Secular variation of hemispheric phase differences in the solar cycle

TL;DR

This study analyzes 300 years of sunspot data to reveal long-term variations in hemispheric phase differences and their correlation with sunspot latitudinal distribution, using cross-recurrence plots.

Contribution

It demonstrates that hemispheric phase differences are not stochastic but exhibit secular variations and long-term anticorrelation with sunspot distribution.

Findings

Hemispheric phase leading changes approximately every 50-100 years.

Long-term anticorrelation between phase differences and latitudinal sunspot distribution.

Identified historical shifts in hemispheric dominance near 1783, 1875, 1928, and 1968.

Abstract

We investigate the phase difference of the sunspot cycles in the two hemispheres and compare it with the latitudinal sunspot distribution. If the north-south phase difference exhibits a long-term tendency, it should not be regarded as a stochastic phenomenon. We use datasets of historical sunspot records and drawings made by Staudacher, Hamilton, Gimingham, Carrington, Spouml;rer, and Greenwich observers, as well as the sunspot activity during the Maunder minimum reconstructed by Ribes and Nesme-Ribes. We employ cross-recurrence plots to analyse north-south phase differences. We show that during the last 300 years, the persistence of phase-leading in one of the hemispheres exhibits a secular variation. Changes from one hemisphere to the other leading in phase were registered near 1928 and 1968 as well as two historical ones near 1783 and 1875. A long-term anticorrelation between the hemispheric phase differences in the sunspot cycles and the latitudinal distribution of sunspots was traced since 1750.