Preprints
https://doi.org/10.5194/egusphere-2022-402
https://doi.org/10.5194/egusphere-2022-402
 
13 Jun 2022
13 Jun 2022

Revisiting the tropical Atlantic western boundary circulation from a 25-year time series of satellite altimetry data

Djoirka Minto Dimoune1, Florence Birol2, Fabrice Hernandez1,2, Fabien Léger2, and Moacyr Araujo1,3 Djoirka Minto Dimoune et al.
  • 1Laboratorio de Oceanografia Física Estuarina e Costeira (LOFEC), Departamento de Oceanografia da Universidade Federal de Pernambuco (UFPE), Cidade Universitária, Avenida Arquitetura s/n, 50740-550 Recife, PE, Brazil
  • 2LEGOS, Université de Toulouse, CNES, CNRS, IRD, 18 avenue Edouard Belin, 31400, France
  • 3Brazilian Research Network on Global Climate Change (Rede CLIMA), Av. dos Astronautas, 1758, 01227-010 São José dos Campos, SP, Brazil

Abstract. Geostrophic currents derived from altimetry are used to investigate the surface circulation in the Western Tropical Atlantic over the 1998–2017 period. Using six horizontal sections defined to capture the current branches of the study area, we investigate their respective variations at both seasonal and interannual time-scales as well as the spatial distribution of these variations. Our results show that the central branch of the South Equatorial Current, the North Brazil Current component located south of the equator, the Guyana Current and the northern branch of the South Equatorial Current at 42° W have similar annual cycles, with maxima/minima during boreal winter-spring/October–November. In contrast, the seasonal cycles of the North Brazil Current branch located between the equator and 7–8° N, the North Brazil Current retroflected branch and the North Equatorial Countercurrent show maxima/minima during boreal fall/May. West of 42° W, an eastward current is observed between 0°–2° N, identified as the equatorial extension of the retroflected branch of the North Brazil Current. It is part of a large cyclonic circulation observed between 0°–6° N and 35°–45° W during boreal spring. The North Equatorial Countercurrent shows a two-core structure during the second half of the year, when we also observe the two regions where the North Brazil Current retroflects. The latter can be related to the wind stress curl seasonal changes. At interannual scales, depending on which side of the equator, the North Brazil Current exhibits two opposite scenarios related to the tropical Atlantic Meridional Mode phases. The interannual variability of the North Equatorial Countercurrent and of the northern branch of the South Equatorial Current (in terms of both strength and/or latitudinal shift) at 42° W are also associated to the Atlantic Meridional Mode, while they are associated to the zonal mode phases at 32° W.

Djoirka Minto Dimoune et al.

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Djoirka Minto Dimoune et al.

Djoirka Minto Dimoune et al.

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Short summary
The study of the surface current branches derived from satellite data in the northwest tropical Atlantic show similar seasonal variability, except the North Brazil Current branch which enter into Guyana Current and which also show a similar variability to the currents in the southwest. A cyclonic circulation and a surface eastward flow are shown in the equatorial region. The year-to-year variations of the currents are related to the tropical Atlantic climate modes, depending on their location.