Subtidal Response To Wind Forcing In The South Brazil Bight During Winter (models, Shelf, Coastal)

Subtidal variability in the South Brazil Bight, from Cabo Frio (23(DEGREES)S) to Cabo de Santa Marta (28(DEGREES) 40' S), and the associated atmospheric forcing, are examined for two winter periods: 1 August - 3 November, 1978; and 15 July - October, 1979.Meteorological records from Arvoredo to Cabo Frio show high alongcoast correlation. The dominant 9.6 day perturbation in both atmospheric pressure and wind propagates equatorward from Cananeia, with alongcoast speed of about 12-14 m/s. Both meteorological signals suggest poleward propagation from Cananeia to Arvoredo, indicating that the 9.6 day disturbances hit the coast near Cananeia and from that region propagate in both directions along the South Brazil Bight coast.Observed sea level fluctuations show significant alongshore coherence between Sao Francisco and Cabo Frio, for periods greater than 3 days. Modeling of sea level response at Ubatuba, using the theory of continental shelf waves generated by remote wind forcing, presents results that are similar to the observed response.Nearshore currents in the Canal de Sao Sebastiao show high correlation with local wind. Correlation is larger for a time lag of 12 h, wind leading current.The wind-driven circulation is simulated with a non-linear, barotropic, one-way nested model. The model coarse grid topography incorporates a realistic shelf, extending from Cabo de Santa Marta to Cabo Frio, and a deep ocean region. Boundary conditions are no normal flow at the coast, radiative condition at the cross-shelf open boundaries and adiabatic condition at the alongshelf open boundary. The model medium grid extends from Santos to Parati, and from the coast to the 100 m isobath. The model fine grid covers the Canal of Sao Sebastiao.Impulsive uniform wind stress experiments show that a coastally trapped response is achieved within 30 h of the imposition of the wind. The sudden imposition of the wind appears to excite the first normal model of the region.Simulations for a period of 10 days, using adjusted NMC winds as forcing, produces sea level oscillations and currents that are in reasonable agreement with observations. (Abstract shortened with permission of author.)