The simulations with the HadCM3 model were among the first available to analyze future projections. This is reflected in the literature, which mainly describes the variables temperature and precipitation for South America. The aim of this paper is to investigate the changes in the atmospheric circulation over southeastern South America associated to extreme cold events in the most critical future emission scenario A2 for the period 2081-2100, with respect to the climatological reference period 1961-1990. To do that the HadCM3 model is used as well as the NCEP/NCAR reanalysis. Were identified the five most extreme events of daily mean negative temperature in 850 hPa from May to September over three areas: Wet Pampa (area 1), Uruguay and southern Brazil (area 2), eastern Paraguay, northern Argentina and southern Brazil (area 3). The obtained circulation patterns are analyzed in both, the reanalysis and the HadCM3 simulations of the present and future climate. In the present climate, with the exception of the area 3 that borders the tropics, the model simulates a more extended northward incursion of the 0oC isotherm than the reanalysis. It also shows more intense negative temperature anomalies, which have more latitudinal extension. Despite the fact that the configurations of the pressure fields are similar to that of the reanalysis, except for the area 3, a further inland penetration of the continental anticyclone is appreciated, with an intensification of the anomalies over the respective areas. The model also tends to simulate a more intense 850 hPa southerly wind component, capturing the high level deep trough over the continent and displaying a properly configured subtropical jet, which is typical of these extreme events. In the future scenario, the model does not project extreme cold events of below 0oC temperatures for area 3. The model also restricts the incursion of the 0oC isotherm to more southerly latitudes in the other two areas with respect to the simulation of the present climate. These facts are consistent with the mean temperature increase projected by the model for South America.

Keywords: Future projections, extreme cold events, climate scenarios, climatic change.