| NSF Org: |
OCE Division Of Ocean Sciences |
| Recipient: |
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| Initial Amendment Date: | August 23, 2010 |
| Latest Amendment Date: | August 23, 2010 |
| Award Number: | 1029672 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Eric C. Itsweire
OCE Division Of Ocean Sciences GEO Directorate for Geosciences |
| Start Date: | September 1, 2010 |
| End Date: | August 31, 2015 (Estimated) |
| Total Intended Award Amount: | $547,502.00 |
| Total Awarded Amount to Date: | $547,502.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
266 WOODS HOLE RD WOODS HOLE MA US 02543-1535 (508)289-3542 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
266 WOODS HOLE RD WOODS HOLE MA US 02543-1535 |
| Primary Place of
Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): | PHYSICAL OCEANOGRAPHY |
| Primary Program Source: |
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| Program Reference Code(s): | |
| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.050 |
ABSTRACT
Gravity currents and nonlinear internal waves with trapped cores are common features in the coastal ocean. Propagating gravity currents can generate large-amplitude nonlinear internal waves, while shoaling nonlinear internal waves can develop re-circulating cores of trapped fluid. The project is a collaborative study of the dynamics of gravity currents and nonlinear internal waves with trapped cores, including parallel complementary laboratory experiments. Wave tank experiments will focus on the stages of transition between steady gravity currents and internal wave generation,and theory and experiments for waves with trapped cores. The project will investigate: what types of core circulations are possible, how they depend on the wave generation mechanism, the development of shear instabilities, how long core fluid is trapped, and the implications for long-range mass transport. Experimental results will be compared with high-resolution non-hydrostatic numerical calculations.
The results of this study could lead to substantial insights in coastal ocean circulation, mixing, and near-field river plume behavior. A major emphasis of the experimental and numerical studies is the dissemination of key results to collaborators to improve interpretation of field observations and parameterizations in regional models. As a key unknown in larval dispersal, horizontal transport by trapped cores can be of use to biologists modeling benthic population connectivity. The project will support the Ph.D. thesis work of two graduate graduate students, and involve one or more GFD fellows.
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PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
The principal goals of this project were to develop theoretical and numerical models of the dynamics of gravity currents, internal bores, and large-amplitude internal solitary waves with trapped cores and to conduct complementary laboratory experiments to test these models. This effort is motivated numerous oceanographic and atmospheric examples of the coupled dynamics of gravity currents and large internal solitary waves, including the Columbia River outflow and the Morning Glory phenomena in Australia. These currents and waves are associated with turbulent vertical mixing and horizontal mass transport of bio-geo-chemical signals as are thus important in understanding and assessing the health of coastal ocean environments.
During this project we have accomplished several pieces of work including development of theoretical and numerical models of gravity currents propagating into stratified ambient fluids. Flows of this type occur, for example, at the mouth of an estuary when pulses of buoyant fresh river water are discharged into the coastal ocean. These currents intact with the ambient stratification to produce, in some situations, large-amplitude internal waves as shown in image 3 (where the gravity current is dense rather than buoyant). The work was the first to develop a general theory for gravity currents in stratified ambients.
We have also explored the dynamics of large-amplitude internal solitary waves with trapped cores. These waves, unlike many other waves in the ocean, can trap a vortex of fluid that is transported with the wave. Thus the mass transport is much more efficient than the usual wave-induced mass transport. This work has developed theoretical models of these waves and tested the theories against numerical models and laboratory experiments. Image 2 shows laboratory realizations of the circulation and density fields of several trapped-core internal solitary waves. This research has shown that these waves are stable and able to propagate for large distance while transporting fluid in the wave core.
Another focus of the research has been on the dynamics of internal hydraulic jumps through theoretical and numerical models. The flows are transitions between smooth and turbulent states much like hydraulic jumps downstream of weirs in channel or river flow. However, these jumps reside within the body of the fluid (thus are internal). The turbulence leads to regions of intense vertical mixing. Image 1 shows a three-dimensional numerical model calculation of an internal jump illustrating the transition from smooth, nearly two-layered upstream flow, to a turbulent downstream region of intense vertical mixing.
These results on the structure, dynamics, mixing and transport in internal waves, gravity currents, and internal hydraulic jumps will be useful for the biological and chemical oceanographic communities where geochemical and larval transport in coastal regions is critical to the health of these sensitive environments.
Last Modified: 11/30/2015
Modified by: Karl R Helfrich
