| NSF Org: |
OCE Division Of Ocean Sciences |
| Recipient: |
|
| Initial Amendment Date: | September 14, 2011 |
| Latest Amendment Date: | August 26, 2014 |
| Award Number: | 1129129 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Eric C. Itsweire
OCE Division Of Ocean Sciences GEO Directorate for Geosciences |
| Start Date: | September 15, 2011 |
| End Date: | August 31, 2015 (Estimated) |
| Total Intended Award Amount: | $586,202.00 |
| Total Awarded Amount to Date: | $586,202.00 |
| Funds Obligated to Date: |
|
| History of Investigator: |
|
| Recipient Sponsored Research Office: |
4333 BROOKLYN AVE NE SEATTLE WA US 98195-1016 (206)543-4043 |
| Sponsor Congressional District: |
|
| Primary Place of Performance: |
WA US 98105-6698 |
| Primary Place of
Performance Congressional District: |
|
| Unique Entity Identifier (UEI): |
|
| Parent UEI: |
|
| NSF Program(s): | PHYSICAL OCEANOGRAPHY |
| Primary Program Source: |
|
| Program Reference Code(s): | |
| Program Element Code(s): |
|
| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.050 |
ABSTRACT
Intellectual Merit:
Breaking internal tides are known to be a major driver of deep-ocean diapycnal mixing. However, much of the energy input into them is in the first few modes, which can propagate 1000's of kilometers before breaking. As a result, little is known about where and how they break, in spite of the known sensitivity of global circulation models to the geography of mixing. Therefore, this study will construct a global map of low-mode internal tide energy flux and dissipation by application of state-of-the-art techniques to a combination of satellite altimetry, moorings, and a numerical model. The approach captures both the non-uniform barotropic-to-baroclinic tide conversion near rough topography as well as patchiness due to the non-uniform dissipation of low-mode internal tides.
The global coverage of satellite altimeters makes them the only practical observational tool available for the task. However the poor spatial resolution of any single satellite, and the inability of altimetry to detect temporally incoherent signals, have hampered the interpretation of past altimetric estimates of low-mode internal tide energy and energy flux. This study addresses these shortcomings in order to produce the needed global maps:
(1) To address the low-resolution problem, the team will expand on their previous work (in which they used the T/P-Jason tandem mission) by combining multiple satellite altimetric data from T/P- Jason, T/P-Jason tandem, GFO, and ERS. The multi-satellite technique was recently demonstrated in the North Pacific, and showed that spatial resolution is improved to the point where the altimetric estimates agree with high-resolution numerical models.
(2) To understand the loss of coherence of internal tide propagating in an ever-changing ocean, the PIs will analyze a new high-resolution global simulation that includes a realistic internal tide field as well as realistic meso- and large-scale ocean circulations. The model estimate of how the non- uniform moving ocean makes internal tide incoherent will be validated by the analysis of several long moored time series collected around the globe.
With these improvements, the techniques should now be up to the task of mapping the low-mode internal tide's energy flux and dissipation on the globe. In doing so, this project will lead to a better understanding of the processes that affect the propagation and dissipation of internal tide on a global scale.
Broader Impacts:
The primary broader impact of this work will be an improved understanding and a parameterization of the magnitude and geography of dissipation, of known importance to general circulation models. In addition, the team will provide maps of altimetrically-observed internal tide quantities to all researchers as well as the public via a website and/or direct communication with the PI's. In addition to being of great use in planning experiments, such maps will be of relevance for a variety of physical and biogeochemical studies. The maps and the model simulations will be used in community outreach programs such as APL's K-12 volunteer list and Seattle's Pacific Science Center. The study will also educate three undergraduate students as part of the Washington Space Grant program, a joint program between Washington State and NASA seeking to encourage students at the University of Washington to pursue science careers.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
Note:
When clicking on a Digital Object Identifier (DOI) number, you will be taken to an external
site maintained by the publisher. Some full text articles may not yet be available without a
charge during the embargo (administrative interval).
Some links on this page may take you to non-federal websites. Their policies may differ from
this site.
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.
About 1 TW (1012 W) of barotropic tidal energy is converted to baroclinic motions in the deep ocean at rough topographic features such as ridges. Most of the baroclinic tidal energy is in the first lowest baroclinic modes, which can propagate 1000’s of km. Thus the fate of low-mode internal tides and the geography of the internal tide induced ocean mixing are largely unknown. The near-global coverage of satellite altimetry makes it the only practical observational tool available for this task. However, the poor spatial resolution of any single satellite, and its inability to detect temporally incoherent signals, have hampered the interpretation of past altimetric estimates of internal tide energy and energy flux. In this project, we have made advances by addressing these issues via a combined effort from multisatellite altimetry, in situ moorings, and numerical model.
We have taken the following measures to construct global maps of internal tides, energy flux, and dissipation. (1) We used 50 satellite-years of altimeter data in 1992–2012 from multiple satellite missions including ERS-1/2, Jason-1/2, TOPEX/Poseidon, and Geosat Follow-On. (2) We developed a two-dimensional plane wave fit method to suppress mesoscale contamination by extracting internal tides with both spatial and temporal coherence and to separately resolve multiple internal tidal waves. (3) To understand the loss of coherence of internal tide propagating in an ever-changing ocean, we analyzed a high-resolution global simulation that includes a realistic internal tide field as well as realistic meso- and large-scale ocean circulations.
Our main outcomes are listed as following:
(1) We constructed global maps of mode-1 M2, S2, O1 and K1 internal tides from multisatellite altimetry. For each tidal constituent, amplitude, phase, vertical modal structure, and ratio of the sea-surface to maximal interior displacements were obtained. Individual internal tidal beams were isolated from the decomposed internal tide field.
(2) We computed global energy and energy flux for each tidal constituent (M2, S2, O1 and K1). The globally integrated M2 internal tidal energy is 36 PJ (1 PJ = 1015 J).
(3) We obtained, for the first time, global maps of the internal-tide driven mixing from the divergence of the satellite estimated energy flux. A map of highly inhomogeneous mixing in the world ocean was revealed.
(4) We simulated global internal tides using a high-resolution, eddy-allowing numerical model (GOLD). The geographic beam patterns from satellite and GOLD agree very well. We constructed global maps of the incoherent fraction of internal tides. These are necessary parameters for correctly interpreting the company satellite results, by quantifying the loss of coherence of the internal tide as it propagates through time-dependent mesoscale currents.
(5) We analyzed about 80 historical moorings for comparison with our satellite and modeling results. We found that the satellite derived and modeled internal tides agree with moored measurements well.
Our research may help construct realistic parameterization of the magnitude and geography of dissipation, of known importance to general circulation models. Our satellite and modeled internal tides are thus vitally important to improve the understanding of the large-scale ocean circulation and the ocean’s response to global climate change. Our global maps may be used for planning field experiment (such as the Tasman Tidal Dissipation Experiment). They may be used for making internal tide correction to in situ (e.g., Argo floats) and satellite (e.g., SWOT satellite) measurements, when internal tides are un-wanted signals. Our satell...
Please report errors in award information by writing to: awardsearch@nsf.gov.
