A regime view of future atmospheric circulation changes in Northern mid-latitudes

Abstract. Future wintertime atmospheric circulation changes in the Euro-Atlantic (EAT) and Pacific-North American (PNA) sectors are studied from a Weather Regimes perspective. The CMIP5 and CMIP6 historical simulations performance in reproducing the observed regimes is first evaluated, showing a general improvement of CMIP6 models, more evident for EAT. The circulation changes projected by CMIP5 and CMIP6 scenario simulations are analyzed in terms of the change in the frequency and persistence of the regimes. In the EAT sector, significant positive trends are found for the frequency and persistence of NAO+ for SSP245, SSP370 and SSP585 scenarios, with a concomitant decrease in the frequency of the Scandinavian Blocking and Atlantic Ridge regimes. For PNA, the Pacific Through regime shows a significant increase, while the Bering Ridge is predicted to decrease in all scenarios analyzed. The spread among the model responses is linked to different levels of warming in the Polar Stratosphere, the North Atlantic and the Arctic.