COMPARISON OF LINEAR BAROCLINIC INSTABILITY THEORY WITH THE EDDY STATISTICS OF A GENERAL CIRCULATION MODEL.

Abstract

The linear instability of two zonal mean flows, one computed by a general circulation model and the other corresponding to the observed winter zonal mean flow, is presented. For these calculations, the authors utilize a numerical primitive equation model, where the spherical geometry of the earth has been retained. By comparing the waves predicted by linear theory with the eddies that appear in the general circulation model, it is determined that significant discrepancies exist. For the wavenumber range 1 through 15, the linear theory predicts the maximum growth rate to be for wavenumbers 12-15. The wavenumbers that dominate the intermediate-scale transient eddies in the general circulation model are much longer. It is determined that discrepancies also exist for wavenumber 7-15 in the real atmosphere. It is concluded that these discrepancies must be due to some nonlinear process.