The Brazil Current at subtropical latitudes

Newell Garfield, University of Rhode Island

Abstract

The Brazil Current is the western boundary current component of the South Atlantic subtropical gyre circulation. It is a small current, transporting less than 20 $\times$ 10$\sp6$ m$\sp3$ s$\sp{-1}$ of water where the current is adjacent to the continental margin. The low transport and the shallow water location have hindered descriptions using traditional hydrographic methods. Historical hydrographic data, satellite AVHRR imagery, and recent absolute velocity and temperature measurements are used to develop a more complete picture of the Brazil Current over the latitude range 20 to 31$\sp\circ$S.^ Satellite imagery for the period 1982-87 confirms that the Brazil Current is continuous along the South American continent at least from 19$\sp\circ$S to the region of continental margin separation south of 31$\sp\circ$S. Over this range the inshore Brazil Current front is closely associated with the continental margin, represented by the 200 m isobath. North of the separation region the imagery-determined mean frontal position was generally within 20 km of the 200 m isobath. The variability about the mean position contains two maxima associated with areas of sharp continental margin convex curvature (observed from shore). Results from applying Brazil Current characteristics to a model of local boundary current separation (Ou and De Ruijter, 1986) suggest that separation will not occur in either region under normal flow conditions. A more likely explanation of the observed variability is different distances of local inertial overshoot for different transport values.^ Absolute velocity dropsonde data confirm earlier observations that at 24$\sp\circ$S the Brazil Current is confined to the upper portion of the water column, depths less than 450 m. A representative mean transport is around 7 $\times$ 10$\sp6$ m$\sp3$ s$\sp{-1}$. At 31$\sp\circ$S the Brazil Current vertical extent deepens to around 800 m, and the transport increases to about 18 $\times$ 10$\sp6$ m$\sp3$ s$\sp{-1}$. Part of the increase is due to entrainment of Antarctic Intermediate Water (AAIW) at the base of the Brazil Current. At both locations a significant fraction of the flow can occur in shallow water over the continental shelf, and adjacent to the continental slope there exists a northward flowing AAIW current immediately below the Brazil Current. ^

Subject Area

Physical Oceanography

Recommended Citation

Newell Garfield, "The Brazil Current at subtropical latitudes" (1990). Dissertations and Master's Theses (Campus Access). Paper AAI9106513.
http://digitalcommons.uri.edu/dissertations/AAI9106513

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