A new cold ring wind tunnel facility for studying airborne snow metamorphism

Recent studies suggests that drifting snow particles undergo snow metamorphism while being transported by wind, involving concurrent sublimation and vapor deposition, affecting particle size, shape, specific surface area, and isotopic composition [Walter et al., 2024; Wahl et al., 2024]. This newly identified process of airborne snow metamorphism (ASM) is particularly relevant in polar regions, where snow particles in saltation layers may be transported over long distances and durations before final deposition. As a result, this process strongly influences the microstructure of surface snow, with large scale implications for albedo and climate signals. Experimental investigations of ASM under laboratory conditions has so far been constrained by the lack of facilities providing well controlled boundary conditions.Based on our experience with an exisiting but limitied ring wind tunnel (RWT), we developed a new wind tunnel in a cold laboratory designed to study airborne snow metamorphism under controlled flow and thermal conditions. The obround closed-circuit wind tunnel enables particle transport over long durations while maintaining stable boundary conditions. The facility is installed in a cold laboratory at the WSL Institute for Snow and Avalanche Research SLF, about 2m x 3m x 0.5m (W x L x H) in dimensions, and includes enhanced thermal control, a revised wind turbine integration reducing heating of the air, and snow surface temperature control, allowing independent regulation of air and surface temperatures.We present a first comprehensive characterization of the flow field, including velocity distributions, spatial flow homogeneity, and turbulence properties across a range of wind speeds relevant for snow saltation and suspension. We further present a characterization of the thermal performance of the RWT, demonstrating improved temperature stability of the air and snow surface. The new ring wind tunnel provides a unique experimental facility for studying aerodynamic and thermodynamic impacts on snow particle evolution during snow transport. Generally, the new RWT facility additionally allows for studying a wide range of particle-flow and flow-surface (ice, snow, or water) interaction processes in turbulent cryospheric environments. Walter B, Weigel H, Wahl S, Löwe H (2024) Wind tunnel experiments to quantify the effect of aeolian snow transport on the surface snow microstructure, The Cryosphere, 18, 3633-3652, https://doi.org/10.5194/tc-18-3633-2024Wahl, S., Walter, B., Aemisegger, F., Bianchi, L., & Lehning, M. (2024). Identifying airborne snow metamorphism with stable water isotopes. Cryosphere, 18(9), 4493-4515. https://doi.org/10.5194/tc-18-4493-2024