scholarly journals Subsurface Tropical Instability Waves in the Atlantic Ocean in Model and Observations 

2021 ◽  
Author(s):  
Mia Sophie Specht ◽  
Johann Jungclaus ◽  
Jürgen Bader
Keyword(s):  
Atlantic Ocean ◽  
Vertical Mixing ◽  
Ocean Surface ◽  
Ocean Dynamics ◽  
Upper Ocean ◽  
Tropical Atlantic ◽  
Mean Flow ◽  
Instability Waves ◽  
Tropical Atlantic Ocean ◽  
Tropical Instability Waves

<div> <p><span>Tropical instability waves (TIWs) near the ocean surface are present in all tropical oceans and are known to be important for air-sea interactions and regional climate variability. Recent studies based on observations in the Pacific Ocean found that apart from TIWs at the surface, there also exist subsurface TIWs (subTIWs) which can alter vertical mixing. To date, most studies have focused on TIW related dynamics near the ocean surface. However, to properly assess vertical mixing in the upper ocean, improved understanding of the vertical structure of TIWs and the influence of subTIWs is needed. In this study, </span>we show subTIW<span> presence</span> in the Atlantic Ocean for the first time using mooring observations.<span>Further, we characterize subTIWs in the tropical Atlantic Ocean with a special focus on subTIW spatial and temporal variability and their effect on mixing. For this, data covering almost two decades are used that were generated from a comprehensive, global, high-resolution ocean model forced by the reanalysis ERA5. We find subTIWs between 40 m depth and the thermocline in both model and observations and unlike TIWs, subTIWs are frequently active both north and south of the Equator. The results of our study suggest that subTIWs induce a multi-layer shear structure which has the potential to destabilize the mean flow and thereby cause mixing. These effects are strongest north of the Equator where TIWs and subTIWs act simultaneously, implying possible TIW/subTIW interactions. </span>We conclude that subTIWs are a feature of the tropical Atlantic Ocean with regionally varying implications for vertical mixing and heat fluxes. <span>In addition, subTIWs differ from TIWs in their temporal and regional occurrences Therefore, subTIWs should be considered in </span>f<span>u</span>ture assessments of upper ocean dynamics, particularly in subTIW dominated regions.</p> </div>

scholarly journals Multi-year satellite observations of instability waves in the Tropical Atlantic Ocean

Ocean Science ◽  
2005 ◽  
Vol 1 (2) ◽  
pp. 97-112 ◽  
Author(s):  
A. C. V. Caltabiano ◽  
I. S. Robinson ◽  
L. P. Pezzi
Keyword(s):  
Atlantic Ocean ◽  
Spectral Characteristics ◽  
Coupling Mechanism ◽  
Tropical Atlantic ◽  
Instability Waves ◽  
Tropical Atlantic Ocean ◽  
Tropical Instability Waves ◽  
Zonal Winds ◽  
Meridional Winds ◽  
The Waves

Abstract. Instability waves in the tropical Atlantic Ocean are analysed by microwave satellite-based data spanning from 1998 to 2001. This is the first multi-year observational study of the sea surface temperature (SST) signature of the Tropical Instability Waves (TIW) in the region. SST data were used to show that the waves spectral characteristics vary from year-to-year. They also vary on each latitude north of the equator, with the region of 1° N, 15° W concentrating the largest variability when the time series is averaged along the years. Analyses of wind components show that meridional winds are more affected near the equator and 1° N, while zonal winds are more affected further north at around 3° N and 4° N. Concurrent observations of SST, wind, atmospheric water vapour, liquid cloud water, precipitation rates and wind were used to suggest the possible influence of these waves on the Intertropical Convergence Zone (ITCZ). It seems that these instabilities have a large impact on the ITCZ due to its proximity of the equator, compared to its Pacific counterpart, and the geography of the tropical Atlantic basin. These analyses also suggest that the air-sea coupling mechanism suggested by Wallace can also be applied to the tropical Atlantic region.

scholarly journals Multi-year satellite observations of instability waves in the Tropical Atlantic Ocean

2005 ◽  
Vol 2 (1) ◽  
pp. 1-35 ◽  
Author(s):  
A. C. V. Caltabiano ◽  
I. S. Robinson ◽  
L. P. Pezzi
Keyword(s):  
Atlantic Ocean ◽  
Spectral Characteristics ◽  
Coupling Mechanism ◽  
Tropical Atlantic ◽  
Atlantic Region ◽  
Instability Waves ◽  
Tropical Atlantic Ocean ◽  
Zonal Winds ◽  
Meridional Winds ◽  
The Waves

Abstract. Instability waves in the tropical Atlantic Ocean are analysed by microwave satellite-based data spanning from 1998 to 2001. This is the first multi-year observational study of these waves in the region. Sea surface temperature (SST) data were used to show that the waves spectral characteristics vary from year-to-year. They also vary on each latitude north of the equator, with the region of 1° N, 15° W concentrating the largest variability when the time series is averaged along the years. Analyses of wind components show that meridional winds are more affected near the equator and 1° N, while zonal winds are more affected further north at around 3° N and 4° N. Concurrent observations of SST, wind, atmospheric water vapour, liquid cloud water, precipitation rates and wind were used to demonstrate the possible influence of these waves on the Intertropical Convergence Zone (ITCZ). It seems that these instabilities have a large impact on the ITCZ due to its proximity of the equator, compared to its Pacific counterpart, and the geography of the tropical Atlantic basin. These analyses also suggest that the air-sea coupling mechanism suggested by Wallace can also be applied to the tropical Atlantic region.

EUREC4A-OA/ATOMIC experiment  : Themohaline and dynamical descriptions of mesoscale and submesoscale structures of the Northwest Tropical Atlantic Ocean

2021 ◽  
Author(s):  
Pierre L'Hégaret ◽  
Sabrina Speich ◽  
Yanxu Chen ◽  
Gaston Manta ◽  
Léa Olivier ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
Mesoscale Eddies ◽  
Water Masses ◽  
Ocean Dynamics ◽  
Tropical Atlantic ◽  
Fine Scale ◽  
Surrounding Water ◽  
Tropical Atlantic Ocean ◽  
North Brazil ◽  
Oxygen Concentrations

<p>In January-February 2020, the EUREC4A-OA/ATOMIC experiment took place in the Northwest Tropical Atlantic Ocean with the overall objective of understanding the role of fine scale processes in the internal ocean dynamics and air-sea interaction. Four oceanographic vessels, the French Atalante, German Maria S Merian and Meteor, and the American Ron Brown, closely coordinated with air-borne observations and autonomous ocean platforms (gliders, saildrones, and drifters) to simultaneously measure the ocean and atmosphere east of the island of Barbados and the coast of Guyana in the western Tropical Atlantic. A whole battery of instruments measuring the thermohaline and dynamic characteristics of the region was launched. The fixed CTD stations, reaching great depths while measuring salinity, temperature, and oxygen concentrations, serve as a reference to calibrate and validate other devices, in particular, shallower uCTD, TSG, and MVP, acquired during ship transits, and autonomous gliders and saidrones. Combined, these datasets increase the horizontal resolution and thus the description of structures ranging from mesoscale to fine scale.</p><p>The Northwest Tropical Atlantic Ocean is a dynamical region filled with mesoscale eddies of different origins and transporting various water masses across the region. These eddies have rich and diverse characteristics ranging from shallow cyclonic and anticyclonic eddies to the deep reaching North Brazil Current (NBC) Rings. On the surface, down to 200 m depth, the signatures of shallow cyclones and anticyclones (NBC rings) were measured. The shallow mesoscale eddies, with core centered around a density of 25.5 kg m-3, advect highly saline and warm waters, with low oxygen concentrations compared to the surrounding water masses. Below, evolving at density around 26.7 kg m-3, thick anticyclones were observed, characterized by low temperature and salinity but with high values of oxygen, indicative of a South Atlantic origin. One was observed drifting slowly northward and another one at the NBC retroflection. Similarly, mesoscale cyclonic eddies were also observed both at the surface and at depth. Surface and subsurface eddies are not aligned vertically and they seem to evolve independently. </p><p>The large number and diversity (ship-mounted or autonomous) of observing platforms implemented in the project made made it possible to innovatively sample the upper-ocean frontal scales and stratification. It has been found that the interaction between the particularly fresh waters from the Amazon River, flowing northward along the shelf-break, and NBC rings create a rich variety of submesoscale fronts and a strong barrier layer, leading to interleaving. With the high vertical and horizontal resolutions, we quantify the layering and mixing processes at play.</p>

scholarly journals Lagrangian Study of Tropical Instability Vortices in the Atlantic

2008 ◽  
Vol 38 (2) ◽  
pp. 400-417 ◽  
Author(s):  
Pierre Dutrieux ◽  
Christophe E. Menkes ◽  
Jerome Vialard ◽  
Pierre Flament ◽  
Bruno Blanke
Keyword(s):  
Vertical Mixing ◽  
Ocean Dynamics ◽  
Lagrangian Analysis ◽  
Equatorial Undercurrent ◽  
Instability Waves ◽  
Sources And Sinks ◽  
Tropical Instability Waves ◽  
Trailing Edges ◽  
Convergent Flow ◽  
Lagrangian Study

Abstract Tropical instability waves and tropical instability vortices (TIVs) exert major controls on ocean dynamics, thermodynamics, and biology on intraseasonal to seasonal time scales. To understand the fundamental mechanisms at play, a Lagrangian analysis of the 3D circulation of westward-propagating TIVs was performed in a high-resolution Atlantic Ocean simulation. The model reproduces the main temperature and velocity features of the tropical Atlantic mean state and the TIVs. Lagrangian diagnostics were used to track the water masses transported in vortices and exchanged with surrounding waters. The 3D circulation within vortices is consistent with previous observations and dominated by anticyclonic rotation with downwelling and upwelling near the leading and trailing edges of the vortex, respectively. This convergent flow creates sharp gradients at the TIV southwestern edge, where vertical mixing is most efficient. While TIVs remain highly dynamically coherent throughout their lifetime, significant exchanges occur with their surroundings, with 50% of their water being renewed over one rotation cycle. A detailed investigation of the eddies’ sources and sinks reveals that they mostly transport southern water zonally, while northern waters are mostly passing through or fluxed southward in their lee. A notable source of entrained water is the Equatorial Undercurrent.

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

2007 ◽  
Vol 20 (19) ◽  
pp. 5012-5018 ◽  
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.

Influence of ocean salinity stratification on the tropical Atlantic Ocean surface

2021 ◽  
Author(s):  
Manon Gévaudan ◽  
Julien Jouanno ◽  
Fabien Durand ◽  
Guillaume Morvan ◽  
Lionel Renault ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
Ocean Surface ◽  
Tropical Atlantic ◽  
Salinity Stratification ◽  
Tropical Atlantic Ocean ◽  
Ocean Salinity
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