Abstract
The momentum flux by small-amplitude gravity waves produced by steady-state flow over a three- dimensional circular mountain in an isothermal plane rotating atmosphere is investigated. There is an upward transfer of momentum normal to the basic current by external-type gravity-inertia waves. This momentum transfer yields a flux convergence of momentum primarily in the lowest kilometer of the atmosphere. In contrast, the component of momentum parallel to the basic current is transported downward by internal-type gravity waves. This flux is independent of height and is essentially independent of the earth's rotation. Computed values of this surface drag are comparable with estimates of the frictional drag over ordinary terrain. The dependence of the various drag coefficients on atmospheric and mountain-shape parameters is also presented.
