A NUMERICAL STUDY OF THE BAROTROPIC CIRCULATION OF THE RIO DE LA PLATA ESTUARY: SENSITIVITY TO BATHYMETRY, EARTH ROTATION AND LOW FREQUENCY WIND VARIABILITY.

SIMIONATO, C. G.; DRAGANI, W. C.; MECCIA, V. L.; NUÑEZ, M. N.

ESTUARINE COASTAL AND SHELF SCIENCE

Elsevier Science

Lugar: Amsterdam, The Netherlands; Año: 2004 vol. 61 p. 261 - 273

0272-7714

The barotropic circulation of the Río de la Plata is studied by means of process oriented high resolution 3-D numerical simulations, where its relation to the bathymetry, Earth rotation, river runoff and low frequency wind fluctuations is explored. The model solutions indicate that the circulation at the Río de la Plata is sensitive to bathymetry and Earth rotation. Even though a bimodal circulation pattern has been reported in previous papers, our simulations suggest that in absence of winds the normal path of the estuary flow should be a buoyant plume to the north. When the mean wind blows from directions between SSE and NNW this pattern is intensified. The southward path observed seems to be the result of the wind forcing when it acts from some directions, what explains why this path has only been sporadically registered. The wind driven circulation at the estuary can be explained in terms of two modes of circulation. The first one, prevailing for winds with a cross-river component, is related to an inflow-outflow of water at the exterior part of the estuary and accounts for the seasonal signal observed in the salinity field. The second mode dominates when the wind blows along the estuary axis and has a very distinctive pattern of significant sea level increase or reduction at the upper part of the estuary. This mode accounts for two extreme situations often observed with important social implications: the Sudestada that produces disastrous floodings and the persistent northwest wind, that in occasions results in the collapse of the drinking water supply to the city of Buenos Aires. From the numerical experiments a dynamical classification of the estuary into three different regions with regard to bathymetry, Earth rotation and winds is proposed. They are the upper-central estuary, the exterior estuary and the Samborombón Bay. Our solutions indicate that during the summer this bay has a weak and retentive circulation pattern that favors the biota, allowing the region to become an area of spawning and nursery for several coastal species. Nevertheless, our results also indicate that the situation that favors the fisheries could change sensitively if the mean wind direction suffers even a small shift to the south as, for example, a result of climate change. Results from historical water level data analyzed by other authors suggest that such a shift could be already taking place.