Instabilities and vertical mixing in river plumes: application to the Bay of Biscay
In the Bay of Biscay (north-east Atlantic), long-living eddies and the frontal activity that they induce substantially contribute to mesoscale and submesoscale dynamics. Tides and river plumes also contribute to frontal activity. Biological productivity is sensitive to river plume fronts and to exte...
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2020
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Online Access: | https://archimer.ifremer.fr/doc/00651/76286/77309.pdf https://doi.org/10.1080/03091929.2020.1814275 https://archimer.ifremer.fr/doc/00651/76286/ |
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ftarchimer:oai:archimer.ifremer.fr:76286 2023-05-15T17:38:43+02:00 Instabilities and vertical mixing in river plumes: application to the Bay of Biscay Ayouche, Adam Carton, Xavier Charria, Guillaume Theetten, Sebastien Ayoub, Nadia 2020-09 application/pdf https://archimer.ifremer.fr/doc/00651/76286/77309.pdf https://doi.org/10.1080/03091929.2020.1814275 https://archimer.ifremer.fr/doc/00651/76286/ eng eng Informa UK Limited https://archimer.ifremer.fr/doc/00651/76286/77309.pdf doi:10.1080/03091929.2020.1814275 https://archimer.ifremer.fr/doc/00651/76286/ info:eu-repo/semantics/openAccess restricted use Geophysical And Astrophysical Fluid Dynamics (0309-1929) (Informa UK Limited), 2020-09 , Vol. 114 , N. 4-5 , P. 650-689 River plumes Gironde river (sub)mesoscale instabilities vertical mixing stratification text Publication info:eu-repo/semantics/article 2020 ftarchimer https://doi.org/10.1080/03091929.2020.1814275 2021-09-23T20:36:02Z In the Bay of Biscay (north-east Atlantic), long-living eddies and the frontal activity that they induce substantially contribute to mesoscale and submesoscale dynamics. Tides and river plumes also contribute to frontal activity. Biological productivity is sensitive to river plume fronts and to external forcings (tides and wind). Considering the importance of river plumes, we study here the structure, stability and vertical mixing processes in such river plumes (similar to those generated by the Gironde river). Restratification budget is considered here for evaluating stirring (frontogenetic/frontolytic) or vertical mixing (parametrised here from Ertel potential vorticity mixing) processes. Using high-resolution idealised numerical simulations, we analyse the evolution of the bulge and of the coastal part of this plume and we conduct sensitivity experiments to the river discharge, to southwesterly winds and to M2 tides. The bulge and the coastal current are stable (unstable) in case of moderate (high) river discharge, due to mixed barotropic/baroclinic instabilities. In the unstable case, near surface symmetric and vertical shear instabilities develop in the coastal current and in the core of the bulge where the Rossby number is large. When southwesterly winds blow, the river plume is squeezed near the coast by Ekman transport. The river plume is then subject to frontal symmetric, baroclinic, barotropic and vertical shear instabilities in the coastal part, north of the estuary (its far field). Conversely, in the presence of M2 tides, the river plume is barotropically, baroclinically and symmetrically unstable in its near field. Interior vertical mixing is induced by advective (stirring) and frontogenetic processes. Frontogenesis is dominant in the far-field (in the presence of southwesterlies) or in the near-field (when M2 tide is active). Frontogenesis is important in the far-field region in unforced river plumes (both with moderate and high river discharges). Potential vorticity is eroded in the far-field when southwesterlies blow. This is primarily due to the frictional processes which are dominant at the surface. This study has identified the instabilities which affect a river plume in different cases, and the local turbulent processes which alter the stratification. Article in Journal/Newspaper North East Atlantic Archimer (Archive Institutionnelle de l'Ifremer - Institut français de recherche pour l'exploitation de la mer) Geophysical & Astrophysical Fluid Dynamics 114 4-5 650 689 |
institution |
Open Polar |
collection |
Archimer (Archive Institutionnelle de l'Ifremer - Institut français de recherche pour l'exploitation de la mer) |
op_collection_id |
ftarchimer |
language |
English |
topic |
River plumes Gironde river (sub)mesoscale instabilities vertical mixing stratification |
spellingShingle |
River plumes Gironde river (sub)mesoscale instabilities vertical mixing stratification Ayouche, Adam Carton, Xavier Charria, Guillaume Theetten, Sebastien Ayoub, Nadia Instabilities and vertical mixing in river plumes: application to the Bay of Biscay |
topic_facet |
River plumes Gironde river (sub)mesoscale instabilities vertical mixing stratification |
description |
In the Bay of Biscay (north-east Atlantic), long-living eddies and the frontal activity that they induce substantially contribute to mesoscale and submesoscale dynamics. Tides and river plumes also contribute to frontal activity. Biological productivity is sensitive to river plume fronts and to external forcings (tides and wind). Considering the importance of river plumes, we study here the structure, stability and vertical mixing processes in such river plumes (similar to those generated by the Gironde river). Restratification budget is considered here for evaluating stirring (frontogenetic/frontolytic) or vertical mixing (parametrised here from Ertel potential vorticity mixing) processes. Using high-resolution idealised numerical simulations, we analyse the evolution of the bulge and of the coastal part of this plume and we conduct sensitivity experiments to the river discharge, to southwesterly winds and to M2 tides. The bulge and the coastal current are stable (unstable) in case of moderate (high) river discharge, due to mixed barotropic/baroclinic instabilities. In the unstable case, near surface symmetric and vertical shear instabilities develop in the coastal current and in the core of the bulge where the Rossby number is large. When southwesterly winds blow, the river plume is squeezed near the coast by Ekman transport. The river plume is then subject to frontal symmetric, baroclinic, barotropic and vertical shear instabilities in the coastal part, north of the estuary (its far field). Conversely, in the presence of M2 tides, the river plume is barotropically, baroclinically and symmetrically unstable in its near field. Interior vertical mixing is induced by advective (stirring) and frontogenetic processes. Frontogenesis is dominant in the far-field (in the presence of southwesterlies) or in the near-field (when M2 tide is active). Frontogenesis is important in the far-field region in unforced river plumes (both with moderate and high river discharges). Potential vorticity is eroded in the far-field when southwesterlies blow. This is primarily due to the frictional processes which are dominant at the surface. This study has identified the instabilities which affect a river plume in different cases, and the local turbulent processes which alter the stratification. |
format |
Article in Journal/Newspaper |
author |
Ayouche, Adam Carton, Xavier Charria, Guillaume Theetten, Sebastien Ayoub, Nadia |
author_facet |
Ayouche, Adam Carton, Xavier Charria, Guillaume Theetten, Sebastien Ayoub, Nadia |
author_sort |
Ayouche, Adam |
title |
Instabilities and vertical mixing in river plumes: application to the Bay of Biscay |
title_short |
Instabilities and vertical mixing in river plumes: application to the Bay of Biscay |
title_full |
Instabilities and vertical mixing in river plumes: application to the Bay of Biscay |
title_fullStr |
Instabilities and vertical mixing in river plumes: application to the Bay of Biscay |
title_full_unstemmed |
Instabilities and vertical mixing in river plumes: application to the Bay of Biscay |
title_sort |
instabilities and vertical mixing in river plumes: application to the bay of biscay |
publisher |
Informa UK Limited |
publishDate |
2020 |
url |
https://archimer.ifremer.fr/doc/00651/76286/77309.pdf https://doi.org/10.1080/03091929.2020.1814275 https://archimer.ifremer.fr/doc/00651/76286/ |
genre |
North East Atlantic |
genre_facet |
North East Atlantic |
op_source |
Geophysical And Astrophysical Fluid Dynamics (0309-1929) (Informa UK Limited), 2020-09 , Vol. 114 , N. 4-5 , P. 650-689 |
op_relation |
https://archimer.ifremer.fr/doc/00651/76286/77309.pdf doi:10.1080/03091929.2020.1814275 https://archimer.ifremer.fr/doc/00651/76286/ |
op_rights |
info:eu-repo/semantics/openAccess restricted use |
op_doi |
https://doi.org/10.1080/03091929.2020.1814275 |
container_title |
Geophysical & Astrophysical Fluid Dynamics |
container_volume |
114 |
container_issue |
4-5 |
container_start_page |
650 |
op_container_end_page |
689 |
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1766139269382930432 |