Seasonal variability of the Ekman transport and pumping in the upwelling system off central-northern Chile (∼ 30° S) based on a high-resolution atmospheric regional model (WRF)
Two physical mechanisms can contribute to coastal upwelling in eastern boundary current systems: offshore Ekman transport due to the predominant alongshore wind stress and Ekman pumping due to the cyclonic wind stress curl, mainly caused by the abrupt decrease in wind stress (drop-off) in a cross-sh...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-09-01
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| Series: | Ocean Science |
| Online Access: | http://www.ocean-sci.net/12/1049/2016/os-12-1049-2016.pdf |
| _version_ | 1818067363103244288 |
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| author | L. Bravo M. Ramos O. Astudillo B. Dewitte K. Goubanova |
| author_facet | L. Bravo M. Ramos O. Astudillo B. Dewitte K. Goubanova |
| author_sort | L. Bravo |
| collection | DOAJ |
| description | Two physical mechanisms can contribute to coastal upwelling in
eastern boundary current systems: offshore Ekman transport due to the
predominant alongshore wind stress and Ekman pumping due to the cyclonic
wind stress curl, mainly caused by the abrupt decrease in wind stress
(drop-off) in a cross-shore band of 100 km. This wind drop-off is thought to
be an ubiquitous feature in coastal upwelling systems and to regulate the
relative contribution of both mechanisms. It has been poorly studied along
the central-northern Chile region because of the lack in wind measurements
along the shoreline and of the relatively low resolution of the available
atmospheric reanalysis. Here, the seasonal variability in Ekman transport,
Ekman pumping and their relative contribution to total upwelling along the
central-northern Chile region (∼ 30° S) is evaluated from a
high-resolution atmospheric model simulation. As a first step, the simulation
is validated from satellite observations, which indicates a realistic
representation of the spatial and temporal variability of the wind along the
coast by the model. The model outputs are then used to document the fine-scale
structures in the wind stress and wind curl in relation to the
topographic features along the coast (headlands and embayments). Both wind
stress and wind curl had a clear seasonal variability with annual and
semiannual components. Alongshore wind stress maximum peak occurred in
spring, second increase was in fall and minimum in winter. When a threshold
of −3 × 10<sup>−5</sup> s<sup>−1</sup> for the across-shore gradient of
alongshore wind was considered to define the region from which the winds
decrease toward the coast, the wind drop-off length scale varied between 8
and 45 km. The relative contribution of the coastal divergence and Ekman
pumping to the vertical transport along the coast, considering the estimated
wind drop-off length, indicated meridional alternation between both
mechanisms, modulated by orography and the intricate coastline. Roughly,
coastal divergence predominated in areas with low orography and headlands.
Ekman pumping was higher in regions with high orography and the presence of
embayments along the coast. In the study region, the vertical transport
induced by coastal divergence and Ekman pumping represented 60 and 40 %
of the total upwelling transport, respectively. The potential role of Ekman
pumping on the spatial structure of sea surface temperature is also
discussed. |
| first_indexed | 2024-12-10T15:22:29Z |
| format | Article |
| id | doaj.art-6c8ad5a9996c4d8982964da51c500ca3 |
| institution | Directory Open Access Journal |
| issn | 1812-0784 1812-0792 |
| language | English |
| last_indexed | 2024-12-10T15:22:29Z |
| publishDate | 2016-09-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Ocean Science |
| spelling | doaj.art-6c8ad5a9996c4d8982964da51c500ca32022-12-22T01:43:39ZengCopernicus PublicationsOcean Science1812-07841812-07922016-09-011251049106510.5194/os-12-1049-2016Seasonal variability of the Ekman transport and pumping in the upwelling system off central-northern Chile (∼ 30° S) based on a high-resolution atmospheric regional model (WRF)L. Bravo0M. Ramos1O. Astudillo2B. Dewitte3K. Goubanova4Centro de Estudios Avanzados en Zonas Áridas (CEAZA), Coquimbo, ChileDepartamento de Biología, Facultad de Ciencias del Mar, Universidad Católica del Norte, Coquimbo, ChileCentro de Estudios Avanzados en Zonas Áridas (CEAZA), Coquimbo, ChileLaboratoire d'Etudes en Géophysique et Océanographie Spatiales (LEGOS), Toulouse, FranceCentre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), Toulouse, FranceTwo physical mechanisms can contribute to coastal upwelling in eastern boundary current systems: offshore Ekman transport due to the predominant alongshore wind stress and Ekman pumping due to the cyclonic wind stress curl, mainly caused by the abrupt decrease in wind stress (drop-off) in a cross-shore band of 100 km. This wind drop-off is thought to be an ubiquitous feature in coastal upwelling systems and to regulate the relative contribution of both mechanisms. It has been poorly studied along the central-northern Chile region because of the lack in wind measurements along the shoreline and of the relatively low resolution of the available atmospheric reanalysis. Here, the seasonal variability in Ekman transport, Ekman pumping and their relative contribution to total upwelling along the central-northern Chile region (∼ 30° S) is evaluated from a high-resolution atmospheric model simulation. As a first step, the simulation is validated from satellite observations, which indicates a realistic representation of the spatial and temporal variability of the wind along the coast by the model. The model outputs are then used to document the fine-scale structures in the wind stress and wind curl in relation to the topographic features along the coast (headlands and embayments). Both wind stress and wind curl had a clear seasonal variability with annual and semiannual components. Alongshore wind stress maximum peak occurred in spring, second increase was in fall and minimum in winter. When a threshold of −3 × 10<sup>−5</sup> s<sup>−1</sup> for the across-shore gradient of alongshore wind was considered to define the region from which the winds decrease toward the coast, the wind drop-off length scale varied between 8 and 45 km. The relative contribution of the coastal divergence and Ekman pumping to the vertical transport along the coast, considering the estimated wind drop-off length, indicated meridional alternation between both mechanisms, modulated by orography and the intricate coastline. Roughly, coastal divergence predominated in areas with low orography and headlands. Ekman pumping was higher in regions with high orography and the presence of embayments along the coast. In the study region, the vertical transport induced by coastal divergence and Ekman pumping represented 60 and 40 % of the total upwelling transport, respectively. The potential role of Ekman pumping on the spatial structure of sea surface temperature is also discussed.http://www.ocean-sci.net/12/1049/2016/os-12-1049-2016.pdf |
| spellingShingle | L. Bravo M. Ramos O. Astudillo B. Dewitte K. Goubanova Seasonal variability of the Ekman transport and pumping in the upwelling system off central-northern Chile (∼ 30° S) based on a high-resolution atmospheric regional model (WRF) Ocean Science |
| title | Seasonal variability of the Ekman transport and pumping in the upwelling
system off central-northern Chile (∼ 30° S) based on a
high-resolution atmospheric regional model (WRF) |
| title_full | Seasonal variability of the Ekman transport and pumping in the upwelling
system off central-northern Chile (∼ 30° S) based on a
high-resolution atmospheric regional model (WRF) |
| title_fullStr | Seasonal variability of the Ekman transport and pumping in the upwelling
system off central-northern Chile (∼ 30° S) based on a
high-resolution atmospheric regional model (WRF) |
| title_full_unstemmed | Seasonal variability of the Ekman transport and pumping in the upwelling
system off central-northern Chile (∼ 30° S) based on a
high-resolution atmospheric regional model (WRF) |
| title_short | Seasonal variability of the Ekman transport and pumping in the upwelling
system off central-northern Chile (∼ 30° S) based on a
high-resolution atmospheric regional model (WRF) |
| title_sort | seasonal variability of the ekman transport and pumping in the upwelling system off central northern chile ∼ 30° s based on a high resolution atmospheric regional model wrf |
| url | http://www.ocean-sci.net/12/1049/2016/os-12-1049-2016.pdf |
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