| A study of the variability in the Benguela Current volume transport - :18043 | Office of Oceanic and Atmospheric Research (OAR)
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A study of the variability in the Benguela Current volume transport
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  • Description:
    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 degrees E, decreases from 23 +/- 3 Sv (1 Sv = 10(6) m(3) s(-1)) at 31 degrees S to 11 +/- 3 Sv at 28 degrees S. In terms of variability, the 23-year long time series at 30 and 35 degrees 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 degrees S at the annual period is smaller than at 30 degrees 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 degrees S is weaker than at 35 degrees S. With respect to the forcing, the Sverdrup balance and the observed transport at 30 degrees S exhibit a strong correlation of 0.7. No significant correlation between these parameters is found at 35 degrees S.

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