On the Simulation of Shallow Water Tides in the Vicinity of the Taiwan Banks

Abstract

The Taiwan Banks (Formosa Shoals), a large NE-SW oriented bathymetric feature near the southern end (23°N, 118 - 119°E) of the Taiwan Strait, is a region of extremely shallow water that exerts a profound effect on the propagation of tidal waves. As such waves propagate over the Taiwan Banks, they become distorted and asymmetric due to bottom friction and contribute to the generation of shallow water tides. The POM model was used in present study to simulate the tides in the Taiwan Strait region. Shallow water tidal dynamics in the area of Taiwan Banks are focused. The numerical model was validated against sea level observations from 34 tidal stations located on the coast of Mainland China and Taiwan. Trajectory records from two SVP drifters are used to be compared with the simulations using wavelet-based rotary spectral analysis.

Numerical simulations show that the Taiwan Banks divide, separate and guide the southward propagating branch of an M2 tide along the western boundary of the Taiwan Strait as Kelvin Waves. The eastern branch which dissipates its energy by the bottom friction around the Taiwan Banks and the Penghu Islands gradually diminished along the south-eastern boundary of the Taiwan Strait. The northward propagating M2 dominates the tides in the waters east of the point 119.5°E, 22.8°N along the Penghu Channel instead. Moreover, the patterns of the standing waves of the 1/4 diurnal constituents are identified, it could be therefore hypothesized that the amplification of semi-diurnal tides in the Taiwan Strait is primarily due to the condition of two open ended channel co-oscillations.

Co-oscillations are demonstrated by numerical simulations as well as an SVP drifter record which indicates that the Taiwan Banks act as the generator of the shallow water tides. The shallow water constituents are amplified and propagate southward to the South China Sea and diminish rapidly. From the SVP drifter data and short-time rotary spectral analysis, it is also interesting to note that the 1/5 diurnal constituent becomes significant compared to other shallow water constituents in the local vicinity of Taiwan Banks.

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