A storm-track regime perspective on the connection between cold spells over North America and wet/windy extremes over Europe

The occurrence of cold spells over North America leads, on average, to a zonalisation and intensification of the North Atlantic jet stream and results in an enhanced risk of extreme wind and precipitation events over Europe. Cold spells enhance low-level baroclinicity at the entrance of the North Atlantic storm track and enhance extratropical cyclogenesis next to the East coast of the United States. However, the mechanisms by which this impact propagates from the entrance to the exit of the storm track, where Europe is, remain unclear.

We investigate from a regime perspective the two-way relationship between the occurrence of cold spells over the eastern coast of North America and the North Atlantic storm track. We stratify the occurrence of cold spells over two different regime classifications of the state of the North Atlantic storm track: the first one based on more classical k-means clustering of 500hPa geopotential height, the other based on dynamical system theory. The regimes have been further characterized using diagnostics acquired from dynamical meteorology, as the E vector or the wave activity flux, and display very different patterns of Rossby wave propagation. The analysis will highlight whether the occurrence of cold spells is able to cause shifts in storm track regimes. On the other hand, if the state of the storm track remains unchanged, this would suggest that other factors rather than cold spells modulate the connection to European wind and temperature extremes.