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  1. Abstract

    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.

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  2. Abstract

    Sudden stratospheric warmings (SSWs) significantly influence Eurasian wintertime climate. The El Niño phase of the El Niño–Southern Oscillation (ENSO) also affects climate in that region through tropospheric and stratospheric pathways, including increased SSW frequency. However, most SSWs are unrelated to El Niño, and their importance compared to other El Niño pathways remains to be quantified. We here contrast these two sources of variability using two 200‐member ensembles of 1‐year integrations of the Whole Atmosphere Community Climate Model, one ensemble with prescribed El Niño sea surface temperatures (SSTs) and one with neutral‐ENSO SSTs. We form composites of wintertime climate anomalies, with and without SSWs, in each ensemble and contrast them to a basic state represented by neutral‐ENSO winters without SSWs. We find that El Niño and SSWs both result in negative North Atlantic Oscillation anomalies and have comparable impacts on European precipitation, but SSWs cause larger Eurasian cooling. Our results have implications for predictability of wintertime Eurasian climate.

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