Validation of High-Resolution ICON-LES Using Observations from HEFEX II and HEFEX III Field Campaigns

High-resolution numerical weather prediction (NWP) models are increasingly being used to study the interactions between the atmosphere and glaciers in complex alpine terrain. However, their performance under these conditions has not been sufficiently confirmed by observations, especially at a dekameter scale. This study comprehensively validates the Large-Eddy Simulation (LES) configuration of the ICOsahedral Nonhydrostatic (ICON) model using observations from the HEFEX II (2023) and HEFEX III (2025) field campaigns. Both campaigns included four weeks of intensive observations at Hintereisferner in the Ötztal Alps and were part of the international TEAMx research program, which studies multi-scale transport and exchange processes in mountainous environments.

HEFEX II focused on characterizing the spatial gradients and temporal variability of surface-layer variables, such as temperature, humidity, and wind. HEFEX III utilized coordinated UAV-based vertical profiling in combination with multiple on-glacier lidar systems to resolve atmospheric flow fields and wind patterns within the valley. Together, the two campaigns provide a unique and unprecedented observational dataset in complex glacierized terrain, offering an exceptional basis for model evaluation.

ICON-LES was applied in a one-way nested configuration, achieving a target horizontal resolution of 51 meters over the study area. We assessed model performance using qualitative and quantitative validation approaches, particularly emphasizing the model’s ability to reproduce the spatio-temporal variability of key atmospheric parameters across surface and boundary-layer scales. The results demonstrate strong agreement between ICON-LES simulations and multi-platform observations, indicating that the model realistically captures flow structures and variability in a high alpine glacier environment.

These findings support the use of ICON-LES as a reliable tool for studying atmosphere-glacier interactions and lay the groundwork for future climate impact and feedback studies in complex terrain. At the same time, the analysis highlights the current limitations of high-resolution numerical modeling and emphasizes the importance of using advanced observational techniques and large-eddy simulations together to improve our understanding of processes in mountainous regions.