Measurements of internal gravity waves in a continuously stratified shear flow

A theoretical wave-action model, based on the work of Grimshaw (1974), is presented which describes broadbanded internal wave motions in a stratified shear flow with the viscous terms included. The model shows that in the neighbourhood of the critical level viscosity can have important effects and can stabilize the flow with respect to convective overturning. The predictions of the model are compared with the results of an experimental study where detailed measurements of the velocity and density fields are made within an internal wave packet propagating through a continuously stratified shear flow. The results show that the model accurately predicts the occurrence or non-occurrence of wave overturning due to interactions with the shear, and provides an accurate description of the structure of the wave-induced density and velocity fluctuations in those regions of the flow where the assumptions of the model are satisfied.