Abstract
Sunspot number reconstructions (SNRs) based on dendrochronologically dated radiocarbon concentrations are analyzed through the Empirical Mode Decomposition (EMD) to provide a deeper characterization of the solar activity long-term periodicities and to investigate the role of the Gleissberg and Suess cycles in the grand minima occurrence. The Gleissberg and Suess cycles, with timescales of 60-120 yr and 200-300 yr respectively, represent the most energetic contribution in SNR records. The EMD approach reveals that these cycles are characterized by multiple scales of variation and that the grand minima sequence is produced by the coupling between Gleissberg and Suess cycles, the latter being responsible for the most intense and longest Spörer-like minima, with typical duration longer than 80 yr.
