Disentangling Dynamic Contributions to Summer 2018 Anomalous Weather Over Europe

Abstract

Summer 2018 was one of the driest and hottest experienced over northwestern Europe. In contrast, over southern Europe, it was marked by cooler and wetter conditions with flooding over Greece and Spain. This contrasting pattern was particularly enhanced over a 3-week period starting on 21 June. Two atmospheric patterns are thought to have largely contributed to this anomalous weather: the positive North Atlantic Oscillation (NAO+) and a Wave-7 pattern. Using linear regressions on detrended data, we show that the NAO+ was mainly responsible for the observed seasonal anomalies. However, during the 3-week period, the rare combination of the NAO+ and Wave-7 is necessary to explain the pattern of the observed anomalies. The global warming trend and, to a lesser extent, nonlinear processes are shown to have furthermore strongly modulated the anomalies associated with these two patterns.