人类活动排放的CO2及气溶胶对20世纪70年代末中国东部夏季降水年代际转折的影响

Effects of anthropogenic emissions of CO2 and aerosols on decadal transition of summer precipitation over eastern China in the late 1970s

中文关键词:  中国东部夏季降水  年代际转折  人类活动  地球系统耦合模式  水分收支

英文关键词:Summer precipitation over eastern China  Decadal transition  Anthropogenic emissions  Community Earth System Model  Moisture budget

中文摘要:

      全球变暖背景下，中国东部夏季降水在20世纪70年代末开始较19世纪呈现东北及长江中、下游地区多雨，华北及华南少雨的特征。与此同时，人类活动排放的CO₂及气溶胶量也发生了明显的年代际变化。文中利用地球系统耦合模式（CESM）诊断了中国东部夏季的水分收支对人类活动排放的CO₂及气溶胶年代际变化的响应。发现CO₂排放量增加后，江淮流域的水汽辐合以及中国南方的水汽辐散主要是与质量辐散有关的动力项及与湿度梯度相关的热力项共同作用的结果，但动力作用更显著。气溶胶效应则主要通过动力作用使得江淮流域水汽辐合，而中国南方地区水汽辐散。虽然CO₂和气溶胶对辐射量及温度的影响差别很大，但通过改变温度梯度，热成风效应产生的动力作用都会导致江淮流域上升运动增强，降水增多；而中国南方下沉运动显著，降水减少，与观测结果一致，且CO₂相较于气溶胶的影响更为显著，证实了20世纪70年代末人类活动对中国东部夏季降水年代际转折的影响。

英文摘要:

      In the background of global warming, summer precipitation over eastern China (ECSP) experienced a significant decadal change at the end of the 1970s with positive rainfall anomalies over northeastern China and the middle and lower reaches of the Yangtze River and negative rainfall anomalies over northern and southern China. We examined anthropogenic emissions of CO₂ and aerosols which had discernible decadal transitions around the mid to late 1970s and contributed to the ECSP change, and elucidated the underlying mechanism. Moisture budget over eastern China was calculated using the Community Earth System Model (CESM). The water vapor convergence over the Yangtze-Huai River valley and moisture divergence over southern China in the CO₂ simulation are dominated by the combined effects of the dynamic contribution related to mass divergence and the thermodynamic contribution related to moisture gradients, which have greater effect on the ECSP than that of aerosols. Aerosols forcing contributed to the rainfall increase over the Yangtze-Huai River valley and decrease over southern China primarily by the dynamic effect. The enhanced upward and downward motions caused by changes in temperature gradient led to similar rainfall anomalies over eastern China under the effects of CO₂ and aerosols, although their impacts on radiation and temperature were different. These results confirm that CO₂ and aerosols did have some effect on the decadal transition of ECSP at the end of the 1970s.