A model perspective on the dynamics of the shadow zone of the eastern tropical North Atlantic – Part 1: the poleward slope currents along West Africa
The West African seaboard is one of the upwelling sectors that has received the least attention, and in situ observations relevant to its dynamics are particularly scarce. The current system in this sector is not well known and understood, e.g., in terms of seasonal variability, across-shore structu...
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ftcopernicus:oai:publications.copernicus.org:os66726 2023-05-15T17:36:49+02:00 A model perspective on the dynamics of the shadow zone of the eastern tropical North Atlantic – Part 1: the poleward slope currents along West Africa Kounta, Lala Capet, Xavier Jouanno, Julien Kolodziejczyk, Nicolas Sow, Bamol Gaye, Amadou Thierno 2019-01-07 application/pdf https://doi.org/10.5194/os-14-971-2018 https://os.copernicus.org/articles/14/971/2018/ eng eng doi:10.5194/os-14-971-2018 https://os.copernicus.org/articles/14/971/2018/ eISSN: 1812-0792 Text 2019 ftcopernicus https://doi.org/10.5194/os-14-971-2018 2020-07-20T16:23:08Z The West African seaboard is one of the upwelling sectors that has received the least attention, and in situ observations relevant to its dynamics are particularly scarce. The current system in this sector is not well known and understood, e.g., in terms of seasonal variability, across-shore structure, and forcing processes. This knowledge gap is addressed in two studies that analyze the mean seasonal cycle of an eddy-permitting numerical simulation of the tropical Atlantic. Part 1 is concerned with the circulation over the West African continental slope at the southernmost reach of the Canary Current system, between ∼8 and 20 ∘ N. The focus is on the depth range most directly implicated in the wind-driven circulation (offshore and coastal upwellings and Sverdrup transport) located above the potential density σ t =26.7 kg m −3 in the model (approx. above 250 m of depth). In this sector and for this depth range, the flow is predominantly poleward as a direct consequence of positive wind stress curl forcing, but the degree to which the magnitude of the upper ocean poleward transport reflects Sverdrup theory varies with latitude. The model poleward flow also exhibits a marked semiannual cycle with transport maxima in spring and fall. Dynamical rationalizations of these characteristics are offered in terms of wind forcing of coastal trapped waves and Rossby wave dynamics. Remote forcing by seasonal fluctuations of coastal winds in the Gulf of Guinea plays an instrumental role in the fall intensification of the poleward flow. The spring intensification appears to be related to wind fluctuations taking place at shorter distances north of the Gulf of Guinea entrance and also locally. Rossby wave activity accompanying the semiannual fluctuations of the poleward flow in the coastal waveguide varies greatly with latitude, which in turn exerts a major influence on the vertical structure of the poleward flow. Although the realism of the model West African boundary currents is difficult to determine precisely, the present in-depth investigation provides a renewed framework for future observational programs in the region. Text North Atlantic Copernicus Publications: E-Journals Curl ENVELOPE(-63.071,-63.071,-70.797,-70.797) Ocean Science 14 5 971 997 |
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Open Polar |
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Copernicus Publications: E-Journals |
op_collection_id |
ftcopernicus |
language |
English |
description |
The West African seaboard is one of the upwelling sectors that has received the least attention, and in situ observations relevant to its dynamics are particularly scarce. The current system in this sector is not well known and understood, e.g., in terms of seasonal variability, across-shore structure, and forcing processes. This knowledge gap is addressed in two studies that analyze the mean seasonal cycle of an eddy-permitting numerical simulation of the tropical Atlantic. Part 1 is concerned with the circulation over the West African continental slope at the southernmost reach of the Canary Current system, between ∼8 and 20 ∘ N. The focus is on the depth range most directly implicated in the wind-driven circulation (offshore and coastal upwellings and Sverdrup transport) located above the potential density σ t =26.7 kg m −3 in the model (approx. above 250 m of depth). In this sector and for this depth range, the flow is predominantly poleward as a direct consequence of positive wind stress curl forcing, but the degree to which the magnitude of the upper ocean poleward transport reflects Sverdrup theory varies with latitude. The model poleward flow also exhibits a marked semiannual cycle with transport maxima in spring and fall. Dynamical rationalizations of these characteristics are offered in terms of wind forcing of coastal trapped waves and Rossby wave dynamics. Remote forcing by seasonal fluctuations of coastal winds in the Gulf of Guinea plays an instrumental role in the fall intensification of the poleward flow. The spring intensification appears to be related to wind fluctuations taking place at shorter distances north of the Gulf of Guinea entrance and also locally. Rossby wave activity accompanying the semiannual fluctuations of the poleward flow in the coastal waveguide varies greatly with latitude, which in turn exerts a major influence on the vertical structure of the poleward flow. Although the realism of the model West African boundary currents is difficult to determine precisely, the present in-depth investigation provides a renewed framework for future observational programs in the region. |
format |
Text |
author |
Kounta, Lala Capet, Xavier Jouanno, Julien Kolodziejczyk, Nicolas Sow, Bamol Gaye, Amadou Thierno |
spellingShingle |
Kounta, Lala Capet, Xavier Jouanno, Julien Kolodziejczyk, Nicolas Sow, Bamol Gaye, Amadou Thierno A model perspective on the dynamics of the shadow zone of the eastern tropical North Atlantic – Part 1: the poleward slope currents along West Africa |
author_facet |
Kounta, Lala Capet, Xavier Jouanno, Julien Kolodziejczyk, Nicolas Sow, Bamol Gaye, Amadou Thierno |
author_sort |
Kounta, Lala |
title |
A model perspective on the dynamics of the shadow zone of the eastern tropical North Atlantic – Part 1: the poleward slope currents along West Africa |
title_short |
A model perspective on the dynamics of the shadow zone of the eastern tropical North Atlantic – Part 1: the poleward slope currents along West Africa |
title_full |
A model perspective on the dynamics of the shadow zone of the eastern tropical North Atlantic – Part 1: the poleward slope currents along West Africa |
title_fullStr |
A model perspective on the dynamics of the shadow zone of the eastern tropical North Atlantic – Part 1: the poleward slope currents along West Africa |
title_full_unstemmed |
A model perspective on the dynamics of the shadow zone of the eastern tropical North Atlantic – Part 1: the poleward slope currents along West Africa |
title_sort |
model perspective on the dynamics of the shadow zone of the eastern tropical north atlantic – part 1: the poleward slope currents along west africa |
publishDate |
2019 |
url |
https://doi.org/10.5194/os-14-971-2018 https://os.copernicus.org/articles/14/971/2018/ |
long_lat |
ENVELOPE(-63.071,-63.071,-70.797,-70.797) |
geographic |
Curl |
geographic_facet |
Curl |
genre |
North Atlantic |
genre_facet |
North Atlantic |
op_source |
eISSN: 1812-0792 |
op_relation |
doi:10.5194/os-14-971-2018 https://os.copernicus.org/articles/14/971/2018/ |
op_doi |
https://doi.org/10.5194/os-14-971-2018 |
container_title |
Ocean Science |
container_volume |
14 |
container_issue |
5 |
container_start_page |
971 |
op_container_end_page |
997 |
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1766136440391991296 |