# Recent insights on the penumbra formation process

## TL;DR

This study uses high-resolution solar observations to analyze the rapid formation of penumbrae in active regions, revealing the timing, location, and flow changes associated with penumbra development and contrasting previous findings.

## Contribution

It provides new insights into the timing, location, and flow dynamics of penumbra formation, highlighting the role of flux emergence regions and flow transitions.

## Key findings

- Evershed flow begins within 1-3 hours of penumbra formation.
- Stable penumbra forms facing opposite polarity in flux emergence regions.
- Inverse Evershed flow transitions to classical Evershed flow during penumbra development.

## Abstract

Using high-resolution spectropolarimetric data acquired by \textit{IBIS}, as well as \textit{SDO}/HMI observations, we studied the penumbra formation in AR NOAA 11490 and in a sample of twelve ARs appeared on the solar disk on 2011 and 2012, which were characterized by $\beta$-type magnetic field configuration. The results show that the onset of the classical Evershed flow occurs in a very short time scale, 1-3 hours. Studying the formation of the first penumbral sector around the following proto-spot, we found that a stable penumbra forms in the area facing the opposite polarity, which appears to be co-spatial with an AFS, i.e. in a flux emergence region, in contrast with the results of \cite{Schlichenmaier2010} concerning the leading polarity of AR NOAA 11490. Conversely, analyzing the sample of twelve ARs, we noticed that there is not a preferred location for the formation of the first penumbral sector. We also observed before the penumbra formation an inverse Evershed flow, which changes its sign when the penumbra appears. This confirms the observational evidence that the appearance of the penumbral filaments is correlated with the transition from the inverse Evershed to the classical Evershed flow. Furthermore, the analysis suggests that the time needed to form the penumbra may be related to the location where the penumbra first appears. New high-resolution observations, like those that will be provided by the European Solar Telescope, are expected to increase our understanding of the penumbra formation process.