Morphological study of penumbral formation

TL;DR

This paper observationally investigates the formation of penumbrae in sunspots, identifying multiple pathways such as magnetic flux accumulation, magnetic field emergence, and twisted magnetic tubes, using continuous Hinode observations.

Contribution

It reveals multiple morphological pathways for penumbral formation and emphasizes the role of magnetic field inclination and flux dynamics in this process.

Findings

Multiple paths to penumbral formation identified

Magnetic flux accumulation and emergence are key processes

Magnetic field inclination remains high at flux tube edges

Abstract

Penumbrae are known to be area of mainly horizontal magnetic field surrounding umbrae of relatively large and mature sunspots. In this paper, we observationally studied the formation of penumbrae in NOAA10978, where several penumbral formations were observed in G-band images of SOT/Hinode. Thanks to the continuous observation by Hinode, we could morphologically follow the evolution of sunspots and found that there are several paths to the penumbral formation: (1) Active accumulation of magnetic flux, (2) Rapid emergence of magnetic field, and (3) Appearance of twisted or rotating magnetic tubes. In all of these cases, magnetic fields are expected to sustain high inclination at the edges of flux tube concentration longer than the characteristic growth time of downward magnetic pumping.