Present and Future Projection of the Extreme Cold Events in Southern South America with the HadCM3 Model

MÜLLER GABRIELA V; REPINALDO CINTIA R. R; ANDRADE KELEN M; CAVALCANTI IRACEMA F.A.

Darmstard

Simposio; The Climate Symposium; 2014

EUMETSAT

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/NOAA reanalysis. We identify the five most extreme events of daily mean temperature below 0°C in 850 hPa from May to September over three areas: Wet Pampa (area 1), Uruguay and southern Brazil (area 2) and Paraguay 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 particular, the reanalysis allows assessing the ability of the HadCM3 model in simulating the atmospheric circulation of such events in the present climate, in order to determine the degree of certainty of the future climate simulations. 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 0°C 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 0°C temperatures for area 3. The model also restricts the incursion of the 0°C 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. However, the negative temperature anomalies remain of the same order as those simulated for the present climate, with an intensification of the southerly wind. This intensification is due to the greater pressure gradient anomaly at 850 hPa and the deepening of the trough with the coupling of the polar and subtropical jet projected over areas 1 and 2.