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A meso scale Brazil Current frontal eddy: Observations by ASAR and Radarsat-1 complemented by visible and infrared sensors, in situ data, and numerical modeling

Joao A. Lorenzzetti(1) , Cristina M. Bentz(2) , Milton Kampel(1) , and Audalio Torres Jr.(3)

(1) INPE, Av. Astronautas, 1758, 12227-010 Sao Jose Campos, Brazil
(2) Petrobras, Cidade Universitária, Q.7, Ilha do Fundão , 21949-900 - Rio de Janeiro, Brazil
(3) Universidade Federal do Rio de Janeiro, Cidade Universitária, Ilha do Fundão , 21941-590, Rio de Janeiro, Brazil

Abstract

A series of orbital microwave, infrared and visible images were acquired over the oceanic area off Cape São Tomé, at the SW South Atlantic off Brazil in conjunction with a hydrographic campaign during November 2004. The main oceanographic feature present during that period was a well developed Brazil Current (BC) cyclonic frontal eddy. A sea floor oil seepage was present in the same area and the associated surface slick was captured by the clockwise circulation of the eddy. The thermal contrast between the offshore warm waters of the BC and the cooler shelf waters, which is frequently enhanced by the presence of cold upwelling plumes, seems to modulate the atmospheric stability and so values in the region, making the BC front and the eddy clearly visible in the ASAR and Radarsat-1 images. The oil film captured by the eddy circulation also facilitated the eddy detection in the microwave images. AVHRR SST, MODIS, MERIS and ASTER images clearly confirm the identification of the eddy made with the SAR images. A numerical simulation of the three-dimensional circulation in the region for the observed period was implemented using the POM model. The model was initialized using the results of the Ocean Data Assimilation Experiment (GFDL/NOAA, Univ. Princeton) and it was forced with winds simulated for the region by the GFS model of NCEP. The model was able to generate the BC frontal eddy at the precise location observed with the satellite images. The model results are used to get the 3D view of the eddy and its velocity field. Models results indicate that over the outer shelf up to the 100 m isobath the northward flow of the inshore portion of the eddy spans the whole water column. Maximum water velocities of about 0.5 ms-1 and 0.3 ms-1 were modeled for the offshore and inshore extremes of the eddy, respectively. The offshore upward slope of the pycnocline at the outer shelf and shelf break obtained from CTD casts also confirms the presence of the northward inshore branch of the eddy.

 

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