CoAuthors

Boris Dewitte (LEGOS, Laboratoire d’Etudes en Géophysique et Océanographie Spatiales, Toulouse, France, France); Frédéric Frappart (LEGOS, Laboratoire d’Etudes en Géophysique et Océanographie Spatiales, Toulouse, France, France); Marcel Ramos (CEAZA, Center for Advanced Studies in Arid Zones, La Serena, Chile, Chile); Luis Bravo (CEAZA, Center for Advanced Studies in Arid Zones, La Serena, Chile, Chile); Katerina Goubanova (LEGOS, Laboratoire d’Etudes en Géophysique et Océanographie Spatiales, Toulouse, France, France); Jorge Vazquez (JPL, Jet Propulsion Laboratory/California Institute of Technology, Pasadena, USA, USA); José Rutllant (Department of Geophysics, University of Chile, Santiago, Chile, Chile)

The near-shore surface mesoscale atmospheric circulation in the upwelling systems off Peru and Chile is influential on the Sea Surface Temperature (SST) through various processes. There has been a debate whether or not the so-called "wind drop-off", that is a shoreward decrease of the surface winds, can act as an effective forcing of upwelling through Ekman pumping. Although the wind drop-off has been simulated by high-resolution atmospheric models, it has not been well documented due to uncertainties in the scatterometry-derived wind estimates near the coast associated with land contamination (satellite blind-zone of ~40km). Here we use the along-track altimetry-derived wind data Jason1&2 et ENVISAT satellites on nominal and interleaved tracks, to estimate wind amplitude near shore and document its variability at intraseasonal to seasonal timescales. The wind intensity is estimated through the inversion of the radar backscattering coefficient. The focus is on the drop-off zones and coastal jets associated with topographic effects in the central Peru and Chile regions where large upwelling favourable winds are found at regional scale. The data are first compared to observations of the diffusiometers of previous and current satellite missions (ERS, QuikSCAT, ASCAT) and to the ECMWF, FNL and CFSR reanalyses over the open ocean region, which allows deriving a calibration method of the data. The calibrated data are analysed near the coast, compared to coastal meteorological stations, and interpreted in terms of their coherence with Multi-scale Ultra-high Resolution (MUR) SST data. A comparison with a nested high-resolution (~4km) atmospheric model simulation is presented.