CMIP5气候模式对中国东部夏季降水年代际变化的模拟性能评估

Validation of the CMIP5 Climate Models in Simulating Decadal Variations of Summer Rainfall in Eastern China

使用分类集合的方法评估了第五次耦合模式比较计划(CMIP5)多个耦合模式对中国东部夏季降水年代际变化的模拟性能。结果表明,在评估的38个模式中,仅有6个模式(第1类模式)可以成功再现1970年代末中国东部夏季降水年代际变化的主要特征,即长江流域降水偏多、而华北和华南偏少。这些模式模拟的成功归因于它们能较好再现1970年代末东亚夏季风的年代际减弱及相关的环流场的变化,包括东亚沿海的偏北风异常以及西太平洋副热带高压的偏向西南、强度增强等。而对降水年代际变化模拟很差的第2类模式,则模拟出不出东亚夏季风的这种减弱特征。进一步的分析表明,两类CMIP5模式对太平洋年代际振荡(PDO)空间分布特征都有较好的再现能力,但对PDO年代际转变特征的模拟能力则差异较大。第1类模式能很好地模拟出1970年代末热带海洋的增暖和相关的PDO位相由负到正的转换,而第2类模式所模拟的PDO位相转变与观测完全相反,且也不能模拟出热带中东太平洋海洋的年代际增暖及江淮流域夏季的变冷,因此导致该类模式对1970年代末东亚夏季风的减弱和中国东部夏季雨型的年代际转变没有模拟能力。由此也表明,对耦合模式来说,中国夏季降水年代际变化的模拟能力在很大程度上取决于模式对海洋年代际变化信号的模拟。

The categorization method was used to evaluate the performance of the Coupled Model Inter-comparison Program Phase 5 （CMIP5） climate models in simulating the decadal variation of summer monsoon rainfall in eastern China. Out of the 38 models that were examined, only six （category-1 models） captured the decadal variation of summer rainfall in eastern China in the late 1970s, i.e., increased rainfall in the Yangtze River basin and decreased rainfall in North and South China. The category-1 models simulate the decadal variation of summer rainfall in eastern China well because they are able to capture the decadal weakening of the East Asian Summer Monsoon （EASM） along with the northerly anomaly in the coast of East Asia and changes in the western Pacific subtropical high in the late 1970s. In contrast, the category-2 models, which poorly simulate the decadal variation of summer rainfall in eastern China, fail to reproduce the decadal weakening of the EASM. Further analysis indicates that while most models can reproduce the spatial distribution of the Pacific Decadal Oscillation （PDO）, their accuracy at reproducing the decadal variation of the PDO varies. Category-1 models can reproduce the tropical ocean warming in the late 1970s and the relative phase transition of the PDO. Category-2 models fail to capture the phase transition of the PDO, the tropical ocean warming in the central–eastern Pacific Ocean, and the cooling trend in the Yangtze River basin, which results in low accuracy of these models for reproducing the weakened EASM and the decadal variation of summer rainfall in eastern China after the late 1970s. This indicates that the accuracy of climate models for simulating the decadal variations of sea surface temperature plays an important role in the accuracy of the models’ simulation of the decadal variation of summer rainfall.