Circulation in the Southwestern Atlantic Continental Shelf: satellite altimetry

The circulation in the Southwestern Atlantic Continental Shelf (SWACS) has been mainly studied by numerical models. The objective of this work is to study the circulation in the region with 21-years of altimetry data. To accomplish this goal was first necessary to make a validation of data with in- situ tide gauge data in the region on a seasonal scale. Results show that the Root mean square of the difference between both dataset is lower than 2.1 cm that it is of the same order of magnitude of the altimeter accuracy in the open ocean. Then we analyze the amplitude and phase of the anual cycle in the Continental Shelf (36ºS-54ºS).

Results show that the thermal expansion/contraction effect of the sea water is the main contributor. In the north part of the region, a secondary contributor might be related with th haline effect due to the variation of the Rio de la Plata plume. The analysis of the seasonal circulation through geostrophic currents derived from sea level shows that there is a mean north-northeast current, which is weaker in Winter and stronger in Summer along the shelf break. A time scales lower than the seasonal, the altimetry data could be affected by high frequencies variabilities such as tide and atmospheric forcing. In the particular case of the Rio de la Plata estuary, previous studies have shown that the estuarine circulation is vulnerable to the river run-off and wind variability, especially at sub-annual scales.

Thus, the atmospheric correction that is applied to the altimetry data is important. We analyze the dynamic atmospheric correction obtained with a global barotropic model (MOG2D: Modèle aux Ondes de Gravitè 2-Dimensions) and two regional barotropic models (HamSOM: Hamburg Shelf Ocean Model, SMARA) in the Rio de la Plata estuary. Results show that the global model underestimates the variability of the sea level response to pressure and wind forcing in comparison with the regional models. Then we examine the capabilities of the altimetry data to measure the sea level variability due to freshwater discharges from the main tributaries of Río de la Plata.