In this study, intensities and trends of Hadley, Walker, and monsoon circulations are compared for the IPCC 20th Century simulations and for 21st Century simulations, using the upper tropospheric velocity potential data. As a result, we showed significantly weaker biases in Walker and monsoon circulations for the JJA climate in the IPCC 20th Century simulations. The dispersal in the scatter diagram of the model biases is considerably large. The same analyses are applied for the IPCC 21st Century simulations to investigate the trends of these tropical circulations in response to the projected global warming. As a result, it is anticipated that Hadley, Walker, and monsoon circulations are weakened by 9, 8, and 14%, respectively, by the late 21st Century, according to the ensemble mean of the IPCC model simulations. Considering the large model biases demonstrated for the IPCC 20th Century simulations, further studies are needed to quantify those trends.
2005 by the Meteorological Society of Japan