The signature of mesoscale eddies on the air‐sea turbulent heat fluxes in the South Atlantic Ocean

Bôas, Ana B. Villas; Sato, O. T.; Chaigneau, Alexis; Castelão, Guilherme P.

doi:10.1002/2015gl063105

Cited by 94 publications

(106 citation statements)

References 46 publications

(75 reference statements)

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“…Cheney and Richardson, 1976), bottom stress (de Steur and van Leeuwen, 2009), interaction with internal waves (Polzin, 2010), damping by air-sea fluxes (e.g. Villas Bôas et al, 2015), and generation of Rossby waves (McDonald, 1998;van Sebille et al, 2010). The eddy amplitude high SD values we see close to the BC and EAC retroflections (38 and 31 • S, respectively) indicate that the eddies occurring there are not only large anticyclonic retroflection eddies but eddies of a large range of sizes.…”

Section: Discussionmentioning

confidence: 71%

Eddy surface properties and propagation at Southern Hemisphere western boundary current systems

2015

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Abstract. Oceanic eddies exist throughout the world oceans, but are more energetic when associated with western boundary currents (WBC) systems. In these regions, eddies play an important role in mixing and energy exchange. Therefore, it is important to quantify and qualify eddies associated with these systems. This is particularly true for the Southern Hemisphere WBC system where only few eddy censuses have been performed to date. In these systems, important aspects of the local eddy population are still unknown, like their spatial distribution and propagation patterns. Moreover, the understanding of these patterns helps to establish monitoring programs and to gain insight in how eddies would affect local mixing. Here, we use a global eddy data set to qualify eddies based on their surface characteristics in the Agulhas Current (AC), the Brazil Current (BC) and the East Australian Current (EAC) systems. The analyses reveal that eddy propagation within each system is highly forced by the local mean flow and bathymetry. Large values of eddy amplitude and temporal variability are associated with the BC and EAC retroflections, while small values occur in the centre of the Argentine Basin and in the Tasman Sea. In the AC system, eddy polarity dictates the propagation distance. BC system eddies do not propagate beyond the Argentine Basin, and are advected by the local ocean circulation. EAC system eddies from both polarities cross south of Tasmania but only the anticyclonic ones reach the Great Australian Bight. For all three WBC systems, both cyclonic and anticyclonic eddies present a geographical segregation according to radius size and amplitude. Regions of high eddy kinetic energy are associated with the eddies' mean amplitudes, and not with their densities.

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Section: Discussionmentioning

confidence: 71%

Eddy surface properties and propagation at Southern Hemisphere western boundary current systems

2015

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“…Observational characterizations of mesoscale signatures in mixed‐layer depth have been typically limited to single event field campaigns (see the studies mentioned above). In contrast, satellite observational oceanography has facilitated a range of systematic studies of mesoscale signals in variables measurable from the surface, such as temperature [ Hausmann and Czaja , ], chlorophyll [ Gaube et al ., ], ocean‐atmosphere coupling and air‐sea exchanges [ Chelton et al ., ; O'Neill et al ., ; Frenger et al ., ; Villas Bôas et al ., ], and sea surface height, the latter allowing for a dynamical characterization of mesoscale features for the global ocean [e.g., Chelton et al ., ].…”

Section: Introductionmentioning

confidence: 99%

Observed mesoscale eddy signatures in Southern Ocean surface mixed‐layer depth

2017

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Combining satellite altimetry with Argo profile data a systematic observational estimate of mesoscale eddy signatures in surface mixed‐layer depth (MLD) is provided across the Southern Ocean (SO). Eddy composite MLD anomalies are shallow in cyclones, deep in anticyclones, and increase in magnitude with eddy amplitude. Their magnitudes show a pronounced seasonal modulation roughly following the depth of the climatological mixed layer. Weak eddies of the relatively quiescent SO subtropics feature peak late‐winter perturbations of ±10 m. Much larger MLD perturbations occur over the vigorous eddies originating along the Antarctic Circumpolar Current (ACC) and SO western boundary current systems, with late‐winter peaks of −30 m and +60 m in the average over cyclonic and anticyclonic eddy cores (a difference of ≈ 100 m). The asymmetry between modest shallow cyclonic and pronounced deep anticyclonic anomalies is systematic and not accompanied by corresponding asymmetries in eddy amplitude. Nonetheless, the net deepening of the climatological SO mixed layer by this asymmetry in eddy MLD perturbations is estimated to be small (few meters). Eddies are shown to enhance SO MLD variability with peaks in late winter and eddy‐intense regions. Anomalously deep late‐winter mixed layers occur disproportionately within the cores of anticyclonic eddies, suggesting the mesoscale heightens the frequency of deep winter surface‐mixing events along the eddy‐intense regions of the SO. The eddy modulation in MLD reported here provides a pathway via which the oceanic mesoscale can impact air‐sea fluxes of heat and carbon, the ventilation of water masses, and biological productivity across the SO.

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“…These nonlinear mesoscale eddies trap water into their cores and participate to the general mixing and redistribution of physical and bio-geochemical properties from the coastal regions to the open ocean [Logerwell and Smith, 2001;Barton and Ar ıstegui, 2004;Rubio et al, 2009;Morales et al, 2012;Dong et al, 2014]. Along their paths, they can also modulate the biogeochemistry and ocean productivity [Correa-Ramirez et al, 2007;Marchesiello and Estrade, 2007;Gruber et al, 2011;Stramma et al, 2013;Mahadevan, 2014] but also impact the overlaying atmosphere interactions affecting heat fluxes at the sea-air interface, winds, cloud cover and precipitations [Morrow and Le Traon, 2012;Frenger et al, 2013;Mahadevan, 2014;Villas Bôas et al, 2015].…”

Section: Introductionmentioning

confidence: 99%

Main eddy vertical structures observed in the four major Eastern Boundary Upwelling Systems

2015

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In the four major Eastern Boundary Upwelling Systems (EBUS), mesoscale eddies are known to modulate the biological productivity and transport near‐coastal seawater properties toward the offshore ocean, however little is known about their main characteristics and vertical structure. This study combines 10 years of satellite‐altimetry data and Argo float profiles of temperature and salinity, and our main goals are (i) to describe the main surface characteristics of long‐lived eddies formed in each EBUS and their evolution, and (ii) to depict the main vertical structure of the eddy‐types that coexist in these regions. A clustering analysis of the Argo profiles surfacing within the long‐lived eddies of each EBUS allows us to determine the proportion of surface and subsurface‐intensified eddies in each region, and to describe their vertical structure in terms of temperature, salinity and dynamic height anomalies. In the Peru‐Chile Upwelling System, 55% of the sampled anticyclonic eddies (AEs) have subsurface‐intensified maximum temperature and salinity anomalies below the seasonal pycnocline, whereas 88% of the cyclonic eddies (CEs) are surface‐intensified. In the California Upwelling System, only 30% of the AEs are subsurface‐intensified and all of the CEs show maximum anomalies above the pycnocline. In the Canary Upwelling System, ∼40% of the AEs and ∼60% of the CEs are subsurface‐intensified with maximum anomalies extending down to 800 m depth. Finally, the Benguela Upwelling System tends to generate ∼40–50% of weak surface‐intensified eddies and ∼50–60% of much stronger subsurface‐intensified eddies with a clear geographical distribution. The mechanisms involved in the observed eddy vertical shapes are discussed.

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The signature of mesoscale eddies on the air‐sea turbulent heat fluxes in the South Atlantic Ocean

Cited by 94 publications

References 46 publications

Eddy surface properties and propagation at Southern Hemisphere western boundary current systems

Eddy surface properties and propagation at Southern Hemisphere western boundary current systems

Observed mesoscale eddy signatures in Southern Ocean surface mixed‐layer depth

Main eddy vertical structures observed in the four major Eastern Boundary Upwelling Systems

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