Predicting Geomagnetic Activity Cycles

Abstract The vast majority of solar cycle predictions focus on predicting the 11‐year sunspot cycle, while space weather and geomagnetic activity predictions are largely made for short time scales, from hours up to a month. Here, we aim to predict geomagnetic activity in the solar cycle time scale. We use a 180‐year composite of the geomagnetic index and fit each cycle between two successive sunspot minima with a parameterized asymmetric Gaussian curve. We show that the model reasonably describes the cyclic behavior of using only two free parameters. We present how these parameters can be forecasted using past values and a recently developed sunspot prediction model. Employing these estimated parameter values, we hindcast each past cycle from Solar Cycle 10 onwards and make a prediction for Solar Cycle 25, also estimating the uncertainties using a leave‐one‐out cross‐validation methodology. Each cycle prediction is made at the time of minimum starting the respective cycle. For Solar Cycle 25, our prediction gives the index maximum of (at the original index level) early in the cycle in July 2022, suggesting that Solar Cycle 25, similarly to Solar Cycles 11 and 13, will not have a strong, long‐lasting peak of geomagnetic activity in the late declining phase.