Dissertations / Theses on the topic 'Atmospheric Mathematical models'
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Melton, Roy Wayne. "Parallelizing the spectral method in climate and weather modeling." Diss., Available online, Georgia Institute of Technology, 2004:, 2003. http://etd.gatech.edu/theses/available/etd-04062004-164733/unrestricted/melton%5Froy%5Fw%5F200312%5Fphd.pdf.
Full textZink, Florian. "Gravity waves and turbulence in the lower atmosphere /." Title page, contents and abstract only, 2000. http://web4.library.adelaide.edu.au/theses/09PH/09phz778.pdf.
Full textDionne, Pierre 1962. "Numerical simulation of blocking by the resonance of topographically forced waves." Thesis, McGill University, 1986. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=65542.
Full textKaharabata, Samuel K. "Non-disturbing methods of estimating trace gas emissions from agricultural and forest sources." Thesis, McGill University, 1999. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=35903.
Full textSulphur hexafluoride was also used as an atmospheric tracer in order to estimate CH4 emissions from manure slurry and cattle housed in barns and feedlots. (Abstract shortened by UMI.)
Mahanama, Sarith Prasad Panditha. "Distributed approach of coupling basin scale hydrology with atmospheric processes." Thesis, Hong Kong : University of Hong Kong, 2000. http://sunzi.lib.hku.hk/hkuto/record.jsp?B22088817.
Full textMarks, Marguerite Colasurdo. "Incorporating Chemical Activity and Relative Humidity Effects in Regional Air Quality Modeling of Organic Aerosol Formation." PDXScholar, 2013. https://pdxscholar.library.pdx.edu/open_access_etds/1511.
Full textDrysdale, Euain Fraser. "Modelling of equatorial wave motions in the middle atmosphere." Thesis, University of Oxford, 1998. http://ora.ox.ac.uk/objects/uuid:9ae75869-a15b-465e-af64-c608cca8b34c.
Full textKordova-Vyhnalikova, Jana. "Mathematical modelling of atmospheric pollution : application of some eulerian-lagrangian trajectographic models to the prediction of atmospheric pollution." Université Louis Pasteur (Strasbourg) (1971-2008), 1997. http://www.theses.fr/1997STR13207.
Full textHoldsworth, David A. "Signal analysis with applications to atmospheric radars /." Title page, abstract and contents only, 1995. http://web4.library.adelaide.edu.au/theses/09PH/09phh728.pdf.
Full text廖俊豪 and Chun-ho Liu. "Numerical modelling of atmospheric boundary layer with application to air pollutant dispersion." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1998. http://hub.hku.hk/bib/B31239018.
Full textBhave, Prakash Viththal Seinfeld John H. "Air pollution at the single-particle level : integrating atmospheric measurements with mathematical models /." Diss., Pasadena, Calif. : California Institute of Technology, 2003. http://resolver.caltech.edu/CaltechETD:etd-05252003-091827.
Full textLi, Xianxiang, and 李顯祥. "Large-eddy simulation of wind flow and air pollutant transport inside urban street canyons of different aspect ratios." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2008. http://hub.hku.hk/bib/B40687326.
Full textCheng, Wai-chi, and 鄭偉智. "Wind and pollutant removal of urban street canyons under different thermal stratification by RANS and LES models." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2010. http://hub.hku.hk/bib/B46289653.
Full textSpyksma, Kyle. "On the dynamics and predictability of moist turbulence." Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=103296.
Full textThe model is used to study the small-scale predictability and dynamics of moist and dry shallow convective turbulence. Although moist flows are less predictable than their associated dry flows, we can account for the differences via a simple scaling. Using large-scale (the root-mean-squared vorticity) and small-scale (the dissipation wavenumber, kd) measures, we can reconcile classical predictability statistics from both wet and dry runs, with different lapse rates and relative humidities.
Finally, I present a more thorough investigation of the dynamical differences between wet and dry convective turbulence, and then consider the very small-scale (ℓ ≲ 10 m) variability of liquid water content and compare our high-resolution simulation results to existing in situ cumulus-cloud observations. We find that there is a small decrease in the spatial intermittency of vorticity in wet runs relative to dry ones. This is consistent with the idea that evaporation of the liquid water in the clouds reduces the instabilities that would lead to the most intense vortices. At the same time, the liquid water content spectra show that in these areas of intense mixing and cloud decay, the characteristic scale of variability is shifted to smaller scales compared to a passive scalar. Further integrations in which the convective forcing is removed show that as the amount of liquid water decreases through evaporation, there is delayed decay of the smallest scales of the cloud. These findings may explain the small-scale shallow liquid water content spectra from cumulus-cloud fly-through measurements reported in Davis et al. (1999).
Mandock, Randal Lee Nicholas. "A multiple beam sodar for the measurement of atmospheric turbulence." Diss., Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/25869.
Full textSchultz, Lisa. "Understanding the Greenhouse Effect Using a Computer Model." Fogler Library, University of Maine, 2009. http://www.library.umaine.edu/theses/pdf/SchultzL2009.pdf.
Full textHe, Shu Yu. "Field study on influence of atmospheric parameters and vegetation on variation of soil suction around tree vicinity." Thesis, University of Macau, 2018. http://umaclib3.umac.mo/record=b3868734.
Full textJia, XiaoJing 1977. "The mechanisms and the predictability of the Arctic oscillation and the North Atlantic oscillation /." Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=103026.
Full textCady, Ralph. "An adaptive multi-dimensional Eulerian-Lagrangian finite element method for simulating advection-dispersion." Diss., The University of Arizona, 1989. http://hdl.handle.net/10150/184697.
Full textHang, Jian, and 杭建. "Wind conditions and urban ventilation in idealized city models." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2009. http://hub.hku.hk/bib/B42841471.
Full textLai, Kwong-kei Murphy, and 賴廣麒. "Two-dimensional computational study on indoor/outdoor air quality relationship in urban buildings." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2007. http://hub.hku.hk/bib/B38725149.
Full textComer, Neil Thomas. "Validation and heterogeneity investigation of the Canadian Land Surface Scheme (CLASS) for wetland landscapes." Thesis, McGill University, 2001. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=38173.
Full textCLASS was then tuned for a specific bog location found in the Hudson Bay Lowland (HBL) during the Northern Wetlands Study (NOWES). With bog surfaces better described within the model, testing of CLASS over a highly heterogeneous 169 km2 HBL region is then undertaken. The model is first modified for lake and pond surfaces and then separate runs for bog, fen, lake and tree/shrub categories is undertaken. Using a GIS, the test region under which airborne flux measurements are available is divided into 104 grid cells and proportions of each surface type are calculated within each cell. Findings indicate that although the modelled grid average radiation and flux values are reasonably well reproduced (4% error for net radiation, 10% for latent heat flux and 30% for sensible heat flux), spatial agreement between modelled and observed grid cells is disappointing. (Abstract shortened by UMI.)
Bourouiba, Lydia. "Numerical and theoretical study of homogeneous rotating turbulence." Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=115861.
Full textFirst, using numerical simulations of decaying turbulence over a large range of Ro we identified three regimes. The large Ro regime is similar to non-rotating, isotropic turbulence. The intermediate Ro regime shows strong 3D-to-2D energy transfers and asymmetry between cyclones (corotating) and anticyclones (couter-rotating), whereas at small Ro regime these features are much reduced.
We then studied discreteness effects and constructed a kinematic model to quantify the threshold of nonlinear broadening below which the 2D-3D interactions critical to the intermediate Ro regime are not captured. These results allow for the improvement of numerical studies of rotating turbulence and refine the comparison between results obtained in finite domains and theoretical results derived in unbounded domains.
Using equilibrium statistical mechanics, we examined the hypothesis of decoupling predicted in the small Ro regime. We identified a threshold time, t☆ = 2/Ro2, after which the asymptotic decoupling regime is no longer valid. Beyond t ☆, we show that the quasi-invariants of the decoupled model continue to constrain the system on the short timescales.
We found that the intermediate Ro regime is also present in forced turbulence and that interactions responsible for it are nonlocal. We explain a steep slope obtained in the 2D energy spectrum by a downscale enstrophy transfer. The energy of the 2D modes is observed to accumulate in the largest scales of the domain in the long-time limit. This is reminiscent of the "condensation" observed in classical forced 2D flows and magnetohydrodynamics.
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.
Full textIncludes bibliographical references (p. 284-290).
by Brian Kenneth Arbic.
Ph.D.
WEST, KAREN FRANCES. "AN EXTENSION TO THE ANALYSIS OF THE SHIFT-AND-ADD METHOD: THEORY AND SIMULATION (SPECKLE, ATMOSPHERIC TURBULENCE, IMAGE RESTORATION)." Diss., The University of Arizona, 1985. http://hdl.handle.net/10150/188021.
Full textYang, Lina, and 阳丽娜. "City ventilation of Hong Kong by thermal buoyancy." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2009. http://hub.hku.hk/bib/B42841380.
Full textLuo, Zhiwen, and 罗志文. "City ventilation by slope wind." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2010. http://hub.hku.hk/bib/B46089962.
Full textCheung, Ching, and 張靜. "Effect of heat flux on wind flow and pollutant dispersion in an urban street canyon." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2006. http://hub.hku.hk/bib/B37742498.
Full textMunoz, Esparza Domingo. "Multiscale modelling of atmospheric flows: towards improving the representation of boundary layer physics." Doctoral thesis, Universite Libre de Bruxelles, 2013. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209363.
Full textPrior to the development of the multiscale numerical methodology, one-year of sonic anemometer and wind LiDAR measurements from the FINO1 offshore platform are analyzed. A comprehensive database of offshore measurements in the lowest 250 m of the boundary layer is developed after quality data check and correction for flow distortion effects by the measurement mast, allowing the characterization of the offshore conditions at FINO1. Spectral analysis of high frequency sonic anemometer measurements is used to estimate a robust averaing time for the turbulent fluxes that minimizes non-universal contributions from mesoscale structures but captures the contribution from boundary layer turbulence, employing the Ogive function concept. A stability classification of the measurements is carried out based on the Obukhov length. Results compare well to other surface layer observational studies while vertical wind speed profiles exhibit the expected stability-dependency.
Although NWP models have been extensively used for weather forecasting purposes, a comprehensive analysis of its suitability to meet the wind energy requirements needs to be carried out. The applicability of the WRF mesoscale model to reproduce offshore boundary layer characteristics is evaluated and validated against field measurements from FINO1. The ability of six planetary boundary layer (PBL) parameterizations to account for stability effects is analyzed. Overall, PBL parameterizations are rather accurate in reproducing the vertical structure of the boundary layer for convective and neutral stabilities. However, difficulties are found under stable stratifications, due to the general tendency of PBL formulations to be overdiffusive and therefore, not capable to develope the strong vertical gradients found in the observations. A low-level jet and a very shallow boundary layer cases are simulated to provide further insights into the limits of the parameterizations.
Large-eddy simulations (LES) based on averaged conditions from a convective episode at FINO1 are conducted to understand the mechanisms of transition and equilibration that occur in turbulent one-way nested simulations. The nonlinear backscatter and anisotropy subgrid scale model with a prognostic turbulent kinetic energy equation is found to be capable of providing similar results when performing one-way nested large-eddy simulations to a reference stand-alone domain using periodic lateral boundary conditions. A good agreement is obtained in terms of velocity shear and turbulent fluxes of heat and momentum, while velocity variances are overestimated. A considerable streamwise fetch is needed following each domain transition for appropriate energy levels to be reached at high wavelengths and for the solution to reach quasi-stationary results. A pile-up of energy is observed at low wavelengths on the first nested domain, mitigated by the inclusion of a second nested domain with higher resolution that allows the development of an appropriate turbulent energy cascade.
As the final step towards developing the multiscale capabilities of WRF, the specific problem of the transition from meso- to micro-scales in atmospheric models is addressed. The challenge is to generate turbulence on inner LES domain from smooth mesoscale inflow. Several new methods are proposed to trigger the development of turbulent features. The inclusion of adequate potential temperature perturbations near the inflow boundaries of the LES domain results in a very good agreement of mean velocity profiles, variances and turbulent fluxes, as well as velocity spectra, when compared to periodic stand-alone simulations. This perturbation method allows an efficient generation of fully developed turbulence and is tested under a broad range of atmospheric stabilities: convective, neutral and stable conditions, showing successful results in all the regimes.
Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished
Wells, Judith R. (Judith Roberta). "A laboratory study of localized boundary mixing in a rotating stratified fluid." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/58062.
Full textIncludes bibliographical references (p. 145-148).
Oceanic observations indicate that abyssal mixing is localized in regions of rough topography. How locally mixed fluid interacts with the ambient fluid is an open question. Laboratory experiments explore the interaction of mechanically induced boundary mixing and an interior body of linearly stratified rotating fluid. Turbulence is generated by a vertically oscillating horizontal bar, located at middepth along the tank wall. The turbulence forms a region of mixed fluid which quickly reaches a steady state height and collapses into the interior. The mixed layer thickness ... is independent of the Coriolis frequency f. N is the buoyancy frequency, co is the bar frequency, and the constant, Y=1 cm, is empirically determined by bar mechanics. In initial experiments, the bar is exposed on three sides. Mixed fluid intrudes directly into the interior as a radial front of uniform height, rather than as a boundary current. Mixed fluid volume grows linearly with time ... The circulation patterns suggest a model of unmixed fluid being laterally entrained with velocity, e Nhm, into the sides of a turbulent zone with height hm and width Lf ... where Lf is an equilibrium scale associated with rotational control of bar-generated turbulence. In accord with the model, outflux is constant, independent of stratification and restricted by rotation ... Later experiments investigate the role of lateral entrainment by confining the sides of the mixing bar between two walls, forming a channel open to the basin at one end. A small percentage of exported fluid enters a boundary current, but the bulk forms a cyclonic circulation in front of the bar. As the recirculation region expands to fill the channel, it restricts horizontal entrainment into the turbulent zone. The flux of mixed fluid decays with time.
(cont.) ... The production of mixed fluid depends on the size of the mixing zone as well as on the balance between turbulence, rotation and stratification. As horizontal entrainment is shut down, longterm production of mixed fluid may be determined through much weaker vertical entrainment. Ultimately, the export of mixed fluid from the channel is restricted to the weak boundary current.
by Judith R. Wells.
Ph.D.
Kaspi, Yohai. "Turbulent convection in the anelastic rotating sphere : a model for the circulation on the giant planets." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/45780.
Full textIncludes bibliographical references (p. 207-221).
This thesis studies the dynamics of a rotating compressible gas sphere, driven by internal convection, as a model for the dynamics on the giant planets. We develop a new general circulation model for the Jovian atmosphere, based on the MITgcm dynamical core augmenting the nonhydrostatic model. The grid extends deep into the planet's interior allowing the model to compute the dynamics of a whole sphere of gas rather than a spherical shell (including the strong variations in gravity and the equation of state). Different from most previous 3D convection models, this model is anelastic rather than Boussinesq and thereby incorporates the full density variation of the planet. We show that the density gradients caused by convection drive the system away from an isentropic and therefore barotropic state as previously assumed, leading to significant baroclinic shear. This shear is concentrated mainly in the upper levels and associated with baroclinic compressibility effects. The interior flow organizes in large cyclonically rotating columnar eddies parallel to the rotation axis, which drive upgradient angular momentum eddy fluxes, generating the observed equatorial superrotation. Heat fluxes align with the axis of rotation, contributing to the observed flat meridional emission. We show the transition from weak convection cases with symmetric spiraling columnar modes similar to those found in previous analytic linear theory, to more turbulent cases which exhibit similar, though less regular and solely cyclonic, convection columns which manifest on the surface in the form of waves embedded within the superrotation. We develop a mechanical understanding of this system and scaling laws by studying simpler configurations and the dependence on physical properties such as the rotation period, bottom boundary location and forcing structure. These columnar cyclonic structures propagate eastward, driven by dynamics similar to that of a Rossby wave except that the restoring planetary vorticity gradient is in the opposite direction, due to the spherical geometry in the interior.
(cont.) We further study these interior dynamics using a simplified barotropic annulus model, which shows that the planetary vorticity radial variation causes the eddy angular momentum flux divergence, which drives the superrotating equatorial flow. In addition we study the interaction of the interior dynamics with a stable exterior weather layer, using a quasigeostrophic two layer channel model on a beta plane, where the columnar interior is therefore represented by a negative beta effect. We find that baroclinic instability of even a weak shear can drive strong, stable multiple zonal jets. For this model we find an analytic nonlinear solution, truncated to one growing mode, that exhibits a multiple jet meridional structure, driven by the nonlinear interaction between the eddies. Finally, given the density field from our 3D convection model we derive the high order gravitational spectra of Jupiter, which is a measurable quantity for the upcoming JUNO mission to Jupiter.
by Yohai Kaspi.
Ph.D.
Smy, Louise Ann. "Atmospheric transport and critical layer mixing in the troposphere and stratosphere." Thesis, University of St Andrews, 2012. http://hdl.handle.net/10023/2538.
Full textRao, Meenakshi. "Investigating the Potential of Land Use Modifications to Mitigate the Respiratory Health Impacts of NO2| A Case Study in the Portland-Vancouver Metropolitan Area." Thesis, Portland State University, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10131547.
Full textThe health impacts of urban air pollution are a growing concern in our rapidly urbanizing world. Urban air pollutants show high intra-urban spatial variability linked to urban land use and land cover (LULC). This correlation of air pollutants with LULC is widely recognized; LULC data is an integral input into a wide range of models, especially land use regression models developed by epidemiologists to study the impact of air pollution on human health. Given the demonstrated links between LULC and urban air pollution, and between urban air pollution and health, an interesting question arises: what is the potential of LULC modifications to mitigate the health impacts of urban air pollution?
In this dissertation we assess the potential of LULC modifications to mitigate the health impacts of NO2, a respiratory irritant and strong marker for combustion-related air pollution, in the Portland-Vancouver metropolitan area in northwestern USA. We begin by measuring summer and winter NO2 in the area using a spatially dense network of passive NO 2 samplers. We next develop an annual average model for NO2 based on the observational data, using random forest—for the first time in the realm of urban air pollution—to disentangle the effects of highly correlated LULC variables on ambient NO2 concentrations. We apply this random forest (LURF) model to a 200m spatial grid covering the study area, and use this 200m LURF model to quantify the effect of different urban land use categories on ambient concentrations of NO2. Using the changes in ambient NO2 concentrations resulting from land use modifications as input to BenMAP (a health benefits assessment tool form the US EPA), we assess the NO2-related health impact associated with each land use category and its modifications. We demonstrate how the LURF model can be used to assess the respiratory health benefits of competing land use modifications, including city-wide and local-scale mitigation strategies based on modifying tree canopy and vehicle miles traveled (VMT).
Planting trees is a common land cover modification strategy undertaken by cities to reduce air pollution. Statistical models such as LUR and LURF demonstrate a correlation between tree cover and reduced air pollution, but they cannot demonstrate causation. Hence, we run the atmospheric chemistry and transport model CMAQ to examine to what extent the dry deposition mechanism can explain the reduction of NO2 which statistical models associate with tree canopy.
Results from our research indicate that even though the Portland-Vancouver area is in compliance with the US EPA NO2 standards, ambient concentrations of NO2 still create an annual health burden of at least $40 million USD. Our model suggests that NO2 associated with high intensity development and VMT may be creating an annual health burden of $7 million and $3.3 million USD respectively. Existing tree canopy, on the other hand, is associated with an annual health benefit of $1.4 million USD. LULC modifications can mitigate some fraction of this health burden. A 2% increase in tree canopy across the study area may reduce incidence rates of asthma exacerbation by as much as 7%. We also find that increasing tree canopy is a more effective strategy than reducing VMT in terms of mitigating the health burden of NO 2.
CMAQ indicates that the amount of NO2 removed by dry deposition is an order of magnitude smaller than that predicted by our statistical model. About one-third of the difference can be explained by the lower NO2 values predicted by CMAQ, and one-third may be attributable to parameterization of stomatal uptake.
Yoshida, Yasuko. "Global sources and distribution of atmospheric methyl chloride." Diss., Available online, Georgia Institute of Technology, 2006, 2006. http://etd.gatech.edu/theses/available/etd-06232006-151220/.
Full textRobert Dickinson, Committee Member ; Athanasios Nenes, Committee Member ; David Tan, Committee Member ; Armistead Russell, Committee Member ; Yuhang Wang, Committee Chair.
Powell, James Eckhardt. "Building a Multivariable Linear Regression Model of On-road Traffic for Creation of High Resolution Emission Inventories." PDXScholar, 2017. https://pdxscholar.library.pdx.edu/open_access_etds/3415.
Full textZeng, Tao. "Three-Dimensional Model Analysis of Tropospheric Photochemical Processes in the Arctic and Northern Mid_Latitudes." Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/7648.
Full textZhang, Yan. "The radiative effect of aerosols from biomass burning on the transition from dry to wet season over the amazon as tested by a regional climate model." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/26510.
Full textCommittee Chair: Fu, Rong; Committee Member: Dickinson, Robert E.; Committee Member: Nenes, Athanasios; Committee Member: Webster,Peter J.; Committee Member: Yu, Hongbin. Part of the SMARTech Electronic Thesis and Dissertation Collection.
DeGagne, Julia Lynn. "Acid-Base Equilibria in Organic-Solvent/Water Mixtures and Their Relevance to Gas/Particle Partitioning in the Atmosphere and in Tobacco Smoke." PDXScholar, 2016. http://pdxscholar.library.pdx.edu/open_access_etds/2733.
Full textMazloff, Matthew R. "Production and analysis of a Southern Ocean state estimate." Thesis, Online version, 2006. http://hdl.handle.net/1912/1282.
Full text"September 2006." Bibliography: p. 97-106.
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.
Full textIncludes 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.
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.
Full textCataloged 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.
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.
Full textIncludes 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.
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.
Full textThis 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.
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.
Full text"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.
Habarulema, John Bosco. "A contribution to TEC modelling over Southern Africa using GPS data." Thesis, Rhodes University, 2010. http://hdl.handle.net/10962/d1005241.
Full textHsu, Wei-Ching. "The variability and seasonal cycle of the Southern Ocean carbon flux." Thesis, Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/49079.
Full textZhai, Ping Ph D. Massachusetts Institute of Technology. "Buoyancy-driven circulation in the Red Sea." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/95561.
Full textCataloged from PDF version of thesis.
Includes bibliographical references (pages 175-180).
This thesis explores the buoyancy-driven circulation in the Red Sea, using a combination of observations, as well as numerical modeling and analytical method. The first part of the thesis investigates the formation mechanism and spreading of Red Sea Overflow Water (RSOW) in the Red Sea. The preconditions required for open-ocean convection, which is suggested to be the formation mechanism of RSOW, are examined. The RSOW is identified and tracked as a layer with minimum potential vorticity and maximum chlorofluorocarbon-12. The pathway of the RSOW is also explored using numerical simulation. If diffusivity is not considered, the production rate of the RSOW is estimated to be 0.63 Sv using Walin's method. By comparing this 0.63 Sv to the actual RSOW transport at the Strait of Bab el Mandeb, it is implied that the vertical diffusivity is about 3.4 x10-5 m 2 s-1. The second part of the thesis studies buoyancy-forced circulation in an idealized Red Sea. Buoyancy-loss driven circulation in marginal seas is usually dominated by cyclonic boundary currents on f-plane, as suggested by previous observations and numerical modeling. This thesis suggests that by including [beta]-effect and buoyancy loss that increases linearly with latitude, the resultant mean Red Sea circulation consists of an anticyclonic gyre in the south and a cyclonic gyre in the north. In mid-basin, the northward surface flow crosses from the western boundary to the eastern boundary. The observational support is also reviewed. The mechanism that controls the crossover of boundary currents is further explored using an ad hoc analytical model based on PV dynamics. This ad hoc analytical model successfully predicts the crossover latitude of boundary currents. It suggests that the competition between advection of planetary vorticity and buoyancy-loss related term determines the crossover latitude. The third part of the thesis investigates three mechanisms that might account for eddy generation in the Red Sea, by conducting a series of numerical experiments. The three mechanisms are: i) baroclinic instability; ii) meridional structure of surface buoyancy losses; iii) cross-basin wind fields.
by Ping Zhai.
Ph. D.
Moulton, Melissa (Melissa Root). "Hydrodynamic and morphodynamic responses to surfzone seafloor perturbations." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/104594.
Full textCataloged from PDF version of thesis.
Includes bibliographical references.
Holes and channels were excavated in the surf zone on an ocean beach near Duck, NC, and observations of the subsequent evolution of waves, currents, and the modified seafloor were used to investigate nearshore dynamics. In one set of seafloor perturbation experiments, deep holes with steeply sloping sides were excavated in the inner surfzone seafloor. Observations of the infilling holes were used to make the first field estimates of the surfzone morphological diffusivity, which describes the rate of seafloor smoothing by downslope sediment transport. To improve the temporal resolution of bathymetric estimates, a mapping method was developed to combine infrequent, spatially dense watercraft surveys with continuous, spatially sparse in situ altimeter estimates of the seafloor location. In another set of seafloor perturbation experiments, channels were dredged across the surf zone with the propellers of a landing craft. Alongshore variations in wave breaking caused by the perturbed bathymetry resulted in strong rip currents in the channels under some conditions, whereas alongshore currents bypassed the channels under other conditions. The dynamics of the circulation response for changing wave forcing, bathymetry, and tidal elevation are investigated using the observations, a numerical model, and a parameter based on wave properties and bathymetry.
by Melissa Moulton.
Ph. D.
Schanze, Julian J. (Julian Johannes). "The production of temperature and salinity variance and covariance : implications for mixing." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/79294.
Full textCataloged from PDF version of thesis.
Includes bibliographical references (p. 187-195).
Large-scale thermal forcing and freshwater fluxes play an essential role in setting temperature and salinity in the ocean. A number of recent estimates of the global oceanic freshwater balance as well as the global oceanic surface net heat flux are used to investigate the effects of heat- and freshwater forcing at the ocean surface. Such forcing induces changes in both density and density-compensated temperature and salinity changes ('spice'). The ratio of the relative contributions of haline and thermal forcing in the mixed layer is maintained by large-scale surface fluxes, leading to important consequences for mixing in the ocean interior. In a stratified ocean, mixing processes can be either along lines of constant density (isopycnal) or across those lines (diapycnal). The contribution of these processes to the total mixing rate in the ocean can be estimated from the large-scale forcing by evaluating the production of thermal variance, salinity variance and temperature-salinity covariance. Here, I use new estimates of surface fluxes to evaluate these terms and combine them to generate estimates of the production of density and spice variance under the assumption of a linear equation of state. As a consequence, it is possible to estimate the relative importance of isopycnal and diapycnal mixing in the ocean. While isopycnal and diapycnal processes occur on very different length scales, I find that the surface-driven production of density and spice variance requires an approximate equipartition between isopycnal and diapycnal mixing in the ocean interior. In addition, consideration of the full nonlinear equation of state reveals that surface fluxes require an apparent buoyancy gain (expansion) of the ocean, which allows an estimate of the amount of contraction on mixing due to cabbeling in the ocean interior.
by Julian J. Schanze.
Ph.D.
Zang, Xiaoyun 1971. "Spectral description of low frequency oceanic variability." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/59094.
Full textIncludes bibliographical references (p. 179-187).
A simple dynamic model is used with various observations to provide an approximate spectral description of low frequency oceanic variability. Such a spectrum has wide application in oceanography, including the optimal design of observational strategy for the deployment of floats, the study of Lagrangian statistics and the estimate of uncertainty for heat content and mass flux. Analytic formulas for the frequency and wavenumber spectra of any physical variable, and for the cross spectra between any two different variables for each vertical mode of the simple dynamic model are derived. No heat transport exists in the model. No momentum flux exists either if the energy distribution is isotropic. It is found that all model spectra are related to each other through the frequency and wavenumber spectrum of the stream-function for each mode, ... , where ... represent horizontal wavenumbers, w stands for frequency, n is vertical mode number, and ... are latitude and longitude, respectively. Given ... , any model spectrum can be estimated. In this study, an inverse problem is faced: ... is unknown; however, some observational spectra are available. I want to estimate ... if it exists. Estimated spectra of the low frequency variability are derived from various measurements: (i) The vertical structure of and kinetic energy and potential energy is inferred from current meter and temperature mooring measurements, respectively. (ii) Satellite altimetry measurements produce the geographic distributions of surface kinetic energy magnitude and the frequency and wavenumber spectra of sea surface height. (iii) XBT measurements yield the temperature wavenumber spectra and their depth dependence. (v) Current meter and temperature mooring measurements provide the frequency spectra of horizontal velocities and temperature. It is found that a simple form for ... does exist and an analytical formula for a geographically varying ... is constructed. Only the energy magnitude depends on location. The wavenumber spectral shape, frequency spectral shape and vertical mode structure are universal. This study shows that motion within the large-scale low-frequency spectral band is primarily governed by quasigeostrophic dynamics and all observations can be simplified as a certain function of ... The low frequency variability is a broad-band process and Rossby waves are particular parts of it. Although they are an incomplete description of oceanic variability in the North Pacific, real oceanic motions with energy levels varying from about 10-40% of the total in each frequency band are indistinguishable from the simplest theoretical Rossby wave description. At higher latitudes, as the linear waves slow, they disappear altogether. Non-equatorial latitudes display some energy with frequencies too high for consistency with linear theory; this energy produces a positive bias if a lumped average westward phase speed is computed for all the motions present.
by Xiaoyun Zang.
Ph.D.