东亚季风指数的定义及其与中国气候的关系

利用NCEP/NCAR 850 hPa月平均风场再分析资料,在客观地选定定义地区范围的基础上;定义了一组新的东亚季风指数:西南季风面积和强度指数,东南季风面积和强度指数,偏北季风面积和强度指数.研究了各季风指数的相互关系、季节变化和年际变异.这6个东亚季风指数突出反映了东亚西南季风、东南季风及偏北季风3支季风气流强度和范围变化的特征.分析表明,它们相互之间既有一定联系,又有独立性.各季风指数存在明显的季节变化和年际变化.另外,分析了各季风指数与中国夏季降水和冬季气温的联系,以考察其解释我国气候异常分布的能力.结果表明,这些指数与我国夏季降水和冬季气温有很好的关系,并各自对应有一定的降水和气温分布.特别是西南季风与东南季风影响我国夏季降水的地区有很大差异.因此,我们指出,研究东亚夏季风时,区别西南季风与东南季风是很有必要的,用单一指数不足以表征它们不同的变化.

The Definition of East Asian Monsoon Indices and Their Relationship to Climate in China

A set of new East Asian monsoon indices (EAMI), on the basis of objectively selecting the area defined, have been defined by using the 850 hPa u and v component data reanalyzed by NCAR / NCEP for the period of 1968-1997. Their relationship to each other, seasonal and interannual variability is studied. This set of monsoon indices include the southwest monsoon indices Asw and Sw, southeast monsoon indices A SE and ISE, and north monsoon indices A N and IN, in which A and J in. dicate the area and intensity. The EAMI successfully depict the variability of the southwest monsoon, the southeast monsoon and the north monsoon over China. They have both the relationship and some independence to each other and show considerably seasonal and interannual variability. Further, we analyze the relationship between the EAMI and summer rainfall and winter air temperature in China to evaluate the EAMI's ability in explaining the distribution of climatic anomalies there. The results show that the EAMI corresponds wi th summer rainfall and winter air temperature over China in distinctive patterns. Especially, there is an obvious difference in the effect on summer rainfall anomaly in China be-tween the southwest and southeast monsoons. Therefore, we may point out that it is necessary to distin-guish the southwest monsoon from the southeast monsoon when studying the East Asian summer mon-soon. A single index is not enough to characterize their different variability.