Towards High Resolution Altimetry: evaluation of products in the Southwestern Atlantic. Summary of results from CASSIS project

Martin Saraceno (Universidad de Buenos Aires, Argentina)


Loreley Lago (Universidad de Buenos Aires, Argentina); Guillermina Paniagua (Universidad de Buenos Aires, Argentina); Camila Artana (Mercator, France); Ramiro Ferrari (Universidad de Buenos Aires, Argentina); Alberto Piola (Servicio de Hidrografia Naval, Argentina); Christine Provost (CNRS, France); Raúl Guerrero (Universidad de Mar del Plata, Argentina)

Event: 2020 Ocean Surface Topography Science Team Meeting (virtual)

Session: Salient results from the 2017-2020 OSTST PIs

Presentation type: Type Forum

The CASSIS project is a French-Argentine cooperation to study the circulation in the Southwestern Atlantic from in situ and satellite altimetry data. Seven moorings that measure currents, temperature, conductivity and pressure and a fully equipped oceanographic buoy collected in situ data between December 2014 and May 2017. During the first year (December 2014-November 2015) the moorings were deployed below Jason-2 satellite altimeter track #26, covering the northern portion of the Malvinas Current (MC) and Patagonian continental shelf (PCS). In December 2015 the instruments were recovered and redeployed for a year and a half along a zonal section at 44.7°S. A summary of the results obtained are reviewed here and in complementary presentations in this meeting. In-situ surface currents and geostrophic velocities obtained from satellite altimetry are significantly correlated at the shelf-break (0.7). In the continental shelf, the subsurface barotropic component is also very well correlated (0.74) to the satellite data. During specific events, associated with the presence of mesoscale eddies at the shelf-break and to the passage of synoptic storms at the continental shelf, differences between remote and in-situ currents are larger.
At 41°S the MC is largely modulated by the mesoscale activity that result from the confluence of the MC with the southward flowing Brazil Current. Measurements at 44.7°S showed for the first time the presence of large oscillation in the meridional velocities of the MC and that the eastern and western portions of the current are uncorrelated. Despite satellite altimetry data do not reveal the fine scale structure within the MC, satellite data were useful to track the origin of the large oscillations observed with the in situ data.
Over the continental shelf, in situ data show that the along-shore component of the wind stress modulates the cross-shore pressure gradient that, in turn, modulates the along-shore variability of the shelf currents. In both domains, satellite altimetry data are able to capture the temporal variability of the currents only at temporal scales larger than 20 days. The in situ data collected show that the vertical structure of the water column is a critical information that is needed in the attempt to use satellite altimetry as a proxy of subsurface currents.
Martin Saraceno
Universidad de Buenos Aires