Periodicity of sunspot group number during the Maunder Minimum

Abstract

Applying the Hilbert-Huang Transform (HHT) method to the yearly average sunspot group (SG) number reconstructed by Svalgaard& Schatten, we investigate the periodicity of SG number from 1610 to 2015. Our main findings are summarized below. Periodicities of 3.56 +/- 0.24 (Quasi-Triennial Oscillations), 9.22 +/- 0.13 (Schwabe Cycle), 16.91 +/- 0.99 (Hale Cycle), 49.25 +/- 0.96, 118.64 +/- 2.52 (Centennial Gleissberg Cycle), and 206.32 +/- 4.60 yr are statistically significant in the SG numbers. During the Maunder Minimum (MM), the occurrences of the Schwabe Cycle and the Hale Cycle, extracted from SG numbers, are suspended; before and after the MM, Schwabe Cycle and the Hale Cycle, extracted from SG numbers, all exist. The results of applying the Morlet Wavelet Analysis to the SG number confirm that, for SG number, the occurrence of the Schwabe Cycle is suspended during the MM, and, before and after the MM, the Schwabe Cycle all exist. Then we investigate the periodicity in the annual Be-10 data from 1391 to 1983, which are given in a supplementary file to McCracken & Beer, using HHT and the Morlet wavelet transform. We find that, for the Be-10 data, the Schwabe Cycle and the Hale Cycle persist throughout the MM. Our results support the suggestion that the Schwabe Cycle is too weak to be detected in the sunspot data.