Abstract
The effects of gravity wave drag on medium-range forecasts were determined with the Center for Ocean-Land-Atmosphere Interactions (COLA) GCM in the Department of Meteorology, University of Maryland, College Park. The GCM is a global spectral model developed from a numerical weather prediction model, and incorporating a shallow convection scheme, large scale precipitation, and the cumulus convection scheme of Kuo (1965). Attention is given to representing the barrier effect of mountains on the large-scale atmospheric flow by enhanced orography, and to parameterizing the effects of subgrid scale orography by simulating the effects of vertical momentum transport by gravity waves generated by flow over subgrid scale mountains. The parameterization in the GCM consists in determining the drag due to the gravity waves at the surface and the vertical variation of the drag in the model. Four synoptically independent days were chosen from the Northern Hemispheric winter of 1989-1990. The data for these four days were used to make ten-day forecasts with the model, with and without the gravity wave drag parameterization. Results suggest that the gravity wave drag parameterization improves the medium-range forecasts, which agrees with results from previous studies with other models.