Frequently occurring stormy winds in alpine terrain can transport large amounts of snow from exposed sites to bowls and slopes shadowed from the wind. This changes the local amount of snow, as well as the stratigraphy and the stability of the snow cover. Furthermore, the snow crystals change during transport as they become smaller due to collisions and sublimation. The wind thus changes the properties of the snow and hence snow slab avalanches can often be triggered from snow drift deposits. The wind is known to the experts as the avalanche builder. Through several projects, the SLF studies how snow is transported and where we can expect erosion and deposition in alpine terrain.
In the wind tunnel, the researchers can analyse the transport of snow in a controlled environment. They observe and measure e.g. the velocity, height, trajectory and the flight distance of single snow particles. The results retrieved in the wind tunnel can for instance help in the development of suitable protection measures against snowdrifts and the improvement of snow transport models
1: Wind tunnel
The experiments in the wind tunnel allow a thorough examination of the fundamentals of the drifting snow process. However, they can only represent the complex nature of the process in alpine terrain to a limited extent. The surface structure and the internal properties of the snow cover are highly variable. In some locations, there may for example be fresh snow, which can be transported by light winds. Simultaneously in a different slope aspect, windpacked snow or a crust may have formed, where snow is no longer erodable.
At the Weissfluhjoch Versuchsfeld several researchers therefore investigate how much snow is transported over short distances by turbulent eddies and the corresponding processes involved. In order to do this, the amount of snow that is transported by the wind is measured close to the surface and up to a height of 2 meters. The wind is measured at a resolution of 0.05 s. With the results, the researchers verify and improve snow cover models (SNOWPACK and Alpine3D). The resulting knowledge on snow transport under gusty conditions may later support the avalanche danger forecasters.
|Fig. 2: Weissfluhjoch Versuchsfeld and the instruments to measure drifting snow|