季风与极涡的异常配置下中国夏季大尺度旱涝分布

从冷暖系统配置的角度,选取东亚夏季风(EASM)和7月亚洲区极涡面积(APVA),分析了二者的气候特征与中国夏季降水分布之间的关系.在此基础上,将1951—2010年EASM和APVA的异常配置分为四种类型:A:季风强、极涡大;B:季风强、极涡小;C:季风弱、极涡大;D:季风弱、极涡小.研究发现,二者的异常配置下,中国夏季大尺度旱涝分布在季尺度上表现出多面性特征:A型年,夏季整体偏旱;B型年,夏季南涝北旱;C型年,夏季北涝南旱;D型年,夏季整体偏涝.由此可见,中国夏季旱涝总体分布除了与EASM有关外还与APVA密切相关,二者异常的不同配置下,夏季降水多寡和旱涝分布表现出了显著的差异和规律性,这对夏季降水总体趋势预测有一定的指示意义.此外,通过研究不同配置关系对应大气环流异常特征,并分析不同要素在夏季风和极涡关系变化中的作用,发现不同配置类型下夏季降水表现出的差异和规律性直接取决于环流场的整体配置,其中西太副高和中高纬阻塞形势起主导作用.

The distribution of large-scale drought/flood of summer in China under different configurations of monsoon and polar vortex

From the view of warm and cold system configuration, an East Asian summer monsoon (EASM) index and the Asian polar vortex area (APVA) index in July were selected, and their climatic characteristics and relationships with the distribution of summer rainfall over China were analyzed. On this basis, the relationships between the EASM and APVA in July from 1951 to 2010 were divided into four types: type A, stronger monsoon and bigger polar vortex area; type B, stronger monsoon and smaller polar vortex; type C, weaker monsoon and bigger polar vortex; type D, weaker monsoon and smaller polar vortex. Based on the method of composite analysis, we found that on the seasonal scale, large-scale distributions of summer droughts and floods over China showed multi-faceted characteristics in different configurations of the EASM and the APVA in July. In A type years, the summer rainfall of China was overall less than normal, the region between eastern parts of Northwest and the western parts of North China, and the eastern regions of Northeast suffered from flood, while Yangtze River valley suffered from drought; in B type years, it had flood in South and drought in North, and the precipitation in the south/north of northern regions in the Yangtze River valley was more/less than normal; in C type years, North China was flooded and South of China suffered from drought, while the precipitation in the northern parts of the Huaihe River valley was more than normal; and in the middle and lower reaches of Yangtze River and to its south the precipitation was less than normal; in D type years, the overall summer rainfall was more than normal, with the precipitation core lying in the middle and lower reaches of Yangtze River. Thus, it can be seen that the distribution of summer rainfall is not only related to the EASM, but also to the PAVA in July. Under different configurations of the both, the precipitation and its distribution display obvious difference and regularity, which, to some extent, have effects on predicting the total trend of summer rainfall. Besides, by discussing the anomaly characteristics of atmospheric circulation due to different configurations and by analyzing the influences of different meteorological factors on the relationship between the monsoon and the polar vortex, we can conclude that the difference and regularity of summer rainfall directly depend on the configurations of circulation. Among them, the western Pacific subtropical high and the blocking situation in the mid and high latitudes are the overriding factors.
Keywords： East Asian summer monsoon the area of the polar vortex in Asia distribution of drought/flood atmospheric circulation