On the Characteristics, Driving Forces and Inter-decadal Variability of the East Asian Summer Monsoon

The present paper has reanalyzed and reassessed the basic characteristics, the driving forces and the inter-decadal variability of the East Asian summer monsoon with new-inputs of data and research findings. It includes four parts:(1) the basic characteristic features and properties of the East Asian summer monsoon; (2) the driving forces of the East Asian summer monsoon; (3) the inter-decadal variability of the East Asian summer monsoon, and (4) the association of the East Asian monsoon with the global monsoon. The results obtained here have shown that the East Asian summer monsoon is an important and integrated part of the Asian summer monsoon system, with the monsoonal airflow of tropical origin. It is the main circulation and precipitation system in summer to shape the weather and climate in East Asia. The main forces that drive the East Asian summer monsoon consist of three kinds:external forcing, coupled forcing and internal variability. Among them, the anthropogenic external forcing (e.g., greenhouse gas, urbanization effect, and aerosols), which is an emerging driving force, is changing the properties and evolution trend of the East Asian summer monsoon. As a nature factor, the coupled forcing of oceanic and land-surface processes is the main cause of the inter-decadal variability of the East Asian summer monsoon. The coordinated effect of the Pacific Decadal Oscillation (PDO) and the Atlantic Multi-decadal Oscillation (AMO) is the dominant forcing for the 30-40 year period. Since the 1960s, the East Asian summer monsoon has experienced a strong-weak-strong inter-decadal scale evolution, along with the PDO and AMO. Correspondingly, the precipitation pattern in East China has also shifted from the "North flooding and South drought" pattern to the "North drought and South flooding" pattern with increasing precipitation in North China in the recent decade. Actually, this inter-decadal variation is consistent with the change of the Afro-Asian summer monsoon system. In the present century, influenced by increasing climate warming, the summer monsoon precipitation belt will continue to advance northward, and therefore northern and western China will have persistent above-normal precipitation scenarios. Finally, it is indicated that the Afro-Asian summer monsoon is well corresponding to the concept of the global monsoon compared to other regional monsoons worldwide.