Characteristics of Seasonal Wind and Wind-driven Current in the Gulf of Thailand

Abstract

The Gulf of Thailand is bounded by Latitude 6° to 14°N and Longitude 99° to 105°E.  It is located on the continental shelf connecting to South China Sea via the southern entrance. The Gulf is border by Thailand, Cambodia and Vietnam on the eastern, northern and western side respectively.  The Gulf receives high solar radiation throughout the year. The NE and SW monsoon controls the local weather around the Gulf.  The monsoonal wind plays an important role in controlling the wind pattern, rainfall over Thailand, and also controlling water circulation in the Gulf of Thailand.  The project objective is to simulate wind regime over the Gulf and wind-driven circulation in the Gulf of Thailand during the year 2000-2002. The study time span cover La Niña, normal and El Niño period respectively. The study is accomplished through to use of WRF model and 2-D water circulation model. Wind regime from WRF model was the input to the water circulation model. Statistical analysis was performed on the wind data in order to study the effect of El Niño and La Niña events on the wind pattern over the Gulf of Thailand. Wind pattern from the WRF model was comparable to the satellite (observed) wind. Winddriven circulation was similar to the results of earlier studies.  During rainy season, the westerly and southwesterly wind from the Indian Ocean caused the wind-driven current in the Gulf and the upper Gulf to flow in a clockwise direction.  Small eddies existed some locations in the Gulf.  During winter, high pressure system from Siberia caused wind in South China Sea to flow from the east to Gulf entrance. While inside the Gulf, the wind deflected to NE wind and caused the wind-driven circulation in the Gulf and the upper Gulf to flow in a counterclockwise direction. During summer, wind from South China Sea blew from the east direction. While inside the Gulf, the wind deflected to SE wind. And the SE wind deflected to S wind when entering the upper Gulf of Thailand. The pattern of wind-driven current in the Gulf was similar to that in during the winter.  When easterly wind was strong near the lower eastern coast of the Gulf, there would be a northward flow of water along the coast.  The effect of the El Niño event increased wind speed over the Gulf and deflect the wind direction by 10°.  On the other hand, the effect of the La Niña event reduced wind speed over the Gulf and deflects the wind direction by the same degree.  The wind-driven circulation pattern did not change with the El Niño / La Niña event.