Atmospheric circulation associated with 3D heat wave types in Middle Europe

Heat waves are phenomena associated with large negative impacts on society and environment. We evaluate links between atmospheric circulation and three-dimensional (3D) heat wave types in Middle Europe (one of the PRUDENCE regions) over 19792022. Heat waves are classified according to their 3D structure of positive temperature anomalies in ERA5 into near-surface (HWG), lower-tropospheric (HWL), higher-tropospheric (HWH), and omnipresent (HWO) types. The JenkinsonCollison classification is used to identify circulation types (CTs) with increased frequency during the individual heat wave types, and their climatological characteristics (including mean temperature anomaly, precipitation, and Climatic Water Balance index defined as potential evapotranspiration minus precipitation) are studied in station-based E-OBS data. We show that the surface temperature anomalies are largest during HWG (+7.1 C), while HWL are the driest heat wave type according to mean daily precipitation (0.4 mm). At the same time, HWG types show the driest conditions before HW onset. In all heat wave types there is a large increase in the frequency of southern CTs compared to the JuneSeptember climatology, but differences among the heat wave types are found for other CTs. In HWG, the most frequent CT is U (undefined), corresponding to little pronounced pressure pattern over Middle Europe with no clear role of anticyclonic circulation or flow direction. The expected pattern of increased anticyclonic and decreased cyclonic flow is clearly manifested only for HWH and to a lesser degree for HWO and HWL types, while it is reversed for HWG. The analysis contributes to a better understanding of the interrelationships between heat waves, atmospheric circulation, and other driving mechanisms.