| NSF Org: |
OCE Division Of Ocean Sciences |
| Recipient: |
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| Initial Amendment Date: | September 15, 2012 |
| Latest Amendment Date: | September 15, 2012 |
| Award Number: | 1233598 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Eric C. Itsweire
OCE Division Of Ocean Sciences GEO Directorate for Geosciences |
| Start Date: | September 1, 2012 |
| End Date: | August 31, 2015 (Estimated) |
| Total Intended Award Amount: | $99,939.00 |
| Total Awarded Amount to Date: | $99,939.00 |
| 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 Road Woods Hole MA US 02543-1501 |
| 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): |
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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
Climate-scale ocean models unanimously stress the key regulatory function played by the oceanic overturning circulation in the Earth's climate and biogeochemical cycles over decadal and longer time scales. Yet in their quest to resolve many topical climate problems, the models' credibility is challenged by their extreme sensitivity to the representation of mixing processes in the Southern Ocean. This peculiarity of model behavior reflects the unique role of mixing in mediating the vertical and horizontal transports of water masses in the Antarctic Circumpolar Current (ACC), which shape the overturning circulation through their respective impacts on the overturning rate and inter-ocean exchange. The Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES) has collected a wealth of data to quantify mixing, including the spreading of a chemical tracer and of 150 floats at two different depths. The goal of this proposal is to analyze the tracer and float data to estimate the vertical and horizontal variations in lateral eddy mixing. The principal investigators' previous work has shown that tracer and floats are, by themselves, insufficient to accurately constrain these variations. Therefore the data will be analyzed together with surrogate tracers and floats advected with a numerical simulation of the regions under study.
Intellectual Merit: This project tackles the formidable problem of quantifying the role of small-scale eddies in the large-scale circulation. Because these eddies are so challenging to observe and model, it is difficult to quantify their large-scale effect. Indeed the ocean uptake of heat and carbon over the next century in climate models can be very different in models that parameterize mesoscale eddies compared to models that explicitly resolve them. This implies that present parameterizations, which either ignore or improperly represent the horizontal and vertical variations in mesoscale eddy mixing, may not have the skill to make accurate climate projections. The goal of this project is to ground new understanding of eddy mixing in data and use these results to develop new parameterizations for climate models. The connection between data and models is key to ensure that the DIMES experiment will have a long term legacy in the climate community.
Broader Impacts: This project addresses the important problem of quantifying mixing by eddies in the ocean and their role in the climate system. Furthermore the work should be seen in the wider context of studies of eddy-mean flow interaction in turbulent flows. The ideas have importance for the general circulation of the atmosphere and of planetary atmospheres, particularly those of the gas giants such as Jupiter. Indeed, parametrically, the ocean is closely akin to Jupiter, with an eddy scale that is hundreds of times smaller than that of the large-scale circulation. Finally, there is a strong educational component through the training of three graduate students and two post-docs, and the development of new curricula to introduce students in the MIT/WHOI Joint Program to the role of the Southern Ocean in the climate system.
The DIMES project is a process study sponsored by the U.S. CLIVAR (climate variability and predictability) program.
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.
This grant was a continuation of an earlier grant that involved the manufacture, deployment and data analysis of neutrally buoyant RAFOS floats as part of the DIMES experiment. Both projects were collaboartive efforts with K. Speer and colleagues at Florida State University. An initial deployment of floats was at the depth of the passive tracer, nominally 1500 m, in the Southeastern Pacific within the Circumpolar Current. A second deployment occurred further east in the path of the tracer and at two nominal depths of 1500 m and 700 m. Under this grant, the data was further analyzed and a paper describing the circulation and eddy diffusion in the Southern Ocean was completed (D. Balwada, et. al., 2015. Circulation and Stirring in the Southeast Pacific Ocean and the Scotia Sea sectors of the Antarctic Circumpolar Current. Journal of Physical Oceanography, submitted).
The eddy kinetic energy is higher than the mean kinetic energy everywhere in the sampled domain by about 50%. The time-averaged flow has jets within the Circumpolar Current that are topographically controlled only in the Scotia Sea. Upstream in the Southeast Pacific, excepth for a chain of seamounts, the jets are unconstrained by topography. The lateral diffusivities across the Circumpolar Current are 500m^2/s and 1000 m^2/s at 700 m and 1500 m depth, respectively.
Last Modified: 12/23/2015
Modified by: W. Brechner Owens
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