Arctic Polar Vortex Strengthening on Seasonal Scales After Extreme Solar Proton Events: Quantitative Evidence for an Ozone–Dynamics Feedback

Abstract. Energetic particle precipitation (EPP) has long been known to influence the polar middle atmosphere. Extreme solar proton events (SPEs), the most intense type of EPP, are expected to influence the Arctic polar vortex (APV); however, their impacts and underlying pathways remain poorly understood. Here, we examine APV variability and the associated stratospheric processes following the two most extreme late-October SPEs, using the ERA5 reanalysis data. Both events were followed by persistent ozone depletion, cooling of the polar stratosphere, and sustained strengthening of the APV from autumn into late winter and spring. The ozone, temperature, and APV anomalies evolve coherently over time, with the APV transitioning from a relatively weak background state to a strongly enhanced state with respect to the climatological distribution. Thermodynamic budget diagnostics reveal that the temperature anomalies were dominated by dynamical cooling rather than by direct radiative cooling from ozone depletion. This dynamical cooling was accompanied by a tendency for downward planetary wave refraction at high latitudes and associated changes in wave–mean flow interactions. Collectively, these results provide quantitative evidence that extreme SPEs can influence the seasonal APV variability through coupled ozone and dynamical processes.