Variability and Trends in Surface Meteorology and Air-Sea Fluxes at a Site off Northern Chile

Time series of surface meteorology and air-sea exchanges of heat, freshwater, and momentum collected from a long-term surface mooring located 1600 km west of the coast of northern Chile are analyzed. The observations, spanning 2000-10, have been withheld from assimilation into numerical weather prediction models. As such, they provide a unique in situ record of atmosphere-ocean coupling in a trade wind region characterized by persistent stratocumulus clouds. The annual cycle is described, as is the interannual variability. Annual variability in the air-sea heat flux is dominated by the annual cycle in net shortwave radiation. In austral summer, the ocean is heated; the 9-yr mean annual heating of the ocean is 38 W m(-2). Ocean cooling is seen in 2006-08, coincident with La Nina events. Over the full record, significant trends were found. Increases in wind speed, wind stress, and latent heat flux over 9 yr were 0.8 ms(-1), 0.022 N m(-2), and 20 W m(-2) or 13%, 29%, and 20% of the respective 9-yr means. The decrease in the annual mean net heat flux was 39 W m(-2) or 104% of the mean. These changes were found to be largely associated with spring and fall. If this change persists, the annual mean net air-sea heat flux will change sign by 2016, when the magnitude of the wind stress will have increased by close to 60%.