正压原始方程有限区域谱模式的预报试验

本文包括四方面内容; (1)给出一个单向嵌套的有限区域浅水波方程谱模式的具体方案及其预报试验结果。这个模式基于文献。其特点是:基本展开函数为“修正的双傅氏级数”,它由两部分组成:正交双博氏级数及非正交的线性函数,这两部分之间互不正交。 (2)对同一实例,比较了谱方法,差分法,假谱法24h,48h预报结果。甚至同格距缩小一半的差分法相比,谱方法预报效果仍优于差分法预报效果。 (3)试验了谱模式的固定边界、刚体边界、侧边界条件随时间变化但不加松弛处理,以及侧边界条件随时间变化加松弛处理四种方案。结果表明,合理的边界条件及有效的边界处理方法对谱模式来说是至关重要的。 (4)提出并试验了谱模式的一种地形区计算方案,有助于谱模式中对陡峭地形的处理。

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.