Transport variability of the Brazil Current from observations and a data assimilation model
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 At...
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doaj-ba7a6119d5554e26918761bbd609f8af2020-11-25T01:29:50ZengCopernicus PublicationsOcean Science1812-07841812-07922018-06-011441743610.5194/os-14-417-2018Transport variability of the Brazil Current from observations and a data assimilation modelC. Schmid0S. Majumder1S. Majumder2National Oceanic and Atmospheric Administration, Atlantic Oceanographic and Meteorological Laboratory, Miami, Florida, USANational Oceanic and Atmospheric Administration, Atlantic Oceanographic and Meteorological Laboratory, Miami, Florida, USACooperative Institute for Marine and Atmospheric Studies, University of Miami, Miami, FL, USAThe 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 10<sup>6</sup> m<sup>3</sup> s<sup>−1</sup>) 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.https://www.ocean-sci.net/14/417/2018/os-14-417-2018.pdf |
collection |
DOAJ |
language |
English |
format |
Article |
sources |
DOAJ |
author |
C. Schmid S. Majumder S. Majumder |
spellingShingle |
C. Schmid S. Majumder S. Majumder Transport variability of the Brazil Current from observations and a data assimilation model Ocean Science |
author_facet |
C. Schmid S. Majumder S. Majumder |
author_sort |
C. Schmid |
title |
Transport variability of the Brazil Current from observations and a data assimilation model |
title_short |
Transport variability of the Brazil Current from observations and a data assimilation model |
title_full |
Transport variability of the Brazil Current from observations and a data assimilation model |
title_fullStr |
Transport variability of the Brazil Current from observations and a data assimilation model |
title_full_unstemmed |
Transport variability of the Brazil Current from observations and a data assimilation model |
title_sort |
transport variability of the brazil current from observations and a data assimilation model |
publisher |
Copernicus Publications |
series |
Ocean Science |
issn |
1812-0784 1812-0792 |
publishDate |
2018-06-01 |
description |
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
10<sup>6</sup> m<sup>3</sup> s<sup>−1</sup>) 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. |
url |
https://www.ocean-sci.net/14/417/2018/os-14-417-2018.pdf |
work_keys_str_mv |
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