Abstract
An improved scheme for a spectral model has been investigated in this paper. Through the introduction of a reference atmosphere, prognostic variables become smoother on the tilted sigma-surface over the mountains or a frontal zone, and hence truncation errors are reduced. As a result, the problems of the Gibbs waves and of negative values of model topography over the sea, which are encountered in current spectral models, can be solved by the improved scheme. For comparison we have performed numerical integrations of barotropic and baroclinic Rossby-Haurwitz waves, and the predictions of real cases both with the improved scheme and the current scheme in a spectral model. The results show that the scheme presented in this paper is better than the current scheme.
