Normal Mode Initialization for a Multilevel Grid-Point Model. Part I: Linear Aspects

Abstract

In Part I of this paper we review initialization methods for numerical weather prediction models, leading up to the development of schemes based on the normal modes of the forecast model. We present the derivation of the normal modes of ECMWF's multilevel global grid-point model, and compare the horizontal normal modes with those obtained using alternative finite-difference schemes. The impact of stability-enhancing Fourier filtering procedures on the normal modes is also discussed. Finally in Part I we apply linear normal mode initialization to a nine-level version of the model with 3.75° horizontal resolution. The application of nonlinear normal mode initialization to this model is presented in Part II.