What dynamics drive future wind scenarios for coastal upwelling off Peru and Chile?
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The dynamics of the Peru–Chile upwelling system (PCUS) are primarily driven by alongshore wind stress and curl, like in other eastern boundary upwelling systems. Previous studies have suggested that upwelling-favorable winds would increase under climate change, due to an enhancement of the thermally-driven cross-shore pressure gradient. Using an atmospheric model on a stretched grid with increased horizontal resolution in the PCUS, a dynamical downscaling of climate scenarios from a global coupled general circulation model (CGCM) is performed to investigate the processes leading to sea-surface wind changes. Downscaled winds associated with present climate show reasonably good agreement with climatological observations. Downscaled winds under climate change show a strengthening off central Chile south of 35°S (at 30°S–35°S) in austral summer (winter) and a weakening elsewhere. An alongshore momentum balance shows that the wind slowdown (strengthening) off Peru and northern Chile (off central Chile) is associated with a decrease (an increase) in the alongshore pressure gradient. Whereas the strengthening off Chile is likely due to the poleward displacement and intensification of the South Pacific Anticyclone, the slowdown off Peru may be associated with increased precipitation over the tropics and associated convective anomalies, as suggested by a vorticity budget analysis. On the other hand, an increase in the land–sea temperature difference is not found to drive similar changes in the cross-shore pressure gradient. Results from another atmospheric model with distinct CGCM forcing and climate scenarios suggest that projected wind changes off Peru are sensitive to concurrent changes in sea surface temperature and rainfall.
KeywordsRegional climate change Peru–Chile upwelling system Dynamical downscaling Upwelling-favorable winds Climate scenarios
The LMDz-ESP05 simulations were performed on Brodie, the NEC SX8 computer at Institut du Développement et des Ressources en Informatique Scientifique (IDRIS), Orsay, France. The LMDz-SA1 simulations were performed on Calcul Intensif pour le Climat, l’Atmosphère et la Dynamique (CICLAD), a PC cluster at IPSL, within the framework of previous research supported by the European Commission’s Seventh Framework Programme (FP7/2007–2013) under Grant Agreement N°212492 (CLARIS LPB. A Europe-South America Network for Climate Change Assessment and Impact Studies in La Plata Basin), CNRS/LEFE Program, and CONICET PIP 112-200801-00399. A. Belmadani was supported by the Agence Nationale de la Recherche (ANR) Peru Ecosystem Projection Scenarios (PEPS, ANR-08-RISK-012) project. Additional support was provided by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC), by the National Aeronautics and Space Administration (NASA) through Grant NNX07AG53G, and by the National Oceanic and Atmospheric Administration (NOAA) through Grant NA11NMF4320128, which sponsor research at the IPRC. A. Belmadani is now supported by the Universidad de Concepcion (UdeC). V. Echevin and C. Junquas are supported by the Institut de Recherche pour le Développement (IRD). F. Codron is supported by the Université Pierre et Marie Curie (UPMC). K. Takahashi is supported by the Instituto Geofisico del Peru (IGP) and had partial support from the Laboratoire d’Etudes en Géophysique et Océanographie Spatiales (LEGOS) and the Université Paul Sabatier. This work is a contribution of the IRD DISCOH International Mixed Laboratory. K. Hamilton, A. Lauer, and Y. Wang are thanked for fruitful discussions. This is the IPRC/SOEST publication #1028/9047.
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