Modulation of the occurrence of heatwaves over the Euro-Mediterranean region by the intensity of the Atlantic multidecadal variability

• Published in: Journal of Climate
• Main Authors: Qasmi, Saïd, Sanchez-Gomez, Emilia, Ruprich-Robert, Yohan, Boé, Julien, Cassou, Christophe
• Other Authors: Barcelona Supercomputing Center
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Meteorological Society (AMS) 2021
• Subjects: Àrees temàtiques de la UPC::Desenvolupament humà i sostenible::Degradació ambiental::Canvi climàtic; Climatology; North Atlantic oscillation; Climatic changes; Heat waves (Meteorology); Europe; North Atlantic Ocean; Extreme events; Climate variability; Multidecadal variability; Simulació per ordinador; Climatologia; Laure; North Atlantic
• Online Access: http://hdl.handle.net/2117/340277; https://doi.org/10.1175/JCLI-D-19-0982.1

The influence of the Atlantic multidecadal variability (AMV) and its amplitude on the Euro-Mediterranean summer climate is studied in two climate models, namely CNRM-CM5 and EC-Earth3P. Large ensembles of idealized experiments have been conducted in which North Atlantic sea surface temperatures are relaxed toward different amplitudes of the observed AMV anomalies. In agreement with observations, during a positive phase of the AMV both models simulate an increase (decrease) in temperature of 0.2°–0.8°C and a decrease (increase) in precipitation over the Mediterranean basin of 0.1–0.2 mm day−1 (northern half of Europe) compared to a negative phase. Heatwave durations over the Mediterranean land regions are 40% (up to 85% over the eastern regions) longer for a moderate amplitude of the AMV. Lower and higher amplitudes lead to longer durations of ~30% and ~100%, respectively. A comparison with observed heatwaves indicates that the AMV can considerably modulate the current anthropogenically forced response on heatwaves durations depending on the area and on the AMV amplitude. The related anticyclonic anomalies over the Mediterranean basin are associated with drier soils and a reduction of cloud cover, which concomitantly induce a decrease (increase) of the latent (sensible) heat flux, and an enhancement of the downward radiative fluxes over lands. It is found that both tropical and extratropical forcings from the AMV are needed to trigger mechanisms, which modulate the atmospheric circulation over the Euro-Atlantic region. The amplitude of the local climate response over the Mediterranean basin evolves linearly with the amplitude of the AMV. However, the strength of this relationship differs between the models, and depends on their intrinsic biases. This work was supported by a grant from Electricité de France (EDF), by the French National Research Agency (ANR) in the framework of the MORDICUS project (Grant AgreementANR-13-SENV-731 0002), and by theEuropean Union’s Horizon 2020 Research and Innovation Programme in the framework (i) of the PRIMAVERA project (Grant Agreement 641727) and (ii) of the Marie Skłodowska-Curie grant INADEC (Grant Agreement 800154). The figures were produced with the NCAR Command Language Software (http://dx.doi.org/10.5065/ D6WD3XH5). The authors are grateful to Marie-Pierre Moine, Laure Coquart, and Isabelle d’Ast for technical help to run the CNRM-CM5 model, and to the three anonymous reviewers who provided helpful comments on earlier drafts of the manuscript. Peer Reviewed Postprint (published version)