IMPACT OF SUBGRID-SCALE OROGRAPHY PARAMETERIZATION ON THE SIMULATION OF OROGRAPHIC FLOWS

A subgrid-scale orography parameterization based upon the use of an ef fective roughness length has been implemented in a mesobeta-scale mode l. The impact of such a parameterization is investigated in the framew ork of orographic flow simulations. Three mountain flow situations obs erved during the Pyrenees Experiment (PYREX) are studied. When subgrid -scale orography is accounted for, the mountain wave amplitude is redu ced, the blocking is increased, the leeside low-level turbulence is in tensified, and the regional wind characteristics are modified. Detaile d comparisons made with the PYREX data indicate that the inclusion of subgrid orography yields a significant improvement in the model result s.