Abstract

Continuous observations of sunspot penumbrae with the Solar Optical Telescope aboard \textit{Hinode} clearly show that the outer boundary of the penumbra fluctuates around its averaged position. The penumbral outer boundary moves inward when granules appear in the outer penumbra. We discover that such granules appear one after another while moving magnetic features (MMFs) are separating from the penumbral ``spines'' (penumbral features that have stronger and more vertical fields than those of their surroundings). These granules that appear in the outer penumbra often merge with bright features inside the penumbra that move with the spines as they elongate toward the moat region. This suggests that convective motions around the penumbral outer boundary are related to the disintegration of magnetic flux in the sunspot. We also find that dark penumbral filaments frequently elongate into the moat region in the vicinity of MMFs that detach from penumbral spines. Such elongating dark penumbral filaments correspond to nearly horizontal fields extending from the penumbra. Pairs of MMFs with positive and negative polarities are sometimes observed along the elongating dark penumbral filaments. This strongly supports the notion that such elongating dark penumbral filaments have magnetic fields with a ``sea serpent''-like structure. Evershed flows, which are associated with the penumbral horizontal fields, may be related to the detachment of the MMFs from the penumbral spines, as well as to the formation of the MMFs along the dark penumbral filaments that elongate into the moat region.