How well do we know the surface impact of sudden stratospheric warmings?

Sudden stratospheric warmings (SSWs) are key to understanding and predicting subseasonal Northern Hemisphere winter climate variability. Here we study the uncertainty in the surface response to SSWs in reanalysis data by constructing synthetic composites based on bootstrapping the 39 events observed during the 1958-2019 period. We find that the well-known responses in the North Atlantic and European regions following SSWs are consistently present, but their magnitude and spatial pattern vary considerably across the synthetic composites. We further find that this uncertainty is unrelated to stratospheric polar vortex strength and is instead the result of independent tropospheric variability. Our findings provide a basis for evaluating the fidelity of the surface response to SSWs in models.