Long Nonlinear Internal Waves and Quasi-Steady Lee Waves

摘要

Previous observation of large amplitude internal gravity waves generated by tidal flow over a submarine ridge in Massachusetts Bay have motivated the author to consider the general problem of internal gravity wave generation by time-dependent flow of a stratified, inviscid fluid over topography. An internal Korteweg and deVries type equation for the stream function is derived using a three parameter expansion method, where the three small parameters correspond to nonlinear, dispersive, and non-Boussinesq effects. Simple analytic models and laboratory experiments are used to examine mixing and the generation of quasi-steady lee waves. A tall, rapidly oscillating ridge acts to mix the stratified fluid near the ridge; the circulation set up by the collapse of the mixed fluid is determined. In the second study, ray theory is used to analyse lee waves generated behind a low ridge being slowly towed periodically through a stratified fluid. (Author)