ON THE BOUSSINESQ APPROXIMATION AND ITS ROLE IN THE THEORY OF INTERNAL WAVES.

Most studies of the dynamics of fluids with weak density gradients use the Boussinesq approximation, which neglects density variations in the inertial terms of the equations of motion. The significance of this approximation is investigated. As a general matter, care is called for in the use of the approximation if quantities other than the non-dimensional density difference are small. Also, the very existence of certain phenomena of interest and importance may depend onthe small terms neglected by the Boussinesq approximation. This is illustrated by an investigation of solitary waves in a stratified fluid system. Author