A New Formula for Predicting Solar Cycles

A new formula for predicting solar cycles based on the current theoretical understanding of the solar cycle from the flux transport dynamo is presented. Two important processes—fluctuations in the Babcock-Leighton (BL) mechanism and variations in the meridional circulation (MC), which are believed to be responsible for irregularities of the solar cycle—are constrained using observational data. We take the polar field near minima of the cycle as a measure of the randomness in the BL process, and the decay rate near the minima as a consequence of the change in MC. We couple these two observationally derived quantities into a single formula to predict the amplitude of the future solar cycle. Our new formula suggests that cycle 25 would be a moderate cycle. Whether this formula for predicting the future solar cycle can be justified theoretically is also discussed using simulations from the flux transport dynamo model.