Validation of Thorpe-scale-derived vertical diffusivities against microstructure measurements in the Kerguelen region
The Thorpe scale is an energy-containing vertical overturning scale of large eddies associated with shear-generated turbulence. This study investigates indirect estimates of vertical diffusivities from the Thorpe scale method in the polar front region east of the Kerguelen Islands based on fine-scal...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2014-12-01
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| Series: | Biogeosciences |
| Online Access: | http://www.biogeosciences.net/11/6927/2014/bg-11-6927-2014.pdf |
| _version_ | 1828235943680671744 |
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| author | Y.-H. Park J.-H. Lee I. Durand C.-S. Hong |
| author_facet | Y.-H. Park J.-H. Lee I. Durand C.-S. Hong |
| author_sort | Y.-H. Park |
| collection | DOAJ |
| description | The Thorpe scale is an energy-containing vertical overturning scale of large
eddies associated with shear-generated turbulence. This study investigates
indirect estimates of vertical diffusivities from the Thorpe scale method in
the polar front region east of the Kerguelen Islands based on fine-scale
density profiles gathered during the 2011 KEOPS2 (KErguelen Ocean and Plateau compared Study 2) cruise. These diffusivities
are validated in comparison with diffusivities estimated from the turbulence
dissipation rate directly measured via a TurboMAP (Turbulence ocean Microstructure Acquisition Profiler) microstructure profiler.
The results are sensitive to the choice of the diffusivity parameterization
and the overturn ratio <i>R</i><sub>o</sub>, and the optimal results have been obtained from the
parameterization by Shih et al. (2005) and the <i>R</i><sub>o</sub> = 0.25 criterion, rather
than the parameterization by Osborn (1980) and the <i>R</i><sub>o</sub> = 0.2 criterion
originally suggested by Gargett and Garner (2008).
<br><br>
The Thorpe-scale-derived diffusivities in the KEOPS2 region show a high
degree of spatial variability, ranging from a canonical value of
<i>O</i>(10<sup>−5</sup>) m<sup>2</sup> s<sup>−1</sup> in the Winter Water layer and in the area
immediately north of the polar front to a high value of <i>O</i>(10<sup>−4</sup>) m<sup>2</sup> s<sup>−1</sup>
in the seasonal thermocline between the surface mixed layer and
the Winter Water. The latter high diffusivities are found especially over
the shallow plateau southeast of the Kerguelen Islands and along the polar
front that is attached to the escarpment northeast of the islands. The
interaction of strong frontal flow with prominent bottom topography likely
causes the observed elevated mixing rates. |
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| id | doaj.art-05f18f5ded1c4cab9e564ec79bea3898 |
| institution | Directory Open Access Journal |
| issn | 1726-4170 1726-4189 |
| language | English |
| last_indexed | 2024-04-12T20:23:21Z |
| publishDate | 2014-12-01 |
| publisher | Copernicus Publications |
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| series | Biogeosciences |
| spelling | doaj.art-05f18f5ded1c4cab9e564ec79bea38982022-12-22T03:17:55ZengCopernicus PublicationsBiogeosciences1726-41701726-41892014-12-0111236927693710.5194/bg-11-6927-2014Validation of Thorpe-scale-derived vertical diffusivities against microstructure measurements in the Kerguelen regionY.-H. Park0J.-H. Lee1I. Durand2C.-S. Hong3MNHN-Sorbonne Universités, UPMC, Univ Paris 06, CNRS-IRD, LOCEAN Laboratory, Muséum National d'Histoire Naturelle, 43, rue Cuvier, 75005 Paris, FranceKorea Institut of Ocean Science & Technology, Ansan, KoreaMNHN-Sorbonne Universités, UPMC, Univ Paris 06, CNRS-IRD, LOCEAN Laboratory, Muséum National d'Histoire Naturelle, 43, rue Cuvier, 75005 Paris, FranceKorea Institut of Ocean Science & Technology, Ansan, KoreaThe Thorpe scale is an energy-containing vertical overturning scale of large eddies associated with shear-generated turbulence. This study investigates indirect estimates of vertical diffusivities from the Thorpe scale method in the polar front region east of the Kerguelen Islands based on fine-scale density profiles gathered during the 2011 KEOPS2 (KErguelen Ocean and Plateau compared Study 2) cruise. These diffusivities are validated in comparison with diffusivities estimated from the turbulence dissipation rate directly measured via a TurboMAP (Turbulence ocean Microstructure Acquisition Profiler) microstructure profiler. The results are sensitive to the choice of the diffusivity parameterization and the overturn ratio <i>R</i><sub>o</sub>, and the optimal results have been obtained from the parameterization by Shih et al. (2005) and the <i>R</i><sub>o</sub> = 0.25 criterion, rather than the parameterization by Osborn (1980) and the <i>R</i><sub>o</sub> = 0.2 criterion originally suggested by Gargett and Garner (2008). <br><br> The Thorpe-scale-derived diffusivities in the KEOPS2 region show a high degree of spatial variability, ranging from a canonical value of <i>O</i>(10<sup>−5</sup>) m<sup>2</sup> s<sup>−1</sup> in the Winter Water layer and in the area immediately north of the polar front to a high value of <i>O</i>(10<sup>−4</sup>) m<sup>2</sup> s<sup>−1</sup> in the seasonal thermocline between the surface mixed layer and the Winter Water. The latter high diffusivities are found especially over the shallow plateau southeast of the Kerguelen Islands and along the polar front that is attached to the escarpment northeast of the islands. The interaction of strong frontal flow with prominent bottom topography likely causes the observed elevated mixing rates.http://www.biogeosciences.net/11/6927/2014/bg-11-6927-2014.pdf |
| spellingShingle | Y.-H. Park J.-H. Lee I. Durand C.-S. Hong Validation of Thorpe-scale-derived vertical diffusivities against microstructure measurements in the Kerguelen region Biogeosciences |
| title | Validation of Thorpe-scale-derived vertical diffusivities against microstructure measurements in the Kerguelen region |
| title_full | Validation of Thorpe-scale-derived vertical diffusivities against microstructure measurements in the Kerguelen region |
| title_fullStr | Validation of Thorpe-scale-derived vertical diffusivities against microstructure measurements in the Kerguelen region |
| title_full_unstemmed | Validation of Thorpe-scale-derived vertical diffusivities against microstructure measurements in the Kerguelen region |
| title_short | Validation of Thorpe-scale-derived vertical diffusivities against microstructure measurements in the Kerguelen region |
| title_sort | validation of thorpe scale derived vertical diffusivities against microstructure measurements in the kerguelen region |
| url | http://www.biogeosciences.net/11/6927/2014/bg-11-6927-2014.pdf |
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