ON THE CONTRIBUTIONS OF EKMAN TRANSPORT AND PUMPING TO THE DYNAMICS OF COASTAL UPWELLING IN THE SOUTH-EAST PACIFIC

Abstract

We investigate the oceanic circulation in the South-East Pacific (SEP) and Peru-Chile coastal upwelling, using satellite data and a medium resolution, eddy permitting regional model. The data consist in ERS 1 and 2 derived winds and AVHRR SST. Ekman pumping and transport are first calculated from wind data and analysed. Results are compared to the estimate of the zonal extension of upwelling cells obtained from SST data. The time variability of these parameters confirms that the northern and southern parts of the region have different characteristics. Namely, in the northern part, the seasonal cycles of SST and Ekman pumping are not correlated whereas in the southern part, the Ekman transport, pumping and the zonal extension of SST fluctuations exhibit a large coherency. In particular, the maximum in zonal extension takes place during the upwelling favourable conditions (spring to early fall). In an intermediate region satellite derived wind data were not representative of coastal conditions as shown by data from land stations. These observations are compared to model outputs: relations between seasonal and interannual variability of the upwelling with model current variability are derived