Observed And Numerical Study On The Deep Water Circulation In The Luzon Strait And South China Sea

The South China Sea (SCS), which has a complex energetic oceanic dynamics,is the broadest semi-enclosed sea in the western tropic Pacific Ocean. The LuzonStrait, located between Taiwan and Luzon Islands, is the only deep channel thatconnects the SCS and Pacific. Oceanic problems round this domain is always thefocus. However, the studies on deep water circulation in the Luzon Strait and SCSare really sparse, although the deep water across Luzon Strait is the key factor to themain the heat flux balance, SCSTF and deep water circulation transport in the SCSand so on. In this dissertation, current velocity and hydeography data abseved byLADCP and CTD in August2008and July2009is analysed to research the deepwater cirulcation in the Luzon Strait. Numerical experiments are also to configuredto study the spatial structures, seasonal signals and driving mechenism of the deepwater circulation in the Luzon Strait and SCS.Both in-situ observations and simulated results clearly show the existence of adeep water overflow and its detailed pathway in the Luzon Strait. Model simulationsuggests that the deep Pacific water first flows into Luzon Trough through the BashiChannel (1.1Sv,1Sv=1.0×106m3s-1) and the Taitung Canyon (0.4Sv), then trunssouthward along the Luzon Trough, and finally enters the South China Sea mainlythrough two gaps on the Heng-Chun Ridge. The annual mean transports throughthese two gaps are0.5Sv and0.9Sv, respectively. Overall, the annual meantransport of the Luzon Strait overflow is about1.5Sv. Three numerical experimentswith different diapycnal diffusivities confirm that the baroclinic pressure gradientacross the Luzon Strait induced by strong diapycnal mixing in the South China Seais the primary driving mechanism of the Luzon Strait deep circulation. The sensitiveexperiments imply that too coarse horizontal resolution can’t depict the complextopography of Bashi and Taltung Strait and can’t simulate the deep water circulation inthe Luzon strait. Because of the limition of the topography, the geography, bottom friction could give little infulence the deep circulation stuctures.Trough some numerical expriments, the driving mechanism and spatialstructure of the deep water circulation in SCS is also studied. The simulations showsdeep water across the Luzon Strait drives the deep circulation in the SCS circulation.Because of the PV conservation, the deep water in the SCS flows along the PV(bathmetry) isolines and forms a cyclonic ciculation in the deep SCS basin.Influenced by topography and beta effect, the western boundary current is obviouslystrong and the sea mountains could effect the circulation structure. Different to thedeep water circulation in Luzon Strait, the deep SCS water circulation is influencedby bottom friction and geography obviously.