Evolution of the vertical structure of heat waves in Europe at hourly resolution

Abstract We employ hourly temperature data at 19 pressure levels from the ERA5 reanalysis to investigate subdaily characteristics of four heat wave types, defined by their vertical cross-sections of temperature anomalies. Contrasting patterns between individual heat wave types in their subdaily development are shown for three European regions. The near-surface type is the only one associated with a gradual vertical build-up of positive temperature anomalies from the surface upwards. By contrast, the omnipresent heat wave type is characterised by a relatively rapid downward propagation of positive temperature anomalies from higher troposphere towards the surface. The downward propagation is less pronounced but still present for the remaining lower-tropospheric and higher-tropospheric heat wave types. We also analyse vertical stability in terms of lapse rates of potential temperature and show that the previously reported nighttime layers, characterised by lower lapse rates and decoupled from the surface, are typical for the near-surface heat wave type only. These layers are not present under the other heat wave types, even those associated also with positive near-surface temperature anomalies (lower-tropospheric and omnipresent). We conclude that the use of the data with high temporal and vertical resolution highlights different processes linked to individual heat wave types, pointing to a variety of heat wave drivers.