A comparison of the spectral characteristics of the Wolf Sunspot Number (R Z) and Group Sunspot Number (R G)

Abstract

The objective of this paper is to compare the spectral features of the recently derived Group Sunspot Numbers (RG) and the traditional Wolf Sunspot Numbers (RZ) for the 1700–1995 period. In order to study the spectral features of both time series, two methods were used, including: (a) the multitaper analysis and (b) the wavelet analysis. Well-known features of the solar variability, such as the 98.6-yr (Gleissberg cycle), 10–11-yr (Schwabe cycle) and 5-yr (second solar harmonic) periodicities were identified with high confidence using the multitaper analysis. Also observed was a larger amount of power spread in high frequencies for RZ than for RG spectra. Furthermore, a multitaper analysis of two subsets, A (1700–1850) and B (1851–1995), has indicated that the main differences occurred in the first subset and seem to be due to uncertainties in the early observations. The wavelet transform, which allows observing the spectra evolution of both series, showed a strong and persistent 10–11-yr signal that remained during the whole period. The Meyer Wavelet Transform was applied to both RZ and RG. This study indicates that the main spectral characteristics of both series are similar and that their long-term variability has the same behavior.