| NSF Org: |
OCE Division Of Ocean Sciences |
| Recipient: |
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| Initial Amendment Date: | April 12, 2004 |
| Latest Amendment Date: | April 12, 2004 |
| Award Number: | 0351892 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Eric C. Itsweire
OCE Division Of Ocean Sciences GEO Directorate for Geosciences |
| Start Date: | May 1, 2004 |
| End Date: | April 30, 2009 (Estimated) |
| Total Intended Award Amount: | $297,583.00 |
| Total Awarded Amount to Date: | $297,583.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
285 OLD WESTPORT RD NORTH DARTMOUTH MA US 02747-2356 (508)999-8953 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
285 OLD WESTPORT RD NORTH DARTMOUTH MA US 02747-2356 |
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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): |
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| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.050 |
ABSTRACT
0351892/0351905
Intellectual merit: Tracer release studies in the coastal and open ocean suggest that lateral dispersion on scales of 1 to 10 kilometer cannot be explained by shear dispersion or dispersion by lateral intrusions. Dispersion on these scales may be due to stirring by small-scale geostrophic motions, or vortical modes. Analytical and numerical modeling studies support this conclusion. However, a complete description of the generation of vortical modes via geostrophic adjustment of internal wave breaking events, their effect on lateral stirring, and their eventual dissipation is still lacking. The goal of the proposed laboratory experiments is to study lateral stirring by vortical modes formed by geostrophic adjustment of diapycnal mixing events., and to better quantify the importance of vortical mode stirring in the ocean. The main contributions of this work will be to test theoretical predictions for vortical mode stirring when internal wave forcing and breaking are present, and to provide a basis for parameterizing horizontal dispersion rates by vortical mode stirring in the ocean.
Experiments will be conducted using the University of Rhode Island's Graduate School of Oceanography rotating tank facility. A 1 meter diameter, 30 centimeter deep uniformly stratified rotating tank will be used to model conditions in the ocean's stratified interior. Two methods will be used to generate diapycnal mixing events: 1) mechanical stirring in the form of localized grid-forced turbulence, and 2) a quasi-random field of internal waves and wave breaking generated by near resonant forcing of a mode-1 internal wave, and wave-wave interactions to scatter energy into higher modes. The formation of vortical modes and their effects on lateral stirring of a passive fluorescent dye will be examined using a combination of Particle Imaging Velocimetry (PIV), Laser Induced Fluorescence (LIF), and digital video analysis. A major advantage of the proposed laboratory studies over previous analytical and numerical studies is that diapycnal mixing events will ultimately be driven by internal wave breaking rather than some artificially imposed method of mixing. The proposed work will build extensively on analytical and numerical studies by the investigators and collaborators, which predict the amount of lateral dispersion caused by vortical mode stirring. However, these studies did not explicitly include breaking internal waves, but simulated their effects in terms of buoyancy flux. A major focus of this study will be to test theoretical and numerical predictions when large-scale internal wave forcing and diapycnal mixing by internal wave breaking are explicitly included. This will allow an assessment of the effects of large-scale internal waves, the conversion to potential energy through diapycnal mixing by internal wave breaking, and the transfer of energy into vortical modes.
Broader impacts: The proposed work will help provide a quantitative description of vertical mode stirring on scales of 1-10 km in the ocean. Dispersion on these scales affects distributions of physical, biological, and chemical tracers, and is particularly important to understanding global ocean circulation and heat balances, since these scales are approximately the grid scale of state of the art global ocean circulation models. The project is a collaborative effort between the University of Rhode Island and the University of Massachusetts at Dartmouth. It will support one full time graduate student and one undergraduate summer intern per year for four years. We will attempt to fill these positions with candidates from underrepresented groups. The laboratory experiments will also be used to demonstrate internal wave dynamics for physical oceanography courses taught by the investigators.
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