Modelling Persistent Cycles in Solar Activity

Solar activity at decadal time scales is characterised by persistent periodic patterns with global effects on the Earth’s climate. This article deals with the analysis and prediction of the revised monthly sunspot numbers, adopting a recently proposed time-series model for long-range dependent cycles. The methodology is based on the maximum-likelihood estimate of the model parameters and provides optimal signal extraction filters for cycle estimation and prediction. The analysis suggests the presence of stationary cyclical long memory in the sunspot-generating process. Moreover, our formulation provides a reliable method for solar-cycle predictions, yielding forecasts of the future Cycle 25. In particular, we claim a main peak will occur in early 2024 with an amplitude of 114 and an end of the cycle in early 2030.