Simulation of the ocean surface mixed layer under the wave breaking

A one-dimensional mixed-layer model, including a Mellor- Yamada level 2.5 turbulence closure scheme, was implemented to investi- gate the dynamical and thermal structures of the ocean surface mixed layer in the northern South China Sea. The turbulent kinetic ener- gy released through wave breaking was incorporated into the model as a source of energy at the ocean surface, and the influence of the breaking waves on the mixed layer was studied. The numerical simulations show that the simulated SST is overestimated in summer without the breaking waves. However, the cooler SST is simulated when the effect of the breaking waves is considered, the corre- sponding discrepancy with the observed data decreases up to 20% and the MLD calculated averagely deepens 3.8 m. Owing to the wave-enhanced turbulence mixing in the summertime, the stratification at the bottom of the mixed layer was modified and the tempera- ture gradient spread throughout the whole thermocline compared with the concentrated distribution without wave breaking.

A coupled ice-ocean model for the Bohai SeaⅡ.Case study

The coupled ice- ocean model for the Bohai Sea is used for simulating the freezing, melting, and variation of ice cover and the heat bal- ance at the sea- ice, air- ice, and air- sea interfaces of the Bohai Sea during the entire winter in 1998￣1999 and 2000￣2001. The cou- pled model is forced by real time numerical weather prediction fields. The results show that the thermodynamic effects of atmosphere and ocean are very important for the evolvement of ice in the Bohai Sea, especially in the period of ice freezing and melting. Ocean heat flux plays a key role in the thermodynamic coupling. The simulation also presents the different thermodynamic features in the ice covered region and the marginal ice zone. Ice thickness, heat budget at the interface, and surface sea temperature, etc. between the two representative points are discussed.

Estimates of mixing on the South China Sea shelf

Mooring observations aimed at understanding the vertical mixing were carried out on the outer shelf of the South China Sea from April to May in 2002. Temporal and vertical distributions of horizontal velocity shear and Brunt- V!is!l! frequencies are calculated with these observations. Dissipation rate and diapycnal diffusivity are then inferred from the fine-scale parameterization. The temporally and vertically averaged dissipation is 15 nW/kg and the associated diapycnal diffusivity is 2×10-5 m2/s. Daily-averaged diapycnal diffusivity is well related to the tides, larger during the spring tide, and smaller during the neap tide. Depth-averaged diapycnal diffusivity, which is as larger as 5×10-5 m2/s during the spring tide, is 8.3 times that of the neap tide, which is only 6×10-5 m2/s. This is in proportion to the vertical energy flux from barotropic tide to baroclinic tide. During the spring tide, the energy flux from the semi-diurnal and diurnal barotropic tide to the internal tide is 160 mW/m, while it is only 35 mW/m during the neap tide. Vertically, monthly-averaged dissipa- tion rate and associated diapycnal diffusivity are large near the upper mixing layer and the bottom boundary. Dissipation rate is about 30￣100 nW/kg, diapycnal diffusivity is about 4×10-5￣10×10-5 m2/s. However, both of them are quite small in the mid column, where dissipation rate is 3￣10 nW/kg and diapycnal diffusivity is 4×10-6￣40×10-6 m2/s.

The difference between the joint probability distributions of apparent wave heights and periods and individual wave heights and periods

The joint distribution of wave heights and periods of individual waves is usually approximated by the joint distribution of apparent wave heights and periods. However there is difference between them. This difference is addressed and the theoretical joint distributions of apparent wave heights and periods due to Longuet-Higgins and Sun are modified to give more reasonable representations of the joint distribution of wave heights and periods of individual waves. The modification has overcome an inherent drawback of these joint PDFs that the mean wave period is infinite. A comparison is made between the modified formulae and the field data of Goda, which shows that the new formulae consist with the measurement better than their original counterparts.

A High Resolution Forecast Model of Storm Surge Inundation

In order to forecast storm surge inundation, a two-dimensional model is established. In the model, an alternating computation sequence method is used to solve the governing equations, and the dry and wet method is introduced to treat the moving boundary. This model is easy to use. It has a friendly input interface and Arcview GIS is used as the output interface. The model is applied to the Shantou area to simulate the storm surge elevations and inundations caused by Typhoons 6903 ane 0104 using the same relevant parameters. The calculated results agree well with the observations.

Similarity Reductions of Barotropic and Quasi-geostrophic Potential Vorticity Equation

The (2+1)-dimensional nonlinear barotropic and quasi-geostrophic potential vorticity equation without forcing and dissipation on a beta-plane channel is investigated by using the classical Lie symmetry approach. Some types of group-invariant wave solutions are expressed by means of the lower-dimensional similarity reduction equations. In addition to the known periodic Rossby wave solutions, some new types of exact solutions such as the ring solitary waves and the breaking soliton type of vorticity solutions with nonlinear and nonconstant shears are also obtained.

Physical mechanism and numerical simulations of surface layer temperature inversion in tropical ocean

The one-dimensional Kraus- Turner mixed layer model improved by Liu is developed to consider the effect of salinity and the equa- tions of temperature and salinity under the mixed layer. On this basis, the processes of growth and death of surface layer temperature inversion is numerically simulated under different environmental parameters. At the same time, the physical mechanism is preliminari- ly discussed combining the observations at the station of TOGA- COARE 0°N, 156°E. The results indicate that temperature inversion sensitively depends on the mixed layer depth, sea surface wind speed and solar shortwave radiation, etc., and appropriately meteoro- logical and hydrological conditions often lead to the similarly periodical occurrence of this inversion phenomenon.

Comparison of summer ther- mohaline field and circulation structure of the Bohai Sea between 1958 and 2000

The analysis of observed salinity data over 35 years (1961—1996) at four stations around the Bohai Sea, i.e. Huludao, Qinhuangdao, Tanggu and Beihuangcheng, reveals that the salinity of the 4 observation stations has increased 1.1, 1.6, 1.9 and 0.4, respectively. The data also show that over the past 35 years, there have been at least 5 large salin-ity variation processes. The salinity data from two cruises of the Bohai Sea in August 1958 and 2000, show that the salin-ity pattern of the Bohai Sea has changed markedly. Low sa-linity in the sea surface layer around the old Yellow River mouth in August 1958 had been replaced by high salinity in August 2000 and the maximum variation of salinity is over 10.0. In addition, the values and distribution of salinity were almost the same from surface to bottom there in August 2000, but there existed significantly different salinity levels be-tween the surface layer and the deep layer in August 1958. When a comparison is made between the salinity levels of the above-mentioned two years, it is found that the salinity in August 2000 is on average 2.0 higher than that of August 1958 in the main part of the Bohai Sea. The change of tem-perature and salinity field in the Bohai Sea leads to the change of the circulation. The numerical simulation shows that in comparison with the circulation structure of the Bohai Sea in August 1958, the circulation in August 2000 changes markedly. The significant changes of circulation appeared in Bohai Bay, Laizhou Bay and in the middle of the Bohai Sea. The clockwise current loop outside of the Bohai Bay and counterclockwise current loop outside of the Laizhou Bay in August 1958 disappeared in August 2000, and the counterclockwise current loop of the Bohai Bay mi-grated obviously outward. The flow direction in the Laizhou Bay turned 180° around. Corresponding to the variation of the Bohai Sea circulation, the amount of water exchange between the Bohai Sea and the Yellow Sea has also changed. The water exchange rate through the Bohai Strait decreases, on average, 0.7×104 m3/s in August 2000 in contrast to that of August 1958.

TIDAL CONSTITUENTS IN THE BOHAI AND YELLOW SEAS FROM AN ADJOINT NUMERICAL MODEL WITH TOPEX/POSEIDON DATA

Eleven tidal constituents K_1, O_1, P_1, Q_1, M_2, S_2, N_2, K_2, M_4, MS_4 and M_6, which are extracted from 10 years TOPEX/Poseidon altimetry data along track points in the Bohai and Yellow Seas, are assimilated synchronously into a two-dimension non-linear tidal model with adjoint method. And the bias between calculations and observations are provided. The deviations of M_2 are 7.1×10~ -2 m in amplitude and 4.7° in phase-lag. Those of O_1 are 2.8×10~ -2 m and 5.4° accordingly. Compared with other models, our discrepancy is less. It is shown that the precision of the model is more accurate. The co-tidal charts of the eleven constituents are also drawn. The general patterns are in good agreement with those literatures cited.