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1
Nelkien, Haim. "Thermally driven circulation". Woods Hole, Mass. : Woods Hole Oceanographic Institution, 1987. http://hdl.handle.net/1912/3152.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, and (Ph. D.)--Woods Hole Oceanographic Institution, 1987.Cover title. Includes bibliographical references (leaves 181-186).
2
Jones, Matthew Stephen. "Satellite techniques for studying ocean circulation". Thesis, University College London (University of London), 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.568439.
Testo completo
3
Noble, Taryn Lee. "Southern Ocean circulation and sediment sourcing". Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610485.
Testo completo
4
Villanoy, Cesar Laurel. "Modification of the throughflow water properties in the Indonesian seas". Thesis, The University of Sydney, 1993. https://hdl.handle.net/2123/26591.
Testo completoAbstract (sommario):
Vertical mixing in the Indonesian Seas has been considered to be responsible for the apparent freshness of the throughflow when 'it enters the Indian Down. A three-dimensional primitive equation numerical model of the Indonesian Seas forced with a prescribed throughflow, transport consisting of North Pacific waters, is used to determine local dynamic processes which may modify the characteristics of the throughflow properties. The lack of long-term current measurements in the Indonesian Seas presents some difficulties in determining the certainty of the derived velocity fields. As an alternative, the model temperature and salinity fields are compared to observed hydrographic data which has a relatively better coverage throughout the Indonesian Seas. A 15 Sv net transport through the Indonesian Seas is suggested based on the model’s more realistic reproduction of the hydrographic structure compared to a throughflow with a smaller magnitude. A pure North Pacific source for the throughflow is also not capable of producing the salinity structure in the Banda Sea as suggested by previous studies and the required amount of salt to fit the model salinity structure with observations in the Banda Sea is estimated to be 3.3x10‘3 kg.
Most of the throughflow transport occurs in western boundary flows and is largely topographically controlled. The separation of an upper and lower layer circulation pattern is controlled by the depth of the sill in Makassar Strait. Vertical excursions in the vicinity of this sill seen level of the in model results coincide upper salinity maximum with regions where are found. Seasonal large horizontal gradients at the upwelling and longer residence times due to weaker flows in the Banda Sea results in a more effective mixing of the already weakened salinity structure of the waters from Makassar Strait/Flores Sea. Net heat and freshwater flux estimates also reveal significant departures at 200 up to 100 m between the Pacific inflow and Indian outflow, suggesting the considerable redistribution of heat and salt in the Indonesian Seas.
5
Bean, Mark Shawn. "Modelling the thermohaline circulation". Thesis, University of Southampton, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.242716.
Testo completo
6
Bermejo-Bermejo, Rodolfo. "A finite element model of ocean circulation". Thesis, University of British Columbia, 1986. http://hdl.handle.net/2429/26166.
Testo completoAbstract (sommario):
Preliminary results of a two-layer quasi-geostrophic box model of a wind-driven ocean are presented. The new aspects of this work in relation with conventional eddy models are a finite element formulation of the quasi-geostrophic equations and the use of no-slip boundary condition on the horizontal solid boundaries.
In contrast to eddy resolving models that utilize free-slip boundary conditions our results suggest that the obtention of ocean eddies with the no-slip constraints requires a more restricted range of parameters, in particular much lower horizontal eddy viscosity eddy coefficients AH and higher Froude numbers F₁ and F₂. We show explicitly that a given range of parameters, which is eddy generating when the free-slip boundary condition is used, leads to a quasi-laminar flow in both, upper and lower, layers. An analytical model to interpret the numerical results is put forth. It is an extension of an earlier model of Ierley and Young (1983) in that the relative vorticity terms are of primary importance for the dynamics. Thus, it is shown that the boundary layer dynamics is active in the interior of the second layer, and it can be concluded from our method that for given F₁ and F₂ such that the lower layer geostrophic contours are closed, to the existence of the western boundary layer will prevent the homogenization of the potential vorticity so long as AH is large enough to stabilize the northwestern undulations of the flow.Science, Faculty of
Earth, Ocean and Atmospheric Sciences, Department of
Graduate
7
Mohammad, Rezwan. "Some aspects of the Atlantic ocean circulation". Doctoral thesis, Stockholm : Department of Meteorology, Stockholm University, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-473.
Testo completo
8
McAufield, Ewa Katarzyna. "Lagrangian study of the Southern Ocean circulation". Thesis, University of Cambridge, 2019. https://www.repository.cam.ac.uk/handle/1810/288743.
Testo completoAbstract (sommario):
The Southern Ocean is an important region for the sequestration of heat, carbon dioxide and other tracers. The Southern Ocean circulation is typically described in a circumpolarly averaged sense as a Meridional Overturning Circulation (MOC), but the detailed 3-D pathways that make up this circulation remain poorly understood. We use Lagrangian particle trajectories, obtained from eddy permitting numerical models, to map out and quantify different aspects of the 3-D circulation. We first introduce various definitions used to quantify efficient export from the Antarctic Circumpolar Current (ACC) to the subtropical gyres. Using these definitions, we show that the permanent northward export varies by water mass and occurs in localised regions; with 11 key pathways identified. We then examine the dynamics setting the location and efficiency of the identified pathways, which includes the investigation of the role of diapycnal mixing and the impact of short and long time variability in the flow. Although we show that the flow of particles in the 3-D model is predominantly isopycnal, we find that particles that are forced to remain on isopycnals lead to approx. 60% lower export (mainly via three pathways) than identical releases where the diapycnal component of advection is included. Enhanced upward mixing near rough topography, and downward mixing in the southeast Pacific, were shown to be mostly responsible for the export. In addition, we show that most of the export pathways are mainly influenced by timescales from 90 days to 20 years, which suggests that mesoscale eddies are not the leading-order importance in the northward export from the ACC to the subtropical gyres. However, we also find that mesoscale eddies and the mean-ACC flow play a significant role in setting the export from the ACC in some pathways. These results highlight the role of temporal variability and vertical transport in enhancing the northward flow from the ACC by allowing transport across barotropic streamlines and onto more efficiently exporting isopycnals. In addition, the asymmetrical response of the studied quantities emphasises the importance of the three dimensions in understanding the dynamics driving the overturning circulation. We also demonstrated that the annually repeating velocity fields, which are commonly used for trajectory calculations, increase the diapycnal transport of particles and as a consequence, increase the overall 20-year northward export from the ACC by approx. 10%. In the study of the meridional overturning circulation, we diagnose the geographical distribution of the streamwise averaged diffusivity calculated from meridional displacements of the Lagrangian particles. We examine streamwise averaging using both latitude and equivalent latitude and argue that the latter gives a more useful measure. Reconciling tracer and particle horizontal diffusivities, we show that in the ACC, the average diffusivity peaks between 1500m and 2500m with an average value of 1500 m$^{2}$/s and that it is highest near the topographic features. We compare the exact diffusivity and its approximation to show that an assumption of time homogeneity does not hold and therefore that standard expressions for diffusivity that assume time homogeneity are of limited usefulness. Finally, we use the calculated trajectories to provide a streamwise averaged 2-D advection-diffusion model of the Southern Ocean MOC and then examine the extent to which this 2-D model can capture the overall effect of the actual 3-D transport.
9
Wang, Xiaoli Ph D. Massachusetts Institute of Technology. "Global thermohaline circulation and ocean-atmosphere coupling". Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/58357.
Testo completo
10
Li, Hui. "Numerical modeling of South China Sea circulation /". View abstract or full-text, 2005. http://library.ust.hk/cgi/db/thesis.pl?AMCE%202005%20LI.
Testo completo
11
Davidson, Fraser. "Wind driven circulation in Trinity and Conception Bays /". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape9/PQDD_0020/NQ47495.pdf.
Testo completo
12
Moore, A. M. "Data assimilation in ocean models". Thesis, University of Oxford, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.375276.
Testo completo
13
Roberts, Natalie Laura. "Investigating North Atlantic ocean circulation using radiogenic isotopes". Thesis, University of Cambridge, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.607824.
Testo completo
14
Cameron, Adele Jane. "Ocean circulation during Eocene extreme "greenhouse" climatic warmth". Thesis, Open University, 2016. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.699820.
Testo completoAbstract (sommario):
The Early Eocene (47-56 Ma) 'greenhouse' climate represented the warmest climatic conditions witnessed in the last 90 million years, with peak Eocene warmth (the Early Eocene Climatic optimum, EECO) occurring around 50-52 Ma (Sexton et al. 2006; Bijl et al. 2009; Zachos et al. 2008; Littler et al. 2014) with subsequent global cooling thereafter (Sexton et al. 2006; Zachos et al. 2008). Ocean circulation plays a critical role in redistributing thermal energy across the planet and providing ventilation to the deepest parts of the ocean. Understanding how it may have operated in a globally warm world with little equator-to-pole gradients is paramount to understanding how it may respond to increasing temperatures today. The prevailing view of the early Eocene ocean was that deep-water formation was confined to the Southern Ocean, with little or no deep-water formation in the North Atlantic, unlike today. This study explores whether there is evidence for deep-water formation in the high latitude North Atlantic during the extreme climatic warmth of the early Eocene and its stability across transient climatic excursions. It also explores the strength and vigour of ocean circulation and whether this was influenced by the global decline in temperature following early Eocene peak-warmth. It utilises the neodymium isotopic signature of fossilised fish teeth (εNd) that is widely utilised to trace the movements of deep-water masses and can be used to reconstruct paleooceanic circulation along with detrital εNd that is an indicator of sediment provenance. It combines these with fish tooth rare earth element concentrations and sediment core XRF. Four key locations are utilised. Two on the Newfoundland margin in the West North Atlantic, and one from the high North Atlantic in the Labrador Sea, both idea1 locations to identify the potential outputs of North Atlantic deep-water formation. The fourth site is Demerara Rise in the Equatorial Atlantic, chosen to monitor changes in the dominant source of deep-water sources from the North or the South.
15
Sugimura, Peter Joseph. "Arctic Ocean circulation in an idealized numerical model". Thesis, Online version of original thesis, 2008. http://hdl.handle.net/1912/2501.
Testo completo
16
Senan, Retish. "Intraseasonal Variability Of The Equatorial Indian Ocean Circulation". Thesis, Indian Institute Of Science, 2004. https://etd.iisc.ac.in/handle/2005/297.
Testo completoAbstract (sommario):
Climatological winds over the equatorial Indian Ocean (EqlO) are westerly most of the year. Twice a year, in April-May ("spring") and October-December ("fall"), strong, sustained westerly winds generate eastward equatorial jets in the ocean. There are several unresolved issues related to the equatorial jets. They accelerate rapidly to speeds over lms"1 when westerly wind stress increases to about 0.7 dyne cm"2 in spring and fall, but decelerate while the wind stress continues to be westerly; each jet is followed by westward flow in the upper ocean lasting a month or longer.
In addition to the semi-annual cycle, the equatorial winds and currents have strong in-traseasonal fluctuations. Observations show strong 30-60 day variability of zonal flow, and suggest that there might be variability with periods shorter than 20 days in the central EqlO. Observations from moored current meter arrays along 80.5°E south of Sri Lanka showed a distinct 15 day oscillation of equatorial meridional velocity (v) and off-equatorial zonal velocity (u). Recent observations from current meter moorings at the equator in the eastern EqlO show continuous 10-20 day, or biweekly, oscillations of v. The main motivation for the present study is to understand the dynamics of intraseasonal variability in the Indian Ocean that has been documented in the observational literature.
What physical processes are responsible for the peculiar behavior of the equatorial jets? What are the relative roles of wind stress and large scale ocean dynamics? Does intraseasonal variability of wind stress force intraseasonal jets? What is the structure and origin of the biweekly variability? The intraseasonal and longer timescale variability of the equatorial Indian Ocean circulation is studied using an ocean general circulation model (OGCM) and recent in
Abstract ii
situ observations. The OGCM simulations are validated against other available observations. In this thesis, we document the space-time structure of the variability of equatorial Indian Ocean circulation, and attempt to find answers to some of the questions raised above.
The main results are based on OGCM simulations forced by high frequency reanalysis and satellite scatterometer (QuikSCAT) winds. Several model experiments with idealized winds are used to interpret the results of the simulations. In addition to the OGCM simulations, the origin of observed intraseasonal anomalies of sea surface temperature (SST) in the eastern EqlO and Bay of Bengal, and related air-sea interaction, are investigated using validated satellite data.
The main findings of the thesis can be summarized as:
• High frequency accurate winds are required for accurate simulation of equatorial Indian
Ocean currents, which have strong variability on intraseasonal to interannual time scales.
• The variability in the equatorial waveguide is mainly driven by variability of the winds;
there is some intraseasonal variability near the western boundary and in the equatorial
waveguide due to dynamic instability of seasonal "mean" flows.
• The fall equatorial jet is generally stronger and longer lived than the spring jet; the fall
jet is modulated on intraseasonal time scales. Westerly wind bursts can drive strong
intraseasonal equatorial jets in the eastern EqlO during the summer monsoon.
• Eastward equatorial jets create a westward zonal pressure gradient force by raising sea
level, and deepening the thermocline, in the east relative to the west. The zonal pressure
force relaxes via Rossby wave radiation from the eastern boundary.
• The zonal pressure force exerts strong control on the evolution of zonal flow; the decel
eration of the eastward jets, and the subsequent westward flow in the upper ocean in the
presence of westerly wind stress, is due to the zonal pressure force.
• Neither westward currents in the upper ocean nor subsurface eastward flow (the ob
served spring and summer "undercurrent") requires easterly winds; they can be gener
ated by equatorial adjustment due to Kelvin (Rossby) waves generated at the western
(eastern) boundary.
• The biweekly variability in the EqlO is associated with forced mixed Rossby-gravity
(MRG) waves generated by intraseasonal variability of winds. The biweekly MRG wave in has westward and upward phase propagation, zonal wavelength of 3000-4500 km and phase speed of 4 m s"1; it is associated with deep off equatorial upwelling/downwelling.
Intraseasonal SST anomalies are forced mainly by net heat flux anomalies in the central and eastern EqlO; the large northward propagating SST anomalies in summer in the Bay of Bengal are due to net heat flux anomalies associated with the monsoon active-break cycle. Coherent variability in the atmosphere and ocean suggests air-sea interaction.
17
Senan, Retish. "Intraseasonal Variability Of The Equatorial Indian Ocean Circulation". Thesis, Indian Institute Of Science, 2004. http://hdl.handle.net/2005/297.
Testo completoAbstract (sommario):
Climatological winds over the equatorial Indian Ocean (EqlO) are westerly most of the year. Twice a year, in April-May ("spring") and October-December ("fall"), strong, sustained westerly winds generate eastward equatorial jets in the ocean. There are several unresolved issues related to the equatorial jets. They accelerate rapidly to speeds over lms"1 when westerly wind stress increases to about 0.7 dyne cm"2 in spring and fall, but decelerate while the wind stress continues to be westerly; each jet is followed by westward flow in the upper ocean lasting a month or longer.
In addition to the semi-annual cycle, the equatorial winds and currents have strong in-traseasonal fluctuations. Observations show strong 30-60 day variability of zonal flow, and suggest that there might be variability with periods shorter than 20 days in the central EqlO. Observations from moored current meter arrays along 80.5°E south of Sri Lanka showed a distinct 15 day oscillation of equatorial meridional velocity (v) and off-equatorial zonal velocity (u). Recent observations from current meter moorings at the equator in the eastern EqlO show continuous 10-20 day, or biweekly, oscillations of v. The main motivation for the present study is to understand the dynamics of intraseasonal variability in the Indian Ocean that has been documented in the observational literature.
What physical processes are responsible for the peculiar behavior of the equatorial jets? What are the relative roles of wind stress and large scale ocean dynamics? Does intraseasonal variability of wind stress force intraseasonal jets? What is the structure and origin of the biweekly variability? The intraseasonal and longer timescale variability of the equatorial Indian Ocean circulation is studied using an ocean general circulation model (OGCM) and recent in
Abstract ii
situ observations. The OGCM simulations are validated against other available observations. In this thesis, we document the space-time structure of the variability of equatorial Indian Ocean circulation, and attempt to find answers to some of the questions raised above.
The main results are based on OGCM simulations forced by high frequency reanalysis and satellite scatterometer (QuikSCAT) winds. Several model experiments with idealized winds are used to interpret the results of the simulations. In addition to the OGCM simulations, the origin of observed intraseasonal anomalies of sea surface temperature (SST) in the eastern EqlO and Bay of Bengal, and related air-sea interaction, are investigated using validated satellite data.
The main findings of the thesis can be summarized as:
• High frequency accurate winds are required for accurate simulation of equatorial Indian
Ocean currents, which have strong variability on intraseasonal to interannual time scales.
• The variability in the equatorial waveguide is mainly driven by variability of the winds;
there is some intraseasonal variability near the western boundary and in the equatorial
waveguide due to dynamic instability of seasonal "mean" flows.
• The fall equatorial jet is generally stronger and longer lived than the spring jet; the fall
jet is modulated on intraseasonal time scales. Westerly wind bursts can drive strong
intraseasonal equatorial jets in the eastern EqlO during the summer monsoon.
• Eastward equatorial jets create a westward zonal pressure gradient force by raising sea
level, and deepening the thermocline, in the east relative to the west. The zonal pressure
force relaxes via Rossby wave radiation from the eastern boundary.
• The zonal pressure force exerts strong control on the evolution of zonal flow; the decel
eration of the eastward jets, and the subsequent westward flow in the upper ocean in the
presence of westerly wind stress, is due to the zonal pressure force.
• Neither westward currents in the upper ocean nor subsurface eastward flow (the ob
served spring and summer "undercurrent") requires easterly winds; they can be gener
ated by equatorial adjustment due to Kelvin (Rossby) waves generated at the western
(eastern) boundary.
• The biweekly variability in the EqlO is associated with forced mixed Rossby-gravity
(MRG) waves generated by intraseasonal variability of winds. The biweekly MRG wave in has westward and upward phase propagation, zonal wavelength of 3000-4500 km and phase speed of 4 m s"1; it is associated with deep off equatorial upwelling/downwelling.
Intraseasonal SST anomalies are forced mainly by net heat flux anomalies in the central and eastern EqlO; the large northward propagating SST anomalies in summer in the Bay of Bengal are due to net heat flux anomalies associated with the monsoon active-break cycle. Coherent variability in the atmosphere and ocean suggests air-sea interaction.
18
Friedrichs, Marjorie Anne MacWhorter. "Meridional circulation in the tropical North Atlantic /". Online version of thesis as technical report, 1993. http://hdl.handle.net/1912/616.
Testo completo
19
Robinson, Natalie J. "An oceanographic study of the cavity beneath the McMurdo Ice Shelf, Antarctica : a thesis submitted to the Victoria University of Wellington in fulfilment of the requirements for the degree of Master of Science in Geophysics /". ResearchArchive@Victoria e-Thesis, 2005. http://hdl.handle.net/10063/48.
Testo completo
20
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.
Testo completo
21
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.
Testo completo
22
Faria, Antonio Fernando Garcez. "A simple quasi-three dimensional model of longshore currents over arbitrary profile". Thesis, [Monterey, Calif. : Naval Postgraduate School], 1995. http://catalog.hathitrust.org/api/volumes/oclc/35646712.html.
Testo completo
23
Straub, David Nicholas. "Some effects of large scale topography in a baroclinic ocean /". Thesis, Connect to this title online; UW restricted, 1990. http://hdl.handle.net/1773/11003.
Testo completo
24
Springer, Scott R. "Dynamics of western boundary currents in simple models of low-latitude circulations /". Thesis, Connect to this title online; UW restricted, 1994. http://hdl.handle.net/1773/11010.
Testo completo
25
Dixon, Jeffrey S. "The circulation and variability in the western Arctic Ocean : model results". Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2003. http://library.nps.navy.mil/uhtbin/hyperion-image/03sep%5FDixon.pdf.
Testo completoAbstract (sommario):
Thesis (M.S. in Meteorology and Physical Oceanography)--Naval Postgraduate School, September 2003.Thesis advisor(s): Wieslaw Maslowski, Stephen Okkonen. Includes bibliographical references (p. 103-107). Also available online.
26
Xu, Weimin 1965. "A C-grid ocean circulation model and eddy simulation". Thesis, McGill University, 1994. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=28555.
Testo completoAbstract (sommario):
We have developed a C-grid primitive equation ocean general circulation model with Cartesian and $ beta$-plane geometry. Temperature is the only state variable. The C-grid gives better results than the B-grid in reproducing the growth rates of linear unstable modes of the Raileigh-Benard equations. A semi-implicit scheme is used to treat the Coriolis term, which is important for efficient integration in coarse resolution large scale modelling studies. A new viscosity term which has a damping effect only on the divergence field associated with gravity waves is also introduced. The model can reproduce sucessfully most of the coarse resolution model results of other studies. The biharmonic and Smagorinsky frictional parameterizations are not as efficient as our scheme in eliminating noise in the vertical velocity field.This model is used to study the effects of no slip or free slip boundary conditions on the energetics and northward heat transport in the eddy resolving regime. The divergence dissipation term is used only in the subpolar gyre region, where the Rossby radius of deformation is not well resolved. This term has little effect elsewhere in the model domain. The eddy energetics is sensitive to the lateral boundary conditions used. Increasing vertical resolution can increase the basin average and midlatitude free jet energetics, but its effect is much less than that due to different lateral boundary conditions. The northward heat transports by eddies and mean flow are also examined.
The effect of a restoring condition is compared to a zero heat capacity atmospheric model as a surface boundary condition for the eddy resolving model. Two significant differences are found with the use of the zero heat capacity atmospheric model. First, both eddy and mean kinetic energy near the midlatitude free jet are increased. Second, the vertical profiles of standard temperature deviation (eddy available potential energy) become more realistic.
An analysis of the mean advection and eddy convergence terms in the mean momentum equations shows that both enhanced horizontal resolution and the zero heat capacity atmospheric model can increase the midlatitude jets in the surface and deep layers. The eddy momentum convergence in midlatitudes is the dominant ageostrophic contribution to both the mean zonal flow and its variation. The mean advection is consistently less important. The effects of eddies have been further investigated by using the mean vorticity equation. The results again show that the eddy convergence term is the most important ageostrophic term, and can be as important as the geostrophic effect. The mean vorticity equation budget shows a similar sensitivity to the horizontal resolution and zero heat capacity atmospheric model as for the momentum equations.
27
Martin, Matthew J. "Data assimilation in ocean circulation models with systematic errors". Thesis, University of Reading, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365425.
Testo completo
28
Mitsis, Christos. "Lagrangian studies, circulation and mixing in the Southern Ocean". Thesis, University of East Anglia, 2013. https://ueaeprints.uea.ac.uk/45250/.
Testo completoAbstract (sommario):
Oceans play a vital role as one of the major components of Earth's climate system. The study of oceanic processes and the complexity inherent in dynamic ows is essential for understanding their regulatory character on the climate's variability. A key region for the study of such intrinsic oceanic variability is the Southern Ocean. In the form of a wind-driven, zonally unbounded, strong eastward ow, the Antarctic Circumpolar Current (ACC) circumnavigates the Antarctic continent connecting each of the ocean basins. The dynamics of the ACC, which is characterised by the absence of land barriers, apart from when crossing Drake Passage, have long been a topic of debate [Rintoul et al., 2001]. The main interests of this study focus on inferring and mapping the dynamic variability the ACC exhibits by means of transient disturbances [Hughes, 2005] (such as mesoscale eddies) and subsequent mixing from Lagrangian trajectories. The distribution of eddy transport and intensity, the mixing of conservative quantities and ow dynamics through to the interaction of eddy kinetic energy, mean ow and topography are examined. The sparseness of observations in the Southern Ocean and the necessity to understand the role of the oceanic circulation in the climate by a holistic approach highlights computational ocean circulation models as indispensable. In the context of this study, output from the run401 of the Ocean Circulation and Climate Advance Model (OCCAM) 1/12� ocean model, developed at the U.K. National Oceanography Centre, is utilised. In order to deduce the temporal and spatial variability of the ow dynamics, as well as its vertical distribution, simulation of monthly releases of passive particles using di�erent schemes (i.e. cluster or linear alignment) on isobaric and isoneutral surfaces was conducted. An analysis of the Lagrangian trajectories reveals the characteristics of the dynamics that control the ow and depict regions of enhanced eddy activity and mixing. The model's ability to simulate real oceanic ows is established through comparison with a purposeful release of the tracer CF3SF5, which is conducted as part of the DIMES experiment (http://dimes.ucsd.edu/). We �nd that topography plays a fundamental role in the context of Southern Ocean mixing through the association of high EKE regions, where the interaction of vortical elements and multi �lamented jets in non-parallel ows supports an e�ective mechanism for eddy stirring, resulting in the enhanced dispersion of particles. Suppression of mixingin regions where the ow is delineated by intensi�ed and coherent, both in space and time, jets (strong PV gradients) signifying the separation of the ow in di�erentiated kinematic environments, is illustrated. The importance of a local approximation to mixing instead of the construction of zonal averages is presented. We present the caveats of classical di�usion theory in the presence of persistent structures and �nd that values of 1000-2000 m2 s
29
Shepherd, James Robert. "Modelling ocean circulation with large-scale semi-geostrophic equations". Thesis, Imperial College London, 1999. http://hdl.handle.net/10044/1/51559.
Testo completoAbstract (sommario):
The Large-scale Semi-Geostrophic Equations (LSGE, Salmon[73]) are three-dimensional equations valid for an ocean with a rigid lid and length scales much greater than the internal deformation radius (about 40km). In this thesis I reduce the LSGE to a pair of two-dimensional equations via the ansatz that the temperature is independent of the vertical co-ordinate. I refer to these as the Depth-Independent-Temperature (DIT) equations. Whilst this is regarded as a paradigm for the entire ocean, the reduction is similar in spirit to that utilised by many authors for modelling the mixed layer of the ocean. The equations of this thesis differ from the work of such mixed layer models because they involve no ad hoc vertical averaging and so solutions to these equations are also solutions to the full three-dimensional LSGE. The DIT are arguably the simplest equations for ocean circulation to include the effects of inertia, topography and baroclinicity. The DIT are studied both analytically and numerically. It is shown that the model exhibits baroclinic instabilities and analogies are drawn with classical Rayleigh-Benard convection. It is shown that both viscosity and thermal diffusivity are required to avert an ultra-violet catastrophe. Numerical simulations of turbulence demonstrate that the long-time behaviour resembles barotropic flow and that the temperature is reduced to the role of a passive tracer unless large-scale thermal structure is imposed externally on the flow. One of the advantages of the current model over the more widely used quasi-geostrophic models is that there is no restriction on the vertical extent of the bottom topography. This allows the simulation of idealised oceanic basin circulations in which the depth of the ocean vanishes smoothly at boundaries. These ocean simulations are used to study the sensitivity of the model to the Rossby Number, Ekman Number and forcing parameters. Comparison of a barotropic and a DIT ocean reveals the influence of baroclinicity in the latter model. Characteristic features of the Gulf Stream such as meandering, recirculation gyres and the shedding of warm and cold core rings are reproduced by the DIT model and the simple nature of the equations permits an interpretation of these features.
30
Chechelnitsky, Michael Y. (Michael Yurievich) 1972. "Adaptive error estimation in linearized ocean general circulation models". Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/58516.
Testo completoAbstract (sommario):
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), 1999.Includes bibliographical references (p. 206-211).
Data assimilation methods, such as the Kalman filter, are routinely used in oceanography. The statistics of the model and measurement errors need to be specified a priori. In this study we address the problem of estimating model and measurement error statistics from observations. We start by testing the Myers and Tapley (1976, MT) method of adaptive error estimation with low-dimensional models. We then apply the MT method in the North Pacific (5°-60° N, 132°-252° E) to TOPEX/POSEIDON sea level anomaly data, acoustic tomography data from the ATOC project, and the MIT General Circulation Model (GCM). A reduced state linear model that describes large scale internal (baroclinic) error dynamics is used. The MT method, closely related to the maximum likelihood methods of Belanger (1974) and Dee (1995), is shown to be sensitive to the initial guess for the error statistics and the type of observations. It does not provide information about the uncertainty of the estimates nor does it provide information about which structures of the error statistics can be estimated and which cannot. A new off-line approach is developed, the covariance matching approach (CMA), where covariance matrices of model-data residuals are "matched" to their theoretical expectations using familiar least squares methods. This method uses observations directly instead of the innovations sequence and is shown to be related to the MT method and the method of Fu et al. (1993). The CMA is both a powerful diagnostic tool for addressing theoretical questions and an efficient estimator for real data assimilation studies. It can be extended to estimate other statistics of the errors, trends, annual cycles, etc. Twin experiments using the same linearized MIT GCM suggest that altimetric data are ill-suited to the estimation of internal GCM errors, but that such estimates can in theory be obtained using acoustic data. After removal of trends and annual cycles, the low frequency /wavenumber (periods> 2 months, wavelengths> 16°) TOPEX/POSEIDON sea level anomaly is of the order 6 cm2. The GCM explains about 40% of that variance. By covariance matching, it is estimated that 60% of the GCM-TOPEX/POSEIDON residual variance is consistent with the reduced state linear model. The CMA is then applied to TOPEX/POSEIDON sea level anomaly data and a linearization of a global GFDL GCM. The linearization, done in Fukumori et al.(1999), uses two vertical mode, the barotropic and the first baroclinic modes. We show that the CMA method can be used with a global model and a global data set, and that the estimates of the error statistics are robust. We show that the fraction of the GCMTOPEX/ POSEIDON residual variance explained by the model error is larger than that derived in Fukumori et al.(1999) with the method of Fu et al.(1993). Most of the model error is explained by the barotropic mode. However, we find that impact of the change in the error statistics on the data assimilation estimates is very small. This is explained by the large representation error, i.e. the dominance of the mesoscale eddies in the TIP signal, which are not part of the 20 by 10 GCM. Therefore, the impact of the observations on the assimilation is very small even after the adjustment of the error statistics. This work demonstrates that simultaneous estimation of the model and measurement error statistics for data assimilation with global ocean data sets and linearized GCMs is possible. However, the error covariance estimation problem is in general highly underdetermined, much more so than the state estimation problem. In other words there exist a very large number of statistical models that can be made consistent with the available data. Therefore, methods for obtaining quantitative error estimates, powerful though they may be, cannot replace physical insight. Used in the right context, as a tool for guiding the choice of a small number of model error parameters, covariance matching can be a useful addition to the repertory of tools available to oceanographers.
by Michael Y. Chechelnitsky.
Ph.D.
31
Rodrigues, Regina Rodrigues. "An observational and numerical study of the South Atlantic circulation /". View online ; access limited to URI, 2004. http://0-wwwlib.umi.com.helin.uri.edu/dissertations/dlnow/3160038.
Testo completo
32
Zhang, Zhenxi. "Modeling downwelling circulation over continental shelf in the northern South China Sea /". View abstract or full-text, 2009. http://library.ust.hk/cgi/db/thesis.pl?AMCE%202009%20ZHANG.
Testo completo
33
Smith, Robin Stuart. "Ocean circulation and climate dynamics under idealised continental configurations in a coupled ocean-atmosphere model". Thesis, University of Southampton, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.402045.
Testo completo
34
Woo, Lai Mun. "Summer circulation and water masses along the West Australian coast". University of Western Australia. Centre for Water Research, 2005. http://theses.library.uwa.edu.au/adt-WU2005.0122.
Testo completoAbstract (sommario):
The Gascoyne continental shelf is located along the north-central coastline of Western Australia between latitudes 21° and 28°S. This study presents CTD and ADCP data together with concurrent wind and satellite imagery, to provide a description of the summer surface circulation pattern along the continental margin, and the hydrography present in the upper 1km of ocean, between latitudes 21° and 35°S. It also discusses the outcome of a numerical modelling study that examined the physical factors contributing to a bifurcation event persistently observed in satellite imagery at Point Cloates. The region comprises a complex system of four surface water types and current systems. The Leeuwin Current dominated the surface flow, transporting lower salinity, warmer water poleward along the shelf-break, and causing downwelling. Its signature ‘aged’ from a warm (24.7°C), lower salinity (34.6) water in the north to a cooler (21.9°C), more saline (35.2) water in the south, as a result of 2-4Sv geostrophic inflow of offshore waters. The structure and strength of the current altered with changing bottom topographies. The Ningaloo Current flowed along the northernmost inner coast of the Gascoyne shelf, carrying upwelled water and re-circulated Leeuwin Current water from the south. Bifurcation of the Ningaloo Current was seen south of the coastal promontory at Point Cloates. Numerical modelling demonstrated a combination of southerly winds and coastal and bottom topography off Point Cloates to be responsible for the recirculation, and indicated that the strength of southerly winds affect recirculation. Hypersaline Shark Bay outflow influenced shelf waters at the Bay’s mouth and to the south of the Bay. The Capes Current, a wind-driven current from south of the study region was identified as a cooler, more saline water mass flowing northward. Results of the hydrography study show five different water masses present in the upper-ocean. Their orientations were affected by the geopotential gradient driven Leeuwin Current/Undercurrent system at the continental margin. The Leeuwin Undercurrent was found at the shelf-slope, carrying (>252 μM/L) Subantarctic Mode Water at a depth of 400m
35
Goodman, Paul Joseph. "The role of North Atlantic Deep Water formation in the thermohaline circulation /". Thesis, Connect to this title online; UW restricted, 2000. http://hdl.handle.net/1773/10025.
Testo completo
36
Johnson, Gregory Conrad. "Near-equatorial deep circulation in the Indian and Pacific Oceans /". Thesis, Woods Hole, Mass. : Woods Hole Oceanographic Institution, 1990. http://hdl.handle.net/1912/2637.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Woods Hole Oceanographic Institution and Massachusetts Institute of Technology, 1990.Funding was provided by the Office of Naval Research and a Secretary of the Navy Graduate Fellowship in Oceanography. References : p. 117-121.
37
Zika, Jan David Climate & Environmental Dynamics Laboratory Faculty of Science UNSW. "Quantifying ocean mixing from hydrographic data". Awarded by:University of New South Wales. Climate & Environmental Dynamics Laboratory, 2010. http://handle.unsw.edu.au/1959.4/44872.
Testo completoAbstract (sommario):
The relationship between the general circulation of the ocean and, along-isopycnal and vertical mixing is explored. Firstly, advection down isopycnal tracer gradients is related to mixing in specific regions of the ocean. Secondly, a general inverse method is developed for estimating both mixing and the general circulation. Two examples of down gradient advection are explored. Firstly the region of Mediterranean outflow in the North Atlantic. Given a known transport of warm salty water out of the Mediterranean Sea and the mean hydrography of the eastern North Atlantic, the vertical structure of the along-isopycnal mixing coefficient, K, and the vertical mixing coefficient, D, is revealed. Secondly, the Southern Ocean Meridional Overturning Circulation, SMOC, is investigated. There, relatively warm salty water is advected southward, along-isopycnals, toward fresher cooler surface waters. The strength and structure of the SMOC is related to K and D by considering advection down along-isopycnal gradients of temperature and potential vorticity. The ratio of K to D and their magnitudes are identified. A general tool is developed for estimating the ocean circulation and mixing; the \textit{tracer-contour inverse method}. Integrating along contours of constant tracer on isopycnals, differences in a geostrophic streamfunction are related to advection and hence to mixing. This streamfunction is related in the vertical, via an analogous form of the depth integrated thermal wind equation. The tracer-contour inverse method combines aspects of the box, beta spiral and Bernoulli methods. The tracer-contour inverse method is validated against the output of a layered model and against in-situ observations from the eastern North Atlantic. The method accurately reproduces the observed mixing rates and reveals their vertical structure.
38
Schopp, Richard. "Circulation de grande échelle à mi-profondeur dans l'Atlantique nord-est : Etude de processus". Brest, 1987. http://www.theses.fr/1987BRES2015.
Testo completoAbstract (sommario):
Plusieurs mecanismes sont proposes pour expliquer le courant vers le nord observe a mi-profondeur dans le bassin est du nord atlantique. Ces mecanismes sont bases sur les deux forcages pouvant mettre en mouvement l'ocean: d'une part le forcage par le vent et d'autre part le forcage thermodynamique. Dans le premier mecanisme, reposant sur les hypotheses de la thermocline ventilee, la couche a mi-profondeur dans le tourbillon subtropical est mise en mouvement par la suction d'ekman dans le tourbillon subpolaire oa cette couche affleure la surface. Le passage d'eau necessaire pour aller d'un tourbillon a l'autre, revelant une condition de bloquage d'une onde de rossby barocline non-dispersive par un courant zonal barotrope a la jonction des deux tourbillons, permet de realiser un ajustement temporel de la solution stationnaire trouvee a partir d'un ocean au repos. Un modele ventile a fond plat a egalement ete realise dans le tourbillon subtropical mettant en evidence d'autres caracteristiques dans l'atlantique nord-est. Le deuxieme volet de l'etude concerne principalement le forcage pouvant resulter de processus doubles diffusifs a la base de l'intrusion mediterraneenne. Ce mecanisme permet au sel de chuter de creer localement des gradients horizontaux de densite, qui, a leur tour, permettent de generer des cisaillements de courant geostrophiques. Un courant vers le nord, base sur cette dynamique, est realise par l'injection d'une source de sel sur le bord est de ce bassin simulant l'apport par la mediterranee
39
Cummins, Patrick F. "A quasi-geostrophic circulation model of the Northeast Pacific Ocean". Thesis, University of British Columbia, 1989. http://hdl.handle.net/2429/29082.
Testo completoAbstract (sommario):
A limited-area quasi-geostrophic numerical model with mesoscale resolution is developed to study the circulation in the Northeast Pacific Ocean. The model domain extends from the British Columbia/Alaska coast out to 170°W and down to 45°N, and incorporates the coastline geometry and bottom topography of the region.
In a benchmark experiment, the circulation is driven with a steady, climatological wind stress curl field. Statistical properties of the solution are determined from a long-term integration and compared with observations from the Gulf of Alaska. The cyclonic circulation of the model basin contains the analogue of a meandering Alaska Current. At the head of the Gulf, this current flows into an intense boundary current corresponding to the Alaskan Stream. Within the model Alaska Current, anticyclonic closed streamline features are occasionally generated which are representative of the Sitka Eddy, ln the upstream region, the model Alaskan Stream displays large amplitude aperiodic meanders, while, in the downstream region, the boundary current separates and is subject to smaller amplitude lateral meandering due to topographic waves. The occurrence of perturbations with similar characteristics in the Alaskan Stream has recently been verified in satellite AVHRR imagery.
The model is also used to examine the effects of bottom topography and seasonal wind forcing on the circulation of the subpolar gyre. The characteristics of the Alaskan Stream are shown to depend crucially on the presence of the Aleutian Trench. In an experiment with a flat bottom and steady forcing, the most energetic signal is due to mesoscale eddies with a 100 day period associated with barotropic wave propagation along the Aleutian arc. Bottom topography eliminates this signal by inhibiting the nonlinear transfer of energy between the first baroclinic and the barotropic mode, thereby stabilizing the model Alaskan Stream to baroclinic instability. Experiments with a climatological seasonal cycle in the wind field show that the bottom topography has an important influence in moderating the intensity of the seasonal response. This result is used to explain the discrepancy between observations of seasonal variability in the volume transport of the Alaskan Gyre and the transport obtained in previous numerical modelling studies.Science, Faculty of
Earth, Ocean and Atmospheric Sciences, Department of
Graduate
40
Cirano, Mauro School of Mathematics UNSW. "Wintertime Circulation within the Southeast Indian Ocean: a Numerical Study". Awarded by:University of New South Wales. School of Mathematics, 2000. http://handle.unsw.edu.au/1959.4/17820.
Testo completoAbstract (sommario):
A numerical study is made of the wintertime circulation within the Southeast Indian Ocean (SEIO). The downwelling favourable winds result in a continuous eastward Coastal Current (CC) extending from Cape Leeuwin to the eastern coast of Tasmania, where it forms a confluence with the south branch of the East Australian Current. An additional forcing mechanism for the CC is the Leeuwin Current in the western part of the domain. The study here is divided in two parts: (1) available data and the wintertime averaged results from the Ocean Circulation and Climate Advanced Model (OCCAM) are analysed to provide a first order description of the large-scale circulation; (2) a high resolution model (Princeton Ocean Model) is nested within OCCAM to examine the shelf-slope circulation within the eastern SEIO. The nested model is forced with climatological monthly average winds and several experiments were run to simulate the effects of surface fluxes of density, enhanced bottom friction and stronger winds. In summary, the shelf-slope circulation is governed by a surface south-eastward CC that carries around 2 Sv and reaches velocities of up to 50 cm/s, where the shelf is narrowest. The core of the current is generally constrained to the shelf-break region. Zonal winds and geostrophic control of the CC lead to a transport of 1 Sv through Bass Strait and a north-eastward jet that is directed into the strait between King Is. and Tasmania. Further south, the CC is poleward and known as the Zeehan Current (ZC). Between Cape Leeuwin and Tasmania and over the slope region, a westward current (the Flinders Current) is found at depths of 500-1000 m and has an associated transport of 5-7 Sv. The current is shown to result from a northward Sverdrup transport in the deep ocean. Meso-scale eddies are shown to result from baroclinic instability and have wavelengths of around 250 km and transports of 3-4 Sv, and can dominate the slope circulation. A comparison of the numerical results is also made with two current meter data sets and results show an interannual variability in the ZC strength, that is probably related to ENSO.
41
Kiss, Andrew Elek, e Andrew Kiss@anu edu au. "Dynamics of laboratory models of the wind-driven ocean circulation". The Australian National University. Research School of Earth Sciences, 2001. http://thesis.anu.edu.au./public/adt-ANU20011018.115707.
Testo completoAbstract (sommario):
This thesis presents a numerical exploration of the dynamics governing
rotating flow driven by a surface stress in the " sliced cylinder " model
of Pedlosky & Greenspan (1967) and Beardsley (1969), and its close
relative, the " sliced cone " model introduced by Griffiths & Veronis
(1997). The sliced cylinder model simulates the barotropic wind-driven
circulation in a circular basin with vertical sidewalls, using a depth
gradient to mimic the effects of a gradient in Coriolis parameter. In the
sliced cone the vertical sidewalls are replaced by an azimuthally uniform
slope around the perimeter of the basin to simulate a continental slope.
Since these models can be implemented in the laboratory, their dynamics
can be explored by a complementary interplay of analysis and numerical
and laboratory experiments. ¶
In this thesis a derivation is presented of a generalised
quasigeostrophic formulation which is valid for linear and moderately
nonlinear barotropic flows over large-amplitude topography on an f-plane,
yet retains the simplicity and conservation properties of the standard
quasigeostrophic vorticity equation (which is valid only for small depth
variations). This formulation is implemented in a numerical model based
on a code developed by Page (1982) and Becker & Page (1990). ¶
The accuracy of the formulation and its implementation are confirmed by
detailed comparisons with the laboratory sliced cylinder and sliced cone
results of Griffiths (Griffiths & Kiss, 1999) and Griffiths & Veronis
(1997), respectively. The numerical model is then used to provide insight
into the dynamics responsible for the observed laboratory flows. In the
linear limit the numerical model reveals shortcomings in the sliced cone
analysis by Griffiths & Veronis (1998) in the region where the slope and
interior join, and shows that the potential vorticity is dissipated in an
extended region at the bottom of the slope rather than a localised region
at the east as suggested by Griffiths & Veronis (1997, 1998). Welander's
thermal analogy (Welander, 1968) is used to explain the linear
circulation pattern, and demonstrates that the broadly distributed
potential vorticity dissipation is due to the closure of geostrophic
contours in this geometry. ¶
The numerical results also provide insight into features of the flow at
finite Rossby number. It is demonstrated that separation of the western
boundary current in the sliced cylinder is closely associated with a
" crisis " due to excessive potential vorticity dissipation in the viscous
sublayer, rather than insufficient dissipation in the outer western
boundary current as suggested by Holland & Lin (1975) and Pedlosky
(1987). The stability boundaries in both models are refined using the
numerical results, clarifying in particular the way in which the western
boundary current instability in the sliced cone disappears at large
Rossby and/or Ekman number. A flow regime is also revealed in the sliced
cylinder in which the boundary current separates without reversed flow,
consistent with the potential vorticity " crisis " mechanism. In addition
the location of the stability boundary is determined as a function of the
aspect ratio of the sliced cylinder, which demonstrates that the flow is
stabilised in narrow basins such as those used by Beardsley (1969, 1972,
1973) and Becker & Page (1990) relative to the much wider basin used by
Griffiths & Kiss (1999). ¶
Laboratory studies of the sliced cone by Griffiths & Veronis (1997)
showed that the flow became unstable only under anticyclonic forcing. It
is shown in this thesis that the contrast between flow under cyclonic and
anticyclonic forcing is due to the combined effects of the relative
vorticity and topography in determining the shape of the potential
vorticity contours. The vorticity at the bottom of the sidewall smooths
out the potential vorticity contours under cyclonic forcing, but distorts
them into highly contorted shapes under anticyclonic forcing. In
addition, the flow is dominated by inertial boundary layers under
cyclonic forcing and by standing Rossby waves under anticyclonic forcing
due to the differing flow direction relative to the direction of Rossby
wave phase propagation. The changes to the potential vorticity structure
under strong cyclonic forcing reduce the potential vorticity changes
experienced by fluid columns, and the flow approaches a steady free
inertial circulation. In contrast, the complexity of the flow structure
under anticyclonic forcing results in strong potential vorticity changes
and also leads to barotropic instability under strong forcing. ¶
The numerical results indicate that the instabilities in both models
arise through supercritical Hopf bifurcations. The two types of
instability observed by Griffiths & Veronis (1997) in the sliced cone are
shown to be related to the western boundary current instability and
" interior instability " identified by Meacham & Berloff (1997). The
western boundary current instability is trapped at the western side of
the interior because its northward phase speed exceeds that of the
fastest interior Rossby wave with the same meridional wavenumber, as
discussed by Ierley & Young (1991). ¶
Numerical experiments with different lateral boundary conditions are also
undertaken. These show that the flow in the sliced cylinder is
dramatically altered when the free-slip boundary condition is used
instead of the no-slip condition, as expected from the work of Blandford
(1971). There is no separated jet, because the flow cannot experience a
potential vorticity " crisis " with this boundary condition, so the western
boundary current overshoots and enters the interior from the east. In
contrast, the flow in the sliced cone is identical whether no-slip,
free-slip or super-slip boundary conditions are applied to the horizontal
flow at the top of the sloping sidewall, except in the immediate vicinity
of this region. This insensitivity results from the extremely strong
topographic steering near the edge of the basin due to the vanishing
depth, which demands a balance between wind forcing and Ekman pumping on
the upper slope, regardless of the lateral boundary condition. The
sensitivity to the lateral boundary condition is related to the
importance of lateral friction in the global vorticity balance. The
integrated vorticity must vanish under the no-slip condition, so in the
sliced cylinder the overall vorticity budget is dominated by lateral
viscosity and Ekman friction is negligible. Under the free-slip condition
the Ekman friction assumes a dominant role in the dissipation, leading to
a dramatic change in the flow structure. In contrast, the much larger
depth variation in the sliced cone leads to a global vorticity balance in
which Ekman friction is always dominant, regardless of the boundary
condition.
42
Holland, David M. "Numerical simulation of the Arctic Sea ice and ocean circulation". Thesis, McGill University, 1993. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=41114.
Testo completoAbstract (sommario):
A numerical model study of the seasonal cycle of sea-ice cover and ocean circulation in the Arctic Ocean is presented. The investigation is carried out in four parts using the coupled sea ice-ocean model of Oberhuber (1993a). The Oberhuber model is the first global ocean general circulation model to use Lagrangian isopycnal coordinates. First, a sensitivity study is given of the sea-ice model, which is both dynamic and thermodynamic. The robustness of the sea-ice component in an uncoupled mode is demonstrated. Secondly, the addition of a snow model to the coupled sea ice-ocean model of Oberhuber (1993a) is described. The inclusion of snow is shown to be important for obtaining a good simulation of ice thickness in both the Arctic and Antarctic. Thirdly, the coupled ice-ocean model is used to investigate the general circulation of the Artic Ocean and its connection with the North Atlantic. The cyclonic motion of the Atlantic layer within the Arctic is correctly simulated. Fourthly, a sensitivity study of the Arctic mixed-layer circulation is presented.
43
Beare, Matthew Ivor. "The development of a general purpose parallel ocean circulation model". Thesis, University of East Anglia, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.266748.
Testo completo
44
Holgate, Simon John. "The Late Ordovician deep ocean circulation and the carbon cycle". Thesis, University of Liverpool, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.272742.
Testo completo
45
Ito, Takamitsu 1976. "The biogeochemistry and residual mean circulation of the southern ocean". Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/30290.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2005.Includes bibliographical references (p. 233-244).
I develop conceptual models of the biogeochemistry and physical circulation of the Southern Ocean in order to study the air-sea fluxes of trace gases and biological productivity and their potential changes over glacial-interglacial timescales. Mesoscale eddy transfers play a dominant role in the dynamical and tracer balances in the Antarctic Circumpolar Current, and the transport of tracers is driven by the residual mean circulation which is the net effect of the Eulerian mean circulation and the eddy-induced circulation. Using an idealized, zonally averaged model of the ACC, I illustrate the sensitivity of the uptake of transient tracers including CFC11, bomb-[Delta]¹⁴C and anthropogenic CO₂ to surface wind stress and buoyancy fluxes over the Southern Ocean. The model qualitatively reproduces observed distribution of CFC11 and bomb-[Delta]¹⁴C , and a suite of sensitivity experiments illustrate the physical processes controlling the rates of the oceanic uptake of these tracers. The sensitivities of the uptake of CFC11 and bomb-[Delta]¹⁴C are largely different because of the differences in their air-sea equilibration timescales. The uptake of CFC11 is mainly determined by the rates of physical transport in the ocean, and that of bomb-[Delta]¹⁴C is mainly controlled by the air-sea gas transfer velocity. Anthropogenic CO₂ falls in between these two cases, and the rate of anthropogenic CO₂ uptake is affected by both processes. Biological productivity in the Southern Ocean is characterized with the circum- polar belt of elevated biological productivity, "Antarctic Circumpolar Productivity Belt".
(cont.) Annually and zonally averaged export of biogenic silica is estimated by fitting the zonally averaged tracer transport model to the climatology of silicic acid using the method of least squares. The pattern of export production inferred from the inverse calculation is qualitatively consistent with recent observations. The pattern of inferred export production has a maximum on the southern flank of the ACC. The advective transport by the residual mean circulation is the key process in the vertical supply of silicic acid to the euphotic layer where photosynthesis occurs. In order to illustrate what sets the position of the productivity belt, I examined simulated biological production in a physical-biogeochemical model which includes an explicit ecosystem model coupled to the phosphate, silica and iron cycle. Simulated patterns of surface nutrients and biological productivity suggest that the circumpolar belt of elevated biological productivity should coincide with the regime transition between the iron-limited Antarctic zone and the macro-nutrients limited Subantarctic zone. At the transition, organisms have relatively good access to both micro and macro-nutrients. Kohfeld (in Bopp et al.; 2003) suggested that there is a distinct, dipole pattern in the paleo-proxy of biological export in the Southern Ocean at the LGM. I hypothesize that observed paleo-productivity proxies reflect the changes in the position of the Antarctic Circumpolar Productivity Belt over glacial-interglacial timescales. Increased dust deposition during ice ages is unlikely to explain the equatorward shift in the position of the productivity belt due to the expansion of the oligotrophic region and the poleward shift of the transition between the iron-limited regime and the macro-nutrient limited regime.
(cont.) I develop a simple dynamical model to evaluate the sensitivity of the meridional overturning circulation to the surface wind stress and the stratification. The theory suggest that stronger surface wind stress could intensify the surface residual flow and perturb the position of the productivity belt in the same sign as indicated by the paleo-productivity proxies. Finally, I examined the relationship between the surface macro-nutrients in the polar Southern Ocean and the atmospheric pCO₂. Simple box models developed in 1980s suggests that depleting surface macro-nutrients in high latitudes can explain the glacial pCO₂ drawdown inferred from polar ice cores. A suite of sensitivity experiments are carried out with an ocean-atmosphere carbon cycle model with a wide range of the rate of nutrient uptake in the surface ocean. These experiments suggest that the ocean carbon cycle is unlikely to approach the theoretical limit where "pre- formed" nutrient is completely depleted due to the dynamics of deep water formation. The rapid vertical mixing timescales of convection preclude the ventilation of strongly nutrient depleted waters. Thus it is difficult to completely deplete the "preformed" nutrients in the Southern Ocean even in a climate with elevated dust deposition in the region, suggesting some other mechanisms for the cause of lowered glacial pCO₂.
by Takamitsu Ito.
Ph.D.
46
Hines, Adrian. "Models of large-scale wind and buoyancy driven ocean circulation". Thesis, Keele University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389607.
Testo completo
47
Fujio, Shinzo. "Diagnostically Derived World Ocean Circulation and the Water Mass Formation". 京都大学 (Kyoto University), 1992. http://hdl.handle.net/2433/168820.
Testo completoAbstract (sommario):
本文データは平成22年度国立国会図書館の学位論文(博士)のデジタル化実施により作成された画像ファイルを基にpdf変換したものであるKyoto University (京都大学)
0048
新制・課程博士
博士(理学)
甲第4974号
理博第1371号
新制||理||765(附属図書館)
UT51-92-J21
京都大学大学院理学研究科地球物理学専攻
(主査)教授 今里 哲久, 教授 奥西 一夫, 教授 廣田 勇
学位規則第4条第1項該当
48
Youngs, Madeleine Kendall. "Residual overturning circulation and its connection to Southern Ocean dynamics". Thesis, Massachusetts Institute of Technology, 2020. https://hdl.handle.net/1721.1/129068.
Testo completoAbstract (sommario):
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), 2020Cataloged from student-submitted PDF of thesis.
Includes bibliographical references (pages 135-145).
Over the last 20 years, our understanding of the meridional overturning circulation has improved, but primarily in a two-dimensional, zonally-averaged framework. In this thesis, I have pushed beyond this simplification and shown that the additional complexity of meanders, storm tracks, and other zonal asymmetries is necessary to reproduce the lowest-order behavior of the overturning circulation. First I examined the role of basin width for determining whether the Atlantic or Pacific oceans experience deep convection. I used a two layered model and a rectangular single-basin model to show that the basin width, in combination with scalings for the overturning circulation make the overturning relatively weaker in the wider basin, priming it for a convection shut down.
In addition to this large-scale work, I have examined Southern Ocean-like meanders using a hierarchy of idealized models to understand the role of bottom topography in determining how the large-scale circulation responds to climate change scenarios. These are useful because they preserve the lowest-order behavior, while remaining simple enough to understand. I tested the response of the stratification and transport in the Southern Ocean to changes in wind using a highly-idealized two-layer quasi-geostrophic model. In addition to showing that meanders are necessary to reproduce the behavior of the Southern Ocean, I found that strong winds concentrate the baroclinic and barotropic instabilities downstream of the bottom topography and weaken the instabilities elsewhere due to a form-drag process. With weak winds, however, the system is essentially symmetric in longitude, like a flat-bottomed ocean.
This result is consistent with observations of elevated turbulence down-stream of major topography in the Southern Ocean. My next study investigated a more realistic Southern Ocean-like channel, with and without bottom topography, and examined the three-dimensional circulation in order to understand where vertical transport occurs and develop a picture of the pathways taken by each individual water parcel. I found that the vertical transport happens in very isolated locations, just downstream of topography. Finally, I added a biogeochemical model to my simulations and found that carbon fluxes are enhanced near topography, again highlighting the role of zonal asymmetries.
by Madeleine Kendall Youngs.
Ph. D.
Ph.D. Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution)
49
Marson, Juliana Marini. "Meltwater Impacts on the Ocean Circulation since the Last Glacial Maximum". Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/21/21135/tde-29052015-165852/.
Testo completoAbstract (sommario):
During the last 21,000 years, the planet underwent major changes. The atmospheric CO2 concentration increased ∼50% (Monnin et al., 2001) and the mean global temperature increased 4.0±0.8°C until pre-industrial times (Annan and Hargreaves, 2013). As a consequence of this warming, the huge ice sheets that covered North America, Northern Europe and part of Eurasia melted and the polar and subpolar ocean surface received a large amount of freshwater from these retracting ice sheets. The input of freshwater alters pressure gradients on the sea surface and also the density of water masses. Since the ocean circulation is partially driven by density differences, the deglacial meltwater has the potential to affect the ocean circulation. In this PhD thesis, the impacts of meltwater input since the Last Glacial Maximum into the high latitudes, especially of the Atlantic Ocean, are studied using the results of a transient simulation of the last 22 thousand years with NCAR-CCSM3. The main results show that: (1) the Atlantic Meridional Overturning Circulation (AMOC) slowed down during freshwater discharge events near dense water formation regions; (2) North Atlantic Deep Water (NADW) was absent in the beginning of the deglaciation, while its intermediate version -- Glacial North Atlantic Intermediate Water (GNAIW) -- was being formed; (3) GNAIW was a fresh and cold water mass, very similar to the Antarctic Intermediate Water (AAIW) in the thermohaline domain; (4) the deep and abyssal Atlantic basin was dominated by AABW in the first half of the simulation; (5) the transition from GNAIW to NADW occurred after the Heinrich Stadial 1; (6) when the NADW appeared, around 12 thousand years ago (ka), AABW retracted and was constrained to lie near the bottom; (7) the presence of a low-salinity layer in the Southern Ocean surface around ∼14,000 years ago prevented the release of heat from deep waters to the atmosphere, warming the AABW; (8) the Antarctic Coastal Current (ACoC) was reinforced by the meltwater discharge from the Antarctic ice sheet. Using the Indian Ocean as a comparison, it was observed that the North Atlantic affected the western tropical Indian through atmosphere, while climatic variations associated with the Southern Hemisphere were transmitted via ocean -- especially through intermediate waters. Although the initial conditions in the glacial and modern ocean are different, this study may be used to foresee the possible responses of the ocean to the accelerated melting of glaciers and ice sheets, which are associated with dramatic climate changes.Durante os últimos 21.000 anos, o planeta sofreu grandes mudanças. A concentração de CO2 atmosférico aumentou cerca de ∼50% (Monnin et al., 2001) e a temperatura média global aumentou 4,0±0,8°C até a época pré industrial (Annan and Hargreaves, 2013). Como consequência deste aquecimento, os grandes mantos de gelo que cobriam a América do Norte, o norte da Europa e parte da Eurásia derreteram e o oceano polar e subpolar recebeu grandes quantidades de água doce destes mantos em retração. A entrada de água doce altera gradientes de pressão na superfície do mar e também a densidade de massas de água. Como a circulação oceânica é parcialmente forçada por diferenças de densidade, a água de degelo tem o potencial de afetar esta circulação. Nesta tese de Doutorado, os impactos da entrada de água de degelo no oceano desde o Último Máximo Glacial em altas latitudes, especialmente do Oceano Atlântico, são estudados usando os resultados de uma simulação transiente dos últimos 22 mil anos com o modelo NCAR-CCSM3. Os principais resultados mostram que: (1) a circulação de revolvimento meridional do Atlântico enfraqueceu durante eventos de descarga de água doce próxima a regiões de formação de água densa; (2) a Água Profunda do Atlântico Norte (APAN) estava ausente no começo da deglaciação, enquanto sua versão intermediária -- Água Glacial Intermediária do Atlântico Norte (AGIAN) -- era formada; (3) AGIAN era uma massa d\'água doce e fria, semelhante à Água Intermediária Antártica (AIA) no domínio termohalino; (4) as camadas profundas e de fundo da bacia do Atlântico eram dominadas pela Água de Fundo Antártica (AFA) na primeira metade da simulação; (5) a transição de AGIAN para APAN ocorreu após o Heinrich Stadial 1; (6) quando a APAN apareceu, cerca de 12 mil anos atrás (ka), a AFA retraiu e ficou limitada às camadas de fundo; (7) a presença de uma camada de baixa salinidade na superfície do Oceano Austral há ∼14 mil anos impedia a liberação de calor das águas profundas para a atmosfera, aquecendo a AFA; (8) a Corrente Costeira Antártica foi intensificada pela descarga de água de degelo proveniente do manto de gelo Antártico. Usando o Oceano Índico como comparação, foi observado que o Atlântico Norte afetou o Índico oeste tropical através de processos atmosféricos, enquanto variações climáticas associadas ao Hemisfério Sul foram transmitidas via oceano -- especialmente através das camadas intermediárias. Embora as condições iniciais dos oceanos glacial e moderno sejam diferentes, este estudo pode ser usado para prever as possíveis respostas do oceano ao presente derretimento acelerado de geleiras e mantos de gelo associado a mudanças climáticas abruptas.
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Auger, Matthis. "Variability and Changes of Hydrography and Circulation in the Subpolar Southern Ocean". Electronic Thesis or Diss., Sorbonne université, 2022. http://www.theses.fr/2022SORUS086.
Testo completoAbstract (sommario):
L’océan Austral est une région centrale pour la circulation océanique globale et le climat. Il est cependant également en première ligne du changement climatique, notamment par son absorption importante de chaleur et de carbone anthropique. Par conséquent, l’océan Austral a connu de grands changements dans sa structure hydrographique et sa circulation dans les dernières décennies. Sa région subpolaire, au sud du courant circumpolaire Antarctique, abrite une circulation grande échelle importante pour la production des masses d'eau et leur contenu de chaleur et de carbone, pour les interactions océaniques avec la banquise et les plateformes glaciaires, avec des conséquences sur l'élévation du niveau de la mer. C’est également une région très peu observée, en particulier en hiver lorsque celle-ci est couverte par la banquise. Par conséquent, la réponse locale de la circulation et de la structure hydrographique de l’océan Austral subpolaire à des interactions avec l’atmosphère, la cryosphère et la grande échelle est toujours sujette à de nombreuses recherches. Dans cette thèse, je contribue à observer la variabilité et les changements à long terme de l’hydrographie et de la circulation de l’océan Austral subpolaire, et à documenter les mécanismes qui contrôlent leur variabilité. J’observe d’abord les changements à long terme de la température de la couche supérieure de l’océan Austral, à partir de transects répétés par bateau pendant 25 années. En plus des changements déjà bien documentés, je montre le réchauffement et la remontée des eaux chaudes de subsurface, à une vitesse plus importante qu’estimée auparavant et de façon plus forte que la variabilité interannuelle. Je présente ensuite un jeu de données de hauteur de mer, qui consiste en six années de mesures sur l’ensemble de l’océan Austral au sud de 50°S. Ce jeu de données me permet d’explorer la variabilité de la circulation de l’océan Austral subpolaire, et notamment sur le cycle saisonnier de la circulation grande échelle et de l’activité méso-échelle sous la glace. À l’échelle saisonnière, la circulation des gyres de Weddell, de Ross et le courant de pente Antarctique sont principalement dictés par trois modes de variabilités, reliés à la tension de vent en surface et sa modulation par la glace de mer. La circulation de méso-échelle est faible sous la banquise hors du courant de pente Antarctique, alors que la zone marginale de glace semble favoriser la génération de tourbillons cycloniques. Les implications de ces résultats pour les mécanismes physiques de l’océan Austral et ses changements à long terme sont discutéesThe Southern Ocean is central to the global oceanic circulation and climate. This region is however on the frontline of human-induced climate change, through intense uptake of anthropogenic heat and carbon. Consequently, the Southern Ocean has experienced important changes in its hydrography and circulation over the last decades. Its subpolar part, south of the Antarctic Circumpolar Current, hosts large circulation systems of importance for the production of water masses and their associate heat and carbon content, for ocean interactions with sea-ice and ice-shelves, and consequently for global mean sea level. Observations are still sparse in that region, particularly in wintertime when it is covered by sea ice. Thus, the regional response of the subpolar Southern Ocean hydrography and circulation to interactions with the atmosphere, cryosphere, and background circulation at various spatial and time scales is still under active research.In this thesis, I contribute to observing the variability and long-term changes of the hydrography and circulation of the subpolar Southern Ocean, and to unveil the mechanisms driving their variability. I first observe the long-term temperature changes in the upper layer of the Southern Ocean, from repeated ship-based measurement transects over 25 years. Besides previously documented trends, I refine the monitoring on the still poorly observed warming and shallowing of the warm subsurface water of the Southern Ocean. The long term warming is stronger than interannual variability, and the shallowing rate is 3 to 9 times the previously estimated one. In a second part, I develop and exploit an ocean topography dataset, spanning six years of measurements over the whole Southern Ocean south of 50°S. This dataset allows me to explore the variability of the subpolar Southern Ocean circulation, particularly the seasonal cycle of the large-scale circulation and the mesoscale variability under sea ice. At the seasonal scale, the circulation of the Weddell and Ross gyres, and the Antarctic Slope Current are mainly dictated by three modes of variability, principally linked to the surface stress of the wind on the surface of the ocean and its modulation by the sea ice. The mesoscale variability is weak outside the energetic Antarctic slope current in the pack ice, while the marginal ice zone seems to be a region with enhanced cyclonic eddies generation. The implications of these results on the physical processes of the Southern Ocean and its long-term changes are discussed