Vertical structure, energetics, and dynamics of the Brazil Current System at 22°S–28°S

Journal of Geophysical Research: Oceans - Tập 119 Số 1 - Trang 52-69 - 2014
César B. Rocha1,2, Ilson Carlos Almeida da Silveira1, Belmiro Mendes de Castro1, José Antônio Moreira Lima3
1Instituto Oceanográfico, Universidade de São Paulo, São Paulo, Brazil
2Now at Scripps Institution of Oceanography, University of California San Diego La Jolla, California USA
3Centro de Pesquisas e Desenvolvimento Leopoldo A. Miguez de Mello Petróleo Brasileiro S. A., Rio de Janeiro Brazil

Tóm tắt

We use four current meter moorings and quasi‐synoptic hydrographic observations in conjunction with a one‐dimensional quasi‐geostrophic linear stability model to investigate downstream changes in the Brazil Current (BC) System between 22°S and 28°S. The data set depict the downstream thickening of the BC. Its vertical extension increases from 350 m at 22.7°S to 850 m at 27.9°S. Most of this deepening occurs between 25.5°S and 27.9°S and is linked to the bifurcation of the South Equatorial Current at intermediate depths (Santos bifurcation), which adds the Antarctic Intermediate Water flow to the BC. Geostrophic estimates suggest that the BC transport is increased by at least 4.3 Sv (∼70%) to the south of that bifurcation. Moreover, the Santos bifurcation is associated with a substantial increase in the barotropic component of the BC System. On average, the water column average kinetic energy (IKE) is 70% baroclinic to the north and 54% barotropic to the south of the bifurcation. Additionally, the BC shows conspicuous mesoscale activity off southeast Brazil. The water column average eddy kinetic energy accounts for 30–60% of the IKE. Instabilities of the mean flow may give rise to these mesoscale fluctuations. Indeed, the linear stability analysis suggests that the BC System is baroclinically unstable between 22°S and 28°S. In particular, the model predicts southwestward‐propagating fastest growing waves (∼190 km) from 25.5°S to 27.9°S and quasi‐standing most unstable modes (∼230 km) at 22.7°S. These modes have vertical structures roughly consistent with the observed eddy field.

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Journal of Geophysical Research: Oceans

Tập 119 Số 1

52-69

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