Transient development of perturbations in inviseid stratified shear flow is investigated. Use is made of closed form analytic solutions that allow concise identification of optimally growing plane-wave solutions for the case of an unbounded flow with constant shear and stratification. For the case of channel flow, variational techniques are employed to determine the optimally growing disturbances.

The maximum energy growth attained over a specific time in internal decreases continuously with increasing stratification and no special significance attaches to Ri = 0.25. Indeed, transient growth can be substantial even for Ri = O( 1 ). A general lower bound on the energy growth attained by an optimal perturbation in a stratified flow over a given time internal is the square root of the growth attained by the corresponding perturbation in unstratified flow. Enhanced perturbations in mean flow with Ri < 0.4 produce regions with locally negative total density gradient, which are expected to overturn. Although the perturbations are of wave form, buoyancy fluxes mediate transfer between perturbation kinetic and potential energy during transient development. this implying that buoyancy flux is not a determinative diagnostic for distinguishing between waves and turbulence in stratified flows.