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  • 1
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    Caribbean Current and eddies as observed by surface drifters (2006)
    Details
    Publication Date: 2017-01-04
    Description: Author Posting. © The Author, 2004. This is the author's version of the work. It is posted here by permission of Elsevier B. V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part II: Topical Studies in Oceanography 52 (2005): 429-463, doi:10.1016/j.dsr2.2004.11.001.
    Description: Recent satellite-tracked surface drifter trajectories were analyzed to describe the mean currents and eddies in the Caribbean Sea. The structure of the Caribbean Current and its variability were determined from high-resolution ½ degree maps of the mean velocity and eddy kinetic energy. Looping drifter trajectories were used to identify discrete cyclones and anticyclones, and their characteristics were described and related to the structure of the mean flow. The translation rate of eddies in different areas was found to be similar to the mean velocity of the local background flow fields suggesting that the eddies were largely advected by the background flow. Ten energetic anticyclones translated westward at 13 cm/sec in the Venezuela and Colombia Basins. These anticyclones tended to lie in two bands, centered near 15ºN and 17ºN, coinciding with two jets of the Caribbean Current. The northern weaker jet contains water primarily from the North Atlantic, the southern stronger jet contains water from the tropical and South Atlantic. The anticyclones are thought to have formed in the eastern Caribbean from the anticyclonic vorticity derived from North Brazil Current rings. The ring vorticity enters the eastern Caribbean through island passages and is probably amplified by the anticyclonic shear on the northern side of the jets. Southwest of Cuba a cyclone-anticyclone pair was observed to slowly (~ 2 cm/sec) translate westward into the Yucatan Current. The cyclone was tracked for 10.5 months with four drifters, making it the longest-tracked of the Caribbean eddies.
    Description: Funding was provided by National Science Foundation grants OCE 97-29765 and OCE 01-36477.
    Keywords: Surface drifters ; Caribbean Current ; Caribbean eddies ; Eddies ; North Brazil Current rings ; Meridional overturning circulation ; Intra-Americas Seas ; Caribbean Sea ; Colombia Basin ; Venezuela Basin ; Yucatan Basin ; Antilles
    Repository Name: Woods Hole Open Access Server
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  • 2
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    Eddies and friction : removal of vorticity from the wind-driven gyre (2008)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-05-25
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2003
    Description: Inertial terms dominate the single-gyre ocean model and prevent western-intensification when the viscosity is small. This occurs long before the oceanically-appropriate parameter range. It is demonstrated here that the circulation is controlled if a mechanism for ultimate removal of vorticity exists, even if it is active only in a narrow region near the boundary. Vorticity removal is modeled here as a viscosity enhanced very near the solid boundaries to roughly parameterize missing boundary physics like topographic interaction and three dimensional turbulence over the shelf. This boundary-enhanced viscosity allows western-intensified mean flows even when the inertial boundary width, is much wider than the frictional region because eddies flux vorticity from within the interior streamlines to the frictional region for removal. Using boundary-enhanced viscosity, western-intensified calculations are possible with lower interior viscosity than in previous studies. Interesting behaviors result: a boundary-layer balance novel to the model, calculations with promise for eddy parameterization, eddy-driven gyres rotating opposite the wind, and temporal complexity including basin resonances. I also demonstrate that multiple-gyre calculations have weaker mean circulation than single-gyres with the same viscosity and subtropical forcing. Despite traditional understanding, almost no inter-gyre flux occurs if no-slip boundary conditions are used. The inter-gyre eddy flux is in control only with exactly symmetric gyres and free slip boundaries. Even without the inter-gyre flux, the multiple-gyre circulation is weak because of sinuous instabilities on the jet which are not present in the single-gyre model. These modes efficiently flux vorticity to the boundary and reduce the circulation without an inter-gyre flux, postponing inertial domination to much smaller viscosities. Then sinuous modes in combination with boundary-enhanced viscosity can control the circulation.
    Keywords: Eddies ; Turbulent boundary layer ; Ocean-atmosphere interaction ; Mathematical models
    Repository Name: Woods Hole Open Access Server
    Type: Thesis
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  • 3
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    Monthly variability in upper ocean biogeochemistry due to mesoscale eddy activity in the Saragasso Sea (2009)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-05-25
    Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution May 2001
    Description: A comparison of monthly biogeochemical measurements made from 1993 to 1995, combined with hydrography and satellite altimetry, was used to observe the impacts of nine eddy events on primary productivity and particle flux in the Sargasso Sea. Measurements of primary production, thorium-234 flux, nitrate+nitrite, and photosynthetic pigments made at the US JGOFS Bermuda Atlantic Time-series Study (BATS) site were used. During the three years of this study, four out of six high thorium- 234 flux events over 1000 dpm/m2/d occurred during the passage of an eddy. Primary production nearly as high as the spring bloom maximum was observed in two modewater eddies (May 1993 and July 1995). The 1994 spring bloom at BATS was suppressed by the passage of an anticyclone. Distinct phytoplankton community shifts were observed in mode-water eddies, which had an increased percentage diatoms and dinoflagelletes, and in cyclones, which had an increased percentage cyanobacteria (excluding Prochlorococcus). The difference in the observations of mode-water eddies and cyclones may result from the age of the eddy, which was very important to the biological response. In general, eddies that were one to two months old elicited a large biological response; eddies that were three months old may show a biological response and were accompanied by high thorium flux measurements; eddies that were four months old or older did not show a biological response or high thorium flux. Our conceptual model depicting the importance of temporal changes during eddy upwelling and decay fit the observations well in all 7 upwelling eddies. Additional information is needed to determine the importance of deeper mixed layers and winter mixing to the magnitude of the eddy impacts. Also, sampling generally captured only the beginning, end, and lor edge of an eddy due to the monthly to semi-monthly frequency of the measurements made at BATS. Lagrangian studies, higher resolution time-series, and/or more spatial coverage is needed to provide additional information for improved C and N budgets in the Sargasso Sea and to complete our understanding of the temporal changes that occur in an eddy.
    Description: Funding for this work was provided by NASA and NSF through the JGOFS Synthesis and Modeling Program.
    Keywords: Eddies ; Biogeochemistry
    Repository Name: Woods Hole Open Access Server
    Type: Thesis
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  • 4
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    Evolution of the Irminger Current anticyclones in the Labrador Sea from hydrographic data (2007)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-05-25
    Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2006
    Description: The continuous supply of heat and fresh water from the boundaries to the interior of the Labrador Sea plays an important role for the dynamics of the region and in particular, for the Labrador Sea Water formation. Thus, it is necessary to understand the factors governing the exchange of properties between the boundary and interior. A significant fraction of heat and fresh water, needed to balance the annual heat loss and to contribute to the seasonal freshening of the Labrador Sea, is thought to be provided by coherent long-lived anticyclonic eddies shed by the Irminger Current. The population, some properties, rates and direction of propagation of these anomalies are known but the evolution and the mechanism of their decay are still far from obvious. In this work I investigated their water mass properties and evolution under the strong wintertime forcing using hydrographic data from 1990-2004 and a 1-dimensional mixed layer model. There were 50 eddies found in the hydrographic data record, 48 of which were identified as anticyclones. Vertical structure of the eddies was investigated, leading to the categorization of all the anticyclones into three classes: 12 - with a fresh surface layer and no mixed layer, 18 - without a fresh layer and at least one mixed layer, and 18 with ambiguous vertical structure. Four eddies of the second group appeared to have cores extending to as deep as 1500 m vertically and an isopycnal displacement of 400-600 m. A number of eddies without a fresh water cap contained Labrador Sea Water from the previous year at mid-depths.
    Keywords: Eddies ; Hydrography
    Repository Name: Woods Hole Open Access Server
    Type: Thesis
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  • 5
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    The East Greenland Coastal Current : structure, variability, and forcing (2008)
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © Elsevier B.V. , 2008. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Progress In Oceanography 78 (2008): 58-77, doi:10.1016/j.pocean.2007.09.006.
    Description: The subtidal circulation of the southeast Greenland shelf is described using a set of high-resolution hydrographic and velocity transects occupied in summer 2004. The main feature is the East Greenland Coastal Current (EGCC), a low-salinity, high-velocity jet with a wedge-shaped hydrographic structure characteristic of other surface buoyancydriven currents. The EGCC was observed along the entire Greenland shelf south of Denmark Strait, while the transect north of the strait showed only a weak shelf flow. This observation, in conjunction with water mass considerations and other supporting evidence, suggests that the EGCC is an inner branch of the East Greenland Current (EGC) that forms south of Denmark Strait. It is argued that bathymetric steering is the most likely reason why the EGC apparently bifurcates at this location. Repeat sections occupied at Cape Farewell between 1997 and 2004 show that the alongshelf wind stress can have a strong influence on the structure and strength of the EGCC and EGC on timescales of 2-3 days. Accounting for the wind-induced effects, the volume transport of the combined EGCC/EGC system is roughly constant (~2 Sv) over the study domain, from 68°N to Cape Farewell near 60°N. The corresponding freshwater transport increases by roughly 60% over this distance (59 to 96 mSv, referenced to a salinity of 34.8). This trend is consistent with a simple freshwater budget of the EGCC/EGC system that accounts for meltwater runoff, melting sea-ice and icebergs, and net precipitation minus evaporation.
    Description: This work was funded by the National Science Foundation grant OCE-0450658. DS was also partially supported by the Woods Hole Oceanographic Institution Academic Programs Office.
    Keywords: Coastal currents ; East Greenland Current ; Sea ice ; Boundary currents ; Arctic freshwater flux
    Repository Name: Woods Hole Open Access Server
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  • 6
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    Thermoconvective eddies in air : application to meteorology (2005)
    Woods Hole Oceanographic Institution | E. Blondel la Rougery : Gauthier-Villars
    Details
    Publication Date: 2022-05-25
    Description: Translated from the French by Carl A. Ronne.
    Description: The object of the present work is a study thermoconvective eddies in a layer of air heated uniformly from below. Being given the importance that these eddies present in meteorlogical phenomena, we have tried to attain three principal objectives: 1. To realize systematic experiments on thermoconvective eddies in air under thicknesses exceeding considerably the scale generally employed by preceding experimenters; 2. To verify experimentally the practical value of the numerical results deriving from the theory of thermoconvective eddies; 3. To complete, by the results acquired in the course of our researches in the laboratory, the theory of thermoconvective eddies in the free atmosphere.
    Keywords: Vortex-motion ; Heat ; Convection ; Eddies
    Repository Name: Woods Hole Open Access Server
    Type: Technical Report
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  • 7
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    Formation of intrathermocline eddies at ocean fronts by wind-driven destruction of potential vorticity (2008)
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    Publication Date: 2022-05-25
    Description: Author Posting. © Elsevier B.V., 2008. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Dynamics of Atmospheres and Oceans45 (2008): 252-273, doi:10.1016/j.dynatmoce.2008.02.002.
    Description: A mechanism for the generation of intrathermocline eddies (ITEs) at wind-forced fronts is examined using a high resolution numerical simulation. Favorable conditions for ITE formation result at fronts forced by “down-front” winds, i.e. winds blowing in the direction of the frontal jet. Down-front winds exert frictional forces that reduce the potential vorticity (PV) within the surface boundary in the frontal outcrop, providing a source for the low-PV water that is the materia prima of ITEs. Meandering of the front drives vertical motions that subduct the low-PV water into the pycnocline, pooling it into the coherent anticyclonic vortex of a submesoscale ITE. As the fluid is subducted along the outcropping frontal isopycnal, the low-PV water, which at the surface is associated with strongly baroclinic flow, re-expresses itself as water with nearly zero absolute vorticity. This generation of strong anticyclonic vorticity results from the tilting of the horizontal vorticity of the frontal jet, not from vortex squashing. During the formation of the ITE, high-PV water from the pycnocline is upwelled alongside the subducting low-PV surface water. The positive correlation between the ITE’s velocity and PV fields results in an upward, along-isopycnal eddy PV flux that scales with the surface frictional PV flux driven by the wind. The relationship between the eddy and wind-induced frictional PV flux is nonlocal in time, as the eddy PV flux persists long after the wind forcing is shut off. The ITE’s PV flux affects the large-scale flow by driving an eddy-induced transport or bolus velocity down the outcropping isopycnal layer with a magnitude that scales with the Ekman velocity.
    Description: This work was supported by NSF grants OCE-03-51191, OCE-05-49699, and OCE-0612058.
    Keywords: Fronts ; Eddies ; Potential vorticity ; Subduction
    Repository Name: Woods Hole Open Access Server
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  • 8
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    Eddy dynamics of ß plumes (2007)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-05-25
    Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2003
    Description: The importance of eddies and nonlinearities in ß-plume dynamics in the deep ocean was investigated using reduced gravity models of the deep ocean forced by a small region of cross isopycnal transport in the interior. The effect of topography on ß-plumes was also examined by placing a Gaussian bump in the forcing region. Despite the fact that the mean flow is weak in the deep ocean interior, it was found that the nonlinearity and instabilities are still important for realistic parameter and forcing values. The flow was dominated by eddies and was remarkably different from what would be expected from a linear solution.
    Description: This study was supported by Woods Hole Oceanographic Institution Academic Programs Office Fellowship and National Science Foundation Grant 89542700.
    Keywords: Eddies ; Plumes
    Repository Name: Woods Hole Open Access Server
    Type: Thesis
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  • 9
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    Baroclinic vortices over a sloping bottom (2008)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
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    Publication Date: 2022-05-25
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1996
    Description: Nonlinear quasigeostrophic flows in two layers over a topographic slope are considered. The evolution depends on the size of two parameters which indicate the degree of nonlinearity at depth. The first measures the importance of relative vorticity advection and the second of stretching vorticity. Two types of isolated vortex are used to examine the parameter dependence. An initially barotropic vortex remains barotropic only when the first parameter is large, otherwise topographic waves dominate at depth. An Initially surface-trapped vortex larger than deformation scale is baroclinically unstable when the second is large, but is stabilized by the slope otherwise. Both parameters are also relevant to cascading geostrophic turbulence. If the stretching parameter is large, a "barotropic cascade" occurs at the deformation radius (Rhines, 1977) and the cascade "arrests" when the relative vorticity parameter is order unity. If small, layer coupling is hindered and the cascade is arrested at the deformation scale, with the flow dominated by isotropic surface vortices. In both cases, the distinction between vortices and waves is transparent when viewing potential vorticity. It is more difficult to identify waves and vortices from the streamfunction fields, because the waves are present in both layers.
    Description: Funding for this research was provided by Office of Naval Research Coastal Science Code, grants N00014-92-J-1643 and N00014-92-J-1528.
    Keywords: Rossby waves ; Eddies ; Ocean circulation ; Turbulence ; Submarine topography
    Repository Name: Woods Hole Open Access Server
    Type: Thesis
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