Inter‐Solar‐Cycle Variability of Extreme Geomagnetic Storms

Abstract The occurrence of extreme space weather events, and, in particular, severe geomagnetic storms, while rare, can result in disproportionately large societal consequences. Accurate estimates of their likelihood over the timescale of a solar cycle or longer can provide crucial and actionable information for policymakers. In this study, we refine several previous estimates for the probability of extreme geomagnetic storms. In particular, we extend the analysis to show how the probability varies from one cycle to the next. We find that the probability of an extreme event varies by more than two orders of magnitude from the weakest to the strongest cycles observed over the last years. With the most recent sunspot number data suggesting that Cycle 25 is approximately larger than Cycle 24, and comparable to Cycle 20, we estimate that the probability of a Carrington‐level event ( nT) over the next decade will be % ( 95% CI) for a power‐law distribution and % ( 95% CI) for a log‐normal distribution, notably less than the value obtained using data spanning the entire interval over which we have measurements (% ( 95% CI) and % ( 95% CI), respectively).