# Study of Sunspot Penumbra to Umbra Area Ratio using Kodaikanal White-light Digitized Data

## TL;DR

This study analyzes long-term sunspot area ratios using digitized Kodaikanal data and confirms findings with SOHO/MDI data, revealing size-dependent variations and stability over solar cycles.

## Contribution

Introduces an automated umbra extraction method and provides new insights into sunspot area ratio behavior over multiple solar cycles and different datasets.

## Key findings

- Ratio increases with sunspot size from 5.5 to 6.
- No long-term trend for small sunspots (<100 μhem).
- Method validated with SOHO/MDI data.

## Abstract

We study the long-term behaviour of sunspot penumbra to umbra area ratio by analyzing the recently digitized Kodaikanal white-light data (1923-2011). We implement an automatic umbra extraction method and compute the ratio over eight solar cycles (Cycles 16-23). Although the average ratio doesn't show any variation with spot latitudes, cycle phases and strengths, it increases from 5.5 to 6 as the sunspot size increases from 100 $\mu$hem to 2000 $\mu$hem. Interestingly, our analysis also reveals that this ratio for smaller sunspots (area $<$ 100 $\mu$hem) does not have any long-term systematic trend which was earlier reported from the Royal Observatory, Greenwich (RGO) photographic results. To verify the same, we apply our automated extraction technique on Solar and Heliospheric Observatory (SOHO)/Michelson Doppler Imager (MDI) continuum images (1996-2010). Results from this data not only confirm our previous findings, but also show the robustness of our analysis method.