HIGH-RESOLUTION SIMULATIONS OF JANUARY AND JULY CLIMATE OVER THE WESTERN ALPINE REGION WITH A NESTED REGIONAL MODELING SYSTEM

High resolution January and July present day climatologies over the ce ntral-western Alpine region are simulated with a Regional Climate Mode l (RegCM) nested within a General Circulation Model (GCM). The RegCM w as developed at the National Center for Atmospheric Research (NCAR) an d is run at 20km grid point spacing. The model is driven by output fro m a ''present day'' climate simulation performed with the GCM ECHAM3 o f the Max Planck Institute for Meteorology (MPI) at T106 resolution (s imilar to 120km). Five January and July simulations are conducted with the nested RegCM and the results for surface air temperature and prec ipitation are compared with a gridded observed dataset and a dataset f rom 99 observing stations throughout the Swiss territory. The driving ECHAM3 simulation reproduces well the position of the northeastern Atl antic jet, but underestimates the jet intensity over the Mediterranean . Precipitation over the Alpine region in the ECHAM3 simulation is clo se to observed in January but lower than observed in July. Compared to the driving GCM, the nested RegCM produces more precipitation in both seasons, mostly as a result of the stronger model orographic forcing. Average RegCM temperature over the Swiss region is 2-3 degrees higher than observed, while average precipitation is within 30% of observed values. The spatial distribution of precipitation is in general agreem ent with available gridded observations and the model reproduces the o bserved elevation dependency of precipitation in the summer. In the wi nter the simulated observed. Precipitation frequencies are overestimat ed, while precipitation intensities show a reasonable agreement with o bservations, especially in the winter. Sensitivity experiments with di fferent cumulus parameterizations, soil moisture initialization and mo del topography are discussed. Overall, the model performance at the hi gh resolution used here did not deteriorate compared to previous lower resolution experiments.