Regional Mountain Conference

The atmospheric boundary layer (ABL) over mountainous regions, such as the European Alps, plays a key role in controlling surface–atmosphere exchange processes, with direct implications for mountain weather, air quality, and climate. Owing to strong topographic heterogeneity, the Alpine boundary layer exhibits a wide range of interacting motions, spanning small-scale turbulence and coherent thermals, as well as thermally driven slope and valley circulations. Despite recent advances in high-resolution modelling, the three-dimensional structure of these flows, their evolution and role in vertical exchange processes remain insufficiently understood.

In this study, we investigate the structure of the convective Alpine boundary layer using the ICON model in large-eddy simulation (LES) mode. Real-case simulations are performed at horizontal grid spacings down to 65 m using a nested-domain configuration over highly complex Alpine terrain. A brief evaluation against observations from the TEAMx field campaign is presented to demonstrate the realism of the simulated boundary-layer structure. The main focus of the analysis is on the spatial organization, persistence, and diurnal evolution of the resulting coherent structures. The simulations reveal that thermals preferentially form at distinct locations tied to topography and surface forcing, exhibiting a robust diurnal cycle. These coherent structures play a central role in mediating vertical exchange of heat and momentum between the surface and the free atmosphere, while their interaction with slope and valley flows modulates boundary-layer depth and ventilation efficiency.

By providing a detailed three-dimensional view of boundary-layer processes over the Alps, this work advances process understanding of Alpine meteorology and demonstrates the value of LES for studying surface–atmosphere exchange and transport in complex terrain. The insights gained may provide guidance for constraining the representation of exchange processes in weather and climate models applied to mountainous regions.