Determination Of Differential Rotation Of Sun Using Sunspots As Tracers

Priyadarshi, Aditya (2019) Determination Of Differential Rotation Of Sun Using Sunspots As Tracers. Masters thesis, Indian Institute of Science Education and Research Kolkata.

PDF (MS dissertation of Aditya Priyadarshi (14MS087)) 14MS087.pdf - Submitted Version Restricted to Repository staff only Download (3MB)

Abstract

The Sun rotates differentially, and its differential rotation can be measured by tracking the features on its surface. In this work, we look for the variation in the differential rotation of the Sun using the white light digitised data of Kodaikanal Solar Observatory from 1923 to 2011 which includes cycle 16 - 23. We developed an automatic algorithm based on image correlation technique to track the position of the sunspots. Then, we determine the differential rotation rate of the Sun using the displacement of the sunspots with a known time difference. The rotation rates obtained from Kodaikanal digitised data show a slow downward trend in the equatorial rotation rate. We observed smaller sunspots rotate faster than the larger ones. Considering different phases of the solar cycle, the rotation rate differs at high latitudes, while the equatorial rate is approximately the same. All our findings are consistent with the previous results. To check the robustness of our method we have applied our algorithm on the space-based data from Michelson Doppler Imager (MDI) onboard Solar and Heliospheric Observatory (SOHO), and Helioseismic and Magnetic Imager (HMI) onboard Solar Dynamics Observatory (SDO). The result obtained from the space-based data is in good agreement with the findings from Kodaikanal digitised data.

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