Long-term variation of sunspot penumbra to umbra area ratio: A study using Kodaikanal white-light Digitized Data

TL;DR

This study analyzes long-term changes in sunspot structures using digitized data, revealing how the penumbra to umbra area ratio varies with sunspot size and providing insights into magnetic field evolution and solar dynamo processes.

Contribution

It introduces an automated algorithm for identifying sunspot regions and analyzing their area ratios from historical digitized images, enhancing understanding of sunspot evolution.

Findings

The penumbra to umbra ratio increases with sunspot size up to 100 msh.

The ratio stabilizes to a constant value for larger sunspots.

Results aid in understanding magnetic field evolution and solar dynamo models.

Abstract

A typical sunspot, as seen in white-light intensity images, has a two part structure: a dark umbra and a lighter penumbra. Such distinction primarily arises due to the different orientations of magnetic fields in these two regions. In this study, we use the Kodaikanal white-light digitized data archive to analyze the long-term evolution of umbral and penumbal area. We developed an 'automated algorithm' to uniquely identify the sunspot umbra (including the calculation of penumbra to umbra ratio) from these digitized intensity images. Our analysis reveals that the ratio increases slightly with the increase of sunspot area upto 100 msh but eventually settles down to a constant value after that.This study, not only allows us to better understand the evolution of an individual spot and its corresponding magnetic field but this is also beneficial for solar dynamo studies which aim to reproduce such structures using a MHD theory.