Mean vertical and horizontal structure of the subtropical circulation in the South Atlantic from three-dimensional observed velocity fields

2014 ◽  
Vol 91 ◽  
pp. 50-71 ◽  
Author(s):  
Claudia Schmid
Keyword(s):  
Three Dimensional ◽  
Velocity Fields ◽  
South Atlantic ◽  
The South ◽  
Horizontal Structure

scholarly journals A study of the variability in the Benguela Current volume transport

Ocean Science ◽  
2018 ◽  
Vol 14 (2) ◽  
pp. 273-283 ◽  
Author(s):  
Sudip Majumder ◽  
Claudia Schmid
Keyword(s):  
Energy Density ◽  
Three Dimensional ◽  
Atlantic Water ◽  
Volume Transport ◽  
South Atlantic ◽  
The South ◽  
Meridional Transport ◽  
Data Set ◽  
Argo Floats ◽  
Benguela Current

Abstract. The Benguela Current forms the eastern limb of the subtropical gyre in the South Atlantic and transports a blend of relatively fresh and cool Atlantic water and relatively warm and salty Indian Ocean water northwestward. Therefore, it plays an important role not only for the local freshwater and heat budgets but for the overall meridional heat and freshwater transport in the South Atlantic. Historically, the Benguela Current region is relatively data sparse, especially with respect to long-term velocity observations. A new three-dimensional data set of the horizontal velocity in the upper 2000 m that covers the years 1993 to 2015 is used to analyze the variability in the Benguela Current. This data set was derived using observations from Argo floats, satellite sea surface height, and wind fields. Since Argo floats do not cover regions shallower than 1000 m, the data set has gaps inshore. The main features of the horizontal circulation observed in this data set are in good agreement with those from earlier studies based on limited observations. Therefore, it can be used for a more detailed study of the flow pattern as well as the variability in the circulation in this region. It is found that the mean meridional transport in the upper 800 m between the continental shelf of Africa and 3∘ E, decreases from 23 ± 3 Sv (1 Sv = 106 m3 s−1) at 31∘ S to 11 ± 3 Sv at 28∘ S. In terms of variability, the 23-year long time series at 30 and 35∘ S reveals phases with large energy densities at periods of 3 to 7 months, which can be attributed to the occurrence of Agulhas rings in this region. The prevalence of Agulhas rings is also behind the fact that the energy density at 35∘ S at the annual period is smaller than at 30∘ S because the former latitude is closer to Agulhas Retroflection and therefore more likely to be impacted by the Agulhas rings. In agreement with this, the energy density associated with mesoscale variability at 30∘ S is weaker than at 35∘ S. With respect to the forcing, the Sverdrup balance and the observed transport at 30∘ S exhibit a strong correlation of 0.7. No significant correlation between these parameters is found at 35∘ S.

Space Weather Effects on Proton Flux Variations in the South Atlantic Anomaly: A Numerical Study performed by Test Particle Simulations

2020 ◽  
Author(s):  
Kirolosse Girgis ◽  
Tohru Hada ◽  
Shuichi Matsukiyo
Keyword(s):  
Geomagnetic Storm ◽  
Space Weather ◽  
Test Particle ◽  
Three Dimensional ◽  
South Atlantic ◽  
Proton Flux ◽  
Storm Event ◽  
Time Varying ◽  
The South ◽  
South Atlantic Anomaly

<p>In this study, we assess the hourly variations of the three-dimensional proton flux distribution inside the South Atlantic Anomaly (SAA) during a geomagnetic storm. We have developed a relativistic three-dimensional guiding center test particle simulation code in order to compute the proton trajectories in a time-varying magnetic field background provided by Tsyganenko model TS05 and the corresponding time-varying inductive electric field. The Dst index is the main input parameter to the simulation model, while the maximum proton flux, the area of the SAA calculated below a selected threshold, and the penetration depth of the protons are the main output variables investigated in this study were. Since the LEO spacecraft and human-related activities are already affected by space weather conditions, the South Atlantic Anomaly (SAA) is also believed to create an additional source of risk. As the radiation environment depends essentially on the particle flux, the objective of this study is to estimate quantitatively the proton flux variations inside the South Atlantic Anomaly (SAA) in quiet and in storm conditions. So far, it was found that after several drift periods, the protons in the South Atlantic Anomaly (SAA) could penetrate to lower altitudes during geomagnetic storm event, and that, the SAA maximum flux value and the corresponding area, varied differently with respect to altitudes. Numerical results were compared with observations by NOAA 17 and RD3R2 instrument mounted on International Space Station (ISS).</p>

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

Ocean Science ◽  
2018 ◽  
Vol 14 (3) ◽  
pp. 417-436 ◽  
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.

scholarly journals A Study of the Variability of the Benguela Current

2017 ◽  
Author(s):  
Sudip Majumder ◽  
Claudia Schmid
Keyword(s):  
Energy Density ◽  
Three Dimensional ◽  
Atlantic Water ◽  
South Atlantic ◽  
The South ◽  
Wind Fields ◽  
Meridional Transport ◽  
Data Set ◽  
Benguela Current ◽  
Heat Budgets

Abstract. The Benguela Current forms the eastern limb of the subtropical gyre in the South Atlantic and transports a blend of relatively fresh and cool Atlantic water as well as relatively warm and salty Indian Ocean water northward. Therefore, it plays an important role not only for the local freshwater and heat budgets but for the overall meridional heat and freshwater transports in the South Atlantic. Historically, the Benguela Current region is relatively data sparse, especially with respect to long-term observations. A new three dimensional data set of the horizontal velocity in the upper 2000 m that covers the years 1993 to 2015 is used to analyze the variability of the Benguela Current. This data set was derived using observations from Argo floats, satellite sea surface height and wind fields. The main features of the horizontal circulation observed in this data set are in good agreement with those from earlier observations based on more limited data sets. Therefore, it can be used for a more detailed study the flow pattern as well as the variability of the circulation in this region. It is found that the mean meridional transport in the upper 800 m between the continental shelf of Africa and 3° E, decreases from 23 ± 3 Sv at 31° S to 11 ± 3 Sv at 28° S. In terms of variability, the 23-year long timeseries at 30° S and 35° S reveal phases with large energy densities at periods of 3 to 7 months, which can be attributed to the occurrence of Agulhas rings in this region. The prevalence of these rings is also behind the fact that the energy density at 35° S at the annual period is smaller than at 30° S, because the former latitude is closer to Agulhas retroflection and therefore more likely to be impacted by the Agulhas rings. In agreement with this, the energy density associated with mesoscale variability at 30° S is weaker than at 35° S. With respect to the forcing, the significant correlation between the Sverdrup balance derived from the wind stress and the observed transports at 30° S is 0.7. No significant correlation between these parameters was found at 35° S.

POLITICAL AND STRATEGIC COORDINATION AND COOPERATION FOR DEVELOPMENT: THE CASES OF ZPCSA AND GGC

2016 ◽  
Vol 31 (2) ◽  
pp. 19-36
Author(s):  
Paulo Fagundes Visentini ◽  
Analúcia Danilevicz Pereira
Keyword(s):  
South Atlantic ◽  
Strategic Orientation ◽  
International Affairs ◽  
The South ◽  
Strategic Issues ◽  
Strategic Coordination ◽  
Regional Order ◽  
Energy Products ◽  
A Site ◽  
Political Economic

The creation of the Zone of Peace and Cooperation of the South Atlantic (ZPCSA) in 1986 and the Gulf of Guinea Commission (GGC) in 2001 was about changes in the distribution of world power. This article argues that though they emerged at different times, their strategic orientation converges in a number of areas related to the significant interests in the South Atlantic as an area of stability in the region to be marked by strong political, economic and military ties. They also converge on the ideal for development, security and greater projection of power and influence in international affairs. The South Atlantic being a route of passage and trade, as a means of access and flow of energy products, the region became a site for new calculations of regional strategic powers about world affairs. The article also argues that ZPCSA and GGC are therefore crucial for the regional order and the development of higher capacities for cooperation on strategic issues. The actual point of convergence extends to ensuring the sovereignty through dialogue between the states in the region that are involved.

Observed seasonal regimes of North-South Atlantic Ocean interbasin exchange

2019 ◽  
Author(s):  
Hamed D. Ibrahim
Keyword(s):  
North Atlantic ◽  
Climate Models ◽  
South Atlantic ◽  
Meridional Overturning Circulation ◽  
Volume Flux ◽  
The South ◽  
The North ◽  
Basin Scale ◽  
Interbasin Exchange ◽  
North And South

North and South Atlantic lateral volume exchange is a key component of the Atlantic Meridional Overturning Circulation (AMOC) embedded in Earth’s climate. Northward AMOC heat transport within this exchange mitigates the large heat loss to the atmosphere in the northern North Atlantic. Because of inadequate climate data, observational basin-scale studies of net interbasin exchange between the North and South Atlantic have been limited. Here ten independent climate datasets, five satellite-derived and five analyses, are synthesized to show that North and South Atlantic climatological net lateral volume exchange is partitioned into two seasonal regimes. From late-May to late-November, net lateral volume flux is from the North to the South Atlantic; whereas from late-November to late-May, net lateral volume flux is from the South to the North Atlantic. This climatological characterization offers a framework for assessing seasonal variations in these basins and provides a constraint for climate models that simulate AMOC dynamics.

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