Deep-Sea Research I 52 (2005) 221–240 Upper ocean circulation in the western tropical Atlantic in boreal fall 2000 Lothar Stramma a,Ã , Monika Rhein b , Peter Brandt a , Marcus Dengler a , Claus Bo¨ning a , Maren Walter b a Leibniz-Institut fu¨r Meereswissenschaften an der Universita¨t Kiel, Du¨sternbrooker Weg 20, Kiel, 24105 Germany b Institut fu¨r Umweltphysik, Abt. Ozeanographie, Universita¨t Bremen, Postfach 330 440, 28334 Bremen, Germany Received 12 November 2003; received in revised form 4 June 2004; accepted 9 July 2004 Available online 15 December 2004 Abstract The upper ocean large-scale circulation of the western tropical Atlantic from 11.51S to the Caribbean in November and December 2000 is investigated from a new type of shipboard ADCP able to measure accurate velocities to 600m depth, combined with lowered ADCP measurements. Satellite data and numerical model output complement the shipboard measurements to better describe the large-scale circulation. In November 2000 the North Brazil Undercurrent (NBUC) was strongly intensified between 11 and 51S by inflow from the east, hence the NBUC was formed further to the north than in the mean. The NBUC was transporting 23.1Sv northward at 51S, slightly less than the mean of six cruises (Geophysical Research Letters (2002) 29 (7) 1840). At 351W the North Brazil Current (NBC) transported 29.4Sv westward, less than the mean of 13 cruises (Geophysical Research Letters (2003) 30 (7) 1349). A strong retroflection ring had just pinched off the NBC retroflection according to the satellite information. The inflow intotheCaribbeansouthof16.51NoriginatedinpartofaleakagefromtheNBCretroflectionzoneandinpartfromthe North Equatorial Current. A thermocline intensified ring with a transport of about 30Sv was located off Guadeloupe carrying South Atlantic Central Water towards the north. Observed deviations of the November/December 2000 flow field from the November long-term mean flow field were related to an enhanced Intertropical Convergence Zone (ITCZ) associated with an increased North Equatorial Countercurrent (NECC), as well as to boundary current rings and Rossby waves with zonal wavelength of the order of 1000km. At 441W the presence of a Rossby wave associated with an anticyclonic circulation led to a strongly enhanced NBC of 65.0Sv as well as to a combined NECC and EquatorialUndercurrenttransportof52.4Sv,muchstrongerthanduringearliercruises.Whilethe1/31-FLAME model isunabletoreproducedetailsoftheverticaldistributionoftheobservedhorizontalflowat44 1WforNovember2000as well as the horizontal distribution of some of the observed permanent current bands, a climatological simulation with the 1/121-FLAME agrees much better with the observations and provides information on the spreading path between the sections. E.g., the interpretation that the widening in the Antarctic Intermediate Water layer of the westward ARTICLE IN PRESS www.elsevier.com/locate/dsr 0967-0637/$-see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.dsr.2004.07.021 Ã Corresponding author. Tel.: +494316004103; fax: +494316004102. E-mail address: lstramma@ifm-geomar.de (L. Stramma).