HR: 09:15h
AN: OS41A-06 INVITED     [Abstracts]
TI: Nonhydrostatic effects of nonlinear internal wave propagation in the South China Sea
AU: Zhang, Z
EM: zhonghua@stanford.edu
AF: Environmental Fluid Mechanics Laboratory, Dept. of Civil and Environmental Engineering, Stanford University, Stanford, CA 94305-4020, United States
AU: * Fringer, O B
EM: fringer@stanford.edu
AF: Environmental Fluid Mechanics Laboratory, Dept. of Civil and Environmental Engineering, Stanford University, Stanford, CA 94305-4020, United States
AB: It is well known that internal tides are generated over steep topography at the Luzon Strait on the eastern boundary of the South China Sea. These internal tides propagate westward and steepen into trains of weakly nonlinear internal waves that propagate relatively free of dissipation until they interact with the continental shelf on the western side of the South China Sea, some 350 km from their generation point. The rate at which the internal tide transforms into trains of nonlinear waves depends on the Froude number at the generation site, which is defined as the ratio of the barotropic current speed to the local internal wave speed. Large Froude numbers lead to rapid evolution of wave trains while low Froude numbers generate internal tides that may not evolve into wave trains before reaching the continental shelf. Although the evolution into trains of weakly nonlinear waves results from the delicate interplay between nonlinear steepening and nonhydrostatic dispersion, the steepening process is represented quite well, at least from a qualitative standpoint, by hydrostatic models, which contain no explicit nonhydrostatic dispersion. Furthermore, hydrostatic models predict the propagation speed of the leading wave in wave trains extremely well, indicating that its propagation speed depends very weakly on nonlinear or dispersive effects. In order to examine how hydrostatic models introduce dispersion that leads to the formation of wave trains, we simulate the generation and evolution of nonlinear waves in the South China Sea with and without the hydrostatic approximation using the nonhydrostatic model SUNTANS, which can be run in either hydrostatic or nonhydrostatic mode. We show that the dispersion leading to the formation of wave trains in the hydrostatic model results from numerically-induced dispersion that is implicit in the numerical formulation of the advection terms. While the speed of the leading wave in the wave trains is correct, the amplitude and number of waves in the wave trains is not correctly computed by the hydrostatic model. This has important implications for the predictability of wave amplitude upon arrival at the continental shelf using hydrostatic models.
UR: http:suntans.stanford.edu
DE: 3285 Wave propagation (0689, 2487, 4275, 4455, 6934)
DE: 4455 Nonlinear waves, shock waves, solitons (0689, 2487, 3280, 3285, 4275, 6934, 7851, 7852)
DE: 4534 Hydrodynamic modeling
DE: 4544 Internal and inertial waves
DE: 4562 Topographic/bathymetric interactions
SC: Ocean Sciences [OS]
MN: 2007 Joint Assembly