Licenciado

Caribbean Current and eddies as observed by surface drifters

June 2, 2004

P. L. Richardson[1]
Department of Physical Oceanography, MS 29
Woods Hole Oceanographic Institution
Woods Hole, MA 02543, USA
And
Associated Scientists at Woods Hole
Woods Hole, MA 02543, USA

































Abstract

Recent satellite-tracked surface driftertrajectories were analyzed to describe the mean currents and eddies in the Caribbean Sea. The structure of the Caribbean Current and its variability were determined from high-resolution ½ degree maps of the mean velocity and eddy kinetic energy. Looping drifter trajectories were used to identify discrete cyclones and anticyclones, and their characteristics were described and related to thestructure of the mean flow. The translation rate of eddies in different areas was found to be similar to the mean velocity of the local background flow fields suggesting that the eddies were largely advected by the background flow. Ten energetic anticyclones translated westward at 13 cm/sec in the Venezuela and Colombia Basins. These anticyclones tended to lie in two bands, centered near 15ºN and17ºN, coinciding with two jets of the Caribbean Current. The northern weaker jet contains water primarily from the North Atlantic, the southern stronger jet contains water from the tropical and South Atlantic. The anticyclones are thought to have formed in the eastern Caribbean from the anticyclonic vorticity derived from North Brazil Current rings. The ring vorticity enters the eastern Caribbeanthrough island passages and is probably amplified by the anticyclonic shear on the northern side of the jets. Southwest of Cuba a cyclone-anticyclone pair was observed to slowly (~ 2 cm/sec) translate westward into the Yucatan Current. The cyclone was tracked for 10.5 months with four drifters, making it the longest-tracked of the Caribbean eddies.















Six subjectkeywords and regional index terms

Surface drifters, Caribbean Current, Caribbean eddies, eddies, North Brazil Current rings, meridional overturning circulation.

Intra-Americas Seas, Caribbean Sea, Colombia Basin, Venezuela Basin, Yucatan Basin, Antilles.

Geographical bounding coordinates 9-22N, 61-88W.






































1. IntroductionRecently, a large number of satellite-tracked, drogued, drifting buoys measured trajectories in the Caribbean Sea (Fig. 1). Many drifters were launched in the Caribbean during 1998-2000 as part of the “Year of the Ocean-1999” study (Wilson and Leaman, 2000) (Fig. 2). Other drifters were launched east of the Caribbean in other experiments including the North Brazil Current Rings Experiment(Fratantoni and Richardson, 2004); these drifters passed through the Antilles Islands passages adding trajectories in the Caribbean. Taken together, these trajectories provide a unique data set that reveals previously unknown details of the circulation and eddies in the different parts of the Caribbean. The intent of this paper is to analyze these data with the goal of learning more about thecharacteristics of Caribbean eddies in general and specifically about the energetic anticyclones in the eastern Caribbean that might have been generated by North Brazil Current (NBC) rings. Satellite altimetry studies suggest that some NBC rings can pass coherently through the Antilles passages into the Caribbean (Goni and Johns, 2003). The motivation for the present study is to see whether thedrifter data could provide evidence that Caribbean anticyclones are generated by NBC rings.

Although the mean velocity field and velocity variance have been recently mapped for the Caribbean using surface drifters (Wilson and Leaman, 2000; Fratantoni, 2001; Centurioni and Niiler, 2003), and trajectories of drifters looping in eddies have been shown and briefly described (Centurioni and Niiler,...