A model study of the seasonality of sea surface temperature and circulation in the Atlantic North-eastern Tropical Upwelling System

Faye, Saliou; Lazar, Alban; Sow, Bamol Ali; Gaye, Amadou Thierno

doi:10.3389/fphy.2015.00076

Cited by 32 publications

(38 citation statements)

References 41 publications

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“…To determine the air‐sea processes underlying the development of the HS and Atlantic Niño mode, a closed heat budget analysis has been computed interactively by NEMO‐ATLTROP025 model in the TA mixed layer (ML). The temporal variations of the ML temperature are given by a balance of atmospheric (a) and oceanic terms (b‐c), according to the equation (Faye et al, ; Polo et al, ):

\partial_{t} (〈〉, T) = \frac{Q_{s} ((), 1 - F_{z = h}) + Q *}{ρ C_{p} h} - (〈〉, \overset{U_{h}}{true} \cdot \overset{\partial_{h} T}{true}) + (〈〉, D_{l} ((), T)) - (〈〉, w \cdot \partial_{t} T) - \frac{1}{h} {(K_{z} \partial_{z} T)}_{z = h} + italicres

with

(⟨⟩ \cdot) = \frac{1}{h} \int_{- h}^{0} \cdot italicdz

. The brackets denote the vertical integration over the ML with T and h representing the temperature and depth of the ML respectively;

\overset{U_{h}}{true}

and w are the horizontal and vertical currents; D l (T) is the lateral diffusion operator and K z the vertical mixing coefficient.…”

Section: Methodsmentioning

confidence: 99%

“…To determine the air-sea processes underlying the development of the HS and Atlantic Niño mode, a closed heat budget analysis has been computed interactively by NEMO-ATLTROP025 model in the TA mixed layer (ML). The temporal variations of the ML temperature are given by a balance of atmospheric (a) and oceanic terms (b-c), according to the equation (Faye et al, 2015;Polo et al, 2015):…”

Section: Heat Budget Analysismentioning

confidence: 99%

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Ocean Dynamics Shapes the Structure and Timing of Atlantic Equatorial Modes

et al. 2019

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A recent study has brought to light the co-existence of two distinct Atlantic Equatorial Modes during negative phases of the Atlantic Multidecadal Variability: the Atlantic Niño and Horse-Shoe (HS) mode. Nevertheless, the associated air-sea interactions for HS mode have not been explored so far and the prevailing dynamic view of the Atlantic Niño has been questioned. Here, using a forced ocean model simulation, we find that for both modes, ocean dynamics is essential to explain the equatorial SST variations, while air-sea fluxes control the off-equatorial SST anomalies. Moreover, we demonstrate the key role played by ocean waves in shaping their distinct structure and timing. For the positive phase of both Atlantic Niño and HS, anomalous westerly winds trigger a set of equatorial downwelling Kelvin waves (KW) during spring-summer. These dKWs deepen the thermocline, favouring the equatorial warming through vertical diffusion and horizontal advection. Remarkably, for the HS, an anomalous north-equatorial wind stress curl excites an upwelling Rossby wave (RW), which propagates westward and is reflected at the western boundary becoming an equatorial upwelling KW. The uKW propagates to the east, activating the thermocline feedbacks responsible to cool the sea surface during summer months. This RW-reflected mechanism acts as a negative feedback causing the early termination of the HS mode. Our results provide an improvement in the understanding of the TAV modes and emphasize the importance of ocean wave activity to modulate the equatorial SST variability. These findings could be very useful to improve the prediction of the Equatorial Modes.Plain Language Summary A recent study has found how the inter-annual variations of sea surface temperature (SST) in the tropical Atlantic, are organized in two different equatorial modes during negative phases of the Atlantic Multidecadal Variability. These modes, which illustrate a particular and distinct spatial structure, are denoted as Atlantic Niño and Horse-Shoe mode. Here we show that, for both patterns, ocean dynamics is key to generate equatorial SSTs, while the off-equatorial SST anomalies are mainly explained by thermodynamic processes (heat fluxes exchanges). Outstandingly, we demonstrate that ocean waves have a substantial impact in the development and decay of Atlantic Niño and Horse-Shoe modes, shaping their distinct spatial configuration and timing. Our results bring to light the importance of ocean wave activity to explain the modulation of the equatorial Atlantic SST variability, which could be relevant to improve its predictability and associated climatic impacts.

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\partial_{t} (〈〉, T) = \frac{Q_{s} ((), 1 - F_{z = h}) + Q *}{ρ C_{p} h} - (〈〉, \overset{U_{h}}{true} \cdot \overset{\partial_{h} T}{true}) + (〈〉, D_{l} ((), T)) - (〈〉, w \cdot \partial_{t} T) - \frac{1}{h} {(K_{z} \partial_{z} T)}_{z = h} + italicres

with

(⟨⟩ \cdot) = \frac{1}{h} \int_{- h}^{0} \cdot italicdz

. The brackets denote the vertical integration over the ML with T and h representing the temperature and depth of the ML respectively;

\overset{U_{h}}{true}

and w are the horizontal and vertical currents; D l (T) is the lateral diffusion operator and K z the vertical mixing coefficient.…”

Section: Methodsmentioning

confidence: 99%

Section: Heat Budget Analysismentioning

confidence: 99%

Ocean Dynamics Shapes the Structure and Timing of Atlantic Equatorial Modes

et al. 2019

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“…The paths of the water masses highlighted by the Lagrangian simulations can be partly evaluated by the deployment of drifting buoys or dye release experiments in the coastal waters of Senegal. The use of drifting trajectory data from the COCES and COCES2 programs (Faye et al, 2015) could already provide useful information. The non hydrostatic process might be certainly an important limitation particularly in the coastal band (e.g.…”

Section: Discussionmentioning

confidence: 99%

“…The Southern Senegal Upwelling Sector (SSUS) has an intense activity of artisanal and industrial fishing and generally of strong anthropic pressures. Recently, several research activities has focused on this part of Canary current system, including numerous in-situ observations specifically in the upwelling zone located south of Dakar on a broad and shallow continental shelf (Ndoye et al, 2014(Ndoye et al, , 2016(Ndoye et al, , 2017Mbaye et al, 2015;Faye et al, 2015;Capet et al, 2017). Despite these efforts, its dynamics and even its mean circulation patterns are poorly known (Mbaye et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

A numerical modeling study of the Southern Senegal upwelling shelf: Circulation and upwelling source waters

Ndoye¹,

Capet²,

Estrade³

et al. 2018

Afr. J. Environ. Sci. Technol.

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The regional ocean circulation along the Southern Senegal shelf is studied using a numerical model for varying forcing fields during the upwelling season (November-May). The main objective is to study the shelf circulation of the marine environment in the Southern Senegal Upwelling Shelf (SSUS), the Lagrangian pathways by which waters are transported to the surface in the upwelling tongue and the fate of these waters. Model results are compared with hydrographic measurements during UPSEN2-ECOAO survey and satellite images datasets. The upwelling source waters and also the warm nearshore waters are analyzed, from a Lagrangian point of view, by computing the paths of particles that are passively advected by the regional ocean model velocity field (ROMS). It was found that the model is capable of representing the main characteristics of the SSUS whose Sea Surface Temperature (SST) patterns and their variability have an important similarities but the assessment of the current simulated by the model is less obvious because of the few available observations. The present results suggest that high frequency of wind has a strong influence over the mesoscale patterns of the crossshore circulation in association with local topography and the presence of the Cape Verde peninsula. These cross-shore circulations are dominated by an onshore flow around 14.5°N and an offshore flow around 14.1°N. The onshore flow is in agreement with the previous eulerian studies regarding the coastal divergence of the surface flow (upwelling) that was strongly localized within a few tens of kilometers south of the Cape Verde in the Hann Bight. Lagrangian experiments show also very clearly that coastal warm waters are upwelling waters that were advected from Hann Bight and underwent a strong warming by the heat flux from the atmosphere to the ocean in a shallow area (∼10 m); therefore, easy to warm up. All numerical solutions have shown a tendency of upwelling particles remaining on the shelf for more than a month. These results may explain the enrichment of water in the SSUS and suggest the need to consider the whole shelf as a retention area.

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“…Those works had identified the Petite Côte area (southern Cape Verde) and Casamance as nursery areas (Tiedemann and Brehmer, 2017;Brochier et al, 2018), and also an eggs and larvae retention area for small pelagics (Mbaye et al, 2015;Ndour et al, 2018). The effect of topographic features, such as capes and headlands modulates dramatically the onshore movement of upwelled water and favors the formation of stationary coastal upwelling centers (Faye et al, 2015;Capet et al, 2017). The retention of near-shore surface waters plays a major ecological role in the breeding of small pelagic fish (Ndoye et al, 2018).…”

Section: Size Spectrummentioning

confidence: 99%

Identification and Characterization of Critical Sites for Small Pelagic Fish in the Coastal Marine Area of Senegal, West Africa

Ndour

Assiatou²,

Thiam³

et al. 2019

JBLS

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Better management of coastal marine resources generally requires good knowledge of habitats and resources. This need led to the performance of an identification and bioecological characterization study of critical sites for small pelagics in the Senegalese coastal marine zone. Biological and ecological data were collected using beach seines (12 to 28 mm mesh) and surface drifting gillnets (28 to 36 mm mesh) at sites identified by fishermen on the basis of surveys. The results of the study highlight the bioecological characteristics of these sites: (i) the Port-Baie Hann site - a nursery and spawning site with a high diversity for the target species; it is under marine pollution threat; (ii) the Mbodiène-Ngazobil site, with high diversity for target species and the Kafountine-Cap site are nursery and spawning sites under high fishing pressure, (iii) the Diakhanor-Sangomar site - a spawning site under the potential threat of exploration of offshore Sangomar oil in addition to the high fishing pressure. This work is a first flagship contribution to a process that should lead to the development and control of new tools for the effective and sustainable management of small pelagics at national and regional scales.

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A model study of the seasonality of sea surface temperature and circulation in the Atlantic North-eastern Tropical Upwelling System

Cited by 32 publications

References 41 publications

Ocean Dynamics Shapes the Structure and Timing of Atlantic Equatorial Modes

Ocean Dynamics Shapes the Structure and Timing of Atlantic Equatorial Modes

A numerical modeling study of the Southern Senegal upwelling shelf: Circulation and upwelling source waters

Identification and Characterization of Critical Sites for Small Pelagic Fish in the Coastal Marine Area of Senegal, West Africa

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