Dossa A. N. auteur aut IRD Silva A. C. auteur aut IRD Chaigneau Alexis auteur aut IRD Eldin Gérard auteur aut IRD Araujo M. auteur aut IRD Bertrand Arnaud auteur aut IRD text journalArticle eng text/pdf born digital access In the tropical Atlantic Ocean, the North Brazil Undercurrent (NBUC) and the North Brazil Current (NBC) play important roles as near-surface northward paths for the Atlantic meridional overturning circulation. To investigate the meridional evolution of the near-surface western boundary circulation in that region, two surveys were carried out off Northeast Brazil during austral spring 2015 and fall 2017, periods that we show to be representative of typical conditions for the spring and fall seasons. Using conductivity temperature depth oxygen probe and ship-mounted acoustic Doppler current profiler measurements, altimetry data, and numerical reanalysis products, we examine the spatiotemporal variability of the NBUC, providing a comprehensive view of the circulation, including NBUC-NBC transition and the potential impact of mesoscale eddies. The NBUC originating south of 10 degrees S flows equatorward over the continental slope. NBUC mean velocity, transport and vertical extent of the velocity core were higher in spring 2015 (0.81 m s(-1), 15.6 Sv, and >400 m) than in fall 2017 (0.65 m s(-1), 11.0 Sv, and similar to 300 m). The upper limit of the NBUC velocity core rose slightly from 160 m at 9 degrees S to 105 m depth at 6 degrees S. This pattern is associated with a northward increase in current velocity from 0.7 m s(-1) at 9 degrees S to 1 m s(-1) at 5 degrees S. The orographic effect shifts the flow from northeastward south of 7.5 degrees S to northwestward north of 7.5 degrees S, following the shoreline. Besides, altimetry data show that this flow can be locally influenced by mesoscale activity. Farther north, at similar to 4.8 degrees S, data obtained in fall 2017 show that the central branch of the South Equatorial Current (cSEC) enters into the western boundary system where it coalesces with the NBUC to form the NBC, flowing toward the Caribbean Sea. Finally, in fall, the NBUC retroflection does not feed the South Equatorial Undercurrent (SEUC), which, instead originates from retroflections of the cSEC and the equatorial branch of the South Equatorial Current (eSEC). specialized Western Tropical Atlantic North Brazil Undercurrent North Brazil Current Flow-topography interaction Mesoscale activity ADCP BRESIL ATLANTIQUE ZONE TROPICALE 032 190 102475 [15 ] 2021 0079-6611 https://www.documentation.ird.fr/hor/fdi:010080584 10.1016/j.pocean.2020.102475 0079-6611 [F B010080584] https://www.documentation.ird.fr/hor/fdi:010080584 https://www.documentation.ird.fr/intranet/publi/2021/01/010080584.pdf Accès réservé (Intranet de l'IRD) IRD - Base Horizon / Pleins textes 2021-02-08 2025-02-24 fdi:010080584 fre