Dependency of simulated tropical Atlantic current variability on the wind forcing

• Published in: Ocean Science
• Main Authors: Burmeister, Kristin, Schwarzkopf, Franziska U., Rath, Willi, Biastoch, Arne, Brandt, Peter, Lübbecke, Joke F., Inall, Mark
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2024
• Subjects: Curl; North Atlantic
• Online Access: https://pure.uhi.ac.uk/en/publications/cb465516-7d42-4fc9-a2de-4241695cc3f9; https://doi.org/10.5194/os-20-307-2024; https://pureadmin.uhi.ac.uk/ws/files/50007518/os-20-307-2024.pdf; https://egusphere.copernicus.org/preprints/2023/egusphere-2023-1433/

The upper wind-driven circulation in the tropical Atlantic Ocean plays a key role in the basin-wide distribution of water mass properties and affects the transport of heat, freshwater, and biogeochemical tracers such as oxygen or nutrients. It is crucial to improve our understanding of its long-term behaviour, which largely relies on model simulations and applied forcing due to sparse observational data coverage, especially before the mid-2000s. Here, we apply two different forcing products, the Coordinated Ocean-ice Reference Experiments (CORE) v2 and the Japanese 55-year Reanalysis (JRA55-do) surface dataset, to a high-resolution ocean model. Where possible, we compare the simulated results to long-term observations. We find large discrepancies between the two simulations regarding the wind and current field. In the CORE simulation, strong, large-scale wind stress curl amplitudes above the upwelling regions of the eastern tropical North Atlantic seem to cause an overestimation of the mean and seasonal variability in the eastward subsurface current just north of the Equator. The wind stress curl of JRA55-do forcing shows much finer structures, and the JRA55-do simulation is in better agreement with the mean and intraseasonal fluctuations in the subsurface current found in observations. The northern branch of the South Equatorial Current flows westward at the surface just north of the Equator. On interannual to decadal timescales, it shows a high correlation of R=0.9 with the zonal wind stress in the CORE simulation but only a weak correlation of R=0.35 in the JRA55-do simulation. We also identify similarities between the two simulations. The strength of the eastward-flowing North Equatorial Counter Current located between 3 and 10° N covaries with the strength of the meridional wind stress just north of the Equator on interannual to decadal timescales in the two simulations. Both simulations present a comparable mean, seasonal cycle and trend of the eastward off-equatorial subsurface current south of the ...