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Long-term variation of sunspot penumbra to umbra area ratio

A study using Kodaikanal white-light Digitized Data

Published online by Cambridge University Press:  27 November 2018

Bibhuti Kumar Jha ,
Sudip Mandal  and
Dipankar Banerjee Open the ORCID record for Dipankar Banerjee [Opens in a new window]
Bibhuti Kumar Jha
Affiliation:
Indian Institute of Astrophysics, Banglore 560034, India email: bibhuti.kj@iiap.res.in
Sudip Mandal
Affiliation:
Indian Institute of Astrophysics, Banglore 560034, India email: bibhuti.kj@iiap.res.in
Dipankar Banerjee
Affiliation:
Indian Institute of Astrophysics, Banglore 560034, India email: bibhuti.kj@iiap.res.in Center of Excellence in Space Sciences India, IISER Kolkata, Mohanpur 741246, West Bengal, India email: dipu@iiap.res.in
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Abstract

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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 used 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 μHem 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.

Keywords

Sun: sunspotsSun: magnetic fields
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 13 , Symposium S340: Long-term Datasets for the Understanding of Solar and Stellar Magnetic Cycles , February 2018 , pp. 185 - 186
Copyright
Copyright © International Astronomical Union 2018 

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