FORECASTING EXPERIMENTS WITH A BAROTROPIC PRIMITIVE EQUATION LIMITED-AREA SPECTRAL MODEL

Four aspects are coveaed in this paper:(1) A one-way nested limited-area shallow water equation spectral model and its numerics are described. The model is characterized by the adoption of modified double Fourier series which is composed of two parts:orthogonal double Fourier series and nonorthogonal linear functions. And exponential form expansion functions are used for all prognostic variables. (2) Comparative 24 h, 48 h forecasts of a real case are conducted for the spectral method, finite difference method and pseudo-spectral method. Also compared is the forecast of the spectral model with that of a finer version of finite difference model where half of the grid size is used. The results show the superiority of the spectral model. (3) The sensitivity of the results to different formulation of lateral boudary conditions has been tested. It is shown that a suitable boundary condition or effective treatment seems particularly important for limited-area spectral models. (4) A scheme to deal with steep mountain in spectral models is proposed and tested.