A study published in Nature examines how the vertical structure of heat waves in Europe evolves at hourly resolution, a level of detail not previously achieved in this type of analysis. The work addresses an open question in regional climatology: how the column of warm air that characterises these extreme events builds up and breaks down, not only at the surface but throughout the troposphere.

European heat waves are usually studied using surface temperature data or daily-resolution vertical profiles, which leaves out the sequence of processes occurring within a single day. Hourly resolution makes it possible to follow the formation of the boundary layer, the subsidence that compresses it and the associated adiabatic heating, as well as the transition between soil-dominated episodes and episodes dominated by warm-air advection.

The analysis relies on high-frequency atmospheric observations that allow the air column over the affected European regions to be reconstructed during extreme episodes. This information makes it possible to separate the contribution of local heating from that due to air-mass transport, a key distinction for understanding why some heat waves intensify rapidly while others remain stable for several days.

The results show that the vertical structure of heat waves is not static throughout the event, but changes appreciably from one hour to the next. This intra-diurnal variability has direct consequences for risk assessment, because the temperature experienced by the population depends on the dynamics of the air layer close to the ground, and for the validation of regional climate models, which must reproduce not only the intensity but also the temporal profile of the warming.

The work opens the door to a finer characterisation of thermal extremes in Europe, useful both for early detection of dangerous episodes and for improving boundary-layer physics in climate simulations. The next step will be to apply this approach to longer time series and to other regions, and to compare the observed profiles with those produced by state-of-the-art models.