Numerical Study Of Wind In The South China Sea Circulation Dynamics

The wind-driven circulation and its dynamical mechanisms in the SouthChina Sea(SCS) were studied numerically using ECOM-si model with 10'X 10' horizontal resolution and 20 sigma levels. The present workfocuses on the barotropic circulation in winter and summer. A series ofnumerical experiments were carried out to reveal the roles of thefollowing effects in driving the circulation: 1) topography, 2) windstress curl,3) P effect, 4) inertial effect and 5) open boundaryinflow/outflow. The simulated SCS surface circulation is generallycyclonic (anticyclonic) during the winter (summer) monsoon period witha strong western boundary current. The surface circulation in spring andin fall possesses transitional characters between summertime andwintertime. The negative wind stress curl in winter is basic drivingmechanism responsible for the SCS warm current. The SCS stream functionscorresponds well with the Sverdrup transport. The Sea Surface High (SSH)images in winter show almost a reverse pattern of that in summer. Theseasonal variation of SSH reveals the close relation between wind stressand SCS circulation. The Sea Surface High Anomaly (SSHA) indicates thatwinter and summer are dynamically active seasons. The numericalexperiments show that the continental shelf restricts the cyclonic(winter) or anticyclonic (summer) circulation gyres to the SCS deep basin,and the continental shelf in the northern SCS significantly weakens theSCS Warm Current in winter. The wind stress curl is of essentialimportance in driving the interior circulation of the SCS. In summer thepositive and negative wind stress curl generate the cyclonic andanticyclonic gyres respectively in the northwestern and southwestern SCS,and further induce an eastward flow at about 12?N. The beta effect isshown to be critically important in the formation of the western boundary current. The inertial effect (i.e. advective term) plays little role in general circulation of the SCS, but it reduces the .Kuroshio loop current to the southwest of Taiwan to a certain degree. Transport across the open boundaries has significant contribution to the distribution of the stream functions , especially to the boundary current along the northern continental slope and the western shore of the SCS.