The influence of the timing of Sudden Stratospheric Warmings on precipitation anomalies in Europe

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Erika Monnin, Marlene Kretschmer, Inna Polichtchouk 


The Northern Hemisphere stratospheric polar vortex (SPV), a band of fast westerly winds over the pole extending from approximately 10 to 50 km altitude, is a key driver of European winter weather. Extremely weak polar vortex states, so called sudden stratospheric warmings (SSW), are on average followed by dry and cold weather in Northern Europe, as well as wetter and warmer conditions in Southern Europe. However, the surface response of SSWs varies greatly between events, and it is not well understood which factors modulate this difference. Here we address the role of the timing of SSWs within the cold season (December to March) for the precipitation response in Europe. Due to the limited sample size of SSWs in the observational record, hindcasts of the seasonal forecasting model SEAS5 from the European Centre for Medium-Range Weather Forecasts (ECMWF) are analysed. We first evaluate key characteristics of stratosphere-troposphere coupling in SEAS5 against reanalysis data and find them to be reasonably well captured by the model, justifying our approach. We then show that in SEAS5, early winter (December and January) SSWs are followed by more pronounced tropospheric zonal wind and precipitation anomalies compared to late winter (February and March) SSWs. For example, in Scotland the low precipitation anomalies are roughly twice as severe after early winter SSWs than after late winter SSWs. The difference in the response cannot be explained by more downward propagating SSWs in early winter, or by different monthly precipitation climatologies. The role of SSW timing is potentially of use for forecasts and early warnings of European weather on sub-seasonal to seasonal timescales.



Physical Sciences and Mathematics


Sudden Stratospheric Warmings, weather and climate extremes, European weather and climate, Stratosphere-troposphere interactions


Published: 2021-03-26 14:17

Last Updated: 2021-03-26 14:17


CC BY Attribution 4.0 International

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