Research On The Gulf Of Thailand Tidal Current Numerical Simulation And Theoretical Models

The Gulf of Thailand is the largest bay in the South China Sea and has relativelycomplicated tidal regime. In particular, the existence of clockwise amphidromicsystems of semidiurnal tides in the bay mouth area, which is against the general rulefor the northern hemisphere, has attracted the attention of a number of investigators.Moreover, the existence and position of amphidromic point at the top of the Gulf ofThailand produced from numerical investigations are still greatly diverse.Furthermore, the methods used in the previous investigations are basically limited todata analysis and numerical simulation, in lack of theoretical modeling.In this paper we establish a numerical model for the Gulf of Thailand and itsadjacent sea on the basis of FVCOM (Finite Volume Coastal Ocean Model), and atheoretical Two-Rectangular-Gulf Model (TRG Model) on the basis of generalizedTaylor solution.The numerical model is a two-dimensional hydrodynamic ocean tidal model, withunstructured triangular grid, computed with the finite-volume method. The openboundary condition of model is specified by the tidal elevations, which is predictedusing harmonic constants from the global ocean tide model DTU10. The modelsimulates four principal constituents (K1, O1, M2and S2) simultaneously. The averagedeviation of the simulation results from observations at29gauge stations given in theIHO dataset is5.69cm,3.98cm,7.35cm and4.71cm, respectively. Based on thesimulation results, the distribution of tide, tidal current and tidal energy flux in theGulf of Thailand and its adjacent sea are described. Furthermore, two groups ofexperiments are performed to study the sensitivity of the tidal characteristics to thebottom friction coefficient and bottom topography.In the theoretical model the Gulf of Thailand is idealized as two rectangular areasrepresenting the main body of the Gulf and the Bay of Bangkok, respectively. Ageneralized Taylor problem solution, with bottom friction and open boundarycondition considered, is employed to investigate tidal dynamics of K1and M2constituents. The model reproduces well the characteristics of the tides in the Gulf, and provides distributions of tidal current ellipses and tidal energy flux densityvectors. The contributions of the Kelvin and Poincaréwaves to the formation of thetidal waves in the Gulf are revealed, and a theoretical explanation for the formation ofthe amphidromic points is presented. To reveal the dynamic roles of the Bay ofBangkok and open boundary condition in the formation of the M2constituent, twosets of sensitivity experiments are designed. The results of experiments show that, theBay of Bangkok plays a key role in the existence and position for the inneramphidromic point; the westward delay of the phase on the open boundary is anecessity for the formation of the clockwise rotating amphidromic point near themouth of the Gulf.In summary, both the numerical and theoretical models indicates that: the diurnaltide in the Gulf of Thailand is mainly composed of Kelvin waves, and the distributionof its co-phase-lag lines is sensitive to bottom friction and is insensitive to bottomtopography; the semidiurnal tide is composed of weak Kelvin waves and notablePoincaréwaves near the top and the mouth of the Gulf, and the distribution of itsco-phase-lag lines is sensitive to bottom topography, and is mainly controlled by thephase-lag distribution at the mouth of the Gulf.