Structure of the convective boundary layer over complex terrain: ICON-LES and high resolution 3D wind observations during a TEAMx test flight

The atmospheric boundary layer (ABL) over mountainous terrain plays an important role in modulating the exchange of momentum, heat, and moisture between the surface and the free atmosphere. Unlike flat terrain, where boundary layer dynamics are relatively homogeneous, the mountain boundary layer (MoBL) exhibits pronounced heterogeneity driven by the complex interplay of multiscale orographic features. These interactions generate a broad spectrum of atmospheric motions, from turbulent eddies and coherent thermals to thermally and dynamically induced slope and valley flows. Understanding this complexity is essential for improving weather prediction, climate modeling, and air quality assessment in mountainous regions. This study investigates the structure and dynamics of the convective boundary layer (CBL) over highly complex terrain during a TEAMx test flight on 18 September 2024. Specifically, we address the following questions: What are the dominant characteristics of coherent structures in the CBL? How stationary are these features in space and time? What is their diurnal cycle? How does the model compare to observations?

To address these questions, we employ the ICON model in large-eddy simulation (LES) mode at a horizontal resolution of 65 m, using a nested domain configuration (520 m to 65 m) to capture processes across scales. The simulation domain encompasses a region around the Sarntal Alps, one of the TEAMx target areas. The ICON-LES results are compared with novel airborne wind measurements obtained during a test flight of the AIRflows system aboard the TU Braunschweig Cessna F406 research aircraft. AIRflows delivers high-resolution, three-dimensional wind profile measurements along the aircraft track, providing a unique opportunity to validate and evaluate the LES output in real atmospheric conditions. Preliminary results reveal a complex, spatially variable CBL structure with persistent thermal features and localized regions of enhanced turbulence. The comparison with AIRflows data confirms the presence and spatial organization of key dynamical structures captured by the model, while also highlighting discrepancies that inform model improvement. This work contributes to a deeper understanding of the CBL in mountainous regions and demonstrates the value of combining advanced numerical simulations with targeted airborne observations for model validation and process studies.