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  • Tan, P.H., C. Chou, and J.Y. Tu, 2008: Mechanisms of global warming impacts on robustness of tropical precipitation asymmetry. J. Climate, 21, 5585-5602.

Hemispherically and temporally asymmetric tropical precipitation responses to global warming are evaluated in thirteen different coupled atmosphere-ocean climate model simulations. In the late boreal summer, hemispherical averages of the tropical precipitation anomalies from the multimodel ensemble show a strong positive trend in the northern hemisphere and a weak negative trend in the southern hemisphere. In the late austral summer, on the other hand, the trends are reversed. This implies that the summer hemisphere becomes wetter and the winter hemisphere becomes a little drier in the tropics. Thus, the seasonal range of tropical precipitation, differences between wet and dry seasons, is increased. Zonal averages of the precipitation anomalies from the multimodel ensemble also reveal a meridional movement, which basically follows the seasonal migration of the main convection zone. Similar asymmetric features can be found in all thirteen climate model simulations used in this study. Based on the moisture budget analysis, the vertical moisture advection associated with mean circulation is the main contribution for the robustness of the asymmetric distribution of the tropical precipitation anomalies. Under global warming, tropospheric water vapor increases as the temperature rises and most enhanced water vapor is at the lower troposphere. The ascending motion of the Hadley circulation then transports more water vapor upward, i.e., anomalous moisture convergence, and enhances precipitation over main convection zones. On the other hand, the thermodynamic effect associated with the descending motion of the Hadley circulation, i.e., anomalous moisture divergence, reduces the precipitation over the descending regions.

Full Article: http://www.rcec.sinica.edu.tw/~chia/papers/asy-glbwrm-robust-rev.pdf

Last Updated: 2008-11-03

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