A small-scale oceanic eddy off the coast of West Africa studied by multi-sensor satellite and surface drifter data

Alpers, Werner; Brandt, Peter; Lazar, Alban; Dagorne, Dominique; Sow, Bamol Ali; Faye, Saliou; Hansen, Morten W.; Rubino, Angelo; Poulain, Pierre‐Marie; Brehmer, Patrice

doi:10.1016/j.rse.2012.10.032

Cited by 46 publications

(29 citation statements)

References 67 publications

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“…Northern and southern Senegal upwelling sectors have traditionally been described as separated, with the Cape Verde headland being the physical barrier. The frequent occurrence of a filament flushing the northern upwelled waters offshore at Cape Verde, sometimes with the formation of a cold cyclonic eddy [Alpers et al, 2013] exemplifies this separation (e.g., see Figure 2c). A different type of situation where separation is also evident corresponds to Figures 2g, 2h, and 2i.…”

Section: Northern-southern Senegal Connection/separationmentioning

confidence: 90%

SST patterns and dynamics of the southern Senegal‐Gambia upwelling center

et al. 2014

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The southern end of the Canary current system comprises of an original upwelling center that has so far received little attention, the Southern Senegal-Gambia Upwelling Center (SSUC). We investigate its dynamical functioning by taking advantage of favorable conditions in terms of limited cloud coverage. Analyses and careful examinations of over 1500 satellite images of sea surface temperature scenes contextualized with respect to wind conditions confirm the regularity and stability of the SSUC dynamical functioning (as manifested by the recurrence and persistence of particular SST patterns). The analyses also reveal subtle aspects of its upwelling structure: shelf break cooling of surface waters consistent with internal tide breaking/mixing; complex interplay between local upwelling and the Mauritanian current off the Cape Verde headland; complexity of the inner-shelf/mid shelf frontal transition. The amplitude of the diurnal cycle suggests that large uncertainties exist in the SSUC heat budget. The studies limitations underscore the need for continuous in situ measurement in the SSUC, particularly of winds.

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Section: Northern-southern Senegal Connection/separationmentioning

confidence: 90%

SST patterns and dynamics of the southern Senegal‐Gambia upwelling center

et al. 2014

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“…Note, that these calculations represent conservative assumptions about the SACW transport since the contribution of short-lived, non-coherent, and smaller-scale eddies to the SACW transport is not included. For example, the highly energetic cyclone generated at the headland of Cap-Vert discussed in detail by Alpers et al (2013), which has a radius of 10 to 20 km and a Rossby number larger than 1, is not detected by the eddy detection algorithms used in this paper due to its small scale, but certainly contributed to the westward transport of near-coastal water masses.…”

Section: Zonal Eddy-dependent Westward Transport Of Sacwmentioning

confidence: 93%

“…One possible generation area for such eddies is the Cap-Vert headland at about 14.7 • N near the Senegalese coast . Analyzing surface drifter data and high-resolution satellite data, Alpers et al (2013) described the evolution of an energetic sub-mesoscale eddy at the Cap-Vert headland that was presumably generated by flow separation of a wind-forced coastal jet. Earlier studies reported on the importance of eddy transport in the TANWA region (e.g., Hagen, 1985;Barton, 1987;Zenk et al, 1991).…”

Section: Introductionmentioning

confidence: 99%

Occurrence and characteristics of mesoscale eddies in the tropical northeastern Atlantic Ocean

2016

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Abstract. Coherent mesoscale features (referred to here as eddies) in the tropical northeastern Atlantic Ocean (between 12-22 • N and 15-26 • W) are examined and characterized. The eddies' surface signatures are investigated using 19 years of satellite-derived sea level anomaly (SLA) data. Two automated detection methods are applied, the geometrical method based on closed streamlines around eddy cores, and the Okubo-Weiß method based on the relation between vorticity and strain. Both methods give similar results. Mean eddy surface signatures of SLA, sea surface temperature (SST) and sea surface salinity (SSS) anomalies are obtained from composites of all snapshots around identified eddy cores. Anticyclones/cyclones are identified by an elevation/depression of SLA and enhanced/reduced SST and SSS in their cores. However, about 20 % of all anticyclonically rotating eddies show reduced SST and reduced SSS instead. These kind of eddies are classified as anticyclonic mode-water eddies (ACMEs). About 146 ± 4 eddies per year with a minimum lifetime of 7 days are identified (52 % cyclones, 39 % anticyclones, 9 % ACMEs) with rather similar mean radii of about 56 ± 12 km. Based on concurrent in situ temperature and salinity profiles (from Argo float, shipboard, and mooring data) taken inside of eddies, distinct mean vertical structures of the three eddy types are determined. Most eddies are generated preferentially in boreal summer and along the West African coast at three distinct coastal headland regions and carry South Atlantic Central Water supplied by the northward flow within the Mauretanian coastal current system. Westward eddy propagation (on average about 3.00 ± 2.15 km d −1 ) is confined to distinct zonal corridors with a small meridional deflection dependent on the eddy type (anticyclones -equatorward, cyclones -poleward, ACMEs -no deflection). Heat and salt fluxes out of the coastal region and across the Cape Verde Frontal Zone, which separates the shadow zone from the ventilated subtropical gyre, are calculated.

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“…Previous studies have shown the influence of wind for the generation of both: (i) highly nonlinear cyclonic eddies (|Ro| > 1) linked to a wind burst event [Alpers et al, 2013] and (ii) anticyclonic eddies associated with baroclinic instabilities of growing flow meanders set up by shifts in the wind direction [Hansen et al, 2010] or bathymetric constraint of a wind-driven barotropic flow [Schaeffer et al, 2011].…”

Section: Processes Controlling Submesoscale Eddy Formation and Decaymentioning

confidence: 99%

Lagrangian and Eulerian characterization of two counter‐rotating submesoscale eddies in a western boundary current

et al. 2017

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In recent decades, high‐spatial resolution ocean radar and satellite imagery measurements have revealed a complex tangle of submesoscale filaments and eddies, in the surface velocity, temperature, and chlorophyll a fields. We use a suite of high‐resolution data to characterize two counter‐rotating, short‐lived eddies formed at the front between the warm East Australian Current (EAC) and temperate coastal waters (30°S, Eastern Australia). In this region, submesoscale filaments and short‐lived eddies are dynamically generated and decay at time scales of hours to days. Dominant cyclonic filaments of O(1) Rossby number formed along frontal jets and eddy boundaries, generating localized ageostrophic circulations at the submesoscale. Measurements of over‐ocean wind direction and surface currents from high‐frequency radars reveal the influence of the short‐term, small‐scale wind forcing on the surface circulation, enhancement of the horizontal shear, frontal jet destabilization, and the generation and decay of the cyclonic eddy. By contrast, the anticyclonic eddy formation was most likely associated with EAC mesoscale instability and anticyclonic vorticity. Lagrangian tracks show that surface particles can be temporarily trapped in the eddies and frontal convergent zones, limiting their transport. Mixing between EAC‐derived and coastal waters was increased along the frontal regions, and particles starting at the divergent regions around the eddies experienced significant dispersion at submesoscales. The cyclonic cold‐core eddy entrained high chlorophyll a shelf waters on its convergent side, suggesting spiral eddy cyclogenesis.

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A small-scale oceanic eddy off the coast of West Africa studied by multi-sensor satellite and surface drifter data

Cited by 46 publications

References 67 publications

SST patterns and dynamics of the southern Senegal‐Gambia upwelling center

SST patterns and dynamics of the southern Senegal‐Gambia upwelling center

Occurrence and characteristics of mesoscale eddies in the tropical northeastern Atlantic Ocean

Lagrangian and Eulerian characterization of two counter‐rotating submesoscale eddies in a western boundary current

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