Twentieth century simulation of low-frequency atmospheric variability and trends in the Southern Hemisphere as depicted by IPCC FAR4 coupled models.

SOLMAN SILVINA ALICIA

Florianópolis, Brasil

Congreso; XIV Congresso Brasileiro de Meteorologia; 2006

Sociedad Brasilera de Meteorología

The ability of global coupled climate models to simulate the behavior of low-frequency variability patterns of the atmospheric circulation and recent observed trends is studied in an area encompassing southern South America. Last generation 20th century simulations performed with a set of 8 Atmosphere - Ocean General Circulation Models (AOGCMs) participating in the IPCC Fourth Assessment Report (AR4) are analyzed. The patterns analyzed in this study are the Antarctic Annular Mode (AAO) and the Pacific-South America modes (PSA), known as the leading patterns of low-frequency variability in the Southern Hemisphere. Overall, the AOGCMs analyzed are able to capture the broad spatial structure of the main sectorial  modes of observed low-frequency variability, the Antarctic Oscillation mode (AAO) ranging as the first leading mode, and the Pacific South America modes (PSA1 and PSA2) ranging second and third, respectively, though some features appear misplaced. All the models systematically underestimate the variability associated to the modes. Moreover, it has been found that the models are not able to reproduce adequately the magnitude of observed trend towards the positive polarity of the AAO mode.