Atmospheric deserts and extreme weather events: co-occurrence with positive temperature anomalies, thunderstorms, and dust

Abstract. Elevated mixed layers are known to influence near-surface temperatures and the formation of thunderstorms. Here we investigate the generalisation of elevated mixed layers, so called “atmospheric deserts”: air masses originating in hot, dry, deep, convective boundary layers over arid and/or elevated regions. Atmospheric deserts are frequently advected over Europe and can modify temperature profiles throughout the free troposphere, with implications for convective potential. We therefore investigate their co‑occurrence with positive temperature anomalies and thunderstorms over Europe. We also investigate their co-occurrence with dust events, since the source region for atmospheric deserts over Europe is also the main source region for dust events.

For this purpose, atmospheric desert air is tracked during the study period from May 2022 to April 2024, using a direct detection method based on Lagrangian trajectories initiated at a very high spatio-temporal resolution.

Positive temperature anomaly events, thunderstorms, and dust events are identified from ERA5 atmospheric reanalysis, lightning data from Blitzortung.org, and EAC4 atmospheric composition reanalysis, respectively. Conditional probabilities and corresponding odds ratios provide insight into whether the mentioned extreme events occur more frequently in the presence of atmospheric deserts.

The probability of events with positive temperature anomalies, thunderstorms, or dust anomalies is enhanced in the presence of atmospheric deserts in almost the entire domain. In most of the domain, positive temperature anomaly events are more likely given the presence of atmospheric desert air, but trapping of heat under a cap could not be confirmed as the main driver. Lightning probability is clearly enhanced along the atmospheric desert edges, and, in contrast to expectations, also in the atmospheric desert centres. In western Europe, up to 50 % of occurrences of atmospheric desert air are accompanied by unusually high amounts of dust. Dust events co-occur almost exclusively with atmospheric deserts.