Lagrangian tracking of meso and sub-mesoscale features in the Southwestern Atlantic

MARTIN SARACENO; NICOLAS BODNARIUK; LAURA A. RUIZ ETCHEVERRY; JOSEFINA OLASCOAGA; FRANCISCO JAVIER BERON-VERA; CLAUDIA G. SIMIONATO

Congreso; 2023 Ocean Surface Topography Science Team Meeting; 2023

CNES

The Southwestern Atlantic (SWA) is characterized by its large Eddy Kinetic Energy as the result of the confluence of two major western boundary currents, the northward flowing Malvinas Current (MC) and the southward flowing Brazil Current. The study of the SWA has been addressed in the literature based on altimetry data, in situ measurements, regional models and ocean reanalysis. The present study constitutes the first effort to sample a portion of the SWA, with a dense drifter array (N = 62). The drifters, anchored at 15 m depths, were deployed across the MC and the Argentine Continental Shelf along two zonal transects located at 47°S and 47.25°S, between the 8th and the 9th of September 2021. Drifters were set to deliver their position every 10 and 60 minutes, providing accurate Lagrangian trajectories that provide information on a large range of space and time scales of the surface currents. Three regions are clearly identified based on the analysis of the speed of the drifters, of their trajectories and of the spectral density of their velocities: the continental shelf, the slope and the open ocean. The comparison of the trajectories of the drifters with satellite altimetry images shows that, in general, drifters follow mesoscale features that are detectable in satellite altimetry maps. In particular regions, as within the MC, the deployment design of the drifters allowed to show the presence of three jets, while satellite altimetry data suggests only the presence of two. The analysis of drifter trajectories allowed also the study of submesoscale features of the flow (1 to 10 km) that are not observable in satellite altimetry data. Comparison with cloud-free, high-resolution color images, shows that drifter trajectories organized by the mesoscale flow might also locally follow sub-mesoscale features. In frontal regions it was found that drifter velocities double satellite altimetry geostrophic velocities, which suggests that the dynamics at those regions is largely dominated by ageostophic components. We conclude that the deployment of a dense drifter array provides valuable information of the flow that cannot be attained solely based on satellite data.