Interannual variability of the Latitude of Separation of the Brazil Current: Teleconnections and Oceanic Rossby Waves Propagation

Abstract. Brazil Current transports from observations and a model are analyzed to improve our understanding of its structure and variability. The observed transports are derived from a three-dimensional field of the velocity in the South Atlantic covering the years 1993 to 2015 (hereinafter called Argo & SSH). The mean transport of the Brazil Current from 3.8 &pm; 2.2 Sv (1 Sv is 106 m3s−1) at 25° S to 13.9 &pm; 2.6 Sv at 32° S, which corresponds to a mean slope of 1.4 &pm; 0.4 Sv per degree. The Hybrid Coordinate Model (HYCOM) has somewhat higher transports than Argo & SSH (5.2 &pm; 2.7 Sv and 18.7 &pm; 7.1 Sv at 25° S and 32° S), but these differences are small when compared with the standard deviations. Overall, the observed latitude dependence of the transport of the Brazil Current is in agreement with the wind-driven circulation in the super gyre of the subtropical South Atlantic. A mean annual cycle with highest (lowest) transports in austral summer (winter) is found to exist at selected latitudes (24° S, 35° S and 38° S). The significance of this signal shrinks with increasing latitude, mainly due to the mesoscale and interannual variability. In addition, it is found that the interannual variability at 24° S is correlated with the Southern Annular Mode and the Niño 3.4 index. A coupled EOF of the meridional transport and the sea level pressure is used to improve the understanding of the impact of these ocean indexes.

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Quantifying the seasonal and interannual variability of the formation and migration pattern of North Brazil Current Rings

OCEANS 2009 ◽

10.23919/oceans.2009.5422142 ◽

2009 ◽

Cited By ~ 3

Author(s):

Neha Sharma ◽

Steven P. Anderson ◽

Peter Brickley ◽

Carolina Nobre ◽

Matthew L. Cadwallader

Keyword(s):

Interannual Variability ◽

Migration Pattern ◽

Seasonal And Interannual Variability ◽

Brazil Current ◽

North Brazil ◽

North Brazil Current ◽

North Brazil Current Rings ◽

And Migration

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Interannual variability in the Biannual Rossby waves in the tropical Indian Ocean and its relation to Indian Ocean Dipole and El Nino forcing

Ocean Dynamics ◽

10.1007/s10236-009-0236-z ◽

2009 ◽

Vol 60 (1) ◽

pp. 27-40 ◽

Cited By ~ 22

Author(s):

Chellappan Gnanaseelan ◽

Bakshi Hardeep Vaid

Keyword(s):

Indian Ocean ◽

Interannual Variability ◽

El Niño ◽

Indian Ocean Dipole ◽

Rossby Waves ◽

El Nino ◽

Tropical Indian Ocean

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Seasonal-to-Interannual Time-Scale Dynamics of the Equatorial Undercurrent in the Indian Ocean

Journal of Physical Oceanography ◽

10.1175/jpo-d-14-0225.1 ◽

2015 ◽

Vol 45 (6) ◽

pp. 1532-1553 ◽

Cited By ~ 43

Author(s):

Gengxin Chen ◽

Weiqing Han ◽

Yuanlong Li ◽

Dongxiao Wang ◽

Michael J. McPhaden

Keyword(s):

Indian Ocean ◽

Interannual Variability ◽

Rossby Waves ◽

Ocean Model ◽

Western Basin ◽

Equatorial Undercurrent ◽

Eastern Basin ◽

Eastern Boundary ◽

The Indian Ocean ◽

Core Depth

AbstractThis paper investigates the structure and dynamics of the Equatorial Undercurrent (EUC) of the Indian Ocean by analyzing in situ observations and reanalysis data and performing ocean model experiments using an ocean general circulation model and a linear continuously stratified ocean model. The results show that the EUC regularly occurs in each boreal winter and spring, particularly during February and April, consistent with existing studies. The EUC generally has a core depth near the 20°C isotherm and can be present across the equatorial basin. The EUC reappears during summer–fall of most years, with core depth located at different longitudes and depths. In the western basin, the EUC results primarily from equatorial Kelvin and Rossby waves directly forced by equatorial easterly winds. In the central and eastern basin, however, reflected Rossby waves from the eastern boundary play a crucial role. While the first two baroclinic modes make the largest contribution, intermediate modes 3–8 are also important. The summer–fall EUC tends to occur in the western basin but exhibits obvious interannual variability in the eastern basin. During positive Indian Ocean dipole (IOD) years, the eastern basin EUC results largely from Rossby waves reflected from the eastern boundary, with directly forced Kelvin and Rossby waves also having significant contributions. However, the eastern basin EUC disappears during negative IOD and normal years because westerly wind anomalies force a westward pressure gradient force and thus westward subsurface current, which cancels the eastward subsurface flow induced by eastern boundary–reflected Rossby waves. Interannual variability of zonal equatorial wind that drives the EUC variability is dominated by the zonal sea surface temperature (SST) gradients associated with IOD and is much less influenced by equatorial wind associated with Indian monsoon rainfall strength.

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Subannual, Seasonal, and Interannual Variability of the North Atlantic Meridional Overturning Circulation

Journal of Physical Oceanography ◽

10.1175/jpo3049.1 ◽

2007 ◽

Vol 37 (5) ◽

pp. 1246-1265 ◽

Cited By ~ 54

Author(s):

Joël J-M. Hirschi ◽

Peter D. Killworth ◽

Jeffrey R. Blundell

Keyword(s):

Interannual Variability ◽

Time Scales ◽

North Atlantic ◽

Rossby Waves ◽

Density Field ◽

Meridional Overturning Circulation ◽

Overturning Circulation ◽

The North ◽

Meridional Overturning ◽

The North Atlantic

Abstract An eddy-permitting numerical ocean model is used to investigate the variability of the meridional overturning circulation (MOC). Both wind stress and fluctuations of the seawater density contribute to MOC changes on subannual and seasonal time scales, whereas the interannual variability mainly reflects changes in the density field. Even on subannual and seasonal time scales, a significant fraction of the total MOC variability is due to changes of the density field in the upper 1000 m of the ocean. These changes reflect perturbations of the isopycnal structure that travel westward as Rossby waves. Because of a temporally changing phase difference between the eastern and western boundaries, the Rossby waves affect the MOC by modifying the basinwide east–west density gradient. Both the numerical model used in this study and calculations based on Rossby wave theory suggest that this effect can account for an MOC variability of several Sverdrups (Sv ≡ 106 m3 s−1). These results have implications for the interpretation of variability signals inferred from hydrographic sections and might contribute to the understanding of the results obtained from the Rapid Climate Change (RAPID) monitoring array deployed at 26°N in the North Atlantic Ocean.

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Transport variability of the Brazil Current from observations and a data assimilation model

Ocean Science ◽

10.5194/os-14-417-2018 ◽

2018 ◽

Vol 14 (3) ◽

pp. 417-436 ◽

Cited By ~ 9

Author(s):

Claudia Schmid ◽

Sudip Majumder

Keyword(s):

Interannual Variability ◽

Southern Oscillation ◽

Three Dimensional ◽

Austral Summer ◽

Southern Annular Mode ◽

South Atlantic ◽

The South ◽

Meridional Transport ◽

Large Power ◽

Brazil Current

Abstract. The Brazil Current transports from observations and the Hybrid Coordinate Model (HYCOM) model are analyzed to improve our understanding of the current's structure and variability. A time series of the observed transport is derived from a three-dimensional field of the velocity in the South Atlantic covering the years 1993 to 2015 (hereinafter called Argo & SSH). The mean transports of the Brazil Current increases from 3.8 ± 2.2 Sv (1 Sv is 106 m3 s−1) at 25∘ S to 13.9 ± 2.6 Sv at 32∘ S, which corresponds to a mean slope of 1.4 ± 0.4 Sv per degree. Transport estimates derived from HYCOM fields are somewhat higher (5.2 ± 2.7 and 18.7 ± 7.1 Sv at 25 and 32∘ S, respectively) than those from Argo & SSH, but these differences are small when compared with the standard deviations. Overall, the observed latitude dependence of the transport of the Brazil Current is in agreement with the wind-driven circulation in the super gyre of the subtropical South Atlantic. A mean annual cycle with highest (lowest) transports in austral summer (winter) is found to exist at selected latitudes (24, 35, and 38∘ S). The significance of this signal shrinks with increasing latitude (both in Argo & SSH and HYCOM), mainly due to mesoscale and interannual variability. Both Argo & SSH, as well as HYCOM, reveal interannual variability at 24 and 35∘ S that results in relatively large power at periods of 2 years or more in wavelet spectra. It is found that the interannual variability at 24∘ S is correlated with the South Atlantic Subtropical Dipole Mode (SASD), the Southern Annular Mode (SAM), and the Niño 3.4 index. Similarly, correlations between SAM and the Brazil Current transport are also found at 35∘ S. Further investigation of the variability reveals that the first and second mode of a coupled empirical orthogonal function of the meridional transport and the sea level pressure explain 36 and 15 % of the covariance, respectively. Overall, the results indicate that SAM, SASD, and El Niño–Southern Oscillation have an influence on the transport of the Brazil Current.

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