Seasonal and Intraseasonal Climatology of Summer Monsoon Rainfall over Eeat Asia

Abstract

This study attempts to bridge a gap in our knowledge and understanding of the East Asian monsoon by presenting a documentation of the rainfall and intraseasonal rainfall climatology of summer monsoon rainfall over East Asia. The rainfall climatology is viewed both in terms of its regional characteristics and in relation to the large-scale circulation with the aim of bringing to light the myriad phenomena associated with the East Asian monsoon and its relevance to current mainstream research in monsoon and climate dynamics. Specially, climatology of 30-day and 10-day rainfall records from East Asian stations are studied and compared with satellite outgoing longwave radiation and the large-scale circulation field. Results show that climatologically two major monsoon rainfall onsets over East Asia are identified during the period from April to September. The first, known as the Mei-yu (or plum rain), occurs over central China around the beginning or the middle of June, and the second over northeast China during late July. The multiple onsets occur as the major rainbands make rapid transitions or sudden jumps between three somewhat stationary positions over southern China (pre-monsoon rain), central China (the Mei-yu front) and northeastern China (the polar front). Also found are the presence of 40-day and the 20-day oscillations in the rainfall climatology. Both oscillations exhibit structure and propagation consistent with previous studies. Abrupt changes by the major rainbands appear to be related to phase-locking between intraseasonal oscillations, such as the 40-day mode and the 20-day mode, and the seasonal variation. A comparison of the rainfall climatology with that over India is also discussed.