A NEW SNOW PARAMETERIZATION FOR THE METEO-FRANCE CLIMATE MODEL .1. VALIDATION IN STAND-ALONE EXPERIMENTS

Both observational studies and numerical experiments demonstrate the s ensitivity of the atmosphere to variations in the extent and mass of s now cover. There is therefore a need for simple but realistic snow par ameterizations in forecast and climate models. This study describes a new physically-based snow hydrology for use in the Meteo-France climat e model, together with the ISBA land-surface scheme. A restricted numb er of parameters has been added, while preserving a single surface ene rgy budget. The ageing process of the snow pack has been introduced th rough prognostic equations for snow density and snow albedo. Snowmelt computation has been modified over partially snow-covered and vegetate d areas. The new scheme has been validated against field measurements in stand-alone simulations forced by observed meteorological condition s. The results show a strong improvement in the model's performance, t hereby suggesting that a simple one-layer snow model is able to reprod uce the main physical mechanisms governing the snow pack evolution. Pa rt II of the present study will concern the validation in a 3-D experi ment within the Meteo-France climate model.