Sea-level pressure patterns in South America and the adjacent oceans in the IPCC AR4 models

A. DI LUCA; I. CAMILLONI; V.BARROS

Foz de Iguazú, Brasil

Congreso; 8th International Conference of the Southern Hemisphere Meteorology and Oceanography; 2006

American Meteorological Society

During the last years, many authors discussed low-level circulation changes both at regional and global scales  For example, at regional scale, some results show a southward shift of the South Atlantic high (Camilloni, 1999; Camilloni et al. 2005), a displacement to the south of the regional atmospheric circulation over Southeastern South America (Barros et al. 2000) and an enhancement of the easterly winds during the summer months over the Río de la Plata estuary (Simionato et al. 2005). These regional trends seem to be part of a more general hemispheric behaviour. Gibson (1992) showed a poleward shift of 3° of latitude on the maximum wind at 500 hPa in the 1976-1991 period. Van Loon et al (1993) calculated the latitude of the zonally averaged subtropical ridge over the Southern Hemisphere, finding a 2° trend over the 1976-1990 period. More recently, Gillett et al (2003) using outputs from four Global Climate Models (GCM) experiments found that the global pattern of the December-February sea level pressure (SLP) trends during the 1948-1996 period can be attributed to the growing global atmospheric concentration of greenhouse gases and sulphate aerosols. The SLP observed pattern shown by Gillet et al (2003) has predominantly positive trends at the 30º-45° latitude band of the Southern Hemisphere, and a trend of more than 2 hPa in the South Atlantic, off of the Argentine coast. The objective of the present work is to evaluate the ability of a set of global climate models available for the preparation of the Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC) to represent the predominant patterns of SLP over an extense region of the Southern Hemisphere that comprises Southern South America and the South Atlantic and South Pacific oceans. Additionally, those models with good representation of the dominant regional patterns were selected to analyze future scenarios. Predominant patterns of SLP and their evolutions were analyzed under two SRES scenarios. Differences between the forcing of these scenarios are mainly given in terms of atmospheric concentrations of greenhouse gases, ozone and aerosols. (*)(*)