A Study On The Influences Of Coriolis-Stokes Forcing On The Numerical Ocean Modeling

This dissertation consists of two parts. The first part concentrates on the influences of ocean surface velocity (current velocity and wave-induced velocity) on the upper ocean phenomana, including wind stress, surface current field, sea surface temperature, air-sea heat flux and boundary layer thickness. The second part puts insight into the effects of large scale wave-induced Coriolis-Stokes forcing on modeling of the upper ocean currents. In order to achieve those research aims in this dissertation, two coupled models are constructed. They are coupled wind-current model (HYCOM-WINDS) and coupled wave-current model (SWAN-POM).By accounting for the effects of ocean surface velocity (wave-induced surface drift velocity and current velocity) on the drag coefficient, the spatial distribution of drag coefficient and wind stress are computed over the global ocean during 1958-2001, using an empirical drag coefficient parameterization formula based on wave steepness and wind speed. The global ocean current field is generated from the Hybrid Coordinate Ocean Model (HYCOM) and the waves from Wavewatch III (WW3). The spatial variability of the drag coefficient and wind stress are analyzed. Preliminary results indicate that, the ocean surface drift velocity exerts an influence on the wind stress, about 5% in average. The results also show that accounting for the effect of the ocean surface velocity on the wind stress can lead to significant improvement in the modeling of ocean circulation and air-sea interaction processes.In additation, A Wind stress-Current Coupled System (WCCS) consisting of the HYbrid Coordinate Ocean Model (HYCOM) and an improved wind stress algorithm based on Donelan et al. (1997) is developed by using the Earth System Modeling Framework (ESMF). The WCCS is applied to the global ocean to study the interactions between the wind stress and the ocean surface currents. In this study, the ocean surface current velocity is taken into consideration in the wind stress calculation and air-sea heat flux calculation. The wind stress that contains the effect of ocean surface current velocity will be used to force the HYCOM. The results indicate that the ocean surface velocity exerts an important influence on the wind stress, which, in turn, significantly affects the global ocean surface currents, air-sea heat fluxes, and the thickness of ocean surface boundary layer. Comparison with the TOGA TAO buoy data, the sea surface temperature from the wind-current coupled simulation showed noticeable improvement over the stand-alone HYCOM simulation.As for investigation of the large scale wave effects on ocean modeling, first, we found a well-defined zone of swell dominance, termed "swell pool", located in the eastern areas of the Pacific by calculating the global distribution of swell index in 2000. The global monthly mean wave transport for each month of 2000 is derived by taking advantage of the ECWMF reanalysis wave products. By comparing the monthly mean wave transport and monthly mean wind field from QUICKSCAT both of 2000, large difference is found between the Stokes transport direction and the wind direction in eastern area of the Pacific, approximately 90°.This result may serve as an evidence for proving the existence of the swell pool in this region. We also found that the sources of swell in eastern tropical areas of the Pacific mainly locate in the corresponding regions of westerlies of southern and northern Pacific, respectively. A calculation area is defined with boundaries lie on 2.5°N and 2.5°S (from 125°W to the western terrestrial boundary of America) to calculate the swell-caused net Stokes transport into the tropical region. Strong relationships are found between the net Stokes transport across the two latitudinal boundaries and wind intensities, for each specific month. Finally, we summarized the main conclusion of this study.Then, Six experiments configured for three different domains:Global Ocean, South China Sea (SCS) and Western North Atlantic Ocean (WNA) respectively, using the Hybrid Coordinate Ocean Model (HYCOM) are designed to investigate effects of the wave-induced Coriolis-Stokes forcing (hereinafter referred to as CSF) on ocean surface phenomena including circulation, temperature and mixing processes. The CSF calculated using wave variables simulated by the Wave Watch?(WW3) model is incorporated into HYCOM as a boundary condition in addition to wind stress. The results indicate:1) HYCOM is capable of reproducing the ocean circulation futures in all the three domains with different horizontal resolution. Main features of currents in SCS and WNA are successfully modeled, such as the well-known SCS upper layer circulation which subjects to the seasonally reversed monsoon system, and the loop current and eddy-shedding in WNA (Gulf of Mexico); 2) CSF does not fundamentally modify the pattern of current profile in the ocean surface mixed-layer; 3) Over most of the Global Ocean, the direction of Stokes transports are different from that of the changes in depth-integrated current transports caused by CSF; 4) The monthly-mean changes in depth-integrated current transports in the mixed-layer is changing month to month in both direction and magnitude and the CSF plays a more significant role in regions of intensive gyre presents, such as the area near Yucatan Channel; and 5) both Sea Surface Temperature (SST) and Mixed-Layer Depth (MLD) are influenced by CSF.Additationaly, The Stokes drift-driven ocean currents and Stokes drift-induced energy rate input to ocean have been investigated in the ideal experiments by taking advantage of a full coupled wave-current system which consists of the ocean component Princeton Ocean Model (POM), wave component Simulating WAves Nearshore (SWAN) and the coupling frame Model Coupling Toolkit (MCT). The Coriolis-Stokes forcing, which is computed by using the wave parameters from SWAN, has been incorporated into the momentum equation of POM as the core coupling process in the coupled system. Experimental results show that, under the steady state, the scale of Coriolis-Stokes forcing-driven current speed is 0.001 and the maximum current speed is 0.02 m/s. The Stokes drift-induced energy rate input into the ocean within the whole experiment domain is estimated as 2.8505×1010 w which is 14% of the direct wind energy rate input. Taking consideration of the Stokes drift effects, the total mechanical energy rate input within the simulation domain is increased by 13.96%.