Coupling a multi-layered snow model with a GCM

A multi-layered snow model, including most physical processes governing the evolution of snowpacks, has been coupled to a global circulation model (GCM) to improve the representation of snow cover in climate simulations. The snow model (Crocus) includes original features to simulate the evolution of snowpack layering that allows a realistic calculation of snow albedo as a function of the type and size of the crystals of the surface layer. The coupling scheme is based on a synchronous run of the GCM and of the snow model with an exchange of the surface fluxes at every time-step. It was tested in a five-year run at a T42 resolution. The impact on the atmosphere was important over most snow-covered regions and the snowpacks simulated in the different regions present a layering that is realistic and very variable in connection with the climate. The simulated snow cover compares satisfactorily with the present snow climatology.