Validation and Use of Altimetry Products in the Southwestern Atlantic Continental Shelf

LAURA A. RUIZ ETCHEVERRY; MARTIN SARACENO; LORELEY S. LAGO; MELINA M. MARTINEZ

Cadiz

Workshop; 13th Coastal Altimetry Workshop; 2023

ESA

The main objective of this work is to review the effort made by the group Southern Ocean PHYsical oceanogrAphy (SOPHYA) from University of Buenos Aires to validate along track and gridded altimetry products and study the dynamics of sea level at different temporal scales on the Southwestern Atlantic Continental Shelf (SWACS), one of the largest shelves in the Southern Hemisphere.Considering that the SWACS is characterized by large tide amplitudes, it is crucial to correct the altimetry data with an accurate tide model. This work has been done, obtaining that FES2014 is the best model on the mid-shelf, shelf-break and North of 42S. In the estuary of the Río de la Plata, the main source of fresh water on the SWACS, the tide global models did not resolve adequately the 5 leading tide components and a regional model was needed. In this region, the wind influences the sea level, especially at sub-annual scales, and the Dynamic Atmospheric Correction (DAC) was also investigated. The main result was that the global model represents the spatial distribution but underestimated the values, especially in the upper estuary. The gridded altimetry product was validated with tide gauges from PSMSL at annual scale along the coasts and used to analyze the seasonal cycle and long-term trends. The seasonal sea level in the SWACS is dominated by the density changes due to solar radiation, except north of 36S where the wind variability is more important. Moreover, the seasonal sea level pattern derived from altimetry displays a cross-shore gradient that explains the seasonal geostrophic currents observed, being maximum in austral autumn and minimum in austral spring. On the SWACS, the sea level trend estimated with CMEMS and ESA_CCI products is 2.95 and 2.85 mm/yr (1993-2015), respectively and is dominated by the mass changes. The spatial pattern is almost homogeneous that it might indicate that the geostrophic currents are not changing. Part of the effort to use altimetry in the study region was to deploy instruments under Jason tracks. A bottom pressure recorder was moored at 1.3 km from the nominal intersection of two tracks and 0.9 km from the coast. The results from the comparison between in situ and satellite data show that satellite data is more reliable using ALES retracking and tide model TPX08 as close as 4km from de coast. In addition, two bottom-mounted upward looking ADCPs were moored on the Jason-2 track #26 and two along 44.7S. The velocity time series allowed to calculate the geostrophic transport and compared with altimetry in the north portion of SWACS obtaining high correlation at time scales longer than 20 days. It was also studied the interannual sea level variability and its geostrophic transport, observing that the wind in relation with Southern Annular Mode (SAM) is the main forcing. A similar analysis was done at 44.7S. The region presents a barotropic circulation dominated by the meridional wind stress. In addition, the outer shelf is affected by an intra-seasonal signal that the gridded product cannot resolve.