Numerical study of the tides and residual currents in the Qiongzhou Strait

Based on the three-dimensional ECOM model,the tide,tide-induced residual current,wind-driven and density currents in the Beibu (Tonkin) Gulf and Qiongzhou Strait are diagnostically computed in fine grid.The tides and tidal currents in the Beibu Gulf and Qiongzhou Strait are well reproduced.The model results show that the semidiurnal tidal wave propagates eastward from the Beibu Gulf through Qiongzhou Strait,while diurnal tidal waves enter the strait from both the eastern and western sides and interact on the southeast coast of the strait.The formation processes of the residual currents in Qiongzhou Strait in summer (August) and winter (January) are mainly discussed.It is shown that the total residual currents (coupling effect of wind,tide and density) in the strait are westward in both summer and winter.The water volume transported from the east to west into the Beibu Gulf is 0.026 Sv in summer and 0.116 Sv in winter.Numerical experiments indicate that the dominant factor affecting the residual currents in the strait is not the wind stress but the tidal rectification.The westward tide-induced residual current,driven by the tidal rectification,is rather strong in the strait with water volume transport of 0.063 Sv.The wind in summer only reduces the westward tide-induced residual current to a certain extent,and the wind in winter approximately doubles the westward tide-induced residual current through the strait.The density current contributes little to the total residual current in both summer and winter.