Recent progress of research on East Asian summer monsoon
Ding Yihui (1)
(1) National Climate Center, China Meteorological Administration
A comprehensive review of the seasonal march of the East Asian summer monsoon is presented from a climatological perspective. First, the earliest onset of the summer monsoon over the South China Sea (SCS) and the Indo-China Peninsula occurring around mid-May or even earlier, is discussed in terms of low-level wind, upper-level wind, OLR, and rainfall fields. A sudden change in these fields before and after the onset is revealed. This is characterized by a wind switch from low-level easterlies and high-level westerlies to low-level westerlies and high-level easterlies, the rapid growth of convection and increase in rainfalls, and the eastward retreat of the subtropical high.It noted that the onset of the summer monsoon over Indo-China Peninsula and the SCS is preceded by development of circulation features and convective activity in the tropical East Indian Ocean and the Bay of Bengal that is characterized by the development of a twin cyclone crossing the equator, the rapid acceleration of low-level westerlies and a significant increase in convective activity in terms of both areal extent and intensity.
The seasonal march of the climatological summer monsoon displays a distinct stepwise northward and northeastward advance. Over East Asia, two abrupt northward jumps and three stationary periods have been identified while over the western North Pacific three stages in onset and advance of the summer monsoon have been identified. The noted East Asian rainy seasons such as the pre-summer rain season in South China, the Meiyu/Baiu in China and Japan, and Changma in Korea occur normally during the stationary periods of the northward advance of the summer monsoon.
Major physical processes and mechanisms responsible for the onset and seasonal progress are then discussed, with special emphasis on the three controlling factors and related physical mechanisms. The land-sea thermal contrast and the effect of the elevated heat source of the Tibetan Plateau are identified as a pre-condition for the abrupt onset of the Asian summer monsoon in the SCS and Indo-China Peninsula through the rapid reversal of the meridional temperature gradient. The arrival of the intra-seasonal oscillations (ISO) provides a triggering mechanism, along with the several phase-locking wet ISO phases. The intrusion of mid-latitude troughs into the northern SCS and central and northern Indo-China Peninsula is also seen to be another triggering mechanism which induces the convective activity through release of the potential instability, thus enhancing the monsoon trough there through the feedback process of meso-scale convective systems
Submittal Information
Name :
Date :
Ding Yihui
05-Aug-04-15:25:51
Organization :
Theme :
National Climate Center, China Meteorological Asministration
Theme 3
Address :
Presentation :
No.46 Zhongguancun Nan Da Jie, Haidian District, Beijing 100081, PRC