Evolution of moist-baroclinic normal modes in the nonlinear regime

A primitive equation model, in which latent heat release is represented by a small static stability for all ascending air, is used to examine the early stages of nonlinear evolution of moist baroclinic waves, before finite amplitude equilibration sets in. The results here obtained improve previous quasigeostrophic work with regard to the structure of the solutions and reveal the incorrectness of a quasigeostrophic result concerning meridional displacement, which does not occur in the primitive equation model. Approximate formulations of perturbation buoyancy are tested and generally found inappropriate, revealing a high sensitivity of the results to this term.