%0 Journal Article
%T Avalia  o de mudan as na frequ¨ºncia de sistemas frontais sobre o sul da Am¨¦rica do Sul em proje  es do clima futuro Changes in frequency of frontal systems over southern of South America in projections of future climate
%A Kelen Martins Andrade
%A Gabriela V. M¨¹ller
%A Iracema F.A Cavalcanti
%A Mar¨ªa E. Fernandez Long
%J Meteorologica
%D 2012
%I Centro Argentino de Meteor¨®logos
%X A frequ¨ºncia de sistemas frontais sobre o sul da Am¨¦rica do Sul identificada na rean¨¢lise do NCEP/NCAR ¨¦ comparada com as simula  es dos modelos GFDL e Hadley e projetadas no clima futuro. As an¨¢lises para identificar casos de sistemas frontais foram feitas em tr¨ºs regi es que cobrem ¨¢reas do Brasil, Uruguai, Paraguai e Argentina. Esta an¨¢lise foi realizada com o fim de investigar as caracter¨ªsticas de eventos extremos no clima presente e em proje  es do clima futuro. Para o clima presente observou-se que os modelos analisados simularam bem as caracter¨ªsticas sin¨®ticas dos sistemas frontais. No entanto, quando se compara a frequ¨ºncia de ocorr¨ºncia das frentes entre a rean¨¢lise e as simula  es, observa-se que os modelos GFDL e Hadley superestimam seu n¨²mero e apenas o GFDL consegue reproduzir a variabilidade mensal. O modelo Hadley superestima ainda mais em rela  o ao NCEP e GFDL no clima presente. A tend¨ºncia positiva no n¨²mero de frentes observada na ¨¢rea 3 (65oW-60oW, 33oS-38oS) nos resultados da rean¨¢lise n o ¨¦ simulada pelos modelos. Quando os casos mais intensos s o selecionados, o modelo GFDL ¨¦ o que superestima mais o n¨²mero de sistemas frontais. Os dois modelos indicam aumento na frequ¨ºncia de sistemas frontais no futuro nas tr¨ºs ¨¢reas, por¨¦m em menor propor  o na ¨¢rea 3. The frequency of frontal systems reaching the south of South America is compared with reanalysis NCEP/NCAR and results of GFDL and Hadley models for the future climate. Three regions were analyzed to identify the frontal systems, in areas of Brazil, Uruguay, Paraguay and Argentina. The following criteria were used: increase of sea surface pressure, reduction of the temperature and change of the meridional wind at 850hPa, in two consecutive days. Selected cases with temperature drop above five degrees, considered the most intense, were also analyzed. For the present climate it was observed that the models simulated well the synoptic characteristics of frontal systems. However, when comparing the frequency of frontal occurrence between reanalysis data and models simulations, the GFDL and Hadley models overestimated their numbers. The Hadley model overestimates further more than the NCEP and GFDL in present climate. The positive trend observed in area 3 (65oW-60oW, 33oS-38oS) from NCEP reanalysis is not simulated by the models. When the most intense systems are selected, the GFDL model shows higher overestimation in number of frontal systems. Both models indicate an increase of frontal systems frequency in future in the three areas, although less in area 3.
%K Sistemas frontais
%K Clima futuro
%K Am¨¦rica do Sul
%K Frontal systems
%K Climate change
%K South America
%U http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S1850-468X2012000100002