Circulação Atmosférica Associada a Eventos Extremos Frios no Sul da América do Sul: Comparação entre Cenários Climáticos Relativos aos Experimentos cmip3 e cmip5 Utilizando o Modelo GFDL

C. R. R. REPINALDO; GABRIELA V. MÜLLER; D. C. ARANEO; K. M. ANDRADE; I. F.A CAVALCANTI

Florianópolis

Simposio; V Simpósio Internacional de Climatología (SIC), V Encontro Sul Brasileiro de Meteorología y XV Congresso Latino-Americano e Ibérico de Meteolología da FLlSMET; 2013

The purpose of this study is to investigate the atmospheric circulation associated to extreme cold events in the current climate and in a future scenario of regions located in Brazil, Uruguay, Paraguay and Argentina in two different experiments and the ability of the model GFDL of simulate them for the historic period using NCEP/NCAR reanalysis data and the GFDL model in the coupled ocean-atmosphere version. This analysis is realized with daily data from May to September of the period 1961-1990, of the projects CMIP3 and CMIP5 representing the present climate, and the model?s outputs for the period 2081-2100 representing the future scenarios A2 (CMIP3) and RCP 8.5 (CMIP5). The analyzed fields are: Sea level pressure, temperature and wind in 850 hPa and wind in 250 hPa for the five most extreme events of temperature under 0°C in 850 hPa. In the CMIP3 experiment the model tends to overestimate the incursion of the 0°C isotherm and presents more intense negative temperature anomalies in all areas. The model is able to simulate the pressure and anomaly fields, but usually underestimates the incursion of the post-frontal anticyclone and the positive pressure anomalies related to it. The model has difficulty in reproduce the wind direction at 850 hPa, and present higher intensities than the reanalysis. The model also tends to smooth the high level?s trough, but represents the magnitude of the flow. All these factors together suggest that the model tends to simulate more intense cold air incursions, but with a lower latitudinal range. For the future, the model projects less incursion of 0°C isotherm, less intense negative temperature anomalies and greater continental incursion of the post-frontal anticyclone, but with less intense pressure anomalies, suggesting that future cold air incursions of will be less intense but it may present a greater latitudinal range. For CMIP5, the model makes a good simulation of the temperature and anomaly fields when compared to reanalysis, however tends to overestimate the incursion of 0°C isotherm and the intensity of the temperature anomaly in all three areas. In the fields of pressure and anomaly, it is observed that the model overestimates both the high post front and the anomaly related to it in the areas 2 and 3, underestimating them in area 3. For the future scenario, the model projects lower incursion of the 0°C isotherm, however, the negative temperature anomalies remain similar to the climatology simulation. It was also projected a more intense post-frontal anticyclone, but less extensive in terms of latitude, suggesting that the future cold air incursions tends to be less intense, but unlike the CMIP3 experiment, will be less extensive.