Thesis (M.S.)--Joint Program in Oceanography/ Applied Ocean Science and Engineering, Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution, 2006. / "September 2006." Bibliography: p. 97-106.

Thesis (Ph. D.)--University of Rhode Island, 2006. / Typescript. Includes bibliographical references (leaves 246-250).

Thesis (Ph. D.)--University of Washington, 1994. / Vita. Includes bibliographical references (leaves [135]-144).

Estuaries, the regions where runoff of fresh water, soil, and contaminants first encounter the ocean, are also primary fishing and recreation areas. It is therefore important to understand the dynamics associated with mixing and currents within these bodies of water. Pollutants and fresh water from river runoff flow out to sea in the upper layer, while nutrient-carrying oceanic water returns beneath. While there have been many studies of the processes involved in this exchange flow, the dynamics and vertical structure of transverse flows are much less understood, despite the role these currents play in redistributing water properties and momentum throughout the estuary. One such estuary, Juan de Fuca Strait, is an ideal location in which to study estuarine exchange and the resulting cross-channel flows induced by internal friction, primarily because its length and smooth topography reduce the topograpic steering of currents. Historical current meter data from a number of deployments in Juan de Fuca Strait reveal that, while mean along-channel currents are roughly consistent with the thermal wind equation, cross-channel flows are not, particularly at mid-depths where transverse currents are largest. A momentum balance using historical sea level and current meter data suggests that the vertical eddy viscosity Aᵥ ≈ 0.02 m²s⁻¹ at interfacial depths in May. The mean circulation in Juan de Fuca Strait-depths is highly seasonal in nature, however, and larger values may be more appropriate in summer when the estuarine exchange peaks due to the freshet. Stronger friction is in turn associated with elevated mixing rates and increased transverse velocities. An Acoustic Doppler Current Profiler deployed in Juan de Fuca Strait in the summer of 1996 resolved the vertical structure of these velocities. Concurrent Current-Temperature-Depth data reveal that neither the along- nor the cross-channel currents are in geostrophic balance with the hydrographic structure, suggesting that the physical processes associatd with these currents are more localised than the five kilometre scales over which the hydrography was measured. Zooplankton within Juan de Fuca Strait comprise a significant part of the scattering cross-section upon which the ADCP depends. During their dusk migration into the euphotic zone to feed and dawn descent to escape predation, they do not act as passive backscatter targets for the Acoustic Doppler Current Profiler. Vertical migration velocities, measured from the backscatter intensity record, reached 0.03 m s⁻¹, suggesting that significant biases in the measured vertical velocity could be introduced. Little effect was actually seen in the velocity fields, however, even though the cross-sectional fraction of the zooplankton was an order of magnitude larger than the background. Mean currents in Juan du Fuca Strait reveal strong transverse flows at mid-depths, suggestive of interfacial Ekman layers. The along-channel estuarine exchange is significantly enhanced at neap tide, consistent with weaker mixing upstream. The cross-channel flows at interfacial depths are also substantially larger during neap tide, implying a fortnightly modulation of mixing rates within the strait. The ADCP was also used to measure the Reynolds stresses directly. These were found to be more than an order of magnitude larger at neap tide than during spring tide and were consistent with changes in the mean current over the spring-neap cycle. Reynolds stresses were maximal at mid-depth on the transition from ebb to flood, at which time the gradient Richardson numbers were smallest, suggesting that critical layer absorption of internal waves are important dynamically. / Graduate

Preliminary results of a two-layer quasi-geostrophic box model of a wind-driven ocean are presented. The new aspects of this work in relation with conventional eddy models are a finite element formulation of the quasi-geostrophic equations and the use of no-slip boundary condition on the horizontal solid boundaries. In contrast to eddy resolving models that utilize free-slip boundary conditions our results suggest that the obtention of ocean eddies with the no-slip constraints requires a more restricted range of parameters, in particular much lower horizontal eddy viscosity eddy coefficients AH and higher Froude numbers F₁ and F₂. We show explicitly that a given range of parameters, which is eddy generating when the free-slip boundary condition is used, leads to a quasi-laminar flow in both, upper and lower, layers. An analytical model to interpret the numerical results is put forth. It is an extension of an earlier model of Ierley and Young (1983) in that the relative vorticity terms are of primary importance for the dynamics. Thus, it is shown that the boundary layer dynamics is active in the interior of the second layer, and it can be concluded from our method that for given F₁ and F₂ such that the lower layer geostrophic contours are closed, to the existence of the western boundary layer will prevent the homogenization of the potential vorticity so long as AH is large enough to stabilize the northwestern undulations of the flow. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Thesis (Ph. D.)--Stony Brook University, 2003. / Includes bibliographical references (leaves 81-82).

A long and gradual transition between the summer and winter oceanic regimes was observed off Oregon during the autumn of 1980. Hydrographic sections and a single current meter mooring between August and December show the ocean possessed characteristics during fall that have not been observed during other seasons: a slow ascension of the poleward undercurrent and the appearance of a large bottom boundary layer. The decay of summer's southward surface flow was achieved by a series of modest northward wind events during late summer as the effects of southward winds were becoming diminished. The northward wind events had progressively stronger influence on surface currents. The barotropic current fluctuations that are a signature of the summer regime continued during the transitional period. The weekly-to-monthly averaged flow was barotropic during much of the transition. Hydrographic sections and time series of alongshore current shear and temperature show that the leveling of the frontal layer was achieved gradually over a two month time scale. The winter regime was established during eleven days of continuous northward wind stress in early November. / Graduation date: 1987

No description available.

The Asian Seas International Acoustics Experiment (ASIAEX) conducted in April and May of 2001 helped researchers take a major step in understanding the circulation of the northern South China Sea. This region crosses one of the primary sea lanes of communication between Chinese submarine bases and the Pacific theater, therefore making it an extremely valuable source of knowledge for the United States Navy. This thesis provides a qualitative and quantitative analysis of the mesoscale variability in the South China Sea during spring 2001 using observational data from the ASIAEX experiment. An array of moorings (S1-S8) equipped with ADCPs, pressure gauges, temperature and salinity sensors, and current meters, was placed between the southern tip of Taiwan and Dongsha Island (Pratis Reef). Data results show that significant mesoscale features existed in the South China Sea. Mean currents over the continentalshelf were found to be primarily wind driven while flows over the continental slope were forced by the mesoscale features. The South China Sea Warm Current was observed twice over the slope during ASIAEX. A cyclonic meander of the northern gyre propagated onshoreand southwest near S7. Tropical Cyclone Cimaron set up apressure driven flow towards the southwest along the continental shelf, suggesting that a storm this size can influence the circulation in the entire South China Sea. Model results from the Northern South China Sea Nowcast/Forecast System were compared to the observational data. The model gave a good description of the big picture in the South China Sea but was unable to resolve the smaller-scale events. The model was too constrained by topography and had a distinct offset of the alongshore component most likely imposed on by open boundary forcing.

Thesis (Ph. D.)--Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1984. / Includes bibliographical references (p. 175-181).