不同外强迫对20世纪全球季风降水变化趋势的影响——NCAR CCSM3.0模式结果分析

Effects of external forcings on the global monsoon rainfall trend in the 20^(th) century: CCSM3. 0 simulation analysis

利用NACR CCSM3.0气候系统模式的20世纪气候模拟试验(20C3M)结果,在检验模式对全球季风区、季风降水模态以及1979-1999年全球季风降水趋势的模拟性能基础上,研究了全强迫、自然强迫以及人类活动强迫等因子对20世纪全球季风降水变化趋势的可能影响。结果表明:全球季风降水在全强迫的作用下在20世纪呈线性增长趋势,且这个增长趋势主要是由于人类活动强迫影响造成的,进一步分析得到主要是由于人类活动强迫中的温室气体因子影响所导致的.在温室气体强迫作用下会产生"东太平洋冷—西太平洋暖"这一形势,有利于水汽传输合并进入东半球季风区,加上其引起的全球海陆热力差和半球热力差的增大会加大季风低压,使得相应的水汽辐合和越赤道气流的增大从而引起全球季风降水的增长.自然强迫作用下也会引起20世纪全球季风降水的增加,但增长趋势并不明显.而硫酸盐和黑碳气溶胶会减弱全球季风降水在20世纪的增长趋势,硫酸盐气溶胶主要引起北半球季风降水的减少,而黑碳气溶胶主要引起南半球季风降水的减少.

Using these simulations of NCAR CCSM3. 0 climate model driven by natural and anthropogenic forcings（ greenhouse gases,sulfate aerosol,ozone,black carbon aerosol,volcanoes and solar activity） in the project ＂20th Century Climate in Coupled Models＂（ 20C3M） to firstly evaluate this model＇s performances in the global monsoon region,solstitial mode of global precipitation,and the trend of global monsoon rainfall from 1979 to 1999,and then to discuss the possible effects of external forcings in the 20 th century on the global monsoon rainfall trend. Results show that the global monsoon rainfall in full forcing simulation exhibits a distinct increasing trending the 20 th century,which is mainly due to the change of the anthropogenic forcing, especially the greenhouse gases. The simulation driven by the greenhouse gases could produce＂Eastern Pacific（ EP） cooling and the west pacific（ WP） warming＂pattern,which enhances east-west thermal contrast in the Pacific Ocean and results in a rising pressure in the EP and a decreasing pressure over the Indo-Pacific warm pool. This enhanced Pacific zonal thermal contrast tends to amplify the water vapor merged into the monsoon region in the eastern hemisphere. The increasing landocean and inter-hemispheric thermal gradients will enhance the monsoon low pressure along with the water vapor convergence and the cross-equatorial flow,which will increase the global monsoon rainfall with a significant rise trend in the 20 th Century. The global monsoon rainfall in the natural-only forcing experiment shows an increasing trend,but it is not significant at the level of 0. 05.Sulfate and black carbon aerosols will produce the decreasing trends in the global monsoon rainfall trend in the 20 th century,with this trend mainly in the northern hemisphere by the sulfate aerosol and in the southern hemisphere by the black carbon aerosol.