Dynamical system metrics and weather regimes explain the seasonally-varying link between European heatwaves and the large-scale atmospheric circulation

Abstract. Global warming is projected to increase the frequency and intensity of heatwaves in the extended summer period. To better predict heat extremes, it is important to explore the seasonal variations in their drivers. Therefore, we analyze heatwaves in Central Europe using ERA5 reanalysis data over the historical period (1950–2023) for the extended summer months (May–September). We quantify atmospheric persistence, and the link between near-surface temperatures and large-scale atmospheric circulation patterns using dynamical system metrics. This approach is further contextualized by the consideration of weather regimes, which represent the low-frequency variability of the atmosphere over the North Atlantic and Europe. Our results show a maximum in atmospheric persistence in July and August, associated with higher occurrence of Scandinavian Blocking, and relative minima in spring and autumn. The relationship between the large-scale atmospheric circulation and near-surface temperatures exhibits similar seasonal characteristics. For heatwave days, we find a statistically significant anomalous strong link between large-scale atmospheric circulation and surface temperatures from June to September. This relationship is generally not attributable to the occurrence of specific weather regimes. However, heatwaves in July and August are associated with higher atmospheric persistence due to an enhanced frequency of the persistent Scandinavian and European blocking weather regimes. Beyond atmospheric circulation, additional physical drivers of daily maximum temperature during heatwaves are analyzed: While surface net solar radiation shows a particularly strong link in June and July, soil moisture exhibits an anomalously high link in July and August. These findings highlight the critical role of intra-seasonal variations in shaping heatwave dynamics.