Modelling of upwelling in the coastal area of Cabo Frio (Rio de Janeiro - Brazil)

Abstract

A 1 1/2 reduced-gravity model is proposed to study the hydrodynamic and thermodynamic features of the coastal upwelling area of Cabo Frio (Rio de Janeiro-Brazil). The vertical structure of the model is described by an active layer overlaying a deep inert layer where the pressure gradient is set to zero. For the upper layer, the model includes the turbulent version of the momentum. continuity and heat equations. The conservation of heat is represented by a transport equation to describe the thermodynamic changes of the sea surface temperature (SST). The solution domain includes open boundaries in which weakly-retlective conditions are prescribed. Solutions are found numerically on a uniform grid and the fundamental equations are approximated by the finite difference method. Numerical experiments are performed to evaluate the dynamic response of the coastal area of Cabo Frio forced by uniform and non-uniform wind fields. The solutions differ considerably depending on the orientation of the winds. East and northeast winds correlate with colder waters in the zonal coastline of this area and the presence of tlows toward Cabo Frio correlates with north wind components. The proposed model is validated with the numerical simulation of an observed event of upwelling, where a time-dependent and non-uniform wind ficld develops a SST pattern similar as the observations, particularly the extension of the cool water plume in south-west direction and the rapid time variation of the SST.