Ocean and atmosphere influence on the 2015 European heatwave

• Published in: Environmental Research Letters
• Main Authors: Mecking, J V, Drijfhout, S S, Hirschi, J J-M, Blaker, A T
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2019
• Subjects: North Atlantic; Sea ice
• Online Access: http://nora.nerc.ac.uk/id/eprint/525959/; https://nora.nerc.ac.uk/id/eprint/525959/1/Mecking_2019_Environ._Res._Lett._14_114035.pdf; https://doi.org/10.1088/1748-9326/ab4d33

During the summer of 2015, central Europe experienced a major heatwave that was preceded by anomalously cold sea surface temperatures (SSTs) in the northern North Atlantic. Recent observation-based studies found a correlation between North Atlantic SST in spring and European summer temperatures, suggesting potential for predictability. Here we show, by using a high-resolution climate model, that ocean temperature anomalies, in combination with matching atmospheric and sea-ice initial conditions were key to the development of the 2015 European heatwave. In a series of 30-member ensemble simulations we test different combinations of ocean temperature and salinity initial states versus non-initialised climatology, mediated in both ensembles by different atmospheric/sea-ice initial conditions, using a non-standard initialisation method without data-assimilation. With the best combination of the initial ocean, and matching atmosphere/sea-ice initial conditions, the ensemble mean temperature response over central Europe in this set-up equals 60% of the observed anomaly, with 6 out of 30 ensemble-members showing similar, or even larger surface air temperature anomalies than observed.