A New Declining Phase Precursor and an Early Prediction of Cycle 26 Maximum

The overall level of solar activity as seen in the sunspot number (SSN) record paces both the state of the ionosphere and the amplitude and occurrence rates of extreme space weather events. SSN predictions on solar cycle timescales are problematic given the variability in cycle amplitude and duration. The Hilbert transform of 13 month smoothed SSN since 1749 is used to construct a uniform clock for the Schwabe solar cycle, which establishes a clear switch-on and -off of geomagnetic activity seen at Earth and correlates with solar cycle morphology. Cycle SSN maxima are shown to correlate with the SSN at the switch-off of the preceding cycle. The maxima of solar cycles 1–25 are hindcasted with ∼7 yr lead time with good fidelity by this method with coefficient of determination r 2 > 0.7 and Pearson correlation ρ > 0.8. Modeling the current SSN forward to the switch-off of cycle 25 gives an early prediction of a weak-to-moderate upcoming cycle 26 maximum, of intensity less than, or of order, cycle 25. A more precise prediction will be possible in 2.5–3.5 yr when the switch-off of cycle 25 will occur.