Stacked jets in the deep equatorial Atlantic Ocean

Eden, Carsten; Dengler, Marcus

doi:10.1029/2007jc004298

Cited by 29 publications

(33 citation statements)

References 40 publications

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“…A number of processes of potential importance for the control of oxygen levels in the tropical ocean's thermocline are not properly represented in the current model. These include equatorial jets, which cannot be resolved by the coarse-resolution model and which also are notoriously difficult to simulate even in high-resolution models (Brandt et al, 2008;Eden and Dengler, 2008). Sensitivity studies with a somewhat refined lateral grid resolution in the tropics (from 1.8 to 0.9 degrees meridionally), however, showed essentially no change in the simulated DO trends (Somes, C., personal communication, 2011).…”

Section: Modelled Oxygen Changesmentioning

confidence: 99%

Mismatch between observed and modeled trends in dissolved upper-ocean oxygen over the last 50 yr

2012

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Abstract. Observations and model runs indicate trends in dissolved oxygen (DO) associated with current and ongoing global warming. However, a large-scale observation-tomodel comparison has been missing and is presented here. This study presents a first global compilation of DO measurements covering the last 50 yr. It shows declining upperocean DO levels in many regions, especially the tropical oceans, whereas areas with increasing trends are found in the subtropics and in some subpolar regions. For the Atlantic Ocean south of 20 • N, the DO history could even be extended back to about 70 yr, showing decreasing DO in the subtropical South Atlantic. The global mean DO trend between 50 • S and 50 • N at 300 dbar for the period 1960 to 2010 is −0.066 µmol kg −1 yr −1 . Results of a numerical biogeochemical Earth system model reveal that the magnitude of the observed change is consistent with CO 2 -induced climate change. However, the pattern correlation between simulated and observed patterns of past DO change is negative, indicating that the model does not correctly reproduce the processes responsible for observed regional oxygen changes in the past 50 yr. A negative pattern correlation is also obtained for model configurations with particularly low and particularly high diapycnal mixing, for a configuration that assumes a CO 2 -induced enhancement of the C : N ratios of exported organic matter and irrespective of whether climatological or realistic winds from reanalysis products are used to force the model. Depending on the model configuration the 300 dbar DO trend between 50 • S and 50 • N is −0.027 to −0.047 µmol kg −1 yr −1 for climatological wind forcing, with a much larger range of −0.083 to +0.027 µmol kg −1 yr −1 for different initializations of sensitivity runs with reanalysis wind forcing. Although numerical models reproduce the overall sign and, to some extent, magnitude of observed ocean deoxygenation, this degree of realism does not necessarily apply to simulated regional patterns and the representation of processes involved in their generation. Further analysis of the processes that can explain the discrepancies between observed and modeled DO trends is required to better understand the climate sensitivity of oceanic oxygen fields and predict potential DO changes in the future.

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Section: Modelled Oxygen Changesmentioning

confidence: 99%

Mismatch between observed and modeled trends in dissolved upper-ocean oxygen over the last 50 yr

2012

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“…1;Firing 1987;Schott et al 1995Schott et al , 2003Firing et al 1998;Gouriou et al 1999Gouriou et al , 2001Bourlès et al 2002Bourlès et al , 2003Send et al 2002;Ollitrault et al 2006;Eden and Dengler 2008;Ascani et al 2010;Brandt et al 2011Brandt et al , 2012Cravatte et al 2012;Youngs and Johnson 2014). This deep equatorial circulation (DEC; see a list of abbreviations in Tab.…”

Section: Overviewmentioning

confidence: 99%

The Deep Equatorial Ocean Circulation in Wind-Forced Numerical Solutions

Ascani

Firing

McCreary

et al. 2015

Journal of Physical Oceanography

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propagating mostly downward, consistent with observations. We demonstrate that both types of currents arise from the rectification of DEIV, consistent with previous theories. We also find that the EDJs contribute to maintaining the EICs, suggesting that the nonlinear energy transfer is more complex than previously thought. In Solution 2, the DEC is unrealistically weak and less spatially coherent than in the first simulation probably because of its weaker DEIV. Using intermediate solutions, we find that the main reason for this weaker DEIV is the use of realistic coastlines in Solution 2. It remains to be determined, what needs to be modified or included to obtain a realistic DEC in the more realistic configuration.

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“…Our interest here is mostly in the initial spinup period during the first 50 years of the model run during which energy appears to first propagate downward and then be reflected upward from the ocean bottom in the model. The first episode of the spin-up, from the beginning of the Eden and Dengler 2008). The most obvious difference is that the deep jets in the model extend over the whole depth range whereas in the observations they are confined above the depth reached by the Mid-Atlantic Ridge (about 2000 m).…”

Section: Resultsmentioning

confidence: 99%

“…The lack of EDJs in Earth System Models noted above is not limited to these particular models. Even high resolution, realistic ocean models have difficulty representing EDJs (Eden and Dengler 2008;Ascani et al 2015). Nevertheless, idealised model set-ups do support EDJs (e.g.…”

Section: Introductionmentioning

confidence: 99%

“…D 'Orgeville et al (2007) showed, in an idealised study, that destabilisation of Yanai waves (also called Mixed Rossby Gravity waves) generated near the western boundary and that have eastward group velocity into the interior of the ocean, can drive a high baroclinic mode structure following the argument of Hua et al (2008). Eden and Dengler (2008) also investigated the generation of vertically stacked jets in a high resolution ocean model where the energy source was thought to be fluctuations of the Deep Western Boundary Current in the model. Ascani et al (2015) described a mechanism whereby Yanai waves shed from tropical instability waves interact to support the EDJs.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

The emergence of equatorial deep jets in an idealised primitive equation model: an interpretation in terms of basin modes

et al. 2017

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Ocean circulation models do not generally exhibit equatorial deep jets (EDJs), even though EDJs are a recognised feature of the observed ocean circulation along the equator and they are thought to be important for tracer transport along the equator and even equatorial climate. EDJs are nevertheless found in nonlinear primitive equation models with idealised box geometry. Here we analyse several such model runs. We note that the variability of the zonal velocity in the model is dominated by the gravest linear equatorial basin mode for a wide range of baroclinic vertical normal modes and that the EDJs in the model are dominated by energy contained in vertical modes between 10 and 20. The emergence of the EDJs is shown to involve the linear superposition of several such neighbouring basin modes. Furthermore, the phase of these basin modes is set at the start of the model run and, in the case of the reference experiment, the same basin modes can be found in a companion experiment in which the amplitude of the forcing has been reduced by a factor of 1000. We also argue that following the spin-up, energy must be transferred between different vertical modes. This is because the model simulations are dominated by downward phase propagation following the spin-up whereas our reconstructions imply episodes of upward and downward propagation. The transfer of energy between the vertical modes is associated with a decadal modulation of the EDJs.

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Stacked jets in the deep equatorial Atlantic Ocean

Cited by 29 publications

References 40 publications

Mismatch between observed and modeled trends in dissolved upper-ocean oxygen over the last 50 yr

Mismatch between observed and modeled trends in dissolved upper-ocean oxygen over the last 50 yr

The Deep Equatorial Ocean Circulation in Wind-Forced Numerical Solutions

The emergence of equatorial deep jets in an idealised primitive equation model: an interpretation in terms of basin modes

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