Simulations of Seasonal Current Circulations and Its Variabilities Forced by Runoff from Freshwater in the Gulf of Thailand

Abstract

This paper presents the seasonal climatology of currents and elevations in the Gulf of Thailand (GoT) derived from a numerical three-dimensional ocean model. A numerical three-dimensional ocean model, based on the Princeton Ocean Model (POM), with rectangular coordinates in horizontal and vertical sigma coordinates was implemented for the GoT, situated between 6◦ to 14◦N latitude and 99◦ to 105◦E longitude. The Gulf is a relatively shallow body of water with a maximum depth of 83 m and an average depth of 45 m. It was driven at the surface by monthly mean sea surface temperature, salinity and wind stress climatology. In this paper, the simulations of current circulations and sea surface elevations for each season are presented, where the winter, summer, rainy season, and end of the rainy season in Thailand are represented by the months January, May, July, and October, respectively. The simulations in the upper GoT are also described. The results show clockwise circulations during summer and rainy seasons of Thailand. They occur in the central GoT. Two experiments were designed to investigate the effects of freshwater runoff. The freshwater runoff is shown to be the important factor for generating current circulation in the upper GoT at the end of the rainy seasons. The current speed is weakened when the runoff is removed. The sea surface elevations also decrease when the freshwater runoff is removed, especially in October, where it is reduced by about 50 %.