A Normalized Sunspot-Area Series Starting in 1832: an Update

TL;DR

This paper reconstructs a continuous, normalized sunspot-area series from 1832 to 2008 by linking historical and modern data sources, and analyzes its periodicities and the Waldmeier effect.

Contribution

It provides a new, extended sunspot-area series starting in 1832 and compares its properties with sunspot number series, including spectral analysis and Waldmeier effect study.

Findings

Identified periodicities beyond the 11-year solar cycle.

Confirmed the Waldmeier effect in sunspot number series.

Found a weak relationship between the Waldmeier effect and sunspot-area series.

Abstract

A new normalized sunspot-area series has been reconstructed from the series obtained by the Royal Greenwich Observatory and other contemporary institutions for the period 1874 - 2008 and the area series compiled by De la Rue, Stewart, and Loewy from 1832 to 1868. Since the two sets of series do not overlap in time, we used as a link between them the new version of sunspot index number (Version 2) published by SILSO (Sunspot Index and Long-term Solar Observations). We also present a spectral analysis of the normalized area series in search of periodicities beyond the well-known solar cycle of 11 years and a study of the Waldmeier effect in the new version of sunspot-number and the sunspot-area series presented in this study. We conclude that while this effect is significant in the new series of sunspot number, it has a weak relationship with the sunspot-area series.