The purpose of this thesis is to develop a new barotropic ocean model to study ocean dynamics. The model combines for the first time the flexible finite-element method and an accurate semi-Lagrangian advection scheme on unstructured triangular meshes. / In the first part of the work, the semi-Lagrangian method is used for advection experiments on an irregular grid. A cosine hill is advected using a specified flow field corresponding to solid body rotation. A major difficulty is to find an interpolator which is at least fourth order accurate on an unstructured mesh. Such accuracy is needed for the treatment of slow Rossby waves in ocean models. We develop such a method using a kriging interpolating scheme. The results are better than fourth order accurate on an unstructured grid. Such accuracy is achieved at a reasonable computational cost due to the increased flexibility of unstructured meshes and accuracy of the kriging approach. / The second part of the thesis examines the finite-element spatial discretization of the linear inviscid shallow-water equations with a semi-implicit temporal discretization on unstructured meshes. The finite-element velocity-pressure pair should ideally give noise-free results when solving geostrophic balance, and fulfill at the same time certain consistency conditions. We show most of the known finite-element pairs do not satisfy these two requirements simultaneously, except for an unconventional and unnamed low-order element pair. The latter gives good results for experiments on the propagation of gravity waves using the linear inviscid shallow-water equations. / The last part of the thesis examines the coupling between semi-Lagrangian advection and semi-implicit treatment of the linear gravity wave terms on unstructured meshes. We use kriging as interpolator for semi-Lagrangian advection and the unconventional finite-element pair previously examined for the nonlinear shallow-water equations. The propagation of a typical oceanic eddy is simulated without forcing.

We develop a new coupled atmosphere-ocean-sea ice-land surface-ice sheet model for long-term climate change studies. This five-component model incorporates the seasonal cycle, and the three major ocean basins, the Antarctic Circumpolar Current region and the major continents are resolved. The model variables are sectorially averaged across the different ocean basins and continents. / The above coupled model (less the ice sheet component) is first used to simulate the major features of the present day climate. In a global warming (cooling) experiment, the thermohaline circulation (THC) in the North Atlantic Ocean is weakened (intensified) due to the increased (reduced) moisture transport to, and warmer (cooler) sea surface temperatures at northern high latitudes. / Secondly, the above four-component model is employed to investigate the initiation of glaciation, which is accomplished by reducing the solar radiation and increasing the planetary emissivity only in high northern latitudes. When land ice is growing, the THC in the North Atlantic Ocean is intensified, resulting in a warm subpolar North Atlantic Ocean. The intensified THC maintains a large land-ocean thermal contrast at high latitudes, which leads to enhanced land ice accumulation. We conclude that increased fresh water or massive iceberg discharge from land is responsible for a weak or collapsed THC. / Lastly, a dynamic ice sheet model is coupled to the above four-component model. Sensitivity experiments show that a smaller lateral (east-west) ice discharge rate maintains a larger ice volume and extent in our model. Also, a reduced atmospheric CO2 concentration, which is parameterized as an increased planetary emissivity, may lead to the expansion of the ice sheets and hence a larger ice volume and extent. A simple iceberg calving scheme is next introduced to investigate ice sheet-THC interactions on the millennial timescale. We find that the longer the duration of iceberg calving, the longer the time that must elapse before the next calving event can occur. Also, it is shown that the strength of the THC in the North Atlantic Ocean is very sensitive to the discharge rate of the ice sheets. This makes the simulation of the interactions between ice sheets and the THC extremely challenging.

The general circulation of the ocean acts as an energy reservoir. This means that the external forcing (primarily by the wind field) is balanced by dissipation. However, the dissipation is not well understood because energy does not easily cascade forward to small scales where dissipation is active. Approximate geostrophic balance holds over much of the ocean because the advective timescale is typically long compared to the Coriolis timescale. The resulting geostrophic turbulence behaves similarly to 2D turbulence in the sense that energy is not cascaded forward to small scales. In fact, there is an inverse cascade of energy toward large scales for these "balanced" flows. One possible mechanism for dissipation of the balanced flow is nonlinear interactions with unbalanced flow. In this thesis we made an analogy between balanced flow and 2D flow for the unstratified case. We numerically integrated the hydrostatic, barotropic vorticity equation using a pseudo-spectral, triply-periodic model varying the rate of rotation and the level of 3D (corresponding to unbalanced) energy via a 3D forcing. We analysed the energetics of the 2D flow to determine the impact of rotation and the 3D energy level. We found that there is a critical Rossby number between 0.1 and 1 above which there is 2D energy drain and below which there is 2D energy gain. We found that the magnitude of the drain/gain at large scales increases with forcing up to a limiting value. A review of ocean energetics and turbulent 2D-3D interactions is also presented.

New high resolution density fields for the northwestern Atlantic Ocean are calculated from objectively analyzed temperature and salinity fields obtained from archived data. The original data set is the Marine Environment Data Service (MEDS) archived data and is supplemented by a subset of the National Oceanographic Data Centre (NODC) data from J. Reid and by the 1980s additional data of Fukumori and Wunsch (1991). The objective analysis scheme is a modification of that used by Levitus (1982) and uses 37 vertical levels. The scheme is used to calculate the climatological mean (1910-1989) temperature and salinity fields for the summer and the warm and cold seasons. Inverse methods are then applied to these new density fields in order to determine the transport and circulation during these periods. A study of the seasonal and interdecadal variations of the ocean transport and circulation is also presented. The interdecadal analysis is based on temperature and salinity fields analyzed for the warm season of the 1950-1964 and 1965-1981 periods.

The North Water (NOW) is one of the largest polynyas in the Northern Hemisphere, occupying Smith Sound and the northern part of Baffin Bay, between Greenland and Ellesmere Island. While it has long been held that the North Water maintains itself by a southward drift of ice caused by winds and currents, the role of warm water advection by the West Greenland Current (WGC) is still heavily debated. / Over 400 hydrographic CTD stations from the 1997 and 1998 NOW field programs were analysed using theta-S diagrams, property contouring and conservative property tracing in order to better understand the different water mass structures underlying the polynya, as well as their circulation and interaction. These data portray the North Water to be a crossroad in the Arctic Ocean, owing its complexity to the interaction of imported dissimilar water masses over a particularly influential terrain. / Seasonal heat and freshwater budgets were also presented based on a volumetric theta-S census of the polynya domain and an elaboration of Muench's (1971) water mass definitions for northern Baffin Bay. (Abstract shortened by UMI.)

Intraseasonal and interannual variability of sea-ice cover (SIC) in the Gulf of St. Lawrence, including the time of first ice presence (TFIP), time of last ice presence (TLIP), and sea-ice duration (SID), were investigated, using weekly sea ice observations from 1963--1996. For the intraseasonal variations of sea ice, it was found that SIC in different sub-regions displays contrasting features. The largest intraseasonal variations of SIC occur in the Strait of Belle Isle region and in the southwestem Gulf, where the mean SIC is largest and SID is longest. For the interannual variability of sea ice, the largest variability of SIC occurs in the area off mid-Newfoundland, where the mean SIC is small. For the TFIP and TLIP, the largest interannual variability occurs in the area off western Newfoundland and along coasts in the northeast sector of the Gulf, respectively. In addition, sea ice appeared earlier in the coastal regions and disappeared later over the entire Gulf in severe ice years; while sea ice appeared later in the central and eastern Gulf and disappeared earlier over the entire Gulf in light ice years. / Several of the forcing factors influencing sea ice variability in the Gulf of St. Lawrence were examined and mechanisms controlling this variability were discussed. It was found that surface air temperature (SAT), the eastward wind component (u-wind), sea surface temperature (SST), sea surface salinity (SSS), mixed layer depth (MLD), total river runoff, the ocean circulation pattern, and sea-ice advection from the Labrador Sea, all play important roles in explaining sea ice variability in the Gulf. However, the relative contributions of these factors to the observed sea ice variability differ in different subregions. Quantitative relationships between sea ice variability and various forcing factors were investigated using statistical analysis and a simplified Hibler's sea-ice model. Both approaches indicated that the December--April averaged SAT, u-wind, and November SST all contribute to the variability of December--June SIC in the Gulf, with SAT playing the most important role. The analysis also indicated that the dependence of SIC on various forcing factors varies with geographical location. For example, SAT influences sea ice variability mainly in the central Gulf, while the u-wind component effects SIC mainly in the eastern Gulf. In addition, statistical analyses also suggest that SSS values present in the previous November play an important role in determining SIC variability. The linear regression between SIC and three independent variables: December--April SAT, November SST and SSS, accounts for 81% of the total SIC variance. / The statistical analysis and model study also indicated that December SAT, u-wind, November SST, and MLD control the time of first ice presence, with SAT and SST playing the dominant role. The linear regression between TFIP and three independent variables (u-wind, SST, and SSS) accounts for 76% of the total TFIP variance. For TLIP, both SAT and u-wind play an important role.

Time series of temperature and salinity from current meters moored in 1988 and 1990 along the north shore of Baie des Chaleurs were analyzed to characterize the frequency of upwelling events. Upwelling was found to propagate cyclonically with speeds of 40 to 85 km per day. Moderate correlations between $ sigma sb{ rm t}$ and zonal wind stress were found. The interaction of buoyancy, topography, and oscillating wind stress simulated the upwelling in a reduced gravity model. The dominant frequencies of the upwelling events were approximately 4.5 to 10 days. / Three water masses, one between the surface and the thermocline, one straddling the thermocline, and one at the bottom, were found to describe nicely the TS properties of the water column, as observed from the 1991 CTD data. / The observed circulation, from August to October 1990, was cyclonic, with baroclinicity observed in the bottom two layers, and at two stations in the top layers.

Within the context of oceanographic research on northern estuaries in James Bay and Hudson Bay, and in relation with hydroelectric developments and their impact on the physical environment, two studies were undertaken. Both concern the importance of bottom topography, tidal motion and fresh water input on the estuarine processes in these areas. / The first one, in Rupert Bay (south-eastern corner of James Bay), describes tidal and local wind effects on circulation and mixing patterns for summer conditions. An estimate of terms in the lateral momentum equation shows that the centrifugal acceleration, the Coriolis force and the baroclinic pressure gradient are the most important forces at a mid-bay cross section transect. / The second study is concerned with the freshwater plume of Great Whale River (south-eastern Hudson Bay). CTD measurements were used to examine the lift-off point of the plume for under-ice and increasing discharge conditions. Comparison with existing models shows them to be inappropriate for under-ice conditions. Finally, the presence of supercooled water masses in the region of the study is reported.

Thesis (Ph.D.)--University of Washington, 2005. / (UnM)AAI3183345. Source: Dissertation Abstracts International, Volume: 66-07, Section: B, page: 3612. Chair: Michael C. Gregg.

Thesis (Ph.D.)--University of California, San Diego, 2006. / (UMI)AAI3230035. Adviser: Teresa K. Chereskin. Source: Dissertation Abstracts International, Volume: 67-08, Section: B, page: 4317.