A numerical simulation of the upwelling regime off the Chilean coast.

In this study we use a primitive equation model to investigate the oceanic circulation along the chilean coast between 40S and 34S. The numerical model was initialized with climatological fields of temperature and salinity and forced with ECMWF winds for the period 1992-1994. The simulated fields compares favorably with historical observations of this regional coastal upwelling system, showing that local wind forcing, bottom topography and coastline geometry significantly affects the local circulation. The analysis of the numerical results was divided into periods corresponding to El Nino and normal (non-El Nino) years. During normal years, the circulation is characterized by the presence of a surface coastal equatorward jet flowing over a poleward undercurrent that spreads over the continental shelf and slope break. The induced offshore Ekman transport generates coastal upwelling of colder and saltier waters, activity that decreases during events of wind relaxation. Meanderings, coastal jet separation and formation of mesoscale cyclonic and anticyclonic eddies are commonly observed. Analyses of synoptic maps, time series and vorticity balance of external and internal model fields show that southern coastal and offshore oceanic fields are dominated by local winds, while those between Punta Lavapie and latitude 36S are controlled more by remote forcing from the southern region. Analyses for El Nino periods show the upwelling activity to weaken due to a rapid decreases of the equatorward winds. The frequent passage of eastward atmospheric storms also favours the downwelling activity. The relaxation is larger at the southern regions, where the upwelling tends to dissappear.