Gaël Alory (LEGOS, France); Micaël Aguedjou (CNES, France); Yves Morel (LEGOS, France); Camille Cardot (LEGOS, eOdyn, France); Karim Thiam (LEGOS, france); Pierre-Etienne Brilouet (LEGOS, France); Guillaume Morvan (LEGOS, France); Clément Le Goff (LEGOS, France); Séréna Illig (LEGOS, France); Florent Gasparin (LEGOS, France); Julien Jouanno (LEGOS, France); Yann Krien (LEGOS, France); Florent Lyard (LEGOS, France)

The main objective of this project is to evaluate the improvement brought by the new 2D SWOT data to describe and study the 2D mesoscale/submesoscale dynamics in the Eastern Tropical Atlantic Ocean (ETAO). This mesoscale activity is not well known in the ETAO because of a lack of observations and because altimetric signal is more difficult to interpret in the equatorial region. In our previous SWOT-GG project (2020-2024), we based our analysis on numerical simulations to prepare the present project. The tools and results we obtained are applied to the SWOT data. We have shown that most surface vortices are generated near the coast, their radius remains below 50 km and their lifetime is also short (less than 3 months) (Aguedjou et al., 2019; 2021, 2023; Assene et al., 2020; Napolitano et al., 2022). In addition, these vortices interact with a broad range of processes such as the large-scale circulation, the coastal and equatorial waves and other near-coastal bathymetric or dynamical features (intensification of the tidal signal, generation of internal tides, upwelling/downwelling, etc.). This makes them difficult to observe with classical altimetry. SWOT data provide high resolution 2D quasi-synoptic altimetric maps allowing a description of the variability and eddy activity, at high resolution of particular interest in the equatorial region to identify dynamical features such as vortices. Combining SWOT data with other remotely sensed data, high-resolution numerical models, in situ data as well as AIS data, we evaluate the “Observability” of 2D meso-submesoscale activity with SWOT from the coastal regions to the open ocean in this equatorial region (WP1). We study this high-resolution meso-submesoscale activity in the coastal ETAO area along the African coast and islands (WP2) using the SWOT data. We study the meso-submesoscale and wave dynamics in the open equatorial ocean of ETAO (WP3) with SWOT data. We present the main results of the first year of the SWOT-ETAO project. We used daily SWOT (cal/val) at 2km resolution as well as DUACS and MIOST sea level anomalies (SLA), sea surface temperature, salinity and chlorophyll satellite data (SST, SSS, Chl). The Congo river plume and its mesoscale/submesoscale dynamics are analyzed using the SWOT data. A mesoscale anticyclone with a two-year lifespan is also examined using the daily SWOT data over one month. These SWOT data reveal submesoscale vortices around the mesoscale eddy, which were not detected by the nadir altimetry data. Various submesoscale diagnostics are employed to characterize these dynamics, which are observed for the first time, thanks to the SWOT data. Another study from the SWOT-ETAO project is also presented on internal waves offshore off the Congo river using the 250m SWOT data (Le Goff et al., in this meeting).