On mountain wave drag over complex terrain

Mountain wave drag is calculated for rotating, stratified, nonhydrostatic Boussinesq flow over a mountain ridge using linear theory for a variety of mountain profiles representing complex/irregular terrain. The inclusion of a sinusoidal corrugation to the familiar witch-of-Agnesi profile creates a "stegosaurus" profile. The associated drag is greatly enhanced for mesoscale mountains when the corrugation wave-number matches that for the dominant inertia-gravity wave contribution to the cross-mountain surface pressure gradient. Similarly, increasing the jaggedness (by decreasing the exponent b) increases the drag for mesoscale mountains whose topographic spectral intensity, M(k), has the form of a power law:M(k)=mk^-b where k is the zonal wavenumber. Spectral analysis of one-kilometer resolution topographic data for the Appalachian Mountains suggests that a power law profile with b=1.7 accurately represents the topographic spectral intensity and that it yields good estimates of the drag. The application of these results to the parameterization of mountain wave drag in general circulation models is discussed.