Flow and Snow in Complex Terrain: across-scale modelling for a correct surface mass balance

Preferential deposition of snow precipitation, snow transport and snow sublimation modify the mass which gets incorporated into or removed from the seasonal or perennial snow cover. These processes happen at very small scales from snow grain size to larger turbulent eddies and are therefore inaccessible to direct and scale-resolved physics-based modelling in large scale climatological and meteorological models. In extreme environments, these processes are hypothesized, however, to be a major driver of the overall surface mass balance for snow and ice. This contribution presents a variety of modelling strategies to overcome the scale gap. Modelling strategies include bulk approximation, statistical and stationary wind modelling and large eddy simulation. Modelling is supported by measuring local and spatial meteorology and more specifically fluxes and snow distribution. Using a combination of such measurements and the diverse modelling methods it is shown, when and where simple approximations fail. For example, surface flux parameterizations fail during blowing snow. We further suggest how to adequately incorporate these processes in weather models such as the CRYOWRF model and present results that demonstrate the influence of blowing and drifting snow on the surface mass balance in Antarctica, the Alps and High Mountain Asia. We consider the feed-back of blowing snow onto the atmospheric boundary layer and show how it influences local effects such as through katabatic winds.