Interaction between drifting snow and turbulent flow

How does the snow saltation reacts to the unsteady wind forcing is still poorly understood. In our cold wind tunnel we investigate the dynamics of the drifting snow as well as its interaction with the turbulent boundary layer flow.

Among the different processes resulting from the snow-atmosphere interaction the process of drifting snow is a major concern for the snow redistribution in alpine and polar regions. This has also a significant influence on the formation of avalanches. Drifting sand is a serious problem driving erosion and desertification in arid regions. The modeling of wind erosion is therefore of great interest in fields ranging from cryospheric sciences to geomorphological and aeolian research. Among the aeolian processes that shape the Earth’s surface (drifting sand and snow), drifting snow is the least known and investigated, mainly for the difficulty implicated in conducting the experiments.

Why studying drifting snow?

Most numerical descriptions of snow saltation are, however, based on results and parameterizations determined from experimental investigations, often regarding drifting sand. Nevertheless sand and snow particles are profoundly different in shape, aerodynamical, mechanical and thermodynamical properties. Snow crystals are more easily influenced by the meteorological conditions (i.e. temperature and humidity affect the bond strength) and by the saltation itself (the snow crystals reduce in size during multiple impacts with the snow cover) than sand grains. This has a significant impact on the dynamics of the saltation and mark a clear difference between the physics of the two aeolian processes. Observing the drifting of natural snow crystals in controlled conditions is a clear advantage to better characterize the process of drifting snow and its dependence on the wind strength and on the snow cover properties.

The efforts in the development of imaging techniques, recently widely employed in wind tunnel research, to monitor drifting snow and snow cover changes gives us the great opportunity to shed new light on the physics of drifting snow and have the potential to bring the SLF wind tunnel laboratory to lead in the physics of the process.

The interactions between drifting snow and the turbulent boundary layer

Theoretical models of drifting sand and snow often consider the saltation as stationary, representing the process by means of a functional relation between wind and saltation strength, assuming it as stationary and in equilibrium. In recent years it was demonstrated that for drifting sand the saltation is not steady and has a lagged feedback to the unsteady wind forcing. This means it never reaches equilibrium. The unsteady characteristic of drifting snow has been proved in recent years by the researchers of the laboratory. The current step involves the characterization of the spatial and temporal dynamics of the drifting snow and its interactions with the turbulent boundary layer flow. We are currently investigating the scales of the snow saltation and of the turbulent flow as well as the coupling between the two systems.