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

arXiv commentAccepted for publication in Solar Physics (15 pages, 10 figures)

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Cited by in corpus (5)

• Extending the Sunspot Area Series from Kodaikanal Solar Observatory
• Variations of the Internal Asymmetries of Sunspot Groups During their Decay
• Clarifying Physical Properties of Magnetic Fields in Sunspots
• Temporal and Latitudinal Variation in Penumbra-Umbra Ratios of the Sunspots: Analyses of RGO, Kodaikanal and Debrecen Databases
• A Remarkably Accurate Predictor of Sunspot Cycle Amplitude