Numerical simulation of air flow over mountains

The nature of the interaction of atmospheric flow with a mountain range of finite length is investigated. An inviscid, adiabatic primitive equation model is used to simulate steady, vertically-unsheared flow past a mountain range; various cases of mountain height and width are analyzed. A similar model for two-dimensional Boussinesq flow past a mountain on an f-plane is solved analytically following Merkine (1975) for comparison to the numerical solution. Results indicate that the atmospheric response is quite similar to that observed in the Boussinesq model. Ridging over the mountains and responses which damp in the vertical are observed in both models. Differences are noted in the magnitude of the response in the vicinity of the mountains and in the position of the downstream trough. In addition, the effect of finite difference model grid resolution is investigated by comparing simulations based on differing horizontal and vertical resolution. Results indicate that for larger scale mountains, the effect of poorer horizontal resolution is significant; vertical resolution, however, is relatively unimportant. As the horizontal scale of the mountains is reduced, vertical resolution becomes increasingly more important so that the effects of both horizontal and vertical resolution are significant. (Author)