Julian Krüger , Joakim Kjellsson, Robin Pilch Kedzierski, Martin Claus

The occurrence of European heat waves has increased during the two last decades. European heat waves are responsible for social, economic and environmental damage and are projected to increase in magnitude, frequency and duration under global warming, heightening the interest about the contribution of different drivers.
By using the ERA5 Re-analysis product, we performed a two-sided composite analysis to investigate a potential relation between North Atlantic sea surface temperatures (SSTs) and the near-surface air temperature (T2m) over the European continent. Here, we show that in presence of cold North Atlantic SSTs during summer, the distribution of European T2m shifts towards positive anomalies a few days later, increasing the likelihood for heat waves (Downstream analysis). During these events a predominant wave number three pattern in addition to regionally confined Rossby wave activity contribute to a trough-ridge pattern in the North Atlantic-European sector. Specifically, five of 17 European heat waves within the period of 1979 to 2019 could be related to a cold North Atlantic SST event a few days in advance. In the upstream analysis we identify eleven of 17 European heat waves co-existent with below-average North Atlantic SSTs, including five cold North Atlantic SST events.
Based upon our results North Atlantic SSTs provide potential predictive skill of European heat waves.