A numerical model is used to study the transition between various types of periodic and chaotic behavior in a two-layer baroclinic circumferential flow. At small supercriticalityF−Fcand low friction Γ, a type of chaos similar to that predicted by low-order or weakly-nonlinear models is found. However, contrary to the predictions of these relatively simple models, this type of aperiodic behavior, first discovered by E. N. Lorenz in his classic study of thermal convection, occupies only a small bubble in theF− Γ parameter-space. As the supercriticality is increased the aperiodic regime terminates abruptly and a broad band of periodic motions separates the weakly-nonlinear chaotic region from a higher-dimensional type of chaos that occurs at largerF−FcWave-wave vacillation is predicted near the crossing of the wavenumber −1 and wavenumber −2 neutral curves. The calculations are in qualitative agreement with experiments, especially in that the transition to chaos at moderateF−Fc, as Γ is decreased, involves both period-doubling and quasi-periodicity.