Deriving the evolution of snow specific surface area from water vapor physics at the microstructure scale

The specific surface area (SSA) is a crucial parameter to characterize the microstructure of snow. It is one of the main properties controlling the optical and mechanical behavior of snow. Thus, being able to describe the evolution of SSA under the effects of metamorphism is key for detailed numerical snowpack models. This then allows simulating for example the albedo of snow-covered surfaces and its evolution over time. To this end, we propose to derive the law governing the evolution of SSA of snow directly from the physics of water vapor transport at the microstructure scale. We identify the crucial physical parameters for the evolution of the SSA. We show that the evolution of SSA is generally composed of two additive terms: an isothermal contribution and a temperature gradient contribution, each characterized by scalar macroscopic properties relating the evolution of the SSA to the temperature and temperature gradient imposed to the snow. On-going work includes parameterizing these scalar properties in order to obtain a fully-closed and operational law for the evolution of SSA.