Sunspot group tilt angles from drawings for cycles 19-24

TL;DR

This paper presents a new method for measuring sunspot group tilt angles over multiple solar cycles, creating a long-term database that improves accuracy and compares well with previous datasets, but raises questions about cycle strength correlation.

Contribution

Developed an interactive IDL routine for measuring sunspot tilt angles, creating a long-term, more accurate database for solar cycles 19-24, and compared results with existing datasets.

Findings

Cycle averages of tilt angles were obtained and compared.

The method improved accuracy over previous datasets.

Anti-correlation with cycle strength needs further study.

Abstract

The tilt angle of a sunspot group is a critical quantity in the surface transport of magnetic flux and the solar dynamo. To contribute long-term databases of the tilt angle, we developed an IDL routine, which allows the user to interactively select and measure sunspot positions and areas on the solar disc. We measured the tilt angles of sunspot groups for solar cycles 19-24 (1954.6-2017.8), using the sunspot drawing database of Kandilli Observatory. The method is similar to that used in the discontinued Mt. Wilson and Kodaikanal databases, with the exception that sunspot groups were identified manually, which has improved the accuracy of the resulting tilt angles. We obtained cycle averages of the tilt angle and compared them with the values from other datasets, keeping the same group selection criteria. We conclude that the previously reported anti-correlation with the cycle strength needs further investigation.