A MESOSCALE BRAZIL CURRENT FRONTAL EDDY OBSERVED THROUGH AVHRR IMAGES AND 
CURRENT METER MOORINGS 
José L. Stech', Joäo A. Lorenzzetti', Jose M. C. de Souza“ and Carlos E.S. Araujo! 
| National Institute for Space Research - INPE 
Säo José dos Campos, SP Brazil 
? Brazil Petroleum Co. - PETROBRAS 
Rio de Janeiro, RJ Brazil 
Commission VII, Working Group 7 
KEY WORDS: “AVHHR , Frontal Eddy, Brazil Current ” 
ABSTRACT 
During the period from Dec. 29, 1994 to Jan. 17, 1995, a meso-scale oceanic eddy, with a diameter of approximately 
100 km, was detected in thermal infrared AVHRR/NOAA images near the inshore Brazil Current (BC) front SE of 
Cabo Säo Tomé. Beneath surface, the presence of the eddy was observed in current meter mooring data collected 
during this period at depths up to about 350 m as flow perturbations and reversals. The analysis of both data sets 
together with some CTD data collected during the same period indicated that the eddy formation can be related to an 
intensification of a cyclonic meandering of the BC at the continental margin, which was probably associated with 
strong coastal upwelling present on the continental shelf. The AVHRR images showed that large filaments of colder 
water of upwelling origin were advected towards the BC front, wrapping around the eddy. 
INTRODUCTION 
The most conspicous feature of the surface oceanic 
circulation in the Southwestern South Atlantic, south of 
10° S, is the Brazil Current (BC) whose origin is at the 
southernmost portion of the South Equatorial Current. 
The BC represents the western boundary of the 
subtropical circulation in the South Atlantic. Between 
20° and 30°S, its transport appears to be considerably 
smaller than that of analogous current systems in the 
Southern Hemisphere, for example, the Agulhas and 
East Australian Currents. The Brazil Current transport 
estimates vary from 1.9 Sv (Stramma et al, 1990) to 9.4 
SV (Schmid et al, 1995); most of these estimates were 
done using 600 m as the reference level for the 
geostrophic calculations. 
A large uncertainty exists about the spatial and temporal 
variability of the BC (Peterson and Stramma, 1991). The 
BC plays an important role all over the upper 
continental slope and shelf break regions of Brazil and 
Uruguay. Most of the time, the BC is characterized by 
warm temperatures (> 25°C) and high salinity (=37 PSU) 
and a southern flow closely associated with the 
continental margin, well represented in the region by the 
200 m isobath. Meandering and frontal eddies are 
frequently observed south of 21°S, disturbing the 
characteristic southern flow. These instability processes 
present in the BC inshore frontal region can sometime 
grow and generate cyclonic eddies. 
650 
Most of the efforts developed to study the BC have been 
based on the traditional method of hydrographic data 
collection, using oceanographic ships. More recently, 
this method is being complemented by the use of 
moored equipment, satellite tracked drifters and satellite 
images. The high repetitiviness and large scale synoptic 
view provided by the environmental satellites, have 
allowed the observation of the BC and related 
oceanographic features, such as meandering, eddies and 
their life cycles, time and space scales. The analysis of 
these images has proved to be very efficient in 
describing and studing the wind driven seasonal coastal 
upwelling present between Cabo de Sáo Tomé and Cabo 
Frio. For example, Garfield (1990) analysing a large 
data set of infrared images of the BC showed that, 
between 20° and 31°S, the BC is continuous and can be 
characterized by several eddies and meanders to the 
west of the main stream. Stech et al. (1994) presented 
some wintertime features observed from an analysis of à 
set of thermal infrared images. Schmid et al. (1995), by 
using a hydrographic data set, drifting buoy observations 
and satellite imagery studied a BC frontal eddy near 
Vitoria, describing the anatomy of this feature and its 
interaction with the BC. In their paper it is suggested 
that the strengthning of the coastal upwelling might be 
related to the generation of the studied eddy. Stech etal 
(1995) utilized an AVHRR set of images to study the 
seasonal variation of this upwelling. 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B7. Vienna 1996