scholarly journals Deep Western Boundary Current transport variability in the South Atlantic: preliminary results from a pilot array at 34.5° S

2012 ◽  
Vol 9 (2) ◽  
pp. 977-1008 ◽  
Author(s):  
C. S. Meinen ◽  
A. R. Piola ◽  
R. C. Perez ◽  
S. L. Garzoli
Keyword(s):  
Annual Cycle ◽  
Statistical Significance ◽  
South Atlantic ◽  
Western Boundary Current ◽  
Meridional Overturning Circulation ◽  
Western Boundary ◽  
Model Output ◽  
Boundary Current ◽  
The South ◽  
Deep Western Boundary Current

Abstract. The first direct estimates of the temporal variability of the absolute transport of the Deep Western Boundary Current (DWBC) at 34.5° S in the South Atlantic Ocean are obtained using just under one year of data from a line of four pressure-equipped inverted echo sounders. Hydrographic sections collected in 2009 and 2010 confirm the presence of the DWBC, one of the main deep pathways of the Meridional Overturning Circulation, based on neutral density, temperature, salinity, and oxygen values. Both observations confirm that the DWBC reconstitutes itself after breaking into eddies in the western sub-tropical Atlantic near 8° S. The amplitude and spectral character of the DWBC transport variability are comparable with those observed at 26.5° N, where longer records exist, with the DWBC at 34.5° S exhibiting a transport standard deviation of 25 Sv and variations of ~40 Sv occurring within periods as short as a few days. There is little indication of an annual cycle in the DWBC transports, although the observation record is too short to be definitive, and the dominant time scale during the first year of the experiment was about 9–10 days. A "Monte Carlo-style" analysis using 27 yr of model output from the same location as the observations indicates that another 48–60 months of data will be required to encompass a fairly complete span of deep transport variability. The model suggests the presence of an annual cycle in DWBC transport, however the statistical significance of the annual cycle with even 27 yr of model output is low, suggesting that annual period variations in the model are weak as well.

scholarly journals Deep Western Boundary Current transport variability in the South Atlantic: preliminary results from a pilot array at 34.5° S

Ocean Science ◽  
2012 ◽  
Vol 8 (6) ◽  
pp. 1041-1054 ◽  
Author(s):  
C. S. Meinen ◽  
A. R. Piola ◽  
R. C. Perez ◽  
S. L. Garzoli
Keyword(s):  
Annual Cycle ◽  
Statistical Significance ◽  
South Atlantic ◽  
Western Boundary Current ◽  
Meridional Overturning Circulation ◽  
Western Boundary ◽  
Model Output ◽  
Boundary Current ◽  
The South ◽  
Deep Western Boundary Current

Abstract. The first direct estimates of the temporal variability of the absolute transport in the Deep Western Boundary Current (DWBC) at 34.5° S in the South Atlantic Ocean are obtained using just under one year of data from a line of four pressure-equipped inverted echo sounders. Hydrographic sections collected in 2009 and 2010 confirm, based on neutral density, temperature, salinity, and oxygen values, the presence of the DWBC, one of the main deep pathways of the Meridional Overturning Circulation. Both data sets indicate that the DWBC reconstitutes itself after breaking into eddies in the western sub-tropical Atlantic near 8° S. The amplitude and spectral character of the DWBC transport variability are comparable with those observed in the North Atlantic, where longer records exist, with the DWBC at 34.5° S exhibiting a transport standard deviation of 25 Sv and variations of ∼ 40 Sv occurring within periods as short as a few days. There is little indication of an annual cycle in the DWBC transports, although the observational records are too short to be definitive. A Monte Carlo-style analysis using 27 yr of model output from the same location as the observations indicates that about 48–60 months of data will be required to fully assess the deep transport variability. The model suggests the presence of an annual cycle in DWBC transport, however its statistical significance with even 27 yr of model output is low, suggesting that seasonal variations in the model are weak.

scholarly journals The fate of the Deep Western Boundary Current in the South Atlantic

2015 ◽  
Vol 103 ◽  
pp. 125-136 ◽  
Author(s):  
Silvia L. Garzoli ◽  
Shenfu Dong ◽  
Rana Fine ◽  
Christopher S. Meinen ◽  
Renellys C. Perez ◽  
...  
Keyword(s):  
South Atlantic ◽  
Western Boundary Current ◽  
Western Boundary ◽  
Boundary Current ◽  
The South ◽  
Deep Western Boundary Current

scholarly journals Characteristics and causes of Deep Western Boundary Current transport variability at 34.5° S during 2009–2014

2016 ◽  
Author(s):  
Christopher S. Meinen ◽  
Silvia L. Garzoli ◽  
Renellys C. Perez ◽  
Edmo Campos ◽  
Alberto R. Piola ◽  
...  
Keyword(s):  
Volume Transport ◽  
Horizontal Resolution ◽  
Western Boundary Current ◽  
Meridional Overturning Circulation ◽  
Time Variability ◽  
Western Boundary ◽  
Boundary Current ◽  
Meridional Heat Transport ◽  
Data Set ◽  
Deep Western Boundary Current

Abstract. The Deep Western Boundary Current (DWBC) at 34.5° S in the South Atlantic carries a significant fraction of the cold deep limb of the Meridional Overturning Circulation (MOC), and therefore its variability affects both the meridional heat transport and the regional and global climate. Nearly six years of observations from a line of pressure-equipped inverted echo sounders (PIES) have yielded an unprecedented data set for studying the characteristics of the time-varying DWBC volume transport at 34.5° S. Furthermore, the horizontal resolution of the observing array was greatly improved in December 2012 with the addition of two current-and-pressure-equipped inverted echo sounders (CPIES) at the midpoints of three of the existing sites. Regular hydrographic sections along the PIES/CPIES line confirm the presence of recently-ventilated North Atlantic Deep Water carried by the DWBC. The time-mean absolute geostrophic transport integrated within the DWBC layer, defined between 800–4800 dbar, and within longitude bounds of 51.5° W to 44.5° W is −15 Sv (1 Sv = 106 m3 s−1; negative indicates southward flow). The observed peak-to-peak range in volume transport using these integration limits is from −89 Sv to +50 Sv, and the temporal standard deviation is 23 Sv. Testing different vertical integration limits based on time-mean water-mass property levels yields small changes to these values, but no significant alteration to the character of the transport time series. The time-mean southward DWBC flow at this latitude is confined west of 49.5° W, with recirculations dominating the flow further offshore. As with other latitudes where the DWBC has been observed for multiple years, the time variability greatly exceeds the time-mean, suggesting the presence of strong coherent vortices and/or Rossby Wave-like signals propagating to the boundary from the interior.

scholarly journals THE BIFURCATION OF THE WESTERN BOUNDARY CURRENT SYSTEM OF THE SOUTH ATLANTIC OCEAN

2014 ◽  
Vol 32 (2) ◽  
pp. 241 ◽  
Author(s):  
Janini Pereira ◽  
Mariela Gabioux ◽  
Martinho Marta Almeida ◽  
Mauro Cirano ◽  
Afonso M. Paiva ◽  
...  
Keyword(s):  
High Resolution ◽  
Atlantic Ocean ◽  
Ocean Circulation ◽  
South Atlantic ◽  
Western Boundary Current ◽  
South Atlantic Ocean ◽  
Western Boundary ◽  
Intermediate Water ◽  
Boundary Current ◽  
The South

ABSTRACT. The results of two high-resolution ocean global circulation models – OGCMs (Hybrid Coordinate Ocean Model – HYCOM and Ocean Circulation andClimate Advanced Modeling Project – OCCAM) are analyzed with a focus on the Western Boundary Current (WBC) system of the South Atlantic Ocean. The volumetransports are calculated for different isopycnal ranges, which represent the most important water masses present in this region. The latitude of bifurcation of the zonalflows reaching the coast, which leads to the formation of southward or northward WBC flow at different depths (or isopycnal levels) is evaluated. For the Tropical Water,bifurcation of the South Equatorial Current occurs at 13◦-15◦S, giving rise to the Brazil Current, for the South Atlantic Central Water this process occurs at 22◦S.For the Antarctic Intermediate Water, bifurcation occurs near 28◦-30◦S, giving rise to a baroclinic unstable WBC at lower latitudes with a very strong vertical shearat mid-depths. Both models give similar results that are also consistent with previous observational studies. Observations of the South Atlantic WBC system havepreviously been sparse, consequently these two independent simulations which are based on realistic high-resolution OGCMs, add confidence to the values presentedin the literature regarding flow bifurcations at the Brazilian coast.Keywords: Southwestern Atlantic circulation, water mass, OCCAM, HYCOM. RESUMO. Resultados de dois modelos globais de alta resolução (HYCOM e OCCAM) são analisados focando o sistema de Corrente de Contorno Oeste do Oceano Atlântico Sul. Os transportes de volume são calculados para diferentes níveis isopicnais que representam as principais massas de água da região. É apresentada a avaliação da latitude de bifurcação do fluxo zonal que atinge a costa, permitindo a formação dos fluxos da Corrente de Contorno Oeste para o sul e para o norte emdiferentes níveis de profundidades (ou isopicnal). Para a Água Tropical, a bifurcação da Corrente Sul Equatorial ocorre entre 13◦-15◦S, originando a Corrente do Brasil, e para a Água Central do Atlântico Sul ocorre em 22◦S. A bifurcação daÁgua Intermediária Antártica ocorre próximo de 28◦-30◦S, dando um aumento na instabilidade baroclínica da Corrente de Contorno Oeste em baixas latitudes e com um forte cisalhamento vertical em profundidades intermediárias. Ambos os modelos apresentamresultados similares e consistentes com estudos observacionais prévios. Considerando que as observações do sistema de Corrente de Contorno Oeste do Atlântico Sul são escassas, essas duas simulações independentes com modelos globais de alta resolução adicionam confiança aos valores apresentados na literatura, relacionadosaos fluxos das bifurcações na costa do Brasil.Palavras-chave: circulação do Atlântico Sudoeste, massas de água, OCCAM, HYCOM.

scholarly journals How Does Labrador Sea Water Enter the Deep Western Boundary Current?

2008 ◽  
Vol 38 (5) ◽  
pp. 968-983 ◽  
Author(s):  
Jaime B. Palter ◽  
M. Susan Lozier ◽  
Kara L. Lavender
Keyword(s):  
Heat Flux ◽  
Water Mass ◽  
Sea Water ◽  
Western Boundary Current ◽  
Meridional Overturning Circulation ◽  
Labrador Sea ◽  
Western Boundary ◽  
Boundary Current ◽  
Deep Western Boundary Current ◽  
Labrador Sea Water

Abstract Labrador Sea Water (LSW), a dense water mass formed by convection in the subpolar North Atlantic, is an important constituent of the meridional overturning circulation. Understanding how the water mass enters the deep western boundary current (DWBC), one of the primary pathways by which it exits the subpolar gyre, can shed light on the continuity between climate conditions in the formation region and their downstream signal. Using the trajectories of (profiling) autonomous Lagrangian circulation explorer [(P)ALACE] floats, operating between 1996 and 2002, three processes are evaluated for their role in the entry of Labrador Sea Water in the DWBC: 1) LSW is formed directly in the DWBC, 2) eddies flux LSW laterally from the interior Labrador Sea to the DWBC, and 3) a horizontally divergent mean flow advects LSW from the interior to the DWBC. A comparison of the heat flux associated with each of these three mechanisms suggests that all three contribute to the transformation of the boundary current as it transits the Labrador Sea. The formation of LSW directly in the DWBC and the eddy heat flux between the interior Labrador Sea and the DWBC may play leading roles in setting the interannual variability of the exported water mass.

scholarly journals Propagating Modes of Variability and Their Impact on the Western Boundary Current in the South Atlantic

2019 ◽  
Vol 124 (5) ◽  
pp. 3168-3185 ◽  
Author(s):  
Sudip Majumder ◽  
Marlos Goes ◽  
Paulo S. Polito ◽  
Rick Lumpkin ◽  
Claudia Schmid ◽  
...  
Keyword(s):  
South Atlantic ◽  
Western Boundary Current ◽  
Western Boundary ◽  
Boundary Current ◽  
The South ◽  
Modes Of Variability

scholarly journals Wind-Forced Variability of the Remote Meridional Overturning Circulation

2020 ◽  
Vol 50 (2) ◽  
pp. 455-469 ◽  
Author(s):  
Michael A. Spall ◽  
David Nieves
Keyword(s):  
Wind Stress ◽  
Rossby Wave ◽  
Western Boundary Current ◽  
Meridional Overturning Circulation ◽  
Western Boundary ◽  
Boundary Current ◽  
Overturning Circulation ◽  
Deep Western Boundary Current ◽  
Wave Basin ◽  
Meridional Overturning

AbstractThe mechanisms by which time-dependent wind stress anomalies at midlatitudes can force variability in the meridional overturning circulation at low latitudes are explored. It is shown that winds are effective at forcing remote variability in the overturning circulation when forcing periods are near the midlatitude baroclinic Rossby wave basin-crossing time. Remote overturning is required by an imbalance in the midlatitude mass storage and release resulting from the dependence of the Rossby wave phase speed on latitude. A heuristic theory is developed that predicts the strength and frequency dependence of the remote overturning well when compared to a two-layer numerical model. The theory indicates that the variable overturning strength, relative to the anomalous Ekman transport, depends primarily on the ratio of the meridional spatial scale of the anomalous wind stress curl to its latitude. For strongly forced systems, a mean deep western boundary current can also significantly enhance the overturning variability at all latitudes. For sufficiently large thermocline displacements, the deep western boundary current alternates between interior and near-boundary pathways in response to fluctuations in the wind, leading to large anomalies in the volume of North Atlantic Deep Water stored at midlatitudes and in the downstream deep western boundary current transport.

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