A Newly Observed Quasi‐Stationary Subsurface Anticyclone of the North Brazil Undercurrent at 4°S: The Potiguar Eddy

This study describes a newly discovered subsurface anticyclone, called the Potiguar Eddy (PE) centered at about 4° S, 36.5° W, along the western flank of the North Brazil Undercurrent (NBUC). The PE is a quasi‐stationary elliptical feature, with major and minor axes of approximately 330 and 130 km. It extends vertically from 100 m to 400 m, with maximum velocities of 0.6 m s‐1, and recirculates about 2 Sv of waters from the NBUC. Despite the presence of the PE in subpycnocline waters, the surface flow is predominantly northwestward throughout the year. Analysis of moored current meter data revealed a depth‐dependent variability that reaches its highest values between about 100 and 400m, coincident with the PE. This variability is found to be associated with a 20‐to‐30 day second baroclinic mode waves, which can strengthen, weaken, or even reverse the currents of the PE. We highlight the possible causes for this variability to include Coastally Trapped Waves, instabilities, and Tropical Instability Waves, or a combination thereof ‐‐ which opens up new study topics for future research.