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Volume 14, issue 3 | Copyright
Ocean Sci., 14, 417-436, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 07 Jun 2018

Research article | 07 Jun 2018

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

Claudia Schmid1 and Sudip Majumder1,2 Claudia Schmid and Sudip Majumder
  • 1National Oceanic and Atmospheric Administration, Atlantic Oceanographic and Meteorological Laboratory, Miami, Florida, USA
  • 2Cooperative Institute for Marine and Atmospheric Studies, University of Miami, Miami, FL, USA

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±2.2Sv (1Sv is 106m3s−1) at 25°S to 13.9±2.6Sv at 32°S, which corresponds to a mean slope of 1.4±0.4Sv per degree. Transport estimates derived from HYCOM fields are somewhat higher (5.2±2.7 and 18.7±7.1Sv 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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Short summary
An analysis of observed transports in the Brazil Current shows a factor 9 increase between its origin and terminus. The 23-year time series reveals an annual cycle with a maximum in austral summer whose significance decreases on the way south and varies interannually. In addition, 2–4-year long phases with relatively high/low values are observed. A correlation of the transport with the Southern Annular Mode (Niño 3.4 index), with a lag of 6 (8) months, is present at 24° S.
An analysis of observed transports in the Brazil Current shows a factor 9 increase between its...