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The influence of changes in orbital parameters over South American climate using the CPTEC AGCM: simulation of climate during the mid Holocene

Centro de Previsão de Tempo e Estudos Climáticos/Instituto Nacional de Pesquisas Espaciais - CPTEC/INPE, Rodovia Presidente Dutra, 40 km, 12630-000 Cachoeira Paulista, São Paulo, Brazil, luciene{at}cptec.inpe.br

José Antonio Marengo

Centro de Previsão de Tempo e Estudos Climáticos/Instituto Nacional de Pesquisas Espaciais - CPTEC/INPE, Rodovia Presidente Dutra, 40 km, 12630-000 Cachoeira Paulista, São Paulo, Brazil

Climate change has been analysed for the mid Holocene (MH, 6000 years BP) over South America. Simulations have been performed through modification of the orbital parameters and the CO₂ concentration typical of the MH within the CPTEC T062L28 atmospheric general circulation models (AGCM). The results were compared with previous simulations performed by various climate centres around the world and with palaeoclimate indicators. The MH climate simulation shows a wetter behaviour in northeastern South America with a northward shift of the Intertropical Convergence Zone (ITCZ). In central and southeastern South America the simulations show a reduction in precipitation. Some important changes were detected during the MH: (a) the increase in the intensity of the circulation of the South Atlantic subtropical high; (b) the intensification of the northerly flow east of the Andes, south of 20°S; (c) the decrease in moisture transport from the Amazon basin to central and south-southeastern Brazil, which can influence the formation and intensity of the South Atlantic Convergence Zone (SACZ); (d) the reduced intensity of the northeasterly trade winds north of 20°S, which can explain the northward positioning of the ITCZ; and (e) the weakening of the low-level convergence over the Amazon region, which can explain the reduction in precipitation in this region during the MH. A cooling signal was verified during the MH simulation, in accordance with palaeoclimate evidence, that was related to cold air surges coming from the South, which cooled regions east of the Andes and were more common during summer and autumn during the MH.

Key Words: Mid Holocene • South America • general circulation modelling • climate simulation • CPTEC AGCM • palaeoclimate • orbital parameter • palaeoclimate record.

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