Impact of Subgrid-Scale Orography Parameterization on the Simulation of Orographic Flows

A subgrid-scale orography parameterization based upon the use of an effective roughness length has been implemented in a mesobeta-scale model. The impact of such a parameterization is investigated in the framework of orographic flow simulations. Three mountain flow situations observed during the Pyrenees Experiment (PYREX) are studied. When subgrid-scale orography is accounted for, the mountain wave amplitude is reduced, the blocking is increased, the leeside low-level turbulence is intensified, and the regional wind characteristics are modified. Detailed comparisons made with the PYREX data indicate that the inclusion of subgrid orography yields a significant improvement in the model results.