Thèses : « Ocean-atmosphere interaction Mathematical models »

1

Kiss, Andrew Elek. "Dynamics of laboratory models of the wind-driven ocean circulation." View thesis entry in Australian Digital Theses Program, 2000. http://thesis.anu.edu.au/public/adt-ANU20011018.115707/index.html.

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2

Santoso, Agus Mathematics &amp Statistics Faculty of Science UNSW. "Evolution of climate anomalies and variability of Southern Ocean water masses on interannual to centennial time scales." Awarded by:University of New South Wales. School of Mathematics and Statistics, 2005. http://handle.unsw.edu.au/1959.4/33355.

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In this study the natural variability of Southern Ocean water masses on interannual to centennial time scales is investigated using a long-term integration of the Commonwealth Scientic and Industrial Research Organisation (CSIRO) coupled climate model. We focus our attention on analysing the variability of Antarctic IntermediateWater (AAIW), Circumpolar DeepWater (CDW), and Antarctic Bottom Water (AABW). We present an analysis of the dominant modes of temperature and salinity (T - S) variability within these water masses. Climate signals are detected and analysed as they get transmitted into the interior from the water mass formation regions. Eastward propagating wavenumber-1, -2, and -3 signals are identied using a complex empirical orthogonal function (CEOF) analysis along the core of the AAIW layer. Variability in air-sea heat uxes and ice meltwater rates are shown by heat and salt budget analyses to control variability of Antarctic Surface Water where density surfaces associated with AAIW outcrop. The dominant mode in the CDW layer is found to exhibit an interbasin-scale of variability originating from the North Atlantic, and propagating southward into the Southern Ocean. Salinity dipole anomalies appear to propagate around the Atlantic meridional overturning circulation with the strengthening and weakening of North Atlantic Deep Water formation. In the AABW layer, T - S anomalies are shown to originate from the southwestern Weddell Sea, driven by salinity variations and convective overturning in the region. It is also demonstrated that the model exhibits spatial patterns of T - S variability for the most part consistent with limited observational record in the Southern Hemisphere. However, some observations of decadal T - S changes are found to be beyond that seen in the model in its unperturbed state. We further assess sea surface temperature (SST) variability modes in the Indian Ocean on interannual time scales in the CSIRO model and in reanalysis data. The emergence of a meridional SST dipole during years of southwest Western Australian rainfall extremes is shown to be connected to a large-scale mode of Indian Ocean climate variability. The evolution of the dipole is controlled by variations in atmospheric circulation driving anomalous latent heat uxes with wind-driven ocean transport moderating the impact of evaporation and setting the conditions favourable for the next generation phase of an opposite dipole.

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Alves, Jose Henrique Gomes de Mattos Mathematics UNSW. "A Saturation-Dependent Dissipation Source Function for Wind-Wave Modelling Applications." Awarded by:University of New South Wales. Mathematics, 2000. http://handle.unsw.edu.au/1959.4/17786.

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This study reports on a new formulation of the spectral dissipation source term Sds for wind-wave modelling applications. This new form of Sds features a nonlinear dependence on the local wave spectrum, expressed in terms of the azimuthally integrated saturation parameter B(k)=k^4 F(k). The basic form of this saturation-dependent Sds is based on a new framework for the onset of deep-water wave breaking due to the nonlinear modulation of wave groups. The new form of Sds is succesfully validated through numerical experiments that include exact nonlinear computations of fetch-limited wind-wave evolution and hindcasts of two-dimensional wave fields made with an operational wind-wave model. The newly-proposed form of Sds generates integral spectral parameters that agree more closely with observations when compared to other dissipation source terms used in state-of-the-art wind-wave models. It also provides more flexibility in controlling properties of the wave spectrum within the high wavenumber range. Tests using a variety of wind speeds, three commonly-used wind input source functions and two alternative full-development evolution limits further demonstrate the robustness and flexibility of the new saturation-dependent dissipation source term. Finally, improved wave hindcasts obtained with an implementation of the new form of Sds in a version of the WAM model demonstrate its potential usefulness in operational wind-wave forecasting applications.

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Arbic, Brian K. "Generation of mid-ocean eddies : the local baroclinic instability hypothesis." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/53047.

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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), 2000. Includes bibliographical references (p. 284-290). by Brian Kenneth Arbic. Ph.D.

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Agudelo, Paula A. "Role of Local Thermodynamic Coupling in the Life Cycle of the Intraseasonal Oscillation in the Indo-Pacific Warm Pool." Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/19834.

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Intraseasonal oscillations (ISOs) are important elements of the tropical climate with time-scales of 20-80 day. The ISO is poorly simulated and predicted by numerical models. This work presents a joint diagnostic and modeling study of the ISO that examines the hypothesis that local coupling between the ocean and the atmosphere is essential to the existence and evolution of the ISO in the Indo-Pacific warm pool region. Low-level moistening during the transition phase preconditions the atmosphere for deep convection. The vertical structure of ISO from the ECMWF coupled model during different phases of the oscillation as well as the skill of the model in simulating the processes that occur during the transition phase were studied. The forecast skill of the vertical structure associated with the ISO is greater for winter than for summer events. Predictability of the convective period is poor when initialized before the transitional phase. When initialized within the transition period including lower tropospheric moistening, predictability increases substantially, although the model parameterizations appears to trigger convection quickly without allowing an adequate buildup of CAPE during the transition. The model tends to simulate a more stable atmosphere compared to data, limiting the production of deep convective events. Two different one-dimensional coupled models are used to analyze the role of local ocean-atmosphere coupling in generating ISO. The ocean component is a one-dimensional mixed layer model. In the first model the atmospheric component corresponds to the SCCM. Results suggest that convection in the model tends to be "overactive," inhibiting development of lower frequency oscillations in the atmosphere. In the second case, the atmospheric component is a semi-empirical model that allows reproducing the coupled ISO over long integration periods including only local mechanisms. In the semi-empirical scheme the rate of change of atmospheric variables is statistically related to changes in SST. The stable state of this model is a quasi-periodic oscillation with a time scale between 25 and 80 days that matches well the observed ISO. Results suggest that the period of the oscillation depends on the characteristics of the ocean mixed layer, with a higher frequency oscillation for a shallow mixed layer.

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Wei, Jiangfeng. "Land-atmosphere interaction and climate variability." Diss., Available online, Georgia Institute of Technology, 2007, 2007. http://etd.gatech.edu/theses/available/etd-05162007-151312/.

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Thesis (Ph. D.)--Earth and Atmospheric Sciences, Georgia Institute of Technology, 2008. Stieglitz, Marc, Committee Member ; Guillas, Serge, Committee Member ; Fu, Rong, Committee Member ; Curry, Judith, Committee Member ; Dickinson, Robert, Committee Chair.

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Dail, Holly Janine. "Atlantic Ocean circulation at the last glacial maximum : inferences from data and models." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/78367.

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Thesis (Ph. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2012. This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. Cataloged from student-submitted PDF version of thesis. Includes bibliographical references (p. 221-236). This thesis focuses on ocean circulation and atmospheric forcing in the Atlantic Ocean at the Last Glacial Maximum (LGM, 18-21 thousand years before present). Relative to the pre-industrial climate, LGM atmospheric CO₂ concentrations were about 90 ppm lower, ice sheets were much more extensive, and many regions experienced significantly colder temperatures. In this thesis a novel approach to dynamical reconstruction is applied to make estimates of LGM Atlantic Ocean state that are consistent with these proxy records and with known ocean dynamics. Ocean dynamics are described with the MIT General Circulation Model in an Atlantic configuration extending from 35°S to 75°N at 1° resolution. Six LGM proxy types are used to constrain the model: four compilations of near sea surface temperatures from the MARGO project, as well as benthic isotope records of [delta]¹⁸O and [delta]¹³C compiled by Marchal and Curry; 629 individual proxy records are used. To improve the fit of the model to the data, a least-squares fit is computed using an algorithm based on the model adjoint (the Lagrange multiplier methodology). The adjoint is used to compute improvements to uncertain initial and boundary conditions (the control variables). As compared to previous model-data syntheses of LGM ocean state, this thesis uses a significantly more realistic model of oceanic physics, and is the first to incorporate such a large number and diversity of proxy records. A major finding is that it is possible to find an ocean state that is consistent with all six LGM proxy compilations and with known ocean dynamics, given reasonable uncertainty estimates. Only relatively modest shifts from modern atmospheric forcing are required to fit the LGM data. The estimates presented herein succesfully reproduce regional shifts in conditions at the LGM that have been inferred from proxy records, but which have not been captured in the best available LGM coupled model simulations. In addition, LGM benthic [delta]¹⁸O and [delta]¹³C records are shown to be consistent with a shallow but robust Atlantic meridional overturning cell, although other circulations cannot be excluded. by Holly Janine Dail. Ph.D.

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Verdy, Ariane. "Dynamics of marine zooplankton : social behavior, ecological interactions, and physically-induced variability." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/43158.

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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), 2008. Includes bibliographical references (p. [221]-232). Marine ecosystems reflect the physical structure of their environment and the biological processes they carry out. This leads to spatial heterogeneity and temporal variability, some of which is imposed externally and some of which emerges from the ecological mechanisms themselves. The main focus of this thesis is on the formation of spatial patterns in the distribution of zooplankton arising from social interactions between individuals. In the Southern Ocean, krill often assemble in swarms and schools, the dynamics of which have important ecological consequences. Mathematical and numerical models are employed to study the interplay of biological and physical processes that contribute to the observed patchiness. The evolution of social behavior is simulated in a theoretical framework that includes zooplankton population dynamics, swimming behavior, and some aspects of the variability inherent to fluid environments. First, I formulate a model of resource utilization by a stage-structured predator population with density-dependent reproduction. Second, I incorporate the predator-prey dynamics into a spatially-explicit model, in which aggregations develop spontaneously as a result of linear instability of the uniform distribution. In this idealized ecosystem, benefits related to the local abundance of mates are offset by the cost of having to share resources with other group members. Third, I derive a weakly nonlinear approximation for the steady-state distributions of predator and prey biomass that captures the spatial patterns driven by social tendencies. Fourth, I simulate the schooling behavior of zooplankton in a variable environment; when turbulent flows generate patchiness in the resource field, schools can forage more efficiently than individuals. (cont.) Taken together, these chapters demonstrate that aggregation/ schooling can indeed be the favored behavior when (i) reproduction (or other survival measures) increases with density in part of the range and (ii) mixing of prey into patches is rapid enough to offset the depletion. In the final two chapters, I consider sources of temporal variability in marine ecosystems. External perturbations amplified by nonlinear ecological interactions induce transient ex-cursions away from equilibrium; in predator-prey dynamics the amplitude and duration of these transients are controlled by biological processes such as growth and mortality. In the Southern Ocean, large-scale winds associated with ENSO and the Southern Annular Mode cause convective mixing, which in turn drives air-sea fluxes of carbon dioxide and oxygen. Whether driven by stochastic fluctuations or by climatic phenomena, variability of the biogeochemical/physical environment has implications for ecosystem dynamics. by Ariane Verdy. Ph.D.

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Verdy, Ariane. "Variability of zooplankton and sea surface temperature in the Southern Ocean." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/39197.

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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.

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Link, Shmuel G. "Field measurements of a swell band, shore normal, flux divergence reversal." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/67625.

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Thesis (S.M.)--Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Mechanical Engineering; and the Woods Hole Oceanographic Institution), June 2011. Cataloged from PDF version of thesis. Includes bibliographical references (p. 55-56). Throughout this thesis we will discuss the theoretical background and empirical observation of a swell band shore normal flux divergence reversal. Specifically, we will demonstrate the existence and persistence of the energy flux divergence reversal in the nearshore region of Atchafalaya Bay, Gulf of Mexico, across storms during the March through April 2010 deployment. We will show that the swell band offshore component of energy flux is rather insignificant during the periods of interest, and as such we will neglect it during the ensuing analysis. The data presented will verify that the greatest flux divergence reversal is seen with winds from the East to Southeast, which is consistent with theories which suggest shoreward energy flux as well as estuarine sediment transport and resuspension prior to passage of a cold front. Employing the results of theoretical calculations and numerical modeling we will confirm that a plausible explanation for this phenomena can be found in situations where temporally varying wind input may locally balance or overpower bottom induced dissipation, which may also contravene the hypothesis that dissipation need increase shoreward due to nonlinear wave-wave interactions and maturation of the spectrum. Lastly, we will verify that the data presented is consistent with other measures collected during the same deployment in the Atchafalaya Bay during March - April 2010. by Shmuel G. Link. S.M.

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Wortham, Cimarron James Lemuel IV. "A multi-dimensional spectral description of ocean variability with applications." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/79296.

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Thesis (Ph. D.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), February 2013. "February 2013." Cataloged from PDF version of thesis. Includes bibliographical references (p. 175-184). Efforts to monitor the ocean for signs of climate change are hampered by ever-present noise, in the form of stochastic ocean variability, and detailed knowledge of the character of this noise is necessary for estimating the significance of apparent trends. Typically, uncertainty estimates are made by a variety of ad hoc methods, often based on numerical model results or the variability of the data set being analyzed. We provide a systematic approach based on the four-dimensional frequency-wavenumber spectrum of low-frequency ocean variability. This thesis presents an empirical model of the spectrum of ocean variability for periods between about 20 days and 15 years and wavelengths of about 200-10,000 km, and describes applications to ocean circulation trend detection, observing system design, and satellite data processing. The horizontal wavenumber-frequency part of the model spectrum is based on satellite altimetry, current meter data, moored temperature records, and shipboard ADCP data. The spectrum is dominated by motions along a "nondispersive line". The observations considered are consistent with a universal [omega] -² power law at the high end of the frequency range, but inconsistent with a universal wavenumber power law. The model spectrum is globally varying and accounts for changes in dominant phase speed, period, and wavelength with location. The vertical structure of the model spectrum is based on numerical model results, current meter data, and theoretical considerations. We find that the vertical structure of kinetic energy is surface intensified relative to the simplest theoretical predictions. We present a theory for the interaction of linear Rossby waves with rough topography; rough topography can explain both the observed phase speeds and vertical structure of variability. The improved description of low-frequency ocean variability presented here will serve as a useful tool for future oceanographic studies. by Cimarron James Lemuel Wortham, IV. Ph.D.

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Horwitz, Rachel Mandy. "The effect of stratification on wind-driven, cross-shelf circulation and transport on the inner continental shelf." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/77779.

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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.

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Zelenke, Brian Christopher. "An empirical statistical model relating winds and ocean surface currents : implications for short-term current forecasts." Thesis, Connect to the title online, 2005. http://hdl.handle.net/1957/2166.

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Chen, Chia-Jeng. "Hydro-climatic forecasting using sea surface temperatures." Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/48974.

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A key determinant of atmospheric circulation patterns and regional climatic conditions is sea surface temperature (SST). This has been the motivation for the development of various teleconnection methods aiming to forecast hydro-climatic variables. Among such methods are linear projections based on teleconnection gross indices (such as the ENSO, IOD, and NAO) or leading empirical orthogonal functions (EOFs). However, these methods deteriorate drastically if the predefined indices or EOFs cannot account for climatic variability in the region of interest. This study introduces a new hydro-climatic forecasting method that identifies SST predictors in the form of dipole structures. An SST dipole that mimics major teleconnection patterns is defined as a function of average SST anomalies over two oceanic areas of appropriate sizes and geographic locations. The screening process of SST-dipole predictors is based on an optimization algorithm that sifts through all possible dipole configurations (with progressively refined data resolutions) and identifies dipoles with the strongest teleconnection to the external hydro-climatic series. The strength of the teleconnection is measured by the Gerrity Skill Score. The significant dipoles are cross-validated and used to generate ensemble hydro-climatic forecasts. The dipole teleconnection method is applied to the forecasting of seasonal precipitation over the southeastern US and East Africa, and the forecasting of streamflow-related variables in the Yangtze and Congo Rivers. These studies show that the new method is indeed able to identify dipoles related to well-known patterns (e.g., ENSO and IOD) as well as to quantify more prominent predictor-predictand relationships at different lead times. Furthermore, the dipole method compares favorably with existing statistical forecasting schemes. An operational forecasting framework to support better water resources management through coupling with detailed hydrologic and water resources models is also demonstrated.

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Abdolmaleki, Kourosh. "Modelling of wave impact on offshore structures." University of Western Australia. School of Mechanical Engineering, 2007. http://theses.library.uwa.edu.au/adt-WU2008.0055.

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[Truncated abstract] The hydrodynamics of wave impact on offshore structures is not well understood. Wave impacts often involve large deformations of water free-surface. Therefore, a wave impact problem is usually combined with a free-surface problem. The complexity is expanded when the body exposed to a wave impact is allowed to move. The nonlinear interactions between a moving body and fluid is a complicated process that has been a dilemma in the engineering design of offshore and coastal structures for a long time. This thesis used experimental and numerical means to develop further understanding of the wave impact problems as well as to create a numerical tool suitable for simulation of such problems. The study included the consideration of moving boundaries in order to include the coupled interactions of the body and fluid. The thesis is organized into two experimental and numerical parts. There is a lack of benchmarking experimental data for studying fluid-structure interactions with moving boundaries. In the experimental part of this research, novel experiments were, therefore, designed and performed that were useful for validation of the numerical developments. By considering a dynamical system with only one degree of freedom, the complexity of the experiments performed was minimal. The setup included a plate that was attached to the bottom of a flume via a hinge and tethered by two springs from the top one at each side. The experiments modelled fluid-structure interactions in three subsets. The first subset studied a highly nonlinear decay test, which resembled a harsh wave impact (or slam) incident. The second subset included waves overtopping on the vertically restrained plate. In the third subset, the plate was free to oscillate and was excited by the same waves. The wave overtopping the plate resembled the physics of the green water on fixed and moving structures. An analytical solution based on linear potential theory was provided for comparison with experimental results. ... In simulation of the nonlinear decay test, the SPH results captured the frequency variation in plate oscillations, which indicated that the radiation forces (added mass and damping forces) were calculated satisfactorily. In simulation of the nonlinear waves, the waves progressed in the flume similar to the physical experiments and the total energy of the system was conserved with an error of 0.025% of the total initial energy. The wave-plate interactions were successfully modelled by SPH. The simulations included wave run-up and shipping of water for fixed and oscillating plate cases. The effects of the plate oscillations on the flow regime are also discussed in detail. The combination of experimental and numerical investigation provided further understanding of wave impact problems. The novel design of the experiments extended the study to moving boundaries in small scale. The use of SPH eliminated the difficulties of dealing with free-surface problems so that the focus of study could be placed on the impact forces on fixed and moving bodies.

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Mosedale, Timothy James. "North Atlantic Ocean-atmosphere interaction using simple and complex models." Thesis, University of Reading, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.430918.

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Abel, Rafael [Verfasser]. "Aspects of air-sea interaction in atmosphere-ocean models / Rafael Abel." Kiel : Universitätsbibliothek Kiel, 2018. http://d-nb.info/1171800193/34.

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Vimont, Daniel J. "The seasonal footprinting mechanism in the CSIRO coupled general circulation models and in observations /." Thesis, Connect to this title online; UW restricted, 2002. http://hdl.handle.net/1773/10074.

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Wang, Jinbo. "On the warm bias along the South-West African Coast in coupled models : an oceanic perspective /." Online version of original thesis, 2008. http://hdl.handle.net/1912/2502.

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Lee, Craig M. "Observations and models of upper ocean response to atmospheric forcing : wind driven flow, surface heating and near-inertial wave interactions with mesoscale currents /." Thesis, Connect to this title online; UW restricted, 1995. http://hdl.handle.net/1773/11039.

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De, Szoeke Simon P. "Evolution of the cross-equatorial atmospheric boundary layer in the east Pacific : observations and models /." Thesis, Connect to this title online; UW restricted, 2004. http://hdl.handle.net/1773/10083.

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Williams, Paul David. "Nonlinear interactions of fast and slow modes in rotating, stratified fluid flows." Thesis, University of Oxford, 2003. http://ora.ox.ac.uk/objects/uuid:5365c658-ab60-41e9-b07b-0f635909835e.

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This thesis describes a combined model and laboratory investigation of the generation and mutual interactions of fluid waves whose characteristic scales differ by an order of magnitude or more. The principal aims are to study how waves on one scale can generate waves on another, much shorter scale, and to examine the subsequent nonlinear feedback of the short waves on the long waves. The underlying motive is to better understand such interactions in rotating, stratified, planetary fluids such as atmospheres and oceans. The first part of the thesis describes a laboratory investigation using a rotating, two-layer annulus, forced by imposing a shear across the interface between the layers. A method is developed for making measurements of the two-dimensional interface height field which are very highly-resolved both in space and time. The system's linear normal modes fall into two distinct classes: 'slow' waves which are relatively long in wavelength and intrinsic period, and 'fast' waves which are much shorter and more quickly-evolving. Experiments are performed to categorize the flow at a wide range of points in the system's parameter space. At very small background rotation rates, the interface is completely devoid of waves of both types. At higher rates, fast modes only are generated, and are shown to be consistent with the Kelvin-Helmholtz instability mechanism based on a critical Richardson number. At rotation rates which are higher still, baroclinic instability gives rise to the onset of slow modes, with subsequent localized generation of fast modes superimposed in the troughs of the slow waves. In order to examine the generation mechanism of these coexisting fast modes, and to assess the extent of their impact upon the evolution of the slow modes, a quasi-geostrophic numerical model of the laboratory annulus is developed in the second part of the thesis. Fast modes are filtered out of the model by construction, as the phase space trajectory is confined to the slow manifold, but the slow wave dynamics is accurately captured. Model velocity fields are used to diagnose a number of fast wave radiation indicators. In contrast to the case of isolated fast waves, the Richardson number is a poor indicator of the generation of the coexisting fast waves that are observed in the laboratory, and so it is inferred that these are not Kelvin-Helmholtz waves. The best indicator is one associated with the spontaneous emission of inertia-gravity waves, a generalization of geostrophic adjustment radiation. A comparison is carried out between the equilibrated wavenumbers, phase speeds and amplitudes of slow waves in the laboratory (which coexist with fast modes), and slow waves in the model (which exist alone). There are significant differences between these wave properties, but it is shown that these discrepancies can be attributed to uncertainties in fluid properties, and to model approximations apart from the neglect of fast modes. The impact of the fast modes on the slow modes is therefore sufficiently small to evade illumination by this method of inquiry. As a stronger test of the interaction, a stochastic parameterization of the inertia-gravity waves is included in the model. Consistent with the laboratory/model intercomparison, the parameterized fast waves generally have only a small impact upon the slow waves. However, sufficiently close to a transition curve between two different slow modes in the system's parameter space, it is shown that the fast modes can exert a dominant influence. In particular, the fast modes can force spontaneous transitions from one slow mode to another, due to the phenomenon of stochastic resonance. This finding should be of interest to the meteorological and climate modelling communities, because of its potential to affect model reliability.

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Wang, Jinbo S. M. Massachusetts Institute of Technology. "On the warm bias along the South-West African Coast in coupled models : an oceanic perspective." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/45723.

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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), 2008. Includes bibliographical references (p. 64-67). Coupled ocean/atmosphere simulations exhibit systematic warm biases over the South West African (SWA) coastal region. Recent investigations indicate that coastal ocean dynamics may play an important role in determining the SST patterns, but none of them provide a detailed analysis. In this study, I analyze simulations produced both by coupled models and by idealized models. Then results are interpreted on the basis of a theoretical framework. Finally the conclusion is reached that the insufficient resolution of the ocean component in the coupled model is responsible for the warm biases over the SWA coastal region. The coarse resolution used in the ocean model has an artificially stretched coastal side-wall boundary layer, which induces a smaller upwelling velocity in the boundary layer. The vertical heat transport decreases even when the volume transport is unchanged because of its nonlinear relationship with the magnitude of the upwelling velocity. Based on the scaling of the idealized model simulations, a simplified calculation shows that the vertical heat transport is inversely proportional to the zonal resolution over the coastal region. Therefore, increasing the horizontal resolution can considerably improve the coastal SST simulation, and better resolve the coastal dynamics. by Jinbo Wang. S.M.

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Saenger, Casey Pearce. "Low-latitude Western North Atlantic climate variability during the past millennium : insights from proxies and models." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/55163.

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Thesis (Ph.D.)--Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2009. Cataloged from PDF version of thesis. Includes bibliographical references (p. 59-65). Estimates of natural climate variability during the past millennium provide a frame of reference in which to assess the significance of recent changes. This thesis investigates new methods of reconstructing low-latitude sea surface temperature (SST) and hydrography, and combines these methods with traditional techniques to improve the present understanding of western North Atlantic climate variability. A new strontium/calcium (Sr/Ca) - SST calibration is derived for Atlantic Montastrea corals. This calibration shows that Montastrea Sr/Ca is a promising SST proxy if the effect of coral growth is considered. Further analyses of coral growth using Computed Axial Tomography (CAT) imaging indicate growth in Siderastrea corals varies inversely with SST on interannual timescales. A 440-year reconstruction of low-latitude western North Atlantic SST based on this relationship suggests the largest cooling of the last few centuries occurred from -1650-1730 A.D., and was -I°C cooler than today. Sporadic multidecadal variability in this record is inconsistent with evidence for a persistent 65-80 year North Atlantic SST oscillation. Volcanic and anthropogenic radiative forcing are identified as important sources of externally-forced SST variability, with the latter accounting for most of the 20th century warming trend. An 1800-year reconstruction of SST and hydrography near the Gulf Stream also suggests SSTs remained within about I°C of modern values. This cooling is small relative to other regional proxy records and may reflect the influence of internal oceanic and atmospheric circulation. (cont.) Simulations with an atmospheric general circulation model (AGCM) indicate that the magnitude of cooling estimated by proxy records is consistent with tropical hydrologic proxy records. by Casey Pearce Saenger. Ph.D.

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Knochel, Hervé. "Développement et validation d'un modèle numérique de circulation océanique à coordonnées [sigma] pour l'étude climatique de l'Atlantique nord." Université Joseph Fourier (Grenoble), 1998. http://www.theses.fr/1998GRE10256.

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Dans cette these, un modele numerique de circulation generale oceanique est mis en uvre dans le but d'effectuer une etude climatique de l'atlantique nord. Le modele presente la particularite d'utiliser une coordonnee verticale epousant le relief sous-marin (coordonnee ). Il inclut en outre un modele unidimensionnel integral de couche melangee de type krauss-turner pour parametriser la penetration des forcages atmospheriques de surface dans l'ocean. L'etude d'une simulation climatologique type montre la capacite du modele a reproduire les traits dominants de la circulation generale avec en particulier une representation realiste de la trajectoire du gulf stream et de son decollement a cape hatteras. Des etudes de sensibilite du modele sont egalement effectuees, mettant en evidence certains aspects caracteristiques, comme l'importance de la resolution verticale dans la representation de la circulation profonde ou l'amelioration de la penetration des forcages thermohalins du fait de l'utilisation du modele de couche melangee. Ces etudes de simulations climatologiques fournissent un etat climatique moyen de l'ocean, a partir duquel la variabilite interannuelle du modele est etudiee dans le cadre d'une simulation incluant des flux atmospheriques mensuels, issus de la reanalyse ncep/ncar entre 1958 et 1997. L'etude se concentre sur l'eau de la mer du labrador (lsw), montrant une variabilite interannuelle coherente de cette masse d'eau et validant ainsi de maniere tres positive les donnees de forcage du ncep/ncar. La simulation met de plus en evidence une inadequation du parametrage du forcage salin de surface. Malgre cela, le modele reproduit de maniere realiste les periodes observees de forte et faible convection en mer du labrador et fait apparaitre une propagation d'anomalies chaudes et froides dans la circulation cyclonique du gyre subpolaire.

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Mahfouf, Jean-François. "Contribution a la definition d'une parametrisation des transferts entre le sol, la vegetation et l'atmosphere : analyse de sensibilite et insertion dans un modele mesoechelle." Clermont-Ferrand 2, 1986. http://www.theses.fr/1986CLF21010.

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Un modele numerique a mesoechelle (nickerson et al, 1986) comportant un ensemble detaille de parametrisations pour la couche limite planetaire (therry et lacarrere, 1983), la vegetation (deardorff, 1978) et les transferts thermo-hydriques dans le sol (mclumber et pielke, 1981) a ete developpe. Tout d'abord, une version unidimensionnelle nous a permis de realiser un ensemble complet de tests de sensibilite sur l'influence de l'evolution diurne de la basse atmosphere vis a vis de l'etat hydrique du sol, de l'albedo de surface et du type de couvert vegetal notamment. Une comparaison a ete effectuee avec les donnees de l'experience de couche limite "wangara", indiquant un bon accord entre les resultats du modele et l'observation

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Dixit, Sanjay. "Simulation of tropical pacific circulation anomalies with linear atmosphere and ocean models." Thesis, 1987. http://hdl.handle.net/1957/28619.

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A simple atmosphere and ocean model of relevance to El Nino and Southern Oscillation (ENSO) is discussed. Both the atmosphere and ocean models are two layer, three dimensional, linear and baroclinic, and generally follow the Oregon State University coupled general circulation model. However, the parameterization differs considerably from previous work in the treatment of the atmospheric latent heat release. This new parameterization follows the formula used in the theory of conditional instability of the second kind (CISK). In this the latent heat release is proportional to the low level convergence. Utilizing the "Comprehensive Ocean Atmosphere Data Set" (COADS), which contains all oceanic and atmospheric surface variables over the global ocean from 1946-1979, experimental model results are discussed for determination of the validity of the parameterizations. In particular, the years 1957, 1965 and 1972 in which El Nino events occurred are examined. The parameterization is deemed to be realistic, and should permit simulation of the El Nino upon coupling the two models. Graduation date: 1988

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Ahn, Joong Bae. "A study of El Niño/southern oscillation : numerical experiments and data analysis." Thesis, 1990. http://hdl.handle.net/1957/29066.

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For the purpose of investigating the fundamental nature of the interannual oscillation observed in the tropical Pacific in conjunction with El Nino/Southern Oscillation (ENSO), the Comprehensive Ocean Atmosphere Data Set was analyzed. Based upon this analysis, an "intermediate" tropical atmosphere-ocean coupled model was developed. For reason of their particular importance to atmosphere-ocean interactions, moisture processes such as condensation-convergence, evaporation-sea surface temperature and evaporation-wind feedbacks were given special emphasis in both the data analysis and modeling processes. The atmospheric component of the model is based on the first baroclinic mode, which is driven by the atmospheric internal heating. The oceanic model consists of two layers with an imbedded oceanic mixed-layer, by which SST is predicted. The present study has demonstrated that despite the structural simplicity of the oceanic model, it is capable of simulating mean oceanic circulation. In preparation for coupling, individual models were first tested with the use of appropriate time-dependent boundary conditions specified from the composite ENSO data. Both model simulations reproduced the major features associated with the ENSO events. Coupling was performed following the imposition of wind stress anomalies over the western Pacific for a given time period and the removal of all external forcing for a period of eight years thereafter. The coupled responses simulated during the the first two-year period provided reasonable simulations of the following ENSO-like features: the appearance of warm sea-surface temperature anomalies in the central Pacific, deepening/shallowing of mixed-layers in the eastern/western Pacific, weakening of the trades in the central Pacific, strengthening/weakening of the North Equatorial Counter Current/South Equatorial Currents, and enhanced convective activities around the dateline. The long-term coupled integration showed a pattern of interannual oscillation over a period of approximately three years. The results obtained from this coupling study have illustrated (1) that the necessary condition for the interannual oscillation is the interaction between the atmosphere and the ocean and (2) that it is likely that oceanic wave dynamics plays a crucial role in the determination of the growth and decay of ENSO events. Graduation date: 1991

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He, Yun. "A study of the upper ocean processes in the tropical Pacific Ocean using satellite data, in-situ measurements, and numerical models." 1998. http://catalog.hathitrust.org/api/volumes/oclc/42846493.html.

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Jiang, Xingjian. "Role of oceanic heat transport processes in CO₂-induced warming : analysis of simulations by the OSU coupled atmosphere-ocean general circulation model." Thesis, 1986. http://hdl.handle.net/1957/29322.

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The OSU global coupled atmosphere/ocean general circulation model (A/O GCM) has been used to simulate the present (lxCO₂) climate and to investigate a CO₂-induced (2xCO₂) climate change. Previous analysis of the lxCO₂ simulation showed distinct errors in the simulated sea surface temperature (SST) and sea ice which were attributed primarily to the atmospheric GM (AGCM). Analysis of the 2xCO₂ simulation showed that the CO₂-induced warming penetrated into the ocean; this caused a delay in the equilibration of the climate system with an estimated e-folding time of 50-75 years. The present study has two objectives. The principal objective is to answer the question: By what pathways and through which physical processes does the simulated ocean general circulation produce the penetration of the CO₂-induced warming into the ocean? The secondary objective is to evaluate the performance of the oceanic GCM (OGCM) in the lxCO₂ simulation. The comparison of the simulated lxCO₂ internal oceanic fields with the corresponding observations shows that although they are basically similar, there are distinct errors. Further analysis shows that these errors were generated by the OGCM during its spin-up integration prior to its coupling with the AGCM. This study thus shows that it is not sufficient to compare the simulated SST with the observed SST to evaluate the performance of the OGCM. It is also necessary to compare the simulated internal oceanic quantities with the corresponding observed quantities. The global mean analysis of the CO₂-induced climate changes shows that the ocean gains heat at a rate of 3 W/m² due to the CO₂ doubling. This heat penetrates downward into the ocean predominantly through the reduction in the convective overturning. The zonal mean analysis shows that the surface warming increased from the tropics toward the mid-latitudes of both hemispheres and penetrated gradually to the deeper ocean. The oceanic warming penetrated to a greater depth in the subtropics and mid-latitudes than in the equatorial region. A zonal mean heat budget analysis shows that the CO₂-induced warming of the ocean occurs predominantly through the downward transport of heat, with the meridional heat flux being only of secondary importance. In the tropics the penetration of the CO₂-induced heating is minimized by the upwelling of cold water. In the subtropics the heating is transported downward more readily by the downwelling existing there. In the high latitudes the suppressed convection plays the dominant role in the downward penetration of the CO₂-induced heating. Graduation date: 1987

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