DOWNWARD PROPAGATING INTERNAL WAVES GENERATED AT THE BASE OF THE SURFACE-LAYER OF A STRATIFIED FLUID

Downward propagating internal waves are observed in laboratory experim ents. They appear to be generated by the 'obstacle effect' beneath a t urbulent surface layer in a surface stress driven stratified flow expe riment in a rectangular cavity. The obstacles are the perturbations at the base of the surface layer and the shear is created by a combinati on of an internal seiche and the circulation in the upper layer. The p roportion of energy lost from the surface layer is comparable to incre ases in potential energy due to vertical entrainment. Consequently, if conditions are favourable, reduction in vertical entrainment may occu r.