Continental Shelf Research 23 (2003) 1559–1578 Modelling of upwelling–downwelling cycles caused by variable wind in a very sensitive coastal system Carlos A.A.H. Carbonel* Universidade Santa Ursula, ICBA, Rua Jornalista Orlando Dantas 59, Cep. 22231-010, Rio de Janeiro, Brazil Received 21 March 2002; received in revised form 27 March 2003; accepted 31 July 2003 Abstract The hydrothermodynamics of upwelling and downwelling events as a consequence of successively wind field changes areinvestigatedusinga1 1 2 layernumericalmodelforopenandlimitedcoastalregions.Themodelincludestheessential dynamicalprocesses.Solutionsarefoundinaregionaloceanbasinandareforcedbynon-uniformandtime-dependent wind fields. The study case is the Cabo Frio Coast (Rio de Janeiro, Brazil), a very sensitive hydrodynamic coastal system, where the passage of cold fronts modifies completely the NE wind prevailing pattern (favourable to upwelling events) to SW winds (favourable to downwelling). Themodelissuccessfulinsimulatingmanyfeaturesofobservedpatterns.Initially,thenumericalexperimentsinclude a simple corner coastline shape, relevant to the Cabo Frio region, to understand the mechanisms and to clarify the relative importance of different factors in producing the strong property gradients typical of upwelling areas. The coastal ocean is forced by different wind patterns including non-permanent wind field rotations. Later, the goal of this paper, the observed SST variability during typical summer months in the coastal region of Cabo Frio, is simulated numerically. The change of SST is reproduced with a good degree of approximation, when upwelling and downwelling events take place. The role of some physical processes and the initial conditions is clarified, isolating their effects. The obtainedresultsdemonstratethattheexistingtheoryofupperlayerdynamicsformulatedintheproposedsimplemodel account for the observed phenomena on occasion of upwelling–downwelling cycles caused by variable wind in space and time. r 2003 Elsevier Ltd. All rights reserved. Keywords: Upwelling–downwelling events; Wind changes; Numerical modelling; SST simulation; Open boundaries 1. Introduction Thecommoninterpretationofcoastalupwelling is that it is due to a wind-induced divergence. Ekman transport of the surface water away from the coast then results in a vertical motion bringing nutrient-rich water to the surface. The upwelling as well as the circulation near the coastal boundaries is highly variable in space and time. The coastline irregularities and the spatial varia- tion of the wind stress field lead to a three- dimensional circulation. In coastal upwelling regions, the circulation is commonly characterized by the typical forma- tion of plumes of cold surface temperatures. ARTICLE IN PRESS *Av. G. Vargas, LNCC, 333-Quitadinha, Petropolis, RJ 25651-070, Brazil. E-mail address: carloscarbonel@hotmail.com (C.A.A.H. Carbonel). 0278-4343/$-see front matter r 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0278-4343(03)00145-6