The 155-day periodicity of the sunspot area fluctuations in the solar cycle 16 is an alias

TL;DR

This study investigates the 155-day periodicity in sunspot area fluctuations during solar cycle 16, revealing it as an alias of longer periodicities and showing hemispheric differences in its presence.

Contribution

A new method for diagnosing echo-effects in spectral analysis is proposed, clarifying the nature of the 155-day periodicity as a harmonic rather than a true cycle.

Findings

The 155-day periodicity is an alias of 400-500 day cycles.

No significant 155-day fluctuations in the northern hemisphere during maximum activity.

Significant 155-day periodicity observed in the southern hemisphere during maximum activity.

Abstract

The short-term periodicities of the daily sunspot area fluctuations from August 1923 to October 1933 are discussed. For these data the correlative analysis indicates negative correlation for the periodicity of about 155 days, but the power spectrum analysis indicates a statistically significant peak in this time interval. A new method of the diagnosis of an echo-effect in spectrum is proposed and it is stated that the 155-day periodicity is a harmonic of the periodicities from the interval of [400,500] days. The autocorrelation functions for the daily sunspot area fluctuations and for the fluctuations of the one rotation time interval in the northern hemisphere, separately for the whole solar cycle 16 and for the maximum activity period of this cycle do not show differences, especially in the interval of [57, 173] days. It proves against the thesis of the existence of strong positive fluctuations of the about 155-day interval in the maximum activity period of the solar cycle 16 in the northern hemisphere. However, a similar analysis for data from the southern hemisphere indicates that there is the periodicity of about 155 days in sunspot area data in the maximum activity period of the cycle 16 only.