Complementary approaches to characterize the jet stream dynamics in summer and link them to extreme weather in Europe

Recent studies have highlighted the link between upper-level jet dynamics, especially the persistence of certain configurations, and extreme summer weather in Europe. The weaker and more variable nature of the jets in summer makes it difficult to apply the tools developed to study them in winter, at least not without modifications. Here, in order to further investigate this link, we present two complementary approaches to characterize the jet dynamics in summer in the North Atlantic sector.

First, we apply a jet axis detection and tracking algorithm to ERA5 reanalysis data to extract individual jets and classify them in the canonical categories of polar and subtropical jets. Then, we compute a wide range of jet indices on each jet to provide easily interpretable scalar time series representing upper-tropospheric dynamics.

Second, we apply the self-organizing map (SOM) clustering algorithm to the same data to create a distance-preserving, discrete, 2D phase space. The dynamics can then be described by the time series of visited SOM nodes, in which a long stay in a given node relates to a persistent state and a rapid transition between nodes that are far apart relates to a sudden dramatic shift in the configuration of upper-level flow.

We first compare these two approaches to each other to assess their consistency, and then use them to relate the jet dynamics to a known driver of variability, Rossby wave breaking. Finally, we present preliminary results linking persistent jet dynamics to extreme heat events in Europe.