Competition between baroclinic instability and Ekman transport under varying buoyancy forcings in upwelling systems: An idealized analog to the Southern Ocean
International audience Coastal upwelling rates are classically determined by the intensity of the upper-ocean offshore Ekman transport. But (sub)mesoscale turbulence modulates offshore transport, hence the net upwelling rate. Eddy effects generally oppose the Ekman circulation, resulting in so-calle...
Published in: | Journal of Physical Oceanography |
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Main Authors: | , , |
Other Authors: | , , , , |
Format: | Article in Journal/Newspaper |
Language: | English |
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HAL CCSD
2021
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Online Access: | https://hal.archives-ouvertes.fr/hal-03419706 https://hal.archives-ouvertes.fr/hal-03419706/document https://hal.archives-ouvertes.fr/hal-03419706/file/templateV5_resubmission_JPO-D-20-0294_Thomsen_et_al.pdf https://doi.org/10.1175/JPO-D-20-0294.1 |
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Archive ouverte HAL (Hyper Article en Ligne, CCSD - Centre pour la Communication Scientifique Directe) |
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English |
topic |
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean Atmosphere |
spellingShingle |
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean Atmosphere Thomsen, Soeren Capet, Xavier Echevin, Vincent Competition between baroclinic instability and Ekman transport under varying buoyancy forcings in upwelling systems: An idealized analog to the Southern Ocean |
topic_facet |
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean Atmosphere |
description |
International audience Coastal upwelling rates are classically determined by the intensity of the upper-ocean offshore Ekman transport. But (sub)mesoscale turbulence modulates offshore transport, hence the net upwelling rate. Eddy effects generally oppose the Ekman circulation, resulting in so-called “eddy cancellation,” a process well studied in the Southern Ocean. Here we investigate how air–sea heat/buoyancy fluxes modulate eddy cancellation in an idealized upwelling model. We run CROCO simulations with constant winds but varying heat fluxes with and without submesoscale-rich turbulence. Eddy cancellation is consistently evaluated with three different methods that all account for the quasi-isopycnal nature of ocean circulation away from the surface. For zero heat fluxes the release of available potential energy by baroclinic instabilities is strongest and leads, near the coast, to nearly full cancellation of the Ekman cross-shore circulation by eddy effects, i.e., zero net mean upwelling flow. With increasing heat fluxes eddy cancellation is reduced and the transverse flow progressively approaches the classical Ekman circulation. Sensitivity of the eddy circulation to synoptic changes in air–sea heat fluxes is felt down to 125-m depth despite short experiments of tens of days. Mesoscale dynamics dominate the cancellation effect in our simulations which might also hold for the real ocean as the relevant processes act below the surface boundary layer. Although the idealized setting overemphasizes the role of eddies and thus studies with more realistic settings should follow, our findings have important implications for the overall understanding of upwelling system dynamics. |
author2 |
Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques (LOCEAN) Institut Pierre-Simon-Laplace (IPSL (FR_636)) École normale supérieure - Paris (ENS Paris) Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales Toulouse (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-École normale supérieure - Paris (ENS Paris) Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales Toulouse (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-Institut de Recherche pour le Développement (IRD)-Muséum national d'Histoire naturelle (MNHN)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU) |
format |
Article in Journal/Newspaper |
author |
Thomsen, Soeren Capet, Xavier Echevin, Vincent |
author_facet |
Thomsen, Soeren Capet, Xavier Echevin, Vincent |
author_sort |
Thomsen, Soeren |
title |
Competition between baroclinic instability and Ekman transport under varying buoyancy forcings in upwelling systems: An idealized analog to the Southern Ocean |
title_short |
Competition between baroclinic instability and Ekman transport under varying buoyancy forcings in upwelling systems: An idealized analog to the Southern Ocean |
title_full |
Competition between baroclinic instability and Ekman transport under varying buoyancy forcings in upwelling systems: An idealized analog to the Southern Ocean |
title_fullStr |
Competition between baroclinic instability and Ekman transport under varying buoyancy forcings in upwelling systems: An idealized analog to the Southern Ocean |
title_full_unstemmed |
Competition between baroclinic instability and Ekman transport under varying buoyancy forcings in upwelling systems: An idealized analog to the Southern Ocean |
title_sort |
competition between baroclinic instability and ekman transport under varying buoyancy forcings in upwelling systems: an idealized analog to the southern ocean |
publisher |
HAL CCSD |
publishDate |
2021 |
url |
https://hal.archives-ouvertes.fr/hal-03419706 https://hal.archives-ouvertes.fr/hal-03419706/document https://hal.archives-ouvertes.fr/hal-03419706/file/templateV5_resubmission_JPO-D-20-0294_Thomsen_et_al.pdf https://doi.org/10.1175/JPO-D-20-0294.1 |
geographic |
Southern Ocean |
geographic_facet |
Southern Ocean |
genre |
Southern Ocean |
genre_facet |
Southern Ocean |
op_source |
ISSN: 0022-3670 EISSN: 1520-0485 Journal of Physical Oceanography https://hal.archives-ouvertes.fr/hal-03419706 Journal of Physical Oceanography, American Meteorological Society, 2021, 51 (11), pp.3347-3364. ⟨10.1175/JPO-D-20-0294.1⟩ |
op_relation |
info:eu-repo/semantics/altIdentifier/doi/10.1175/JPO-D-20-0294.1 hal-03419706 https://hal.archives-ouvertes.fr/hal-03419706 https://hal.archives-ouvertes.fr/hal-03419706/document https://hal.archives-ouvertes.fr/hal-03419706/file/templateV5_resubmission_JPO-D-20-0294_Thomsen_et_al.pdf doi:10.1175/JPO-D-20-0294.1 |
op_doi |
https://doi.org/10.1175/JPO-D-20-0294.1 |
container_title |
Journal of Physical Oceanography |
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1766206487566221312 |
spelling |
ftccsdartic:oai:HAL:hal-03419706v1 2023-05-15T18:25:12+02:00 Competition between baroclinic instability and Ekman transport under varying buoyancy forcings in upwelling systems: An idealized analog to the Southern Ocean Thomsen, Soeren Capet, Xavier Echevin, Vincent Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques (LOCEAN) Institut Pierre-Simon-Laplace (IPSL (FR_636)) École normale supérieure - Paris (ENS Paris) Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales Toulouse (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-École normale supérieure - Paris (ENS Paris) Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales Toulouse (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-Institut de Recherche pour le Développement (IRD)-Muséum national d'Histoire naturelle (MNHN)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU) 2021 https://hal.archives-ouvertes.fr/hal-03419706 https://hal.archives-ouvertes.fr/hal-03419706/document https://hal.archives-ouvertes.fr/hal-03419706/file/templateV5_resubmission_JPO-D-20-0294_Thomsen_et_al.pdf https://doi.org/10.1175/JPO-D-20-0294.1 en eng HAL CCSD American Meteorological Society info:eu-repo/semantics/altIdentifier/doi/10.1175/JPO-D-20-0294.1 hal-03419706 https://hal.archives-ouvertes.fr/hal-03419706 https://hal.archives-ouvertes.fr/hal-03419706/document https://hal.archives-ouvertes.fr/hal-03419706/file/templateV5_resubmission_JPO-D-20-0294_Thomsen_et_al.pdf doi:10.1175/JPO-D-20-0294.1 ISSN: 0022-3670 EISSN: 1520-0485 Journal of Physical Oceanography https://hal.archives-ouvertes.fr/hal-03419706 Journal of Physical Oceanography, American Meteorological Society, 2021, 51 (11), pp.3347-3364. ⟨10.1175/JPO-D-20-0294.1⟩ [SDU.OCEAN]Sciences of the Universe [physics]/Ocean Atmosphere info:eu-repo/semantics/article Journal articles 2021 ftccsdartic https://doi.org/10.1175/JPO-D-20-0294.1 2022-01-08T23:56:50Z International audience Coastal upwelling rates are classically determined by the intensity of the upper-ocean offshore Ekman transport. But (sub)mesoscale turbulence modulates offshore transport, hence the net upwelling rate. Eddy effects generally oppose the Ekman circulation, resulting in so-called “eddy cancellation,” a process well studied in the Southern Ocean. Here we investigate how air–sea heat/buoyancy fluxes modulate eddy cancellation in an idealized upwelling model. We run CROCO simulations with constant winds but varying heat fluxes with and without submesoscale-rich turbulence. Eddy cancellation is consistently evaluated with three different methods that all account for the quasi-isopycnal nature of ocean circulation away from the surface. For zero heat fluxes the release of available potential energy by baroclinic instabilities is strongest and leads, near the coast, to nearly full cancellation of the Ekman cross-shore circulation by eddy effects, i.e., zero net mean upwelling flow. With increasing heat fluxes eddy cancellation is reduced and the transverse flow progressively approaches the classical Ekman circulation. Sensitivity of the eddy circulation to synoptic changes in air–sea heat fluxes is felt down to 125-m depth despite short experiments of tens of days. Mesoscale dynamics dominate the cancellation effect in our simulations which might also hold for the real ocean as the relevant processes act below the surface boundary layer. Although the idealized setting overemphasizes the role of eddies and thus studies with more realistic settings should follow, our findings have important implications for the overall understanding of upwelling system dynamics. Article in Journal/Newspaper Southern Ocean Archive ouverte HAL (Hyper Article en Ligne, CCSD - Centre pour la Communication Scientifique Directe) Southern Ocean Journal of Physical Oceanography |