Nonlinear, Non-Geostrophic Effects in a Baroclinic Atmosphere

Abstract

The finite amplitude evolution of an unstable baroclinic wave is studied with the primitive equations of motion. A two-level model is used and the variation of the disturbance with latitude is neglected. Solutions for this model are obtained from a nonlinear perturbation expansion and also by numerical integration. Comparison of these solutions gives the range of convergence of the perturbation expansion. The solutions show smaller scale distortions, which are not predicted by the quasi-geostrophic equations, when the disturbance amplitude becomes sufficiently large. The distortions include the development of sharp troughs and flat ridges in the height-contour fields and the production of frontal zones. When the disturbance becomes very large substantial changes occur in some of the zonally averaged fields. The solutions display a cascade of energy to shorter wavelengths.