Eddies in the Tropical Atlantic Ocean and Their Seasonal Variability

Aguedjou, Micael; Dadou, Isabelle; Chaigneau, Alexis; Morel, Yves; Alory, Gaël

doi:10.1029/2019gl083925

Cited by 38 publications

(74 citation statements)

References 48 publications

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“…Finally, the subsurface anticyclonic vortices have no detectable signatures on sea surface height, temperature or salinity (not shown). In fact, the present simulation is consistent with satellite observations where vortices are rarely detected in the Gulf of Guinea and along the equatorial band [68]. It is only close to the coast that surface vortices have been identified, but this is not discussed further here.…”

Section: High Frequency Mesoscale Circulationsupporting

confidence: 91%

“…Even though they offer an interesting and possible mechanism for the generation of subsurface zonal jets, observations are needed to confirm their realism. In particular, equatorial bands and the Gulf of Guinea are known to have few surface vortices [68,69]. The present simulation reveals a very rich and intense mesoscale activity below the pycnocline, with large anticyclonic vortices propagating westward for more than 100 days.…”

Section: Perspectivesmentioning

confidence: 61%

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From Mixing to the Large Scale Circulation: How the Inverse Cascade Is Involved in the Formation of the Subsurface Currents in the Gulf of Guinea

Assene

Morel

Delpech

et al. 2020

Fluids

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In this paper, we analyse the results from a numerical model at high resolution. We focus on the formation and maintenance of subsurface equatorial currents in the Gulf of Guinea and we base our analysis on the evolution of potential vorticity (PV). We highlight the link between submesoscale processes (involving mixing, friction and filamentation), mesoscale vortices and the mean currents in the area. In the simulation, eastward currents, the South and North Equatorial Undercurrents (SEUC and NEUC respectively) and the Guinea Undercurrent (GUC), are shown to be linked to the westward currents located equatorward. We show that east of 20∘ W, both westward and eastward currents are associated with the spreading of PV tongues by mesoscale vortices. The Equatorial Undercurrent (EUC) brings salty waters into the Gulf of Guinea. Mixing diffuses the salty anomaly downward. Meridional advection, mixing and friction are involved in the formation of fluid parcels with PV anomalies in the lower part and below the pycnocline, north and south of the EUC, in the Gulf of Guinea. These parcels gradually merge and vertically align, forming nonlinear anticyclonic vortices that propagate westward, spreading and horizontally mixing their PV content by stirring filamentation and diffusion, up to 20∘ W. When averaged over time, this creates regions of nearly homogeneous PV within zonal bands between 1.5∘ and 5∘ S or N. This mean PV field is associated with westward and eastward zonal jets flanking the EUC with the homogeneous PV tongues corresponding to the westward currents, and the strong PV gradient regions at their edges corresponding to the eastward currents. Mesoscale vortices strongly modulate the mean fields explaining the high spatial and temporal variability of the jets.

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Section: High Frequency Mesoscale Circulationsupporting

confidence: 91%

Section: Perspectivesmentioning

confidence: 61%

From Mixing to the Large Scale Circulation: How the Inverse Cascade Is Involved in the Formation of the Subsurface Currents in the Gulf of Guinea

Assene

Morel

Delpech

et al. 2020

Fluids

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“…Using the technique initially proposed by Chaigneau et al (2008) and Pegliasco et al (2015) and recently used in Trott et al (2018Trott et al ( , 2019 or Aguediou et al (2019), we apply an eddy-tracking algorithm to the GoM. This method first defines each eddy center by identifying local ADT minima (CEs) and maxima (AEs) and then defines each eddy edge as the largest ADT closed contour surrounding the eddy center.…”

Section: Eddy Trackingmentioning

confidence: 99%

Eddy Surface Characteristics and Vertical Structure in the Gulf of Mexico from Satellite Observations and Model Simulations

et al. 2020

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The Gulf of Mexico exhibits strong circulation due to the Loop Current System, along with high mesoscale eddy activity. In order to investigate eddy characteristics, we apply an automatic eddy‐tracking algorithm to absolute dynamic topography maps and analyze the spatial distribution and evolution of eddy attributes including amplitude, radius, and eddy kinetic energy. The Loop Current region in the eastern Gulf of Mexico is an area of robust eddy generation for both cyclonic and anticyclonic eddies. Anticyclonic eddies were generally characterized by smaller amplitudes and larger radii when compared to their cyclonic counterparts. We also examine eddy surface properties including temperature and salinity anomalies as well as chlorophyll‐a concentration and observe how these properties vary between the eastern and western Gulf of Mexico. Persistent features such as the Loop Current System and coastal low‐salinity, highly biologically productive waters dominate eddy properties in the eastern side of the basin. We also apply the eddy‐tracking algorithm to a regional Hybrid Coordinate Ocean Model validated using Argo floats. We find that this model accurately reflects surface characteristics in the mesoscale eddy field as well as the mean vertical eddy structure and use it to extend our analysis of eddy properties with depth. We find that subsurface characteristics of density, salinity, temperature, and velocities vary greatly between eddies in the eastern and western Gulf of Mexico. Through composite analysis of both surface and subsurface eddy properties, we gain a more complete picture of the mechanisms behind the observable characteristics of these eddies.

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“…It is also possible that the dispersive component included in the model did not adequately account for subgridscale dispersion and contributed to the discrepancy between observations and simulations. Most likely, inconsistencies between simulated and observed patterns are related to the relatively coarse spatial resolution of the currents (CROCO, OSCAR and GlobCurrent) used to simulate the particles (Hart-Davis et al, 2018), leading to unresolved eddy energy known to exist in the northern Gulf of Guinea (Djakouré et al, 2014) and the Tropical Atlantic Ocean (Aguedjou et al, 2019). The accuracy as well as the spatial and temporal resolution of the underlying velocity elds have a big impact on Lagrangian trajectories (Haza et al, 2012;Choi et al, 2017;D'Asaro et al, 2018).…”

mentioning

confidence: 99%

Assessment of a Lagrangian model using trajectories of oceanographic drifters and fishing devices in the Tropical Atlantic Ocean

Amemou

Koné

Aman

et al. 2020

Progress in Oceanography

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In the Tropical Atlantic Ocean, we assessed the accuracy of a Lagrangian model (Ichthyop) forced with velocity fields from a hydrodynamical model (CROCO) and two different remote sensing products (GlobCurrent and OSCAR) using trajectories of oceanographic drifters. Additionally, we evaluated the possibility to expand the drifters data using trajectories of GPS-buoy equipped drifting Fish Aggregating Devices (FADs). Tehe observed and simulated trajectories were compared in terms of spatial distribution, velocity distribution and a nondimensional skill score. For the drifters and FADs, the GlobCurrent and OSCAR products lead to similar performances as the CROCO model-ouputs in the broad studied domain. In the Gulf of Guinea, however, the CROCO model performed significantly better than the other two because the parent solution of CROCO benefited from its communication with a child grid of finer resolution in this region. On average, the simulations lead to an underestimation of the drifter and FAD velocities, likely because the spatial resolutions of the forcing products were insufficient and the time frequency at which they were produced were too low to resolve the relevant oceanic processes properly. We found a low skill for all models to simulate FAD trajectories, possibly because of the devices vertical structure that prevent FADs from drifting like water parcels. Our results therefore suggest that in the Tropical Atlantic the FAD dataset may not be appropriate to use for corroborating Lagrangian simulations. Highlights► Assessement of the accuracy of a Lagrangian model forced with different velocity fields using drifters and Fish Aggregating Devices (FADs). ► CROCO, OSCAR and GlobCurrent have the same performance. ► CROCO is better in the Gulf of Guinea than the satellite derived currents. ► The simulations underestimate the drifters and FADs velocities. ► FADs may not be appropriate to use for corroborating Lagrangian simulations.

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Eddies in the Tropical Atlantic Ocean and Their Seasonal Variability

Cited by 38 publications

References 48 publications

From Mixing to the Large Scale Circulation: How the Inverse Cascade Is Involved in the Formation of the Subsurface Currents in the Gulf of Guinea

From Mixing to the Large Scale Circulation: How the Inverse Cascade Is Involved in the Formation of the Subsurface Currents in the Gulf of Guinea

Eddy Surface Characteristics and Vertical Structure in the Gulf of Mexico from Satellite Observations and Model Simulations

Assessment of a Lagrangian model using trajectories of oceanographic drifters and fishing devices in the Tropical Atlantic Ocean

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