A close-ridge small-scale atmospheric flow field and its influence on snow accumulation

The rough, steep, and complex terrain in the alpine environment causes a variety of flow patterns such as blocking, speed-up, or flow separation, which influence precipitation, snow deposition, and ultimately snow distribution on the ground. Cloud-terrain interactions, flow-particle interactions, and snow transport affect snow accumulation patterns, but the relative importance of these processes is not fully understood, in particular, in complex mountainous terrain. A unique combination of measurements and model simulations is used in a local case study during a 2 day snowfall event to demonstrate the current understanding of snow accumulation in very steep alpine terrain. Doppler wind lidar measurements show an eddy-like structure on the leeward side of the Sattelhorn ridge (in the Dischma valley near Davos, Switzerland), which could partly be replicated by Advanced Regional Prediction System (ARPS) flow simulations. Snow deposition measurements with a terrestrial laser scanner show a complex deposition pattern, which is only partially captured by Alpine3D deposition simulations driven by the ARPS flow fields. This shows that additional processes such as avalanches may play a role or that a more refined simulation of flow or flow-particle interactions is required to fully understand snow distribution in very steep mountainous terrain.