CoAuthors

Robin Chevrier (CLS, France); Rosemary Morrow (LEGOS/OMP, Université Toulouse III, France); Oscar Vergara (CLS, France)

Ocean mesoscale eddies are the most energetic component of the ocean dynamics, important for the horizontal fluxes of energy, momentum, and tracers such as heat, carbon and nutrients. Today, observations of smaller scales are limited, and we might be missing 75% of the mesoscale eddies at high latitudes. The future SWOT SAR-interferometry wide-swath altimeter mission aims to provide 2D swath observations of ocean surface topography to characterize the ocean mesoscale and submesoscale circulation from the large scale down to around 15 km wavelength. This research focuses on the understanding of this smaller mesoscale field in the Southern Ocean, with a focus on the Agulhas current. Our main aim is to investigate whether small-scale eddy fluxes reinforce or compensate for the large mesoscale fluxes that we can observe today, and where and when this is occurring. The study of mesoscale eddies and their interaction with the larger scale structures is achieved using various eddy diagnostics: the eddy kinetic energy (eke), strain rate, barotropic energy transfer, anisotropy of eddy variability, and energy flux between scales with a coarse graining approach. We compare the dynamics in key regions of the Agulhas boundary current, the Agulhas Retroflection and Cape Cauldron region, and the meandering Agulhas Current Extension. First, the dataset generated with the hourly MITgcm LLC4320 on a native grid at 1/48-degree is used. A comparison is made with today's observability using reconstructed DUACS maps, based on the optimal interpolation of the along-track sampling of the MITgcm at a coarser 1/10-degree resolution. For the observability with SWOT, diagnostics are finally computed on the simulated SWOT swaths, taking a sea surface height (ssh) based on the 1/48° MITgcm simulation and the SWOT ocean simulator, with and without the SWOT errors. The observable scales for these different diagnostics, and error reduction techniques for SWOT, will be discussed.