THE PATOS-LAGOON SUMMERTIME CIRCULATION AND DYNAMICS

The main aspects of the summertime circulation and dynamics of the Pat os Lagoon, a system located in southern Brazil and considered as one o f the world's largest choked coastal lagoons, are studied through the analysis of time series of wind stress, water level and freshwater dis charge, combined with the results of a barotropic circulation model. T he longitudinal wind component has been verified as the main driving f orce, generating a set-up/set-down mechanism of oscillation with the n odal line in the midlagoon area. The period of this oscillation coinci des with the passages of frontal systems for this region. The sea bree ze acts as a secondary effect, being clearly observed in the northern part of the lagoon. Freshwater discharge is expected to cause variatio ns in water level on the seasonal band and to a lesser degree in the 8 -15 day time-scale. The tidal signal is of importance only near the ex it to the ocean, being strongly reduced in the interior of the lagoon. Model results suggest a wind set-up momentum balance in the longitudi nal direction in the deeper parts of the lagoon; near the margins, the longitudinal momentum balance is mostly of frictional form, with the wind stress being balanced by the bottom friction. In the lateral dire ction, a geostrophic balance is verified in both regions. The wind for ced circulation is characterized by the presence of several cells with downwind velocity near the margins and upwind return flow occurring i n the central areas.