Vertical structure, energetics, and dynamics of the Brazil Current System at 22 degrees S-28 degrees S

TitleVertical structure, energetics, and dynamics of the Brazil Current System at 22 degrees S-28 degrees S
Publication TypeJournal Article
Year of Publication2014
AuthorsRocha C.B, da Silveira I.CA, Castro B.M, Lima J.AM
JournalJournal of Geophysical Research-Oceans
Volume119
Pagination52-69
Date Published2014/01
Type of ArticleArticle
ISBN Number2169-9275
Accession NumberWOS:000331879100004
Keywords20-degrees-s; 28-degrees-s; baroclinic instability; Brazil Current; circulation; energetics; energy; growth; meanders; santos bifurcation; south-atlantic-ocean; southwestern Atlantic; vertical structure; western boundary current
Abstract

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 degrees S and 28 degrees S. The data set depict the downstream thickening of the BC. Its vertical extension increases from 350 m at 22.7 degrees S to 850 m at 27.9 degrees S. Most of this deepening occurs between 25.5 degrees S and 27.9 degrees 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 (approximate to 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 degrees S and 28 degrees S. In particular, the model predicts southwestward-propagating fastest growing waves (approximate to 190 km) from 25.5 degrees S to 27.9 degrees S and quasi-standing most unstable modes (approximate to 230 km) at 22.7 degrees S. These modes have vertical structures roughly consistent with the observed eddy field. Key Points The Brazil Current thickens substantially off southeast Brazil Most of this deepening is associated with the Santos bifurcation The BC becomes more barotropic to the south of the Santos bifurcation

DOI10.1002/2013jc009143
Short TitleJ Geophys Res-Oceans
Integrated Research Themes: 
Student Publication: 
Yes
Student: