Observations and Modeling Forcing Mechanisms for the Coastal Dynamics of the Upper Gulf of Thailand
A numerical model based on the Princeton Ocean Model (130M) with ∼1 km horizontal grid and 21 vertical layers has been used to study the influence of wind stresses, river discharges, surface heat fluxes and tides on the three-dimensional circulation of the upper Gulf of Thailand (UGOT). Analysis of observations, including sea level data, provided additional information to support the model simulations. The UGOT is a shallow coastal system, ∼1°×1° in size with the average depth of only 15 m. Sensitivity studies evaluate how the dynamics is affected by surface wind stresses, river discharges, and surface heat fluxes. The impact of the low latitudes (∼13 °N) on the dynamics is tested by comparing the simulations to results obtained when simulations are modified to mid-latitudes (∼45 °N). The model results show that the circulation in the UGOT is strongly affected by the seasonal monsoon winds, changing from counter-clockwise during the northeast monsoon to clockwise during the southwest monsoon. The vertical distribution of velocities is found to follow the classical wind-driven Ekman dynamics, even though the UGOT is shallow and low latitude. The flow tends to be more barotropic and with the wind direction in the shallow area where the water depth is less than the Ekman layer, while in the deeper channels a two-layer seems to develop. The results from the three-dimensional numerical model are compared well with a simple wind-driven analytical model. The impact of river discharges is the formation of a coastal jet of freshwater along the west coast, whereas the effect of Coriolis parameter is to advect the freshwater plume farther south along the west coast in mid-latitudes compared to low latitude simulations. Satellite sea surface temperature data generally agrees with the simulated spatial structure. The influence of ENSO resulted in up to 2-4°C inter-annual variations in water temperatures in the GOT. Analysis of sea level data shows in general a rate of relative sea level rise in Thailand of 6 mm yr –1, which is ∼3 times faster than the global mean rate; even higher rates (>10 mm yr–1) are found near Bangkok, where the land is sinking. The seasonal sea level cycle shows differences between the stations in the GOT and Andaman Sea, indicating influence from large-scale wind and pressure patterns. A positive/negative correlation between mean sea level anomaly and sea level atmospheric pressure is found at the GOT/Andaman Sea. The results from this research will help to better understand the dynamics of the UGOT and improve future modeling efforts.
Numerical model, Sea level rise, Upper Gulf of Thailand, Oceanography
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