On Pan-Atlantic cold, wet and windy compound extremes

Abstract

The co-occurrence of extreme weather in geographically distinct regions can result in larger impacts than the sum of those associated with the individual events occurring in isolation. Previous work has proposed a connection between extreme cold temperatures over North America and wet and windy weather over Europe. Here, we present a systematic statistical analysis of this link, focusing on extreme occurrences in both continents. We identify wintertime cold air outbreaks (CAOs) for 38 overlapping domains over North America between 1979 and 2020 using ERA5 data. The occurrence of these regional CAOs is then matched to extreme precipitation and wind events over 6 domains in western and central Europe. We find CAOs over the eastern and central USA co-occur with more frequent wind extremes over Iberia, whilst CAOs over eastern Canada are followed by wind extremes over northern Europe and the British Isles. Precipitation extremes exhibit greater variability and typically occur prior to the peak of the CAOs. We find significant increases in Iberian and southern European precipitation extremes occurring in conjunction with CAOs over the eastern USA, consistent with what we found for wind extremes. Indeed, Iberia is one of the hotspot regions for wet and windy extremes co-occurring with CAOs in North America: depending on CAO region, the frequency of extreme precipitation and wind events over Iberia locally can more than double relative to climatology. Results indicate that the location of wet and windy European extremes substantially depends on the North American region affected by CAOs. Although pan-Atlantic extremes are associated with an enhanced upper-level jet stream, their complete dynamical description requires further investigation.