Radar measurements of blowing snow off a mountain ridge

Abstract. Modelling and forecasting wind-driven redistribution of snow in mountainous regions with its implications on avalanche danger, mountain hydrology or flood hazard is still a challenging task often lacking in essential details. Measurements of drifting and blowing snow for improving process understanding and model validation are typically limited to point measurements at meteorological stations, providing no information on the spatial variability of horizontal mass fluxes or even the vertically integrated mass flux. We present a promising application of a compact and low-cost radar system for measuring and characterizing larger scale (hundreds of meters) snow redistribution processes, specifically blowing snow off a mountain ridge. These measurements provide valuable information of blowing snow velocities, frequency of occurrence, travel distances and turbulence characteristics. Blowing snow velocities measured with the radar are validated by comparison against wind velocities measured with a 3D ultrasonic anemometer. A minimal blowing snow travel distance of 60–120 m is reached in 10–20 % of the time during a snow storm, depending on the strength of the storm event. The relative frequency of transport distances decreases exponentially above the minimal travel distance, with a maximum measured distance of 280 m. The travel distance is linearly correlated with the wind velocity, revealing a threshold for snow particle entrainment and transport of 6.75 m s−1. Turbulence statistics did not allow to draw a conclusion on whether low-level low-turbulence jets or highly turbulent gusts are more effective in transporting blowing snow over longer distances. Drone-based photogrammetry measurements of the spatial snow height distribution revealed increased snow accumulation in the lee of the ridge being the result of the measured local blowing snow conditions.