Nonhydrostatic climate simulations of precipitation over complex terrain

A climate version of the nonhydrostatic fifth-generation Penn State/NCAR Me soscale Model has been used to downscale a global climate scenario to cloud -resolving scales over complex terrain (the Alps). After first describing t he model and methodology, we then present comparison results from the model -predicted and ensemble-averaged regional-scale winter and summer season pr ecipitation distribution with results from the global simulation and analyz ed observed precipitation climatologies. Finally, results from the cloud-re solving simulations are compared to the regional simulations. It is shown t hat the degree to which the terrain is resolved in the various runs signifi cantly alters the simulation of the precipitation climatologies. This is ca used not only by the complex interaction of the flow with the topography bu t also by the different treatment of the convective processes (resolved ver sus nonresolved) in the model. Even in winter, the model-simulated seasonal ly averaged precipitation patterns change drastically with every increase i n horizontal resolution. Furthermore, with a horizontal grid resolution of 1 km, when seen on a local scale and over complex terrain, the model-simula ted precipitation patterns are not guaranteed to converge to one solution. This behavior is still more complicated in summer. Here it is shown that pa rameterized convection in the regional model simulation tends to be locked to the mountains, while in the cloud-resolving simulations the convection m oves with the upper level flow, producing precipitation maxima away from th e mountain tops.