Abstract
Introduction
Data & methods
Results
Conclusion
Acknowledgements
References
 

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A combination of surface drifters and high-resolution sea surface temperature data is used in this paper to investigate the characteristics of the eddies found in the South-western Atlantic Ocean in 1993 and 1994. The investigation is made according to the characteristic sizes, rotational periods and rotational velocities of the structures, as well as their associated Rossby numbers and relation to the theoretical local internal Rossby radius of deformation. In the South-western Atlantic, most of the reported eddy activity is related to the Brazil-Malvinas (Falkland) Confluence region, where the eddy characterisation is generally restricted to their sizes and location. Given the relatively few in situ data, most of these structures are described by using only remote sensing images. In the continental shelf, owing to the difficulty on spotting small scale eddies through satellite images, references to these structures are practically unavailable. Moreover, to the present day very few references are available describing kinematic eddy properties such as the rotational period or tangential velocity, for instance. In our study, small scale eddies have been found in both the satellite images and in the buoy trajectories. They were associated with the three currents studied: the Brazil, the Brazilian Coastal and the South Atlantic currents. These eddies were several times smaller than the typical Rossby radius of deformation for the region, indicating extremely turbulent fluxes or wind driven circulation. Rotational periods of these small scale eddies were found to be about 2 days, while the mesoscale eddies presented a mean rotational period of about 17 days. Some of the eddies present in the front between the Brazil Current and the Brazilian Coastal Current were similar to the shelfbreak eddies found in the United States east coast. Inshore eddies, however, seem to be related to current reversals probably caused by the passage of atmospheric fronts. In the Brazil-Malvinas Confluence region, cold core eddies were observed to be formed by breaking off from the crests of high amplitude meanders of the South Atlantic Current. Warm core eddies were present at the Brazil Current reversal zone and in the troughs of the South Atlantic Current in the confluence. Based upon the buoys’ trajectories, empirical relationships were found to link the eddy sizes (perimeter and diameter) with the eddy rotational periods and tangential velocities. The relationships can be useful when no in situ data are available and satellite images are obtained in a regular basis. In this case, individual eddy sizes can be measured in the satellite images and their kinematic properties inferred from the empirical relationships.
 
 

 rbds@soc.soton.ac.uk (c) April 2001, all rights reserved.