CONICET | Buscador de Institutos y Recursos Humanos

The 24-year retrospective forecast data set from the NCEP Climate Forecast System (CFS) is analyzed in order to explore the model behavior over South America. The set covers the period between 1981 and 2004 with 15 forecasts per calendar month. The analysis first concentrated on studying the multi-forecast ensemble mean biases in surface temperature, precipitation, and circulation during the warm season. Warm biases are observed over the Amazon basin being larger during spring than summer, while cold biases are observed over eastern tropical South America and the subtropical plains. Negative precipitation biases are over the Amazon basin and positive ones eastward and particularly along the South Atlantic Convergence Zone. Dry biases are also displayed over the subtropical plains. The model exhibits negative biases in the upper-level circulation, particularly in the Bolivian High anticyclone the Nordeste trough. In general, bias patterns for all of the variables under study get stronger as the leading time increases. An analysis of the CFS ability in representing the climate variability over the La Plata Basin was also made using the Lead 0 multi-run ensemble mean. La Plata Basin is located over southeastern South America and it encompasses the most productive regions of five countries. CFS is able to represent in some extent the interannual variability of both precipitation and surface temperature over the basin, especially the wet anomalies observed in the El Niño summers of 1982-1983, 1986-1987, 1997-1998 and the drought conditions in the La Niña summer of 1988-1989. Moreover, the model captures very well the relationship between the precipitation variability in the basin with that associated with the sea surface temperature variability over the tropical Pacific and Indian Ocean.