scholarly journals IMPACTS OF SOUTHERN HEMISPHERE WESTERLIES ON THE BRAZIL CURRENT AT 30ºS

2018 ◽  
Vol 36 (3) ◽  
pp. 1
Author(s):  
Jessica S. Carvalho ◽  
Fabricio S. C. Oliveira ◽  
Edmo J. D. Campos
Keyword(s):  
Wind Stress ◽  
South Atlantic ◽  
Western Boundary Current ◽  
Subtropical Gyre ◽  
Brazilian Coast ◽  
Western Boundary ◽  
Boundary Current ◽  
The South ◽  
Wind Stress Curl ◽  
Brazil Current

ABSTRACT. Previous studies have pointed out an intensification of the global western boundary currents induced by changes in the wind-stress curl patterns over the oceans. The Brazil Current (BC) is the western boundary current into the South Atlantic Subtropical Gyre, which flows southwards along the Brazilian coast. A numerical model is used to investigate the response of BC to this change in wind forcing between 1960-2010, across 30ºS. The results found here support the increasing trend noticed in the wind-stress curl and a poleward migration of the South Hemisphere westerlies in the past decades. The residual transport of BC at 30_S is composed by its southward main flow and the northward branch of a recirculation cell (Rec) east of the BC. Both the BC and Rec transports showed a decrease trend of 0.10 Sv dec1 and 0.28 Sv dec1, respectively. It suggests a southward migration of Rec in response to changes in the westerlies. The results also indicate a relative intensification in the western boundary transport and a strengthening in the South Atlantic Subtropical Gyre. Keywords: Western Boundary Current, Meridional Transport, HYCOM.RESUMO. Estudos anteriores apontam para uma intensificação das correntes de contorno oeste globais induzidas por mudanças no rotacional do estresse do vento sobre os oceanos. A Corrente do Brasil (CB) é a corrente de contorno oeste do giro Subtropical do Atlântico Sul, que flui para sul ao longo da costa brasileira. Um modelo numérico é usado para investigar a resposta da CB às mudanças na forçante do vento entre 1960-2010, ao longo de 30_S. Os resultados encontrados aqui suportam a tendência de aumento observada no rotacional do estresse do vento e a migração para o polo dos ventos de oeste do hemisfério sul nas ultimas décadas. O transporte residual da CB em 30ºS é composto pelo seu fluxo principal para sul e o braço para norte de uma célula de recirculação (Rec) a leste da CB. Ambos os transportes da CB e Rec mostraram uma tendência de redução de 0,10 Sv dec1 e 0,28 Sv dec1, respectivamente. Isto sugere uma migração para sul da Rec em resposta às mudanças dos ventos de oeste. Os resultados também indicam uma relativa intensificação do transporte na borda oeste e um fortalecimento do giro Subtropical do Atlântico Sul.Palavras-chave: Corrente de Contorno Oeste, Transporte Meridional, HYCOM.

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 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 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 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 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.

Positive Regional Sea Level Anomalies in Southern Brazil Due to Changes in Austral Atmospheric Circulation

2021 ◽  
Author(s):  
Venisse Schossler ◽  
Francisco Aquino ◽  
Jefferson Simões ◽  
Pedro Reis ◽  
Denilson Viana
Keyword(s):  
Sea Level ◽  
Wind Stress ◽  
Southern Annular Mode ◽  
Altimeter Data ◽  
Western Boundary ◽  
Positive Trend ◽  
Boundary Current ◽  
Wind Stress Curl ◽  
Sea Level Anomalies ◽  
Regional Sea Level

Abstract Pressure gradients and winds play an important role in Southern Hemisphere (SH) sea levels, which are currently associated with the positive trend of the Southern Annular Mode (SAM). This study investigated regional sea level anomalies (SLAs) in the southern coast Brazil using altimeter data (1993–2019), post-processed by the X-TRACK (CTOH/LEGOS). We observed a negative SLA from 1993 to 2009 and a positive SLA from 2010 to 2019, with upward trends throughout the evaluation period. We analyzed wind stress curl, pressure, and wind fields at sea level (FNMOC and ERA 5, respectively) in addition to sea surface temperature and height anomalies (SSTA/SSHA-OISST) in the South Atlantic Ocean (SAO) for 1993–2009 and 2010–2019. In relation to the first period, the second shows the enhancement in Hadley and Walker cells and trade winds, in addition to greater SSTA and SSHA in SAO. The SAO subtropical gyre and zonal winds at 45°S contribute to the intensification of the western boundary current. A greater pressure gradient between the SAO surface and the southeast of South America is noteworthy. Regionally, the positive SAM brings an increase in sea level to the study area, caused by greater wind stress and variability in heat flows.

scholarly journals The INALT family – a set of high-resolution nests for the Agulhas Current system within global NEMO ocean/sea-ice configurations

2019 ◽  
Vol 12 (7) ◽  
pp. 3329-3355 ◽  
Author(s):  
Franziska U. Schwarzkopf ◽  
Arne Biastoch ◽  
Claus W. Böning ◽  
Jérôme Chanut ◽  
Jonathan V. Durgadoo ◽  
...  
Keyword(s):  
High Resolution ◽  
Boundary Conditions ◽  
Current System ◽  
Western Boundary Current ◽  
Global Ocean ◽  
Western Boundary ◽  
Boundary Current ◽  
The South ◽  
Agulhas Current ◽  
Mesoscale Dynamics

Abstract. The Agulhas Current, the western boundary current of the South Indian Ocean, has been shown to play an important role in the connectivity between the Indian and Atlantic oceans. The greater Agulhas Current system is highly dominated by mesoscale dynamics. To investigate their influence on the regional and global circulations, a family of high-resolution ocean general circulation model configurations based on the NEMO code has been developed. Horizontal resolution refinement is achieved by embedding “nests” covering the South Atlantic and the western Indian oceans at 1/10∘ (INALT10) and 1/20∘ (INALT20) within global hosts with coarser resolutions. Nests and hosts are connected through two-way interaction, allowing the nests not only to receive boundary conditions from their respective host but also to feed back the impact of regional dynamics onto the global ocean. A double-nested configuration at 1/60∘ resolution (INALT60) has been developed to gain insights into submesoscale processes within the Agulhas Current system. Large-scale measures such as the Drake Passage transport and the strength of the Atlantic meridional overturning circulation are rather robust among the different configurations, indicating the important role of the hosts in providing a consistent embedment of the regionally refined grids into the global circulation. The dynamics of the Agulhas Current system strongly depend on the representation of mesoscale processes. Both the southward-flowing Agulhas Current and the northward-flowing Agulhas Undercurrent increase in strength with increasing resolution towards more realistic values, which suggests the importance of improving mesoscale dynamics as well as bathymetric slopes along this narrow western boundary current regime. The exploration of numerical choices such as lateral boundary conditions and details of the implementation of surface wind stress forcing demonstrates the range of solutions within any given configuration.

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