Hot or Boom? The Influence of Atmospheric Deserts on Heat Wave and Thunderstorm Formation

Atmospheric deserts are air masses originating in the hot, dry boundary layers in semi-arid or desert source regions, which are then advected across target regions with cooler, moister boundary layers. The novel approach in this study tracks the air masses and the development of their properties directly along their path from the source to the target region. This is done using trajectories calculated with the Lagrangian analysis tool (LAGRANTO), which are initiated at a very high spatio-temporal resolution in the source region.

Typical pathways can be identified using k-means-clustering. Based on these clusters, we find that most of the atmospheric desert air is modified along the path due to diabatic processes. Radiative cooling and especially latent heating and cooling in consequence to cloud formation and  re-evaporation of falling precipitation are the main causes for the changes in the thermodynamic properties of the atmospheric desert air.

Due to their higher potential temperature, atmospheric deserts can form a lid over the local boundary layer in the target region. The lid can prevent the local boundary layer from growing, which leads to heat build-up under clear sky conditions. If the atmospheric desert prevails long enough, this can lead to a heat wave. Similarly, the warm air aloft suppresses the formation of thunderstorms in its centre, while at the same time the convective available  potential energy can grow. However, thunderstorms do erupt violently closer to the edges of the atmospheric desert, where the lid can be expected to be higher and weaker and where trigger mechanisms initiate rising motion.

In this study we use case studies from March and June 2022, and June 2021 to analyse the processes modifying the air mass enroute, and its influence on heat wave and thunderstorm formation. In June 2022, Europe experienced extreme heat, in June 2021 tornadoes were observed in Bohemia, and March 2022 can serve as a case from a different season. These diverse case studies are therefore a good starting point for analysing the above questions.