Ray Tracing of Internal waves in the Northern South China Sea
Date Issued
2006
Date
2006
Author(s)
Chao, Yen-Hsiang
DOI
zh-TW
Abstract
Satellite images show that nonlinear internal waves (NLIWs) often exist over the continental shelf of northern South China Sea. When NLIWs enter the continental shelf or encounter bathymetric changes, they will be refracted or diffracted by the change of water depth or be reflected by the obstacles. It often happens that many groups of NLIWs in one satellite image that makes one difficult to distinguish the NLIWs groups that were generated periodically from the same source and from the same generation mechanism, but with 24 hours lag. These NLIWs may be in one or many different satellite images. Tracing the same group of NLIWs will not be a problem if one has consecutive satellite images at short time lags. Without consecutive images, categorizing groups of NLIWs requires ability to predict propagation speed and path of NLIWs over the continental shelf. Because the propagation speed of NLIW (Cn) depends on the stratification, water depth, tidal and mean currents and NLIW amplitude, archived CTD data of April and May in 1995-2001 were used to derive the first baroclinic mode of internal semi-diurnal tide over a grid of 60 by 90 points. Without in situ data on the NLIW amplitude which enhances NLIW propagation speed, satellite images over the shelf are used to estimate the half-width of NLIW fronts and then derive the NLIW propagation speed with KdV (Korteweg - de Vries) theory. Then, simulation of the propagation and refraction of NLIW fronts may be done with Snell’s law. The effect of barotropic tidal current, which is predicted by the tidal model of OSU (Oregon State University), was included in the prediction, but the effect of mean current is ignored because it is much smaller than Cn. Predicted propagation of NLIW fronts were successfully in categorizing NLIWs in one or two consecutive satellite images, even from different satellites. The accuracy of predicted distance, or the mean predicted propagation speed Cn is on the average of 0.04 % with standard deviation of 5.1 %. This accuracy of predicted Cn seems to be better than those derived from mooring data in ASIAEX.
Subjects
非線性內波
模擬
傳遞
nonlinear internal waves
simulation
propagation
Type
thesis
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