Equivalence relations between the Cortie and Zurich sunspot group morphological classifications

TL;DR

This paper proposes a method to convert Cortie sunspot group classifications into Zurich types, facilitating the merging of historical sunspot catalogues and validating the scheme with data from the Valencia Observatory.

Contribution

A novel conversion scheme between Cortie and Zurich sunspot classifications, validated using historical data and comparison across multiple catalogues.

Findings

The conversion scheme accurately reproduces Zurich types from Cortie classifications.

The method performs well within the error margins of different catalogues.

Validation shows the scheme's robustness across historical data sets.

Abstract

Catalogues of sunspots have been available with useful information about sunspots or sunspot groups for approximately the last 150 years. However, the task of merging these catalogues is not simple. In this paper, a method is suggested of converting the types of sunspot groups that were proposed by Cortie (1901) into the well-known Zurich types of sunspot groups. To achieve this, the sunspot catalogue of the Valencia University Observatory (from 1920 to 1928) was used in addition to the descriptions proposed by Cortie. To assess the quality of this conversion scheme, the Zurich type was computed from the Valencia catalogue, and the resulting contribution of each group type was compared to what can be found in other catalogues. The results show that the proposed scheme works well within the errors that are found in the different catalogues.