Climate variability over South America in IPCC-AR4 simulations of the 20th century
Carolina Vera, CIMA/Department of Atmospheric Sciences, University of Buenos Aires-CONICET, Buenos Aires, Argentina; and G. Silvestri
A subset of 20th-century simulations from the IPCC-AR4 models was analyzed to assess the model ability in reproducing the observed mean spatial patterns, seasonal and year-to-year variations, of precipitation in South America during the period 1970-1999.
Most of the models are able to reproduce the basic characteristics of the precipitation seasonal cycle, such as the northwestward and southeastward migration of precipitation over tropical South America and the precipitation maximum observed over the southern Andes. Although, the precipitation in the South Atlantic Convergence Zone and the precipitation maximum over southeastern South America observed during the cold season are not in general well represented. In addition, models are able to somewhat reproduce the main features of the observed year-to-year variability of precipitation in the continent, although with deficiencies in the intensity and location of maximum variability regions. Better standard deviation distributions were found in models with more realistic mean precipitation patterns.
It is known that precipitation year-to-year variability over extensive regions of South America experiences significant modulation by ENSO as well as by the Southern Annular Mode (SAM) or Antarctic Oscillation. Therefore, the signature of both ENSO and SAM onto the variability of both the atmospheric circulation in the Southern Hemisphere (SH) and the precipitation in South America was also analyzed. All models are able to represent a SAM-like structure as the leading pattern of circulation variability in the SH. Nevertheless, considerable dispersion was found among model outputs regarding the ENSO teleconnection patterns in the SH circulation. The analysis revealed that few models are able to represent in some extent the ENSO and SAM signature observed in South America hydroclimate. The study then suggests that climate change projections of regional-to-continental scale hydroclimate variability over South America would be then undermined by the abovementioned limitations in model performance.
Session 1, Model Diagnostics - Climate Change Studies
Monday, 15 January 2007, 10:45 AM-12:00 PM, 214B
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