Free Oscillations of the NCAR Global Circulation Model

Abstract

A procedure is developed for expanding grid-point data into the normal modes of the linearized NCAR GCM. The approach assumes small-amplitude perturbations about a state of rest and involves separation of variables to give vertical and latitudinal structure equations for each longitudinal wavenumber. As an example of the procedure, 30 days of GCM model simulation data are expanded into the normal modes. It is concluded that the time and space computational modes regarded as noise have amplitudes at least an order of magnitude smaller than the dominant Rossby waves. Except for the Kelvin modes, the model gravity waves have magnitudes no larger than the noise level. The largeness of the Kelvin modes suggests that they may be an important part of the model tropical climatology.