Cheikh Tidiane Deme1, Malick Wade2, Mouhamadou Thiam3, and Modou Thioune4
1 Department of Applied Physics, Laboratory of Atmospheric and Ocean Sciences - Materials, Energy, and Devices (LSAO-MED), Gaston Berger University, Saint-Louis, Senegal
2 Department of Applied Physics, Laboratory of Atmospheric and Ocean Sciences - Materials, Energy, and Devices (LSAO-MED), Gaston Berger University, Saint-Louis, Senegal
3 Laboratory of Sciences and Techniques of Water and Environment (LaSTEE), Polytechnic School of Thiès, BP A10 Thiès, Senegal
4 Department of Applied Physics, Laboratory of Atmospheric and Ocean Sciences - Materials, Energy, and Devices (LSAO-MED), Gaston Berger University, Saint-Louis, Senegal
Original language: English
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Abstract
This study examines the interannual variability of ocean circulation in the equatorial Atlantic, with a particular focus on the Equatorial Undercurrent (EUC) and its interactions with sea surface temperature (SST) and precipitation over West Africa. The analysis is based on SODA v2.2.4 ocean reanalysis data for the period 1900–2008 and CRU TS precipitation data spanning 1901-2022. Results reveal significant spatio-temporal variability in EUC depth and highlight strong relationships between EUC fluctuations, SST anomalies in the equatorial Atlantic, and rainfall variability over West Africa. Two main phases characterize the evolution of the EUC. From 1900 to 1960, the EUC exhibits increased depth, indicating a strengthening of ocean circulation. In contrast, the period 1961–2008 is marked by a shallower EUC and weakened circulation. The eastern basin shows greater sensitivity of EUC depth to interannual rainfall variability compared to the western basin, consistent with stronger SST variability in this region. During 1900–1960, a deeper EUC, especially in the eastern basin, is associated with a pronounced Atlantic SST dipole (warmer in the north and cooler in the south), leading to a northward shift of the Intertropical Convergence Zone (ITCZ). This results in increased rainfall over the Sahel and reduced precipitation over the Gulf of Guinea. Conversely, during 1961–2008, a shallower EUC corresponds to a reversal of this precipitation pattern. However, the precipitation dipole weakens in the eastern basin, likely due to changes in large-scale atmospheric circulation.
Author Keywords: EUC, Estern, western, basin, SST, West Africa, Precipitation.
