Energy Budget of Internal Solitary Waves in South China Sea from Continuously Stratified Nonhydrostatic Model

Abstract

An in-house fully nonlinear, nonhydrostatic numerical code is utilized for simulations of internal solitary waves (ISWs) generated by tidal flow over a Gaussian sill topography. A complete, rigorous theoretical framework is then adopted for the energetics analysis of these ISWs. It is found that ISWs contain most of the baroclinic energy in the internal wave field. The nonhydrostatic energy flux is in opposite direction to the hydrostatic and nonlinear fluxes. For fixed tidal excursion parameter (ε), the nonlinear portion of the total baroclinic flux decreases as the slope parameter (γ) increases. In addition, the ISW energy, energy flux and barotropic-to-baroclinic energy conversion rate all peak when the bottom topography is critical (γ = 1). For typical ISWs generated in the Luzon Strait, 87.9% of the total barotropic input energy is converted into baroclinic energy, and the other part of the energy is used for barotropic dissipation. 63.7% of the converted baroclinic energy is radiated far away and the remaining part of the baroclinic energy is dissipated through local mixing. When compared to the energy budget of linear internal tides, the percentages of the energy that are converted and radiated decrease, or equivalently, the percentages of the energy that are used for barotropic and baroclinic dissipations increase. Thus, the emergence of ISWs can effectively enhance both barotropic and baroclinic dissipations.