Darek Bogucki

Shear Induced Decay of Internal Solitary Waves

Thesis Approved September 1991

Internal Solitary Waves (ISWs) are a common feature of the ocean interior, especially close to shelf breaks. They are observed to mix the water column at the site of maximum density gradient. A model is proposed that clarifies the concept of ISW shear- induced mixing for a two-layer system separated by a thin interface with a finite density gradient. The ISW damping due to this process is addressed and the value of the horizontal mixing distance is estimated. A laboratory experiment was performed to determine the amount of interfacial thickening. An optical method to measure interface thickness was developed. The results of the laboratory experiment are found to agree with the proposed model.

A generalized model of ISW-shear induced mixing in a continuously stratified fluid with a stratified upper layer and a homogeneous lower layer is proposed. The ISW mixes the water column from the base of the stratified zone upward by decreasing the initial density gradient, and downward by stratifying the upper portion of the initially mixed lower layer. The ISW damping distance is found to be comparable to field observations. The model estimates of ISW dissipated energy give lower values than observed in the ocean.