The impact of different forcing agents on the residual circulation in Baía de Todos os Santos, Brazil 13°S

Abstract

This study investigates the forcing of the residual circulation in Baía de Todos os Santos (BTS), surrounded by the third largest metropolis in Brazil. The Regional Ocean Modeling System (ROMS) was used to investigate the roles of the tide (TD), wind (WN), net heat flux (HF), freshwater flux (WF) and river discharge (RD) on the residual circulation. We forced the model in the boundaries with tidal elevations and currents from the global tidal model TPX07.2, and at the surface with wind stresses, fresh water and heat fluxes from a combination of NCEP/Reanalises and data from local weather stations. The modeled tidal circulation agrees well with current observations (mean percentage absolute deviation = 17%). The residual velocities have magnitudes smaller than 0.09 m/s. The flow is structured at the by moth with a net-landward flow (positive) in the channel centre and a net-seaward flow on the shoulders for all scenarios (Figures 2a, b and c) but that including the river discharge (Figure 2d). The lateral stratification associated with residuals currents, when forced by TD, WN+TD and HF+WF+WN+TD, is similar to that reported by Xavier (2002) running a barotropic model, and also in good agreement with analytical solutions presented by Li & O'Donnell (2005) for short (4*L/λ < 0.6) channels like the BTS. Adding river discharge to the model (Figure 2d) results in a vertically sheared residual flow across most of the channel, with flow magnitudes similar to that created by the other forcing. The results show that the tide is the main agent on the RC, however, the river discharge can significantly modify it.