NONLINEAR WAVES WITH SEMI-GEOSTROPHIC FLOW

In this paper,the semi-geostrophic approximation (or the geostrophic momentum approximation)is used for analyzing and solving the barotropic and baroclinic atmospheric motions.It is shown that the horizontal nondivergent or quasi-geostrophic approximations cannot reflect the nonliner effect.However,the semi-geostrophic approximation not only filter out the inertia-gravity waves as the quasi-geostrophicapproximation,but also find the solution to the nonlinear equations.The Rossby waves obtained by the semi-geostrophic approximation possess the nonlinear characteristics.Therefore the semi-geostrophic approximation provides a way to discuss the nonlinear problem.