A Remarkably Accurate Predictor of Sunspot Cycle Amplitude

The slopes of the linear relations between sunspot and white light (WL) facular areas at the onset of sunspot cycles 12–21 correlate well with the amplitudes of those cycles between 1878–1980 (Brown and Evans, 1980). We use continuum images from the SOHO Michelson Doppler Imager and SDO Heliospheric Magnetic Imager to show that the relation holds also for cycles 24 and 25. The amplitudes of cycles 12–21 and 24 calculated using this relation agree with the observed amplitudes to within 4% rms. It also enabled us in 2022 to correctly predict a larger cycle 25 than estimated by the International Prediction Panel, 3 years before maximum. The technique offers an objective, physically based predictor of cycle amplitudes 3–4 years ahead of their maxima, given a stable source of continuum full disk photospheric images.