Upper ocean circulation in the western tropical Atlantic in boreal fall 2000

Surface and vertical thermal structures, heat budget in the surface mixing layer, and mass transports are explored in the south-western tropical Atlantic (5oS-25oS / 20oW-47oW). That region, where part of the South Equatorial Current (SEC) enters at its eastern border, is of prime interest by feeding many western boundary currents along the eastern Brazilian edge, and by contributing to the climatic variability over the Northeast Brazil. The Regional Ocean Model System (ROMS) is used here to simulate a seasonal cycle of the ocean circulation with an isotropic horizontal grid resolution of 1/12o and 40 terrain-following layers. Such a high-resolution regional model allows illustrating the complexity of meso-scales phenomena which occur in that region. Model results are compared with the very first annual series of observed thermal profiles available in the region thanks to the three PIRATA-SWE moorings recently deployed. Simulated thermal structure at the upper ocean layers agrees with in-situ data set. Seasonal evolutions of atmospheric and oceanic balances involving in the mixing layer heat budget are locally discussed. The magnitude of oceanic components (mainly the vertical diffusion and the horizontal advection) is about of the same order than of atmospheric forcing, and practically always opposes to it, with some local and seasonal timing differences. Simulated meridional transports across three zonal sections extending from continent to PIRATA sites provide new insight in the knowledge of the western boundary current system. Another section running along the PIRATA-SWE array indicates how the divergence of SEC is complex. This result encourages the need and future expansion of the observational PIRATA array system in that region. Keywords: South Western Tropical Atlantic, Upper Ocean layers, Ocean heat budget, PIRATA-SWE moorings, ROMS

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Influence of El Niño on the Upper-Ocean Circulation in the Tropical Atlantic Ocean

Journal of Climate ◽

10.1175/jcli4292.1 ◽

2007 ◽

Vol 20 (19) ◽

pp. 5012-5018 ◽

Cited By ~ 9

Author(s):

Katja Lohmann ◽

Mojib Latif

Keyword(s):

Atlantic Ocean ◽

Ocean Circulation ◽

El Niño ◽

El Nino ◽

Equatorial Pacific ◽

Upper Ocean ◽

Tropical Atlantic ◽

Tropical Atlantic Ocean ◽

Eastern Equatorial Pacific ◽

Cell Strength

Abstract This study investigates the influence of El Niño on the upper-ocean circulation in the tropical Atlantic Ocean (via changes in the Atlantic trade winds) by analyzing observed sea surface temperature (SST) together with an ocean general circulation model integration forced by the NCEP–NCAR reanalysis. During periods with anomalously warm (cold) eastern equatorial Pacific SST, the southern Atlantic tropical cell is strengthened (weakened). The difference of the cell strength between El Niño and La Niña years is about 20% of the mean cell strength. However, the variability of the cell is not dominated by the remote forcing from the eastern equatorial Pacific but seems to be caused by intrinsic tropical Atlantic variability. A strengthening (weakening) for periods with anomalously warm (cold) eastern equatorial Pacific SST is also found for the zonal surface and subsurface currents. TOPEX/Poseidon altimetry data are used to validate the results based on the OGCM integration.

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Upper Ocean Circulation.

10.21236/ada330409 ◽

1997 ◽

Author(s):

Peter Niiler

Keyword(s):

Ocean Circulation ◽

Upper Ocean

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The impact of ocean-wave coupling on the upper ocean circulation during storm events

10.1002/essoar.10506457.1 ◽

2021 ◽

Cited By ~ 1

Author(s):

Diego Bruciaferri ◽

Marina Tonani ◽

Huw Lewis ◽

John Siddorn ◽

Andrew Saulter ◽

...

Keyword(s):

Ocean Circulation ◽

Ocean Wave ◽

Upper Ocean ◽

Storm Events ◽

Wave Coupling ◽

The Impact

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Study of the air-sea interactions at the mesoscale: the SEMAPHORE experiment

Annales Geophysicae ◽

10.1007/s00585-996-0986-6 ◽

1996 ◽

Vol 14 (9) ◽

pp. 986-1015 ◽

Cited By ~ 50

Author(s):

L. Eymard ◽

S. Planton ◽

P. Durand ◽

C. Le Visage ◽

P. Y. Le Traon ◽

...

Keyword(s):

Boundary Layer ◽

Atmospheric Boundary Layer ◽

Ocean Circulation ◽

Wave Model ◽

Heat Fluxes ◽

Sea Surface ◽

Upper Ocean ◽

Test Model ◽

Model Simulations ◽

Drifting Buoys

Abstract. The SEMAPHORE (Structure des Echanges Mer-Atmosphère, Propriétés des Hétérogénéités Océaniques: Recherche Expérimentale) experiment has been conducted from June to November 1993 in the Northeast Atlantic between the Azores and Madeira. It was centered on the study of the mesoscale ocean circulation and air-sea interactions. The experimental investigation was achieved at the mesoscale using moorings, floats, and ship hydrological survey, and at a smaller scale by one dedicated ship, two instrumented aircraft, and surface drifting buoys, for one and a half month in October-November (IOP: intense observing period). Observations from meteorological operational satellites as well as spaceborne microwave sensors were used in complement. The main studies undertaken concern the mesoscale ocean, the upper ocean, the atmospheric boundary layer, and the sea surface, and first results are presented for the various topics. From data analysis and model simulations, the main characteristics of the ocean circulation were deduced, showing the close relationship between the Azores front meander and the occurrence of Mediterranean water lenses (meddies), and the shift between the Azores current frontal signature at the surface and within the thermocline. Using drifting buoys and ship data in the upper ocean, the gap between the scales of the atmospheric forcing and the oceanic variability was made evident. A 2 °C decrease and a 40-m deepening of the mixed layer were measured within the IOP, associated with a heating loss of about 100 W m-2. This evolution was shown to be strongly connected to the occurrence of storms at the beginning and the end of October. Above the surface, turbulent measurements from ship and aircraft were analyzed across the surface thermal front, showing a 30% difference in heat fluxes between both sides during a 4-day period, and the respective contributions of the wind and the surface temperature were evaluated. The classical momentum flux bulk parameterization was found to fail in low wind and unstable conditions. Finally, the sea surface was investigated using airborne and satellite radars and wave buoys. A wave model, operationally used, was found to get better results compared with radar and wave-buoy measurements, when initialized using an improved wind field, obtained by assimilating satellite and buoy wind data in a meteorological model. A detailed analysis of a 2-day period showed that the swell component, propagating from a far source area, is underestimated in the wave model. A data base has been created, containing all experimental measurements. It will allow us to pursue the interpretation of observations and to test model simulations in the ocean, at the surface and in the atmospheric boundary layer, and to investigate the ocean-atmosphere coupling at the local and mesoscales.

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Simulating the upper ocean circulation on the belize shelf: An application of a triply nested-grid ocean circulation model

Journal of Ocean University of China ◽

10.1007/s11802-005-0052-0 ◽

2005 ◽

Vol 4 (4) ◽

pp. 315-328 ◽

Cited By ~ 2

Author(s):

Jinyu Sheng ◽

Liqun Tang ◽

Liang Wang

Keyword(s):

Ocean Circulation ◽

Circulation Model ◽

Upper Ocean ◽

Ocean Circulation Model ◽

Nested Grid

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Marginal Sea Overflows and the Upper Ocean Interaction

Journal of Physical Oceanography ◽

10.1175/2008jpo3934.1 ◽

2009 ◽

Vol 39 (2) ◽

pp. 387-403 ◽

Cited By ~ 13

Author(s):

Shinichiro Kida ◽

Jiayan Yang ◽

James F. Price

Keyword(s):

Ocean Circulation ◽

Potential Vorticity ◽

Baroclinic Instability ◽

Upper Ocean ◽

Marginal Sea ◽

The Mediterranean ◽

The Difference ◽

Set Up ◽

Numerical Model Experiments ◽

Gyre Circulation

Abstract Marginal sea overflows and the overlying upper ocean are coupled in the vertical by two distinct mechanisms—by an interfacial mass flux from the upper ocean to the overflow layer that accompanies entrainment and by a divergent eddy flux associated with baroclinic instability. Because both mechanisms tend to be localized in space, the resulting upper ocean circulation can be characterized as a β plume for which the relevant background potential vorticity is set by the slope of the topography, that is, a topographic β plume. The entrainment-driven topographic β plume consists of a single gyre that is aligned along isobaths. The circulation is cyclonic within the upper ocean (water columns are stretched). The transport within one branch of the topographic β plume may exceed the entrainment flux by a factor of 2 or more. Overflows are likely to be baroclinically unstable, especially near the strait. This creates eddy variability in both the upper ocean and overflow layers and a flux of momentum and energy in the vertical. In the time mean, the eddies accompanying baroclinic instability set up a double-gyre circulation in the upper ocean, an eddy-driven topographic β plume. In regions where baroclinic instability is growing, the momentum flux from the overflow into the upper ocean acts as a drag on the overflow and causes the overflow to descend the slope at a steeper angle than what would arise from bottom friction alone. Numerical model experiments suggest that the Faroe Bank Channel overflow should be the most prominent example of an eddy-driven topographic β plume and that the resulting upper-layer transport should be comparable to that of the overflow. The overflow-layer eddies that accompany baroclinic instability are analogous to those observed in moored array data. In contrast, the upper layer of the Mediterranean overflow is likely to be dominated more by an entrainment-driven topographic β plume. The difference arises because entrainment occurs at a much shallower location for the Mediterranean case and the background potential vorticity gradient of the upper ocean is much larger.

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Tropical Air–Sea Interactions Accelerate the Recovery of the Atlantic Meridional Overturning Circulation after a Major Shutdown

Journal of Climate ◽

10.1175/jcli4296.1 ◽

2007 ◽

Vol 20 (19) ◽

pp. 4940-4956 ◽

Cited By ~ 81

Author(s):

Uta Krebs ◽

A. Timmermann

Keyword(s):

Ocean Circulation ◽

North Atlantic ◽

Atlantic Meridional Overturning Circulation ◽

Meridional Overturning Circulation ◽

Tropical Atlantic ◽

Trade Winds ◽

The North ◽

Salinity Anomaly ◽

Meridional Overturning ◽

The North Atlantic

Abstract Using a coupled ocean–sea ice–atmosphere model of intermediate complexity, the authors study the influence of air–sea interactions on the stability of the Atlantic Meridional Overturning Circulation (AMOC). Mimicking glacial Heinrich events, a complete shutdown of the AMOC is triggered by the delivery of anomalous freshwater forcing to the northern North Atlantic. Analysis of fully and partially coupled freshwater perturbation experiments under glacial conditions shows that associated changes of the heat transport in the North Atlantic lead to a cooling north of the thermal equator and an associated strengthening of the northeasterly trade winds. Because of advection of cold air and an intensification of the trade winds, the intertropical convergence zone (ITCZ) is shifted southward. Changes of the accumulated precipitation lead to the generation of a positive salinity anomaly in the northern tropical Atlantic and a negative anomaly in the southern tropical Atlantic. During the shutdown phase of the AMOC, cross-equatorial oceanic surface flow is halted, preventing dilution of the positive salinity anomaly in the North Atlantic. Advected northward by the wind-driven ocean circulation, the positive salinity anomaly increases the upper-ocean density in the deep-water formation regions, thereby accelerating the recovery of the AMOC considerably. Partially coupled experiments that neglect tropical air–sea coupling reveal that the recovery time of the AMOC is almost twice as long as in the fully coupled case. The impact of a shutdown of the AMOC on the Indian and Pacific Oceans can be decomposed into atmospheric and oceanic contributions. Temperature anomalies in the Northern Hemisphere are largely controlled by atmospheric circulation anomalies, whereas those in the Southern Hemisphere are strongly determined by ocean dynamical changes and exhibit a time lag of several decades. An intensification of the Pacific meridional overturning cell in the northern North Pacific during the AMOC shutdown can be explained in terms of wind-driven ocean circulation changes acting in concert with global ocean adjustment processes.

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