The Establishment Of The Wave-circulation Coupled Model Based On POM And Its Applications In The Global Ocean And The Coastal Sea

The vertical temperature structures of the ocean generally can be divided into three layers: the surface mixed layer, the thermocline and the layer with weak vertical temperature gradient. An accurate representation of the upper ocean mixing processes and thus the oceanic surface mixed layer (ML) is important for ocean circulation models, whether they are aimed at small-scale coastal simulations or for large-scale global climate simulations. The widely used Mellor-Yamada turbulence closure scheme often underestimates the vertical mixing in the upper ocean with strong stratification, and thus the sea surface temperatures (SST) is overestimated, ML is too shallow and the seasonal thermocline is underestimated, especially during the summer.Yuan Yeli (1979) suggested that there are three mechanisms responsible for the water mixing in the upper ocean: (1) the free buoyancy convection developed with unsteady stratification, (2) the turbulence mixing caused by shear of unsteady velocity field; (3) the wave stirring. In the upper ocean with strong stratification and weak flow shear mixing induced by wave stirring is often larger the former two mechanisms. The M-Y turbulence scheme can describe the mixing induced by the former two mechanisms well, but the wave-induced mixing is not included in it. That is the main reason why the surface mixing layer simulated by the circulation model using M-Y turbulence closure model is too shallow in summer. How to parameterize the wave-induced mixing and apply it into the three-dimensional ocean circulation model is a challenging job.Base on the theory of wave-induced mixing put forward by Yuan Yeli and Qiao Fangli this paper established the MASNUM wave-circulation coupled model, which incorporated the MASNUM wave model and the Princeton Ocean Model (POM). Thecoupling method is that first calculate the wave-number spectrum then compute the wave-induced mixing Bv and put it into the circulation model.The paper firstly applied the MASNUM wave-circulation coupled model into the quasi-global ocean. The simulated significant wave height agrees the Topex/Poseidon altimeter observation well. In the summer upper ocean in the middle and high latitude the wave-induced mixing Bv is larger than the vertical mixing derived from the M-Y turbulence closure model while in the low latitude Bv is smaller than Kh. Comparing the simulated summer upper ocean temperature structure by the wave-circulation coupled model and the original POM with the Levitus data, it suggests there is obvious difference between the result of the original POM and the the Levitus data and the result of the coupled model agrees the Levitus data well. The mixed layer depth in the coupled model result is much deeper than the result of the original POM and it fit the Levitus data well. This suggests that the wave-induced mixing play the key role in forming the summer surface mixed layer in the middle latitude, it is also significant to the upper mixed layer in the tropical area.On the other hand the Yellow Sea Cold Water Mass (YSCWM) as a unique ocean phenomena attracts the interests of many oceanographers, but controversy remains on the bottom layer circulation and the vertical circulation of the YSCWM. Based on the MASNUM wave-circulation coupled model the paper established the MASNUM wave-tide-circulation coupled model by introducing periodical the tidal current in the open boundary. The model is applied to study the circulation pattern of the summer Yellow Sea. The simulated tide, temperature and salinity agree the observation well, the simulated current filed is also confirmed by observation. A comprehensive three-dimensional circulation structure of the Yellow Sea in summer is put forward based in the model result and the observation data:(1) In the surface layer (0-4m), driven by wind the prevailing current direction is northeastward.(2) The upper layer (4-40m) is dominated by a basin scale anti-clockwise (cyclonic) gyre, diagnostic analysis of the momentum balances and sensitive study shows the cyclonic circulation in the upper layers is mainly aquasi-geotropic flow along tidal-induced temperature front, it is also strengthened by the Eulerian residual tidal currents. The stream function of the YS shows the net circulation of the YS is anti-clockwise (cyclonic). (3) In the bottom layer (below 40m) the water diverges from the YS trough towards seashore and the divergence velocity is strong along the temperature front area. The baroclinic pressure gradient force due to the strong tidal induced temperature front in the bottom layer drives the water to diverge. There also exists a weak southward current. Tidal residual current and the northward wind transport in the surface layer may contribute to the formation southward flow in the bottom layer.On the vertical circulation structure, the vertical circulation structures vary along different sections. The upwelling is front-scale instead of basin-scale. The upwelling exists along the bottom slope. The upwelling of the vertical circulation is mainly induced by two mechanisms: the baroclinic pressure gradient force due to the tidal induced temperature front and compensation upwelling of the Ekman transportation. A circulation cell is found in the lower layer of the front near the Korean coast with upwelling along the coastal side of the front and downwelling along the offshore side of the front.The MASNUM wave-circulation coupled model established in this paper successfully solve the problem of the surface mixing layer simulated by the circulation model using M-Y turbulence closure model is too shallow in summer. It is important for ocean circulation models, whether they are aimed at small-scale coastal simulations or for large-scale global climate simulations. The MASNUM wave-tide-circulation coupled model established in this paper also enhanced the ability of the original POM in simulating the circulation in the coastal areas.