一个耦合气候系统模式模拟的中全新世时期亚洲季风系统变化

THE ASIAN MONSOON SYSTEM OF THE MID-HOLOCENE SIMULATED BY A COUPLED GCM

本文分析了一个耦合模式FGOALS_g1.0对工业革命前气候(0ka)和中全新世时期(6ka)亚洲夏季风的模拟结果。在该研究中我们主要分析季风降水变率较大的区域,即东亚夏季风区(20°～45°N,110°～120°E)和印度夏季风区(10°～30°N,70°～80°E)。尽管耦合模式的普遍偏差依然存在,该模式反映出亚洲季风系统是海陆热力性质差异的结果,并较好地模拟出了0ka亚洲夏季风大尺度环流的特点和季节变化的特征。6ka和0ka比较分析的结果表明,6ka时期欧亚大陆增暖,海陆温度梯度加强;印度夏季风降水从南亚大陆北移到30°N附近,位于青藏高原南侧的降水大值中心降水加强;东亚季风区降水则表现为华北地区减少,长江流域和华南地区降水增加的特点。但合理地模拟季风爆发仍然是耦合气候系统模式的难点之一。6ka时期亚洲夏季风变化是和大尺度季风环流的变化联系在一起的,而其根本原因是中全新世时期地球轨道参数变化所引起的太阳辐射变化,北半球季节循环的振幅加强。海陆热力性质的差异所导致海陆温差加大使得北半球的季风环流加强,印度夏季风高空东风在20°～30°N加强,低层赤道东风加强,跨赤道后的西南气流向北推移,从而使得印度夏季风降水雨带北移到30°N附近。东亚季风区的高低空温度场的配置使得副热带高空急流减弱,位置偏南,从而有利于华北地区的高空出现异常的辐合,中层为异常的辐散,抑制了季风降水的发展;长江流域和华南地区则相反,季风降水降水加强。

We analyzed the pre-industrial （Oka） climate and the Asian summer monsoon system of the mid-Holocene （6ka）which were simulated by a coupled model - FGOALS_g1. 0. It is shown that the monsoon should result from the thermal contrast between the land and the ocean. The key Asian monsoon regions were redefined by the maximum precipitation variation in the model, that is, the East Asia monsoon （ 20 ° - 45 °N, 110°-120°E ） and the Indian monsoon region（ 10° -30°N,70° -80°E）. Although the common biases of the non-flux corrected coupled model still exist, FGOALS_ g1. 0 can simulate properly the large-scale circulation and the seasonal cycle of the Asian monsoon system at the time of 0ka. The major characteristics of the 6ka climate are： there was a surface warming over the Euro-Asian continent that enhanced the land sea temperature gradient, so on the one hand the Indian summer monsoon rainfall shifted northward to around 30°N so that the precipitation in the south flank of Tibetan Plateau was enhanced, on the other hand in the East Asia summer monsoon area, the precipitation decreased in North China and increased in South China. The monsoon rainfall change at the time of 6ka was closely related to the monsoon circulation change,which was basically induced by the solar radiation change due to the Earth＇s orbital parameter change during the mid- Holocene. The land-sea temperature gradient was enhanced at the time of 6ka that tended to strengthen the large- scale monsoon circulation. Thus in the Indian monsoon region, the high-level easterly enhanced between 20°- 30°N, the low level equatorial easterly strengthened, and the cross-equator south-west flow moved northwards so that the monsoon rainfall shifted northward to around 30°N. And in the East Asian monsoon region, the vertical and horizontal temperature gradient change resulted in the weakening and south shifting of the subtropical west jet ,which was in favor of the convergence in the upper troposphere and the divergence in the mid-troposphere over North China, respectively. Therefore the monsoonal rainfall was suppressed in North China and enhanced in South China.