Study On Spatial And Temporal Characteristics Of The SCS Western Boundary Current

South China Sea is a semi-enclosed deep basin, surrounded by the Asian mainland,the island of Taiwan, the Philippine Islands, Palawan Island, Kalimantan and theSino-Indian peninsula. The Luzon Strait is the only deep-water channel connected theSouth China Sea and the ocean and is also the most important channel for externalwater entering the SCS. There are several major current systems in the South ChinaSea, such as the exchange between Kuroshio and the SCS water, SCS Warm Current,Vietnam Coastal Current and variety scales of of local eddies. The SCS westernboundary current which includes SCS Warm Current and Vietnam Coastal Currentflows along continental shelf at Northern South China Sea and Indo-China Peninsula.It flows northward in summer and southward in winter. The study on volume transport,the location of the offshore flow and swing of the spindle is still weak at present.Further study on the SCS western boundary current has an important scientificsignificance on the development study of the circulation of the SCS and Nationaldefense and economic development.With high-resolution data of OFES,we study on spatial and temporal charac-teristics of the SCS western boundary current by analyzing the velocity profile，calculating the volume transport， Wavelet Analysis and EOF of a few morerepresentative cross-sections along Vietnam and Hainan Island. We get the results asfollows.(1) The seasonal variation of the SCS western boundary current is significant.Itflows northward in summer and southward in winter. The volume transport of theSCS western boundary current is greater in winter than in summer and greater alongVietnam Peninsula than along Hainan Island.It is7.4±7.0Sv along Vietnam Peninsulawhile0.57±0.5Sv along Hainan Island. (2) The SCS western boundary current does not always flow northword,but leavesthe coast as it arrives the southeast of the Vietnam Peninsula.It leaves the coast around14.0°N as early as in May,but in July and August, it leaves the coast from10.0°N to14.0°N.With the prevalence of the summer monsoon, the velocity of the offshoreflow is larger and the spindle of the offshore flow swings from14.0°N to10.3°N.Besides,The offshore flow has a significant effect on the western boundary currents.(3) The inter-annual variation of the SCS western boundary current is large, itsmain change cycle is about4years. By EOF analysis of the SCS western boundarycurrent velocity, the first mode shows up and down RP change.The positive phasecenter is located at200m depth and the negative phase center is located at1700mdepth nearby. The second mode at the near-shore and far shore changesreversely,which may be caused by local eddy.(4) At the years ENSO events occurred, the spindle of the offshore flow alongVietnam swung southward and the scope of the offshore flow expanded than thenormal years.Besides, the velocity of offshore flow is bigger than normal years andthe volume transport of the SCS western boundary current is much smaller.(5) With the HYCOM Mode,we simulate the South China Sea circulation when theLuzon Strait is closed.We find that the impact of closing the Luzon Strait on the SCSwestern boundary current is Reducing the velocity. The direction and structure of theSCS western boundary current is not changed. This also confirms that the externalwater which enters the SCS through the Luzon Strait has some impact on the SCSwestern boundary current.