A three dimensional diagnostic modeling study of the South China Sea circulation before onset of summer monsoon in 1998

On the basis of the wind data from NCEP and the hydrographic data obtained on 22 April~24 May 1998, the circulation in the South China Sea(SCS) are computed by the three dimensional diagnostic model.The combination of SSH Aderived from T/Paltimeter and numerical results provides a consistent circulation pattern for the SCS, and the main circulation features can be summarized as follows: (1) The Kuro shio intrusion weakens and the pathway of the most of Kuroshio by passes.However, a part of Kuro-shiointrudes west ward above 300 m levels.This west ward intruded flow is located narrowly confined in the continental slope south of China above 300 m levels and does not appear to follow the western boundary throug hout,which agrees with the viewpoint of Qu et al.(2) The basinOscalecy clonicgy redominates in the northern SCS and consists of two cyclonic eddies C2 and C3 above 300 m levels.However, it is separated into two parts by ananti Ocycloniceddy W4 below 300 m levels.The scope of the basinOscale cyclonicgyre is wider in winter than that in the cruise 1.(3) The basinOscale antiOcy clonic gyredominates in the central SCS and consists of the three antiOcyclonic eddies W1, W2 and W3 above 300 m levels.However,below 300 m levels it consists of the anti-Ocy clonic eddies W1, W2 and W4 and extends northward to near 20°N.The cold eddy C1 exists southeast of the antiOcy clonic eddy W1.(4) A northward coastal jetis present at the western boundary near the coast of Vietnamat depths above the 300 m level, and develops northward more far about the distance 3b15c N than that in the cruise 2.(5) Most important dynamical mechanism is because of the joint effect of the baroclinity and relief (JEBAR).The second dynamical mechanism is because of the interaction between the wind stress and relief (IBWSR) under the southeasterly wind.The Sverdrup' relation can not been satisfied in the SCS.