A numerical study of the seasonal variability in the circulation off central Chile

Abstract

The Princeton Ocean Model is used to study the coastal ocean circulation off central Chile (between 30° and 45 °S) and its seasonal transitions in response to monthly mean climatological wind stress and surface heat flux. The model reproduces many of the dominant circulation features, including an equatorward coastal current, coastal upwelling, and a poleward undercurrent. To get the correct seasonal variability in the undercurrent, it was necessary to prescribe the inflow of the undercurrent on the northern model boundary. Meanders and eddies form throughout the simulation period seaward of the coastal current in response to baroclinic instability of the flow. The flow associated with the meanders shows upwelling in the shoreward flow and downwelling in the seaward flow. This upwelling/downwelling pattern is explained by conservation of relative vorticity in the flow. The upwelling velocity associated with the meanders corresponds to a vertical migration of 15-30 m over a typical timescale of the meanders of 1-2 months. It is argued that this upwelling may be important for maintaining observed high phytoplankton biomass and primary production seaward of the coastal zone directly affected by wind-driven upwelling. Copyright 2001 by the American Geophysical Union.