Implementing and testing of a new snow scheme SAST in Simplified Simple Biosphere Model (SSiB)

Based on up to date comprehensive and complex snow cover schemes, a Simple Snow-Atmosphere-Soil Transfer Model (SAST) has been developed. This model includes most important physical processes for simulation of seasonal snow cover change. The model also makes substantial simplification and improvement. For example, based on the analysis of the effect of vapor phase change and vapor movement on mass and energy balances, a formulation of effective heat conductivity has been derived which simplifies the description of complex processes without loss of accuracy. Base on analyses of diurnal and seasonal variations of snow temperature, an efficient snow cover layering system has been developed for better prediction. The volumetric specific enthalpy instead of temperature is used as the prognostic variable. It simplifies the formulations in phase change processes and reduces the computational procedures with an efficient implicit one step test numerical scheme.

The SAST is coupled with SSIB to improve the SSIB prediction potential in snow cover regime. The coupled model includes the vegetation regime, snow cover regime and ground surface regime. Their physical properties are described by the mass and energy balance equations, respectively. Snow cover interacts with both vegetation cover above and ground surface below. In the coupled model, the snow surface temperature and canopy temperature are solved simultaneously to ensure the energy and water conservation in the vegetation-snow interface, which is crucial in the study of snow effects in global as well as regional climate models. Sensitivity has been conducted to further simplied snow model for future GCM studies.

The SAST model has been tested in off line model by using long term Russian and Franch field data. The results show its potential in predicting seasonal snow cover change. These two data sets along with the Mammoth snow data are tested further to validate and evaluate the coupled SSiB/SAST model.