Interdecadal and Interannual Variabilities of the Asian Summer Monsoon and Its Projection of Future Change
亚洲夏季风的年际和年代际变化及其未来预测

The present paper presents a concise summary of our studies on interdecadal and interannual variabilities of the Asian summer monsoon and its projection for recent five years, which can be summarized in the following three aspects: 1) A significant interdecadal weakening of the Asian summer monsoon was identified on the basis of our analysis of a 123-year precipitation dataset in China and studies made by Indian investigators. This variability has caused significant changes in summer precipitation patterns in both East and South Asia. In East Asia, the main monsoon precipitation belt has continuously retreated southward, leading to a precipitation pattern of droughts in North China and floods in South China. The interdecadal change in the preceding winter and spring over the Tibetan Plateau and the sea surface temperature anomaly (SSTA) of the tropical central and eastern Pacific, in addition to the resulting land-sea thermal contrast, are the main drivers for the weakening of the Asian summer monsoon. In the future, the responses of the South and East Asian summer monsoons to a warmer climate will differ, with a continuous weakening in the former and enhanced circulation and precipitation fields in the latter. 2) The interannual variability is mainly characterized by biennial and four-seven-year oscillations. The present paper focuses on formative processes, mechanisms and influences of tropospheric biennial oscillation (TBO) on precipitation in East Asia. The formation and cycle processes of two particular TBO modes, the Yangtze River Valley (YRV) and the Huaihe River Valley (HRV) modes, have been examined. 3) On the basis of previous studies of teleconnection modes in the Asian monsoon region, we suggest the occurrence of low-level teleconnection types propagating along a strong monsoonal airflow belt from South Asia or the western North Pacific to East Asia. Such teleconnection types can exert an important effect on the Meiyu/Baiu season and summer precipitation in North China and Northeast Asia. Finally, it is indicated that global warming will have a more significant effect on the Asian summer monsoon in this century. Therefore, both anthropogenic and natural forcing are important factors in the long-term variation of the Asian summer monsoon.