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 << Back to WCRP CMIP3 Subprojects Tanaka, H. L., N. Ishizaki and A. Kitoh, 2004: Trend and interannual variations of Walker, monsoon, and Hadley circulations defined by velocity potential in the upper troposphere. Tellus, 56A, 250-269. In this study, we attempt to divide global divergent field at the upper troposphere in contributions from the Hadley, Walker, and monsoon circulations, using monthly mean velocity potential field at 200 hPa level. First, the zonal mean of the velocity potential is analyzed to represent the Hadley circulation. The deviation from the zonal mean is then divided in its annual mean and the seasonal cycle parts, which are considered to represent the Walker and monsoon circulations, respectively. The intensities of each circulation are measured by their peaks in the velocity potential field separated in each component. According to this separation, the mean intensities of the Walker, monsoon, and Hadley circulations appear to be 120: 60: 40 (${\times}$10$^{5}$m$^2$ s$^{-1}$) in January and 120: 90: 45 (${\times}$10$^{5}$m$^2$ s$^{-1}$) in July, respectively. Based on this simple definition, interannual variabilities of each circulation are then examined quantitatively using the NCEP/NCAR reanalysis. The time series of the intensity of the Walker circulation coincides with the Southern Oscillation index (SOI), and the intensity has weakened in recent decades. That of the Hadley circulation indicates intensifying trend in boreal winter. Finally, the same analysis is applied for the model atmosphere by the MRI CGCM1 with a gradual increase in CO$_2$ at a compound rate of 1 \%/yr for 150 years. It is shown that the Hadley circulation intensifies by 40\% and the monsoon circulation decays by 20\% in boreal summer when the global warming has occurred in a century later. The result demonstrates that the proposed simple separation of the tropical circulation in the Walker, monsoon, and Hadley components is useful, though it is not rigorous, for the initial assessment of the model response to the global warming. Last Updated: 2007-02-27 << Back to WCRP CMIP3 Subprojects