SNOHATS: Stratified atmospheric turbulence over snow surfaces

Stably stratified turbulence presents particular challenges both from an experimental and a modeling perspective. The damping of the turbulence due to flow stratification and the presence of features such as gravity waves, and Kelvin-Helmholtz instabilities complicate the the application of turbulence similarity theories and the formulation of turbulence models. From an LES perspective, the main problem is that the classic parameterizations of the subgrid scales are often found to be inadequate for stable conditions. To guide the improvement of SGS modeling under stable conditions and, more generally, to understand turbulence dynamics under stable stratification and its interaction with other flow featuers, the Snow-Horizontal Array Turbulence Study (SnoHATS) field study was held at the extensive “Plaine-Morte” glacier in the Swiss Alps (3000 m) from February to April 2006. The snow cover provided stable stratification of the flow over long periods. Two horizontal arrays of 3D sonic anemometers were deployed to allow two dimensional filtering and computation of the three-dimensional strain rate tensors (Fig. 1).