Evolution of Asian Summer Monsoon and the Slowly Varying Disturbances

The evolution of Asian summer monsoon is analyzed by means of decomposition of the atmospheric circulation into basic current and slowly varying monsoon disturbances. It is seen that the major slowly varying disturbances are two vortical couples, one located in the Indian Ocean and Indian Peninsula, and another in the Northern Hemispheric western Pacific Ocean and the East Asia. This indicates that the Asian summer monsoon consists of two branches, the Indian monsoon and the East Asian monsoon. Moreover, the analysis shows that the evolutionary processes of these two vortical couples are rather independent each other, and they all can be qualitatively interpreted by the dynamical theory of wave packet. The different stages of summer monsoon can be very well characterized by the location and in?tensity of the two vortical couples. Besides, in particular years there exists also some quasistationary wave train and its characteristics should be further analyzed.