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. Plain Language Summary: In winter, the average winds about 30 km above the Arctic are usually west‐to‐east. When they are disrupted and reverse directions in an event known as a sudden stratospheric warming, particular surface climate patterns tend to develop over the following 60 days, especially in the North Atlantic and European regions. However, there is a great deal of variation or uncertainty in this response, and that variation can be difficult to measure. We study this uncertainty by building composites or averages of different combinations of observed events, assuming they are interchangeable. Using these synthetic composites, we find that the responses in the North Atlantic and European regions are always present, but they vary in magnitude, location, and shape. We further find that this variation is not a result of how strong or weak the 30 km winds are in each synthetic composite; rather, it results from unrelated noise in the atmospheric system. Our results can be used to inform weather and climate forecasts of the surface impacts associated with these high‐altitude disruptions of the atmospheric circulation. Key Points: Uncertainty in the surface climate response to sudden stratospheric warmings is assessed from bootstrapped composites of 39 observed eventsThe bootstrapped composites show robust but highly variable patterns over the Northern HemisphereThe spread across the composites is due to tropospheric variability that is independent of the stratospheric conditions sampled [ABSTRACT FROM AUTHOR]