Western boundary currents flow along the continents until they eventually separate and turn eastward. Observations show that the separation of some boundary currents is not stationary and occurs in different locations at different times. There is an observational indication that migrations of the separation latitude of western boundary currents are related to changes in their transports. The mechanism of this relationship is yet poorly understood. / We investigate the along-shore drift of a western boundary current separation with a nonlinear reduced gravity model on an f-plane. We consider separation due to a collision with an opposing current. It is shown that, for such a case, stationary collision and separation is possible only for boundary currents with "balanced" transports, i.e., equal near-wall depths. We perturb this solution with a small step-like variation of the transport of the opposing current and focus on the resulting time-dependent flow. / In the first part of the study, we use two different analytical methods to compute the separation latitude's migration rate. The first method involves integrated balances and the second involves the path equation for the separated flow. Using the first approach, it is found analytically that the flow consists of one current intruding into the area occupied by the other. A fully developed intrusion (at $t\rightarrow\infty)$ is steadily propagating. Using the asymptotic expansion based on the scale analysis, we derive the formulae for the migration speed and the width of the steadily propagating intrusion. Using the second approach, the original initial value problem is reduced to a single time-dependent path equation for the separated current. It is shown analytically that, as should be the case, in the limit $t\rightarrow\infty$ the path equation solution is identical to the earlier solution for the steadily propagating intrusion. / In the second part of the study, we use a nonlinear primitive equation numerical model to simulate the collision of boundary currents. A good agreement is found between the asymptotic analytical theory and complete nonlinear numerical solutions. / Application of the theory to the South Atlantic Confluence zone is discussed. It is suggested that variations of the transports of the Brazil and Malvinas currents may be important for observed migrations of the Brazil-Malvinas confluence. / Source: Dissertation Abstracts International, Volume: 57-01, Section: B, page: 0212. / Major Professor: Doron Nof. / Thesis (Ph.D.)--The Florida State University, 1995.

A variational data assimilation method for a reduced gravity model is developed. The method is applied to the equatorial Pacific Ocean. In the variational formalism a cost function measuring the "distance" between the model solution and the observations is minimized. The phase speed of the model is used as a control parameter and the optimal spatial structure giving the best fit of the model to the observations is determined. In the minimization algorithm a conjugate gradient descent direction is used. The method is computationally effective, and for the experiments considered convergence is achieved in ten iterations or less. / Several experiments are performed using the model solutions as observations. It is shown that the assimilation algorithm is able to determine the spatial structure of the phase speed, even if observations are available at only three stations. The estimated phase speed is not sensitive to errors in the observations, and the algorithm gives a unique solution to the problem. / Real sea level observations from three stations are assimilated for two different periods. The year 1979 was chosen to represent a year without an El Nino, while 1982/83 was chosen to represent an El Nino year. For 1979 the assimilation gave a phase speed with higher values in the west and lower values in the east compared to the initial guess of a constant phase speed. Assimilation of observations in 1982/83 gave the opposite picture, with lower values in the west and higher values in the east. This result is consistent with observations. The phase speed is proportional to the depth of the thermocline, and during normal conditions the basic stratification consists of a deep thermocline in the west and a shallow thermocline in the east. During an El Nino the picture is reversed. Calculating the correlation coefficient between the model results and the observations shows that the correlation increased for all the stations during the assimilation, even at stations which were not a part of the assimilation. / Source: Dissertation Abstracts International, Volume: 50-08, Section: B, page: 3374. / Major Professor: James J. O'Brien. / Thesis (Ph.D.)--The Florida State University, 1989.

A new numerical ocean model with multiple isopycnal layers has been used to model the Indian Ocean. Normal vertical modes are used for initialization and in a new open boundary formulation. A 21 year integration with the Hellerman-Rosenstein wind stress is made with a 3.5 layer and a 1.5 layer version of the model. / The solution with three active layers reproduces the observed general circulation and variability of the Indian Ocean, for instance the semi-annual equatorial undercurrent and Yanai wave field in the west. The seasonal changes in the Somali Current system is studied in more detail. It is found that barotropic instability is likely to cause the generation of the Great Whirl in early June. We find a very good agreement between the observed undercurrents and the simulations in the model. Equatorial onshore flow below the thermocline in June is associated with the disappearance of the undercurrent below the Somali current. The return of this undercurrent in the fall is caused by instability of the Great Whirl. Experiments where the duration of the summer monsoon is extended show that the initial decrease in the magnitude of the Great Whirl is due to eastward and downward energy transfer rather that due to relaxation of the wind. The solutions of the model indicate that baroclinic instability plays an important role in the decay of the Great Whirl. / The solution with a single active layer is essentially the same for the upper layer until in the late summer monsoon, when the flow becomes unstable. Different decay patterns of the whirl and associated eddies leads to different flows during the winter monsoon. / Source: Dissertation Abstracts International, Volume: 50-12, Section: B, page: 5524. / Major Professor: James O'Brien. / Thesis (Ph.D.)--The Florida State University, 1989.

Previous results suggest that many higher order coastally trapped wave (CTW) modes are needed to calculate the low-frequency wind-driven alongshore flow over the continental shelf. Large mode number CTW asymptotics suggest that the higher order modes are generated by just the local wind. It is therefore convenient to regard the velocity field as being due to a two dimensional "local" solution driven by local winds and a "remote" solution driven by the alongshore pressure gradient and depending on nonlocal wind stress. The alongshore pressure gradient can be accurately estimated using the lower order CTW modes and the "Local Plus Remote" solution can easily be obtained at a given coastal cross section. Tests using a simple sinusoidal wind forcing and realistic parameters for two different shelves show that the Local Plus Remote (LPR) method can accurately estimate the alongshore flow with the alongshore pressure gradient estimated with only 3 modes. The CTW method fails to accurately represent the alongshore flow field when even 6 modes are used. / The LPR method was applied to the Coastal Ocean Dynamics Experiment (CODE) shelf using realistic winds and the modeled alongshore velocities were compared with observations. In this application a background mean density field with sloping isopycnals and the wind stress curl were also included under the assumption that they are only important to the local part of the solution. Tests using a simple sinusoidal wind forcing confirm that this assumption is reasonable for velocity fields driven predominantly by local winds. The comparison with observed and CTW modeled velocities shows that the higher order modes, the mean density field with sloping isopycnals and the wind stress curl all have an effect on the amplitude and structure of the alongshore flow. The wind stress curl causes significant vertical shear in the inner and mid shelf and this shear compares well with that observed. A simple model for nearly barotropic flow shows that a wind stress with amplitude increasing offshore but with negative curvature (i.e., ($\tau\sb{\rm o}$)$\sb{\rm xx}$ $<$ 0), as observed during CODE, will produce surface intensification of the alongshore flow. Separation of the total modeled response into local and remote components reveals that the wind-driven response during both CODE periods was predominantly driven by local winds on the inner and mid shelf, but it was equally local and remote on the outer shelf. / Source: Dissertation Abstracts International, Volume: 50-12, Section: B, page: 5525. / Major Professor: Allan J. Clarke. / Thesis (Ph.D.)--The Florida State University, 1989.

An attempt is made to predict the sea-surface temperature in the Yellow Sea in winter. A simple numerical model is adopted for the task so that the construction of the adjoint model is tractable. Direct observations of currents and sea-level fluctuations are used to establish the viability of the forward model. Published regional sea-surface temperature distributions then provide a basis for optimizing both the initial condition and the sea-surface heat flux in the integration of the heat equation. The predicted temperature using the optimized initial condition and sea-surface heat flux is then compared to the temperature time series obtained at the current-meter mooring sites to evaluate the success of the procedure. / Three elements prove necessary: (a) a good simulation of heat advection; (b) a good sea-surface heat flux estimate; and (c) an accurate initial condition. / The first part of the dissertation is devoted to the development of the numerical model and a hindcast of the wintertime Yellow Sea circulation in the time window of 13 January to 21 February 1986, when direct observations of currents and temperature are available at six moorings. Northward migration of warm water in the Yellow Sea trough is reproduced, even though the Eularian currents fluctuate with a near-zero mean. It is found that, in the Yellow Sea, sea-level fluctuations are primarily forced remotely by the Kuroshio whereas current fluctuations are primarily forced by the wind. / In the second part, a variational data assimilation procedure of determining both the initial condition and the sea-surface heat flux from heavily smoothed sea-surface temperature data is carried out. The inversely determined sea-surface heat flux is rich in spatial structure. The spatial structure is verified by uncertainty analyses to be statistically significant. The tongue-like pattern of upward sea-surface heat flux at the center of the Yellow Sea is consistent with the existence of a high sea-surface temperature anomaly there. After the data assimilation, the model predicts correctly the temperature time series at the mooring sites. / Source: Dissertation Abstracts International, Volume: 56-06, Section: B, page: 3105. / Major Professor: Ya Hsueh. / Thesis (Ph.D.)--The Florida State University, 1995.

The development and implementation of a new, primitive equation ocean circulation model is described. The model employs finite-difference discretization in the horizontal directions and a linear, Galerkin finite-element discretization in the vertical direction. A novel coordinate transformation is employed to retain fourth-order accuracy in the vertical. / The main emphasis of this work is an extensive discussion of the decisions concerning physical, numerical, and computational issues, including discussions of several competitive (and currently interesting) numerical schemes which were not chosen. The model is compared and contrasted with the current generation of ocean circulation models. The performance of the model is tested in several simple cases. Finally, some future applications of the model are outlined. / A series of high-resolution experiments with the barotropic part of the code are used to discuss the flow along a seamount chain, modelled after the Fieberling Guyot and its neighbors. The basic features of the flow are described and the numerical convergence of the model is demonstrated. The full three-dimensional code is applied to a single-seamount geometry with a variety of amplitudes. / Other specific results of this work include: (1) An analysis of the incomplete cancellation of the pressure terms in the transformed coordinate system, with a simple estimate for the spurious acceleration. (2) An analysis of the semi-Lagrangian advection scheme used in some atmospheric models. The damping of the scheme is described in terms of an equivalent Laplacian or biharmonic viscosity coefficient, and formulae are derived for calculating the resolution required to obtain damping below a desired threshold. (3) A discussion of the three-dimensional semi-implicit scheme. It is shown that the scheme becomes physically ill-posed as the stratification of the fluid goes to zero. / Source: Dissertation Abstracts International, Volume: 51-04, Section: B, page: 1718. / Major Professor: James J. O'Brien. / Thesis (Ph.D.)--The Florida State University, 1990.

The purpose of this work is to study the interaction of two oceanic eddies in contact with each other, and to investigate the long-time evolution of the merged state when merging occurs. The emphasis is put on strong eddies for which the interfaces rise to the surface. We use a reduced-gravity shallow-water model in two distinct dynamical regimes: the frontal-geostrophic approximation, and the full primitive equations. In both cases, equations are solved numerically by a particle-in-cell method in order to handle interfacial surfacing. / A series of experiments shows that the eddy-eddy interaction leads to merging in most situations. However, a marked reluctance to merge was observed with: zero-potential-vorticity eddies, cold-core rings, and vortices of unequal sizes even on a beta-plane. When merging takes place, the resulting state is a single elongated vortex which, depending on the physics at play in that particular experiment, may or may not become axisymmetric. Namely, axisymmetrization occurs in the frontal-geostrophic experiment, while the merged state remains elliptical in the primitive-equation case. A comparison with results of intermediate models sheds some light on this difference. The special case of interaction via eddy pulsation is also simulated with the primitive-equation model to find that two non-touching but pulsating eddies can still merge. The work concludes with a study of the stability of filaments, which are observed to form and break during eddy axisymmetrization. It is found that frontal filaments always break up into a series of eddies. Conservation of mass, energy and potential vorticity explains their number and sizes. Results also show that the eddies accommodate a surplus in angular momentum by either taking a staggered position with respect to the zonal axis of the filament, or acquiring an elliptical shape, or both. / Source: Dissertation Abstracts International, Volume: 51-01, Section: B, page: 0125. / Major Professor: Benoit Cushman-Roisin. / Thesis (Ph.D.)--The Florida State University, 1989.

Source: Dissertation Abstracts International, Volume: 32-12, Section: B, page: 7200. / Thesis (Ph.D.)--The Florida State University, 1971.

Source: Dissertation Abstracts International, Volume: 33-03, Section: B, page: 1212. / Thesis (Ph.D.)--The Florida State University, 1972.

Source: Dissertation Abstracts International, Volume: 35-02, Section: B, page: 0962. / Thesis (Ph.D.)--The Florida State University, 1974.