Local and remote forcing of sea surface temperature in the coastal upwelling system off Chile

An analysis is presented of records of sea surface temperature (SST), sea level and winds collected during the period 1991-1995 along the coast of northern and central Chile (sea level also from the Peru coast in 1991-1994), and of SST from remote sensing during the austral summers of 1991 and 1992 off northern Chile. Large, interannual fluctuations of SST and sea level off northern Chile are linked to vertical displacements of the equatorial thermocline during El Nino-La Nina events. In the intraseasonal, 50-day band, SST and sea level are intimately related all along the coast, whereby SST anomalies lag sea level perturbations by about 12 days. Such sea level fluctuations are due to free, coastal-trapped waves, ultimately forced via equatorial Kelvin waves by 50-day wind events in the western and central tropical Pacific. These results and those of the remote sensing analysis suggest significant remote forcing of SST fluctuations in the coastal zone off Chile by the action of the coastal-trapped waves. Off central Chile, SST is also related to local wind stress in the intraseasonal band. Simulations with a simple, local, wind-driven upwelling/entrainment model capture rather well observed synoptic and intraseasonal oscillations of SST there. Off northern Chile, however, this simple model is not successful in simulating observed SST. An attempt to include effects of coastal-trapped waves into this simple, one-dimensional model did not improve model fit to data at either location. An explanation for the apparent strong influence of these waves on SST along this coast should therefore be sought in other effects not considered by this model such as cross-shelf and alongshore advection.