- 1Goethe Universität Frankfurt am Main, Institut für Atmosphäre und Umwelt, Frankfurt am Main, Germany (quimbayo-duarte@iau.uni-frankfurt.de)
- 2Hans Ertel Centre for Weather Research, Offenbach am Main, Germany
Foehn winds are warm, dry, downslope winds that occur on the lee side of mountain ranges. They result when moist air is forced to ascend on the windward side, cooling and losing moisture as precipitation. As the now-drier air descends on the leeward side, it warms adiabatically, leading to distinct temperature and humidity profiles. In the Alps, the descent of foehn winds is often confined to distinct hotspots where the interplay between complex topography, mountain-induced gravity waves, and flow separation processes focuses the descending air. These hotspots are associated with localized warming and drying, which can significantly influence weather conditions, predictability, and their impact on ecosystems and human activities in the affected regions. Previous studies, utilizing the COSMO model, a numerical weather prediction (NWP) model at 1 km resolution, visualized these hotspots and established their connection to mountain-induced gravity wave. However, the adequacy of a 1 km resolution in accurately capturing flow separation at the mountain surface—a key feature influencing foehn dynamics and predictability—remains an open question.
To address this question, we conducted high-resolution simulations for two case studies: one in the Rhine Valley from February 2017 and another in Meiringen, Switzerland, from March 2022. Simulations were performed using the ICON model in NWP mode at a horizontal resolution of 1.1 km and ICON-LES at resolutions of 520 m, 260 m, and 130 m. For the Meiringen case, we validated our model setup using wind and temperature profiles obtained from the Meiringen Campaign (2021–2022). Meanwhile, the Rhine Valley case, previously analyzed at a resolution of 1 km, was revisited to assess whether higher resolutions provide an improved representation of flow separation dynamics. Additionally, we employ offline trajectories to precisely track the descent locations of the foehn air parcels, providing a detailed assessment of how model resolution influences the spatial distribution of descent hotspots in the Swiss Alps.
Our study is the first to combine trajectory analysis with LES simulations in foehn research, enabling a detailed visualization of foehn trajectories. The ultimate goal of this study is to provide guidance on selecting appropriate model resolutions to enhance the accuracy of research on foehn winds and their associated effects.
How to cite: Quimbayo-Duarte, J., Tian, Y., and Schmidli, J.: Assessing the representation of flow separation in Foehn descent with high-resolution numerical simulations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16472, https://doi.org/10.5194/egusphere-egu25-16472, 2025.