The effect of rotation on the pressure drag force produced by flow around long mountain ridges

The impact of rotation on the orographic drag experienced by air flowing around a wide mountain is investiated. The work builds on numerical modelling studies performed by Olafsson and Bougeault, who investigated the effect of rotation and surface friction on the drag experienced by flow around a single elongated mountain perpendicular to the direction of the flow. The region of parameter space they explored is extended by performing a series of idealized model experiments with a larger range of ridge lengths. The drag force in these simulations is compared with the predictions of a heuristic flow-blocking model devised by Shutts. The results show that Shutts's model overestimates the effect of rotation upon the drag force. However we find that Shutts's model predicts both the drag force exerted on the upstream side of the ridge and the upstream features reasonably well. Finally the implications of the results for NWP parametrizations of subgrid-scale orographic drag are discussed.