Variation rate of sunspot area

TL;DR

This study investigates the rate of change in sunspot areas, analyzing multiple active regions with observational data and testing previous conclusions about umbra and penumbra evolution, supported by a basic magnetohydrodynamic model.

Contribution

It provides a detailed analysis of sunspot area evolution across several active regions and tests prior findings using extensive observational data and a simplified theoretical model.

Findings

Umbra area remains constant during penumbra formation.

Total sunspot area increase is mainly due to penumbra growth.

Observed area evolution is partially explained by a magnetohydrodynamic model.

Abstract

The emergence of the magnetic field through the photosphere has multiple manifestations and sunspots are the most prominent examples of this. One of the most relevant sunspot properties, to study both its structure and evolution, is the sunspot area: either total, umbra or penumbra area. Recently Schlichenmaier et al. (2010) studied the evolution of the active region (AR) NOAA 11024 concluding that during the penumbra formation the umbra area remains constant and that the increase of the total sunspot area is caused exclusively by the penumbra growth. In this presentation the Schlichenmaier's conclusion is firstly tested, investigating the evolution of four different ARs. Hundreds of Intensitygram images from the Helioseismic and Magnetic Imager (HMI) images are used, obtained by the Solar Dynamics Observatory, in order to describe the area evolution of the above ARs and estimate the increase and decrease rates for umbra and penumbra areas, separately. A simple magnetohydrodynamic model is then tentatively used in a first approximation to explain the observed results.