Characteristics of East-Asian Summer Monsoon in the Midlatitudes Revealed by Newly Defined Indices

摘要

The characteristics of East-Asian summer monsoon in the region, which covers Korea, Japan, and the northeastern part of China, are described and the relationship between the monsoon system in the midlatitudes and the variation of the global climate is summarized. Our new summer monsoon index EAWMI, which describes well the characteristics of East-Asian monsoon, is an alternative tool to describe quantitatively the monsoon system in the East Asia region, and could be easily used to reveal the relationship between the summer monsoon and global climate variability. The observational analysis shows that the variation of East-Asian summer monsoon is influenced by the development of WNPSH and that the developing mechanism of WNPSH in summer may be different from that in winter. To investigate the mechanism of the variation of WNPSH and East-Asian summer monsoon, six model experiments using SNU AGCM and SNU AGCM/SOM are performed. The model results show that in the previous winter and the following spring of the strong East-Asian monsoon year, all of the SSTs in the tropical eastern and western Pacific and the Indian Ocean have an important role in the establishment of WNPSH and the variation of the circulation pattern over East Asia in the midlatitudes. However, in summer, the SSTs in the tropical western Pacific and the Indian Ocean are more important than those in the tropical eastern Pacific.