The Trapping of Agulhas Rings in the South Brazil Bight

Abstract

The South Brazil Bight is a section of the Brazilian margin mainly dominated by the poleward Brazil Current flow, their meanderings and eddies. We evaluated the mean mesoscale for the region, and an anticyclonic feature was highlighted over the São Paulo Plateau. Around that feature, cyclonic eddies were also accentuated. The combination of these structures dominate the region, forming an eddy corridor. Using eddy detection dataset, we reveal that the signal on the plateau was directly related to the presence of anticyclones. The cyclones in the region present both local and remote origins, however, most of the anticyclones are from remote sources. More than 95% of these anticyclones were Agulhas Rings, which could or could not have been subjected to splitting or merging processes. On the plateau we observe an average of 5.3 anticyclones per year. However, these rate is related not only to the number of anticyclones but also to the time they remain there. We observe that Agulhas Rings reside in the region for 50.8 days, consequently, they occupy the plateau for almost 75% of the year. During half of the residence time, there is a multi-pattern interaction with cyclones. This relationship between eddies of opposite polarity creates a shielding process. The anticyclones become shielded and trapped by the cyclones, have their progress delayed, and their course deflected toward the Brazil Current. This was the first observation of this process involving the Agulhas Rings and the first study of the subsequent eddy-current interaction in the region.