Nonlinear Normal Mode Initialization of a Limited Area Model

Abstract

Limited area models with pronounced topographic features need to be carefully initialized. We have attempted to adapt the nonlinear normal mode initialization technique developed for large-scale forecast models. A baroclinic model with fixed boundary conditions is considered. The horizontal structure of the normal modes is sinusoidal. Geostrophic and gravity modes are easily separated on the basis of their frequency. The standard procedure proposed by Machenhauer (1977) is found to be useful and leads to significantly better results than a linear balance equation.