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The Southern Westerlies during the last glacial maximum in PMIP2 simulations

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Rojas, Maisa [University of Chile Blanco Encalada, 2002 Santiago, Chile] Moreno, Patricio I. [Institute of Ecology and Biodiversity, Santiago, Chile] Kageyama, Masa [UMR CEA-CNRS-UVSQ 1572, 91191 Gif-sur-Yvette Cedex, France] Crucifix, Michel [UCL] Hewitt, Chris Hope, Pandora [Bureau of Meteorology Research Centre, Melbourne, Australia]

The Southern Hemisphere westerly winds are an important component of the climate system at hemispheric and global scales. Variations in their intensity and latitudinal position through an ice-age cycle have been proposed as important drivers of global climate change due to their influence on deep-ocean circulation and changes in atmospheric CO2. The position, intensity, and associated climatology of the southern westerlies during the last glacial maximum (LGM), however, is still poorly understood from empirical and modelling standpoints. Here we analyse the behaviour of the southern westerlies during the LGM using four coupled ocean-atmosphere simulations carried out by the Palaeoclimate Modelling Intercomparison Project Phase 2 (PMIP2). We analysed the atmospheric circulation by direct inspection of the winds and by using a cyclone tracking software to indicate storm tracks. The models suggest that changes were most significant during winter and over the Pacific ocean. For this season and region, three out four models indicate decreased wind intensities at the near surface as well as in the upper troposphere. Although the LGM atmosphere is colder and the equator to pole surface temperature gradient generally increases, the tropospheric temperature gradients actually decrease, explaining the weaker circulation. We evaluated the atmospheric influence on the Southern Ocean by examining the effect of wind stress on the Ekman pumping. Again, three of the models indicate decreased upwelling in a latitudinal band over the Southern Ocean. All models indicate a drier LGM than at present with a clear decrease in precipitation south of 40A degrees S over the oceans. We identify important differences in precipitation anomalies over the land masses at regional scale, including a drier climate over New Zealand and wetter over NW Patagonia.

Document type Article de périodique (Journal article) – Article de recherche
Access type Accès restreint
Publication date 2009
Language Anglais
Journal information "Climate Dynamics : observational, theoretical and computational research on the climate system" - Vol. 32, no. 4, p. 525-548 (2009)
Peer reviewed yes
Publisher Springer (New York)
issn 0930-7575
e-issn 1432-0894
Publication status Publié
Affiliation UCL - SC/PHYS - Département de physique
Links
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Bibliographic reference Rojas, Maisa ; Moreno, Patricio I. ; Kageyama, Masa ; Crucifix, Michel ; Hewitt, Chris ; et. al. The Southern Westerlies during the last glacial maximum in PMIP2 simulations. In: Climate Dynamics : observational, theoretical and computational research on the climate system, Vol. 32, no. 4, p. 525-548 (2009)
Permanent URL http://hdl.handle.net/2078.1/35871