Characterizing the Surface Impact of Sudden Stratospheric Warmings in the Context of Internal Variability

Sudden stratospheric warmings (SSWs) are key to understanding subseasonal Northern Hemisphere winter climate variability. While the mean response to SSWs in the North Atlantic and Europe is well-established, other features of the response and of its uncertainties are less well-understood. We study the response to SSWs and its uncertainty following the approach used by Deser et al. (2017) to study the Northern Hemisphere extratropical response to the El Niño-Southern Oscillation. In particular, we use bootstrapping with replacement to construct synthetic SSW composites from SSW events in reanalysis, and we examine the differences across these synthetic composites. We find that the canonical responses of a negative North Atlantic Oscillation and a Eurasian cold anomaly in the months following SSWs are robust, though the magnitude and spatial pattern of these anomalies vary considerably across the composites. The surface impact of SSWs in the Pacific is more uncertain. We further study how this uncertainty is related to vortex strength and other atmospheric conditions. We plan to use these results to evaluate the fidelity of weather forecast models in capturing the surface impact of SSWs by comparing both the mean impact as well as the contribution from internal variability with observations.