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Abstract:
With over 24000 casualties attributed to them, the exceptionally warm and persistent summer 2022 European heatwaves once more dramatically demonstrated the need for a deeper understanding of the dynamics of persistent summer weather. Among the key players, persistent double jet states have recently been identified to be linked to more frequent and intense heatwaves in Western Europe (Rousi et al. 2022). This correlation may be attributed to the waveguiding ability of the jet streams for Rossby waves and shows the the generally important role of jet persistence in explaining surface weather extremes. In Winter, the jet dynamics, including the drivers of jet variability, and their interactions with surface weather conditions are well documented (e.g. Madonna et al. 2017) but many questions remain regarding the dynamical processes driving persistence of the Atlantic jets during the summer season. We characterize persistent North Atlantic jet states in summer by applying a broad range of jet indices, clustering techniques and statistical analysis tools to the CESM-LENS2 dataset. We establish links between the persistent states and the eddy-driven or subtropical nature of the jet, as well as with Rossby wave-breaking. Finally, we establish a statistical link between the summer persistent jet states and surface weather extremes.
