Atmospheric deserts and their association with heat, dust andthunderstorm events

Atmospheric deserts originate in the hot, dry and deep convective boundary layers of arid, desert and/or elevated regions and can be transported over thousands of kilometres. They are a concept recently introduced by our group as a generalisation of elevated mixed layers, which retain their well-mixed properties and have been found to influence the formation of thunderstorms and foster high near surface temperatures. Therefore, we assume that the more general atmospheric deserts also have an influence on thunderstorms and high near surface temperature, as well as on dust transport simply due to their origin regions.

The present analysis focuses on tracking atmospheric deserts travelling from Northern Africa to Europe between May 2022 and April 2024, using the Lagrangian Trajectory Analysis Tool (LAGRANTO). We analyse the co-occurrence of atmospheric desert air with anomalously high dust aerosol optical depths or near surface temperatures, as well as lightning occurrence for the European domain (30°W to 60°E and 15° to 73°N). For this purpose, we use atmospheric and aerosol reanalysis data (ERA5 and EAC4) and lightning data from Blitzortung.org. We find that in almost the entire domain it is more likely that near surface positive temperature anomalies occur with atmospheric desert air present, than without. Similarly, anomalous values of dust aerosol optical depth are almost always tied to the presence of an atmospheric desert and in roughly 10–50% of instances when atmospheric desert air is present, it is accompanied by dust. We also investigate the vertical distribution of dust within the AD air mass. Lightning is more likely to happen close to the edge of atmospheric deserts, but also in their centre. While the former was expected from what is known from elevated mixed layers, the latter is surprising and indicates that atmospheric deserts do not inhibit thunderstorm formation in their centres via capping.

Heat, dust, and thunderstorms are often investigated independently, but our results clearly show that they all can be connected to atmospheric deserts. Understanding the relation of atmospheric deserts and the mentioned extremes is crucial for developing theories and better predictions of these events.