ECCE Seminar - Stratospheric Polar Vortex Variability and North American Winter Weather Patterns

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Stratospheric Polar Vortex Variability and North American Winter Weather Patterns

Skillful and actionable subseasonal-to-seasonal (S2S) forecasts (i.e., predictions with leads of 2 to 8 weeks) are in high demand for the public sector and key industries (e.g., energy, agriculture). Northern Hemisphere stratospheric polar vortex (SPV) variability and its coupling to the troposphere is one important source of S2S predictability during the cold season. Such interactions are also important on climate timescales and could inform what future winters will look like. Classically, influences of the SPV on surface weather have been considered via the zonally symmetric, downward influence of either extremely strong or weak vortex episodes. However, stratosphere-troposphere coupling is more diverse and complex than that paradigm suggests. This talk investigates ways that Northern Hemisphere SPV variability can inform tropospheric winter weather patterns, particularly for North America. I will present the dominant regimes of winter weather for North America and illustrate how each is connected to SPV variability. Two regimes – Arctic High and Alaskan Ridge – are particularly important for predicting extreme cold air outbreaks across the Central United States. While Arctic High cold air outbreak events closely follow the classical downward propagation paradigm of stratosphere-troposphere coupling occurring from wave breaking, Alaskan Ridge events are instead associated with a wave reflection mechanism. Hence, antecedent wave-mean flow interactions in the stratosphere may be important to understand for skillful subseasonal predictions of North American winter weather patterns. Then, I will discuss ongoing work on the applications of these concepts, including (a) predictions of energy demand for the Central United States and (b) characterizing recent and future trends in North American winter weather extremes due to climate change. Overall, the findings in these works offer ways of informing decision makers about the potential for winter weather extremes along with benchmarking our modeling systems for their performance in simulating North American winter weather variability across timescales.