VALIDATION OF PRESENT-DAY REGIONAL CLIMATE SIMULATIONS OVER EUROPE - LAM SIMULATIONS WITH OBSERVED BOUNDARY-CONDITIONS

Nested limited-area modelling is one method of down-scaling general ci rculation model (GCM) climate change simulations. To give credibility to this method the nested limited-area model (LAM) must be shown to si mulate local present-day climate conditions fairly accurately. Here se ven different European limited-area models driven by observed boundary conditions (operational weather forecast analyses) are validated agai nst observations, and inter-compared for summer and winter months. Rel atively large biases are found. In summer large positive surface air t emperature biases are found over southeast Europe. The main reason is deficiencies in the surface hydrological schemes causing an unrealisti c drying of the soil. In at least one of the models, most likely sever al of them, an additional factor is an overestimation of incoming sola r radiation. Apart from excessive precipitation in mountainous areas i n some models they generally show a negative bias due to the drying an d decreased advection from the Atlantic. In winter most models have a positive precipitation bias which seems to be caused by an enhancement of advection from the Atlantic and enhanced cyclone activity. Surface air temperature biases are negative probably due to an underestimatio n of the incoming longwave radiation.