Zonal structure and seasonal variability of the Atlantic Equatorial Undercurrent

Johns, William E.; Brandt, Peter; Bourlès, Bernard; Tantet, Alexis; Papapostolou, Alexandros; Houk, Adam

doi:10.1007/s00382-014-2136-2

Cited by 40 publications

(78 citation statements)

References 55 publications

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“…10 with the mean EUC core and thermocline along the Equator represented. The NCCS experiment has a more zonally extended and stronger EUC, which is more realistic when compared to observational studies such as Johns et al (2014) but, still, both weaker and deeper than the observed counterpart, as revealed by the following discussion.…”

Section: Summary and Discussionmentioning

confidence: 61%

“…11f). The results obtained by Johns et al (2014), based on ADCP data, show that the EUC core at 0°E is in fact weaker than at 10°W. But, the values reduce from about 0.6 to 0.5 m s −1…”

Section: Summary and Discussionmentioning

confidence: 95%

“…3a, b, lies between 3-4 , for CTRL and NCCS experiments, respectively, in the tropical Atlantic (figure not shown). Weak easterlies result in weak upwelling, an excessively deep thermocline in the central and eastern parts of the Atlantic and, consequently, warm SST bias in that region (Johns et al 2014, and references therein). But, Johns et al (2014) also mention that the EUC simulated by coupled models is normally weaker, or less extensive zonally, than the observed one.…”

Section: Summary and Discussionmentioning

confidence: 99%

“…Weak easterlies result in weak upwelling, an excessively deep thermocline in the central and eastern parts of the Atlantic and, consequently, warm SST bias in that region (Johns et al 2014, and references therein). But, Johns et al (2014) also mention that the EUC simulated by coupled models is normally weaker, or less extensive zonally, than the observed one. As a consequence, the strong shear between the EUC and the upper opposite currents, which drives strong vertical mixing and , contours) at longitude 10°W for a CTRL, b NCCS experiments, and c the difference between them, and at longitude 0°E for d CTRL, e NCCS, and f the respective difference.…”

Section: Summary and Discussionmentioning

confidence: 99%

“…In this study, the Atlantic equatorial thermocline simulated by both versions of BESM, and by the other selected CMIP5 models, will be compared, to infer whether the new version of the model is able to alleviate such biases, since improvements were noticed in its outgoing longwave radiation and trade winds over the tropical Atlantic. Other reported mechanism for SST biases is a poor representation of the EUC, a subsurface current with a major role in the equatorial circulation since surface waters, which are subducted near 20°N and 20°S and move westward and equatorward, eventually reach the EUC and are carried eastward across the basin, providing cool and salty waters to central and eastern equatorial regions (Johns et al 2014, and references therein). Due to its importance, in this study, the Atlantic EUC simulated by the models is investigated, through a comparison of its core mean depth and seasonal variability with observations provided by the prediction and research array of moored buoys over the Tropical Atlantic (PIRATA) project.…”

Section: Introductionmentioning

confidence: 99%

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Equatorial Atlantic Ocean dynamics in a coupled ocean–atmosphere model simulation

et al. 2015

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The ocean temperatures and zonal currents at the equatorial Atlantic simulated by an improved version of the Brazilian earth system model (BESM), with changes in the cloud cover scheme and optical properties of the atmospheric component, are analyzed and compared to those obtained from a previous version of BESM and also from other seven selected CMIP5 models. It is shown that this updated version of BESM, despite some persistent biases, more accurately represents the surface temperature variation at the Equator and the equatorial thermocline east-west slope. These improvements are associated to a more realistic seasonal cycle achieved for the Atlantic equatorial undercurrent, as well as sea surface temperatures and zonal wind stress. The better simulation of the equatorial undercurrent is, in its turn, credited to a more realistic representation of the surface wind position and strength at the tropical Atlantic by the coupled model. With many of the systematic errors noticed in the previous version of the model alleviated, this version of BESM can be considered as a useful tool for modelers involved in Atlantic variability studies.

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Section: Summary and Discussionmentioning

confidence: 61%

“…11f). The results obtained by Johns et al (2014), based on ADCP data, show that the EUC core at 0°E is in fact weaker than at 10°W. But, the values reduce from about 0.6 to 0.5 m s −1…”

Section: Summary and Discussionmentioning

confidence: 95%

Section: Summary and Discussionmentioning

confidence: 99%

Section: Summary and Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Equatorial Atlantic Ocean dynamics in a coupled ocean–atmosphere model simulation

et al. 2015

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Major role of the equatorial current system in setting oxygen levels in the eastern tropical Atlantic Ocean: A high-resolution model study

Duteil

Schwarzkopf

Böning

et al. 2014

Geophys. Res. Lett.

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Understanding the causes of the observed expansion of tropical ocean's oxygen minimum zones (OMZs) is hampered by large biases in the representation of oxygen distribution in climate models, pointing to incorrectly represented mechanisms. Here we assess the oxygen budget in a global biogeochemical circulation model, focusing on the Atlantic Ocean. While a coarse (0.5°) configuration displays the common bias of too large and too intense OMZs, the oxygen concentration in an eddying (0.1°) configuration is higher and closer to observations. This improvement is traced to a stronger oxygen supply by a more realistic representation of the equatorial and off-equatorial undercurrents, outweighing the concurrent increase in oxygen consumption associated with the stronger nutrient supply. The sensitivity of the eastern tropical Atlantic oxygen budget to the equatorial current intensity suggests that temporal changes in the eastward oxygen transport from the well-oxygenated western boundary region might partly explain variations in the OMZs.

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Mixed layer heat and salinity budgets during the onset of the 2011 Atlantic cold tongue

Schlundt

Brandt

Dengler

et al. 2014

J. Geophys. Res. Oceans

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The mixed layer (ML) temperature and salinity changes in the central tropical Atlantic have been studied by a dedicated experiment (Cold Tongue Experiment (CTE)) carried out from May to July 2011. The CTE was based on two successive research cruises, a glider swarm, and moored observations. The acquired in situ data sets together with satellite, reanalysis, and assimilation model data were used to evaluate box-averaged ML heat and salinity budgets for two subregions: (1) the western equatorial Atlantic cold tongue (ACT) (23 -10 W) and (2) the region north of the ACT. The strong ML heat loss in the ACT region during the CTE was found to be the result of the balance of warming due to net surface heat flux and cooling due to zonal advection and diapycnal mixing. The northern region was characterized by weak cooling and the dominant balance of net surface heat flux and zonal advection. A strong salinity increase occurred at the equator, 10 W, just before the CTE. During the CTE, ML salinity in the ACT region slightly increased.Largest contributions to the ML salinity budget were zonal advection and the net surface freshwater flux. While essential for the ML heat budget in the ACT region, diapycnal mixing played only a minor role for the ML salinity budget. In the region north of the ACT, the ML freshened at the beginning of the CTE due to precipitation, followed by a weak salinity increase. Zonal advection changed sign contributing to ML freshening at the beginning of the CTE and salinity increase afterward.

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Zonal structure and seasonal variability of the Atlantic Equatorial Undercurrent

Cited by 40 publications

References 55 publications

Equatorial Atlantic Ocean dynamics in a coupled ocean–atmosphere model simulation

Equatorial Atlantic Ocean dynamics in a coupled ocean–atmosphere model simulation

Major role of the equatorial current system in setting oxygen levels in the eastern tropical Atlantic Ocean: A high-resolution model study

Mixed layer heat and salinity budgets during the onset of the 2011 Atlantic cold tongue

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