Thesis (M.S.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 1999. / Includes bibliographcial references (p. 117-118). / This thesis describes an attempt to build a box model of the circulation in the eastern North Atlantic and to use it with transient tracer data to infere rates of ventilation in the subtropcial thermocline. The starting point is the analysis of former studies on box models, transient tracer data and the combination of both. The advantages and pitfalls associated with the tracer age approach on the one hand and the inventory approach on the other hand are weighed and the choice set upon the inventory approach is justified. Next the data used is presented and processed, and the results are compared with the known circulation patterns of the basin. The estimates computed fall in the expected and acceptable range. The uncertainties, in particular on the boundary conditions, are acknowledged to be a crucial factor on the following analysis yet only rough estimates can be produced. In particular, the geostrophic velocities at the boundaries can only be determined lest an unknown constant. No internally consistent model can be found that satisfies the linear conservation balances, geostrophy and steadiness assumptions and the boundary conditions imposed. The circulation generated only satisfies mass balance and the boundary conditions to a certain extent. Experience suggests that there are incompatibilities among the various constraints. Two different numerical methods fail to find an acceptable solution. Using the default circulation obtained, the forward problem is formulated and investigated. The resulting tracer distribution and time history is incompatible with the observed field. As a consequence, an attempt is made at the inverse problem in the hope that relaxation of the boundary conditions will provide some insight into the general failure of the model. As there appears to be no feasible solution though, the circulation is further inspected and it is concluded that given its flaws, no boundary condition will be able to generate a tracer field even in partial agreement with the observations. It is finally concluded that transient tracers can be used to dismiss grossly wrong circulation models. / by Gwenaëlle C. Jeunhomme. / M.S.

Thesis (S.M.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences and the Woods Hole Oceanographic Institution), 2000. / Includes bibliographical references (leaves 78-82). / A simple quasi-two dimensional dynamical model of Thermohaline circulation (THC) is developed, assuming that the mixing only occurs near western and eastern boundary layers. When the surface density is prescribed, the climatically important quantities, such as the strength of overturning and meridional heat transport, are related to the zonal integral over the vigorously mixing regions and scaled as (KvΔx)2/3. The numerical results suggest that the density difference between eastern and western boundaries play an important role in the meridional overturning. The eastern boundary is characterized by the upwelling on top of downwelling. The western boundary layer is featured by the universal upwelling. The inefficiency of diffusion heat transport accounts for the narrowness of sinking region and shallowness of overturning cell in one-hemisphere. The experiments with other surface boundary conditions are also explored. The circulation patterns obtained are similar under various surface temperature distributions, suggesting these are very robust features of THC. The role of boundary mixing is further explored in global ocean. The 2 1/2 dynamical model is extended to two-hemisphere ocean. Additional dynamics such as Rayleigh friction and abyssal water properties are taken into account. A set of complicated governing equations are derived and numerically solved to obtain steady state solution. The basic circulation features are revealed in our dynamical model. An equtorially asymmetric meridional circulation is observed due to small perturbation at the surface temperature in the high latitude. The density differences between eastern and western boundaries are distinct in both hemispheres. This is achieved during the spin-up process. Although the dynamical model results agree well with OGCM results in one-hemisphere, several important dynamics are lacking and exposed in two-hemisphere experiments. We need to consider horizontal advection terms which will effectively advect positive density anomalies across the equator and form the deep water for the entire system. / by Hua Ru. / S.M.

Thesis (Ph. D.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 1988. / Includes bibliographical references (leaves 163-172). / A freshwater plume often forms when a river or an estuary discharges water onto the continental shelf. Freshwater plumes are ubiquitous features of the coastal ocean and usually leave a striking signature in the coastal hydrography. The present study combines both hydrographic data and idealized numerical simulations to examine how ambient currents and winds influence the transport and mixing of plume waters. The first portion of the thesis considers the alongshore transport of freshwater using idealized numerical simulations. In the absence of any ambient current, the downstream coastal current only carries a fraction of the discharged fresh water; the remaining fraction recirculates in a continually growing "bulge" of fresh water in the vicinity of the river mouth. The fraction of fresh water transported in the coastal current is dependent on the source conditions at the river mouth. The presence of an ambient current augments the transport in the plume so that its freshwater transport matches the freshwater source. For any ambient current in the same direction as the geostrophic coastal current, the plume will evolve to a steady-state width. A key result is that an external forcing agent is required in order for the entire freshwater volume discharged by a river to be transported as a coastal current. The next section of the thesis addresses the wind-induced advection of a river plume, using hydrographic data collected in the western Gulf of Maine. The observations suggest that the plume's cross-shore structure varies markedly as a function of fluctuations in alongshore wind forcing. Consistent with Ekman dynamics, upwelling favorable winds spread the plume offshore, at times widening it to over 50 km in offshore extent, while downwelling favorable winds narrow the plume width to a few Rossby radii. Near-surface current meters show significant correlations between cross-shore currents and alongshore wind stress, consistent with Ekman theory. Estimates of the terms in the alongshore momentum equation calculated from moored current meter arrays also indicate an approximate Ekman balance within the plume. A significant correlation between alongshore currents and alongshore wind stress suggests that interfacial drag may be important. The final section of the thesis is an investigation of the advection and mixing of a surface-trapped river plume in the presence of an upwelling favorable wind stress, using a three-dimensional model in a simple, rectangular domain. Model simulations demonstrate that the plume thins and is advected offshore by the cross shore Ekman transport. The thinned plume is susceptible to significant mixing due to the vertically sheared horizontal currents. The first order plume response is explained by Ekman dynamics and a Richardson number mixing criterion. / by Derek Allen Fong. / Ph.D.

Thesis (M. Eng. in Ocean Engineering)--Joint Program in Marine Environmental Systems (Massachusetts Institute of Technology, Dept. of Ocean Engineering; and the Woods Hole Oceanographic Institution), 1998. / Includes bibliographical references (leaves 70-71). / Optical imaging techniques can be used to provide a better understanding of the physical properties of particle clouds. The purpose of this thesis is to design, perform and evaluate a set of experiments using optical imaging techniques to characterize parameters such as shape factor and entrainment coefficient which govern the initial descent phase of particle clouds in water. Several different aspects of optical imaging are considered and evaluated such as the illumination, camera, and data acquisition components. A description of the experimental layout and procedure are presented along with a description of the image processing techniques used to analyze the data collected. Results are presented from a set of experiments conducted with particle sizes ranging from 250 to 980um. A shape factor is used to demonstrate how the cloud's shape changes from approximately spherical to approximately hemispherical over depth. The entrainment coefficient is shown to vary both as a function of depth and particle size diameter. The experimental cloud velocity is compared to the output of a simplified version of the model, STFATE, used to simulate the short term fate of dredged materials in water. This analysis provides a method of evaluating the experimental results and examining the feasibility of using the experimental data to refine the input parameters to the model. / by Elizabeth J. Bruce. / M.Eng.

Thesis (M.S.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 1999. / Includes bibliographical references (leaves 92-100). / The linkage between physics and biology is studied by applying a one-dimensional model and a two-dimensional model to the Sargasso Sea and the Gulf of Maine- Georges Bank region, respectively. The first model investigates the annual cycles of production and the response of the annual cycles to external forcing. The computed seasonal cycles compare reasonably well with the data. The spring bloom occurs after the winter mixing weakens and before the establishment of the summer stratification. Sensitivity experiments are also carried out, which basically provide information of how the internal bio-chemical parameters affect the biological system. The second model investigates the effect of the circulation field on the distribution of phytoplankton, and the relative importance of physical circulation and biological sources by using a data assimilation approach. The model results reveal seasonal and geographic variations of phytoplankton concentration, which compare well with data. The results verify that the seasonal cycles of phytoplankton are controlled by both the biological source and the physical advection, which themselves are functions of space and time. The biological source and the physical advection basically counterbalance each other. Advection controls the tendency of the phytoplankton concentration more often in the coastal region of the western Gulf of Maine than on Georges Bank, due to the small magnitude of the biological source in the former region, although the advection flux divergences have greater magnitudes on Georges Bank than in the coastal region of the western Gulf of Maine. It is also suggested by the model results that the two separated populations in the coastal region of the western Gulf of Maine and on Georges Bank are self-sustaining. / by Caixia Wang. / M.S.

Thesis (Ph. D.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 209-215). / Observations from a three-year field program on the inner shelf south of Martha's Vineyard, MA and a numerical model are used to describe the effect of stratification on inner shelf circulation, transport, and sediment resuspension height. Thermal stratification above the bottom mixed layer is shown to cap the height to which sediment is resuspended. Stratification increases the transport driven by cross-shelf wind stresses, and this effect is larger in the response to offshore winds than onshore winds. However, a one-dimensional view of the dynamics is not sufficient to explain the relationship between circulation and stratification. An idealized, cross-shelf transect in a numerical model (ROMS) is used to isolate the effects of stratification, wind stress magnitude, surface heat flux, cross-shelf density gradient, and wind direction on the inner shelf response to the cross-shelf component of the wind stress. In well mixed and weakly stratified conditions, the cross-shelf density gradient can be used to predict the transport efficiency of the cross-shelf wind stress. In stratified conditions, the presence of an along-shelf wind stress component makes the inner shelf response to cross-shelf wind stress strongly asymmetric. / by Rachel Mandy Horwitz. / Ph.D.

Thesis (S.M. in Electrical Engineering)--Joint Program in Oceanography and Oceanographic Engineering (Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science; and the Woods Hole Oceanographic Institution), 2000. / Includes bibliographical references (leaves 64-65). / by James Willard Partan. / S.M.in Electrical Engineering

Thesis (S.M.)--Joint Program in Oceanographic Engineering (Massachusetts Institute of Technology, Dept. of Ocean Engineering, and the and Woods Hole Oceanographic Institution), 2000. / Includes bibliographical references (p. 100-101). / A finite difference computer model is developed to simulate the exposure statistics of a radio frequency buoyant antenna as it is towed in a three-dimensional random seaway. The model allows the user to prescribe antenna properties (length, diameter, density, etc.), sea conditions (significant wave height, development of sea), tow angle, and tow speed. The model then simulates the antenna-sea interaction for the desired duration to collect statistics relating to antenna performance. The model provides design engineers with a tool to predict antenna performance trends, and to conduct design tradeoff studies. The floating antenna envisioned is for use by a submarine operating at modest speed and depth. / by Sam R. Geiger. / S.M.

Thesis (S.M.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2006. / Includes bibliographical references (p. 69-74). / Interactions between physical and biological processes in the Southern Ocean have significant impacts on local ecosystems as well as on global climate. In this thesis, I present evidence that the Southern Ocean circulation affects the variability of zooplankton and sea surface temperature, both of which are involved in air-sea exchanges of carbon dioxide. First, I examine the formation of spatial patterns in the distribution of Antarctic krill (Euphausia superba) resulting from social behavior. Turbulence of the flow is found to provide favorable conditions for the evolution social behavior in an idealized biological-physical model. Second, I analyze observations of sea surface temperature variability in the region of the Antarctic circumpolar current. Results suggest that propagating anomalies can be explained as a linear response to local atmospheric forcing by the Southern Annular Mode and remote forcing by El-Nifio southern oscillation, in the presence of advection by a mean flow. / by Ariane Verdy. / S.M.

Thesis (S.M.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2006. / Includes bibliographical references (p. 97-106). / A modern general circulation model of the Southern Ocean with one-sixth of a degree resolution is optimized to the observed ocean in a weighted least squares sense. Convergence toward the state estimate solution is carried out by systematically adjusting the control variables (prescribed atmospheric state, initial conditions, and open northern boundary at 24.7 S) using the adjoint method. A cost function compares the model state to data from CTD synoptic sections, hydrographic climatology, satellite altimetry, and XBTs. Costs attributed to control variable perturbations ensure a physically realistic solution. An optimized solution is determined by the weights placed on the cost function terms. The state estimation procedure, along with the weights used, is described. A significant result is that the adjoint method is shown tto work at eddy-permitting resolution in the highly-energetic Southern Ocean. At the time of the writing of this thesis the state estimate was not filly consistent with the observations. An analysis of the remaining misfit, as well as the mass transport in the preliminary state, is presented. / by Matthew R. Mazloff. / S.M.