Abstract Nonlinear dynamics of unstable baroclinic disturbances are examined in the context of the Eady model modified by Ekman dissipation at the lower boundary while the upper boundary remains stress-free. Three approaches are used: the asymptotic approach which pivots about the constraints of strong bottom dissipation and weak supercriticality, the ad hoc approach which neglects wave-wave interactions by truncating the wave field to a single wave, and the spectral numerical approach. The time evolution of the disturbance is generally characterized by a “single hump” pattern consisting of a growth stage to a maximum amplitude followed by a decay stage. During the decay stage, the spectral solution develops an amplitude vacillation which, for most parameter settings, becomes chaotic in nature and persists at a mean level substantially below the “hump” maximum and of the order of the initial amplitude. The exceptions are moderate or long waves in a strongly viscous fluid, for which the vacillation decays ...