Three-Dimensional Numerical Simulation of the South China Sea Circulation and Thermohaline Structure.

摘要

The seasonal ocean circulation and thermal structure in the South China Sea (SCS) were studied numerically using the Princeton Ocean Model (POM) with 20 km horizontal resolution and 23 sigma levels conforming to a realistic bottom topography. A sixteen month control run was performed using climatological monthly mean wind stresses, restoring type surface salt and heat, and observational oceanic infow / outflow at the open boundaries. The seasonally averaged effects of isolated forcing terms are presented and analyzed from the following experiments: I) non-linear dynamic effects removed, 2) wind effects removed, 3) open boundary inflow / outflow set to zero. This procedure allowed analysis of the contribution of individual parameters to the general hydrology and specific features of the SCS, for example, coastal jets, mesoscale topographic gyres, and counter currents, Our results show that the POM model has capability of simulating seasonal variations of the SCS circulation and thermohaline structure. The simulated SCS surface circulation is generally anticyclonic (cyclonic) during summer (winter) monsoon period with a strong western boundary current, with a mean maximum speed of 0.5 m/ s (0.95 m/ s), mean volume transport of 5.5 Sv (10.6 Sv), extending to a depth of around 200 m (500 m). During summer, the western boundary current splits and partially leaves the coast: the bifurcation point is at 14 deg. N in May, and shifts south to 10 deg. N in July. A mesoscale eddy in the Sunda Shelf (Natuna Island Eddy) was also simulated. This eddy is anticyclonic (cyclonic) during summer (winter) monsoon with maximum swirl velocity of 0.6 m/ s at the peak of the winter monsoon. The simulation is reasonable comparing to the observations. In general, seasonal circulation patterns and upwelling phenomena are determined and forced by the wind, while the lateral boundary forcing plays a secondary role in determining the magnitude of the circulation velocities.