Abstract
The mesoscale dynamics in the southwestern Atlantic are significantly influenced by the Brazil Current (BC), characterized by features such as meanders and eddies. Among these, mushroom-like eddy dipoles, consisting of paired cyclonic and anticyclonic eddies, play a crucial role in the regional oceanography. This study aims to quantify the occurrence of these eddy dipoles and investigate the underlying dynamic mechanisms driving their formation and evolution. Using satellite-altimetry data from 1993 to 2021, we identified 115 eddy-dipole events with life spans typically less than three weeks. A detailed numerical simulation of a representative event from July 2006, based on a feature-model approach, revealed the formation of a symmetric and stable mushroom-like eddy dipole within three days. The spatial growth rate was determined to be 25 km/day, with a temporal growth rate of 0.20/day. The study found that the western boundary bathymetry along the Brazilian coast is conducive to generating symmetric dipoles, with asymmetric dipoles forming under specific conditions, such as a strong and narrow BC current jet. The formation of symmetric and asymmetric dipoles are closely linked to the conservation of potential vorticity as the southward-flowing BC crosses isobaths from shallower to deeper regions. The frequently observed mushroom-like eddy features near Cabo Frio depend on the coastline’s relative orientation, the strength of the BC, and the magnitude of planetary vorticity. These findings enhance our understanding of the mesoscale processes in the BC and their implications for regional marine dynamics.