On Internal Wave In The Stratified Ocean: Evolution, Breaking And Associated Mixing

The dissertation firstly introduces the primary concepts, observational methods, generation mechanism, distribution, evolution and breaking of internal waves in the stratified ocean. About wave breaking and turbulent mixing, the second chapter presents a summarization in detail, which includes the advective and shear instability, nonlinear interaction and PSI mechanism, reflection over sloping boundary, exchange between strong mixing region in boundary layer and ocean interior, interaction of internal wave with shear current, the parameterizations of turbulent dissipationε, estimations of turbulent flux, mixing efficiency, GM model and stratified turbulence. These are also the base of analysis of numerical simulation results.The evolution and breaking of small amplitude internal propagating waves in stratified ocean is direct numerical simulated using pseudo-spectral method. The author does a series of two-dimensional and three-dimensional tests. Through analysis and compare of the results, he draws the conclusion as the following:1) The breaking of small amplitude and high frequency internal wave is induced by PSI mechanism, i.e. the energy of primary wave transfers to secondary waves, which frequency equals half the primary wave frequency. Besides, the vertical shear overcomes the stratification, and then internal wave breaking occurs.2) The time of wave breaking is inversed to the amplitude of primary wave. About the viscosity coefficient, large(small) viscosity make Kolmogorov(dissipation) scale large(small), and then the energy cascaded to the small scale motions can accumulate difficultly(easy), so the time of wave breaking is delayed(advanced).3) The nonlinear interaction is not only related to Froude number, but also to primary wave frequency. Wave breaking is induced by PSI mechanism for high frequency internal waves, however, about low frequency internal wave, the breaking occurs at the primary wave itself.4) About the diapycnal diffusion coefficient k_ρ, Cox number C_x and mixing efficiencyγ,...