Rainfall Variation of the Asian Summer Monsoon: Diurnal and Intraseasonal Oscillations
Tsing-Chang (Mike) Chen (1), Shih-Yu Wang (1), Wan-Ru Huang (1)
(1) Atmospheric Science Program, Department of Geological and Atmospheric Sciences, Iowa State University
One of the major goals of the GAME is to enhance our understanding of the hydrological cycle of the Asian summer monsoon. Actually, it is also equally important for us to explore the role played by the Asian monsoon hydrological cycle in the global context. It was revealed from previous studies that the Asian summer monsoon undergoes diurnal and intraseasonal (10-24 day and 30-60 day) variations. As depicted by the potential function of water vapor flux (XQ), the global diurnal variation mode propagates westward, opposite to the Earth rotation, and the global 10-24 day and 30-60 day modes propagate eastward. In view of propagations of these global hydrological modes, the following questions are raised: (1)What is the contribution of the Asian monsoon to the global hydrological cycle? (2)What is the link/response of the Asian monsoon hydrological cycle to these global propagating modes? The GAME hydrological data, several global precipitation sources (TRMM, GPCP, GPI), and NCEP/NCAR reanalyses were analyzed to search for answers to the aforementioned two questions. Our major findings are (1)The global precipitation exhibits diurnal and intraseasonal variations which synchronize with these variations in the monsoon hemisphere (60E-120W) including the Asian monsoon. Evidently, the Asian summer monsoon plays a crucial role in determining these global rainfall variations. (2)Although the global diurnal and intraseasonal hydrological modes propagate westward and eastward, respectively, in relatively regular manners, responses of the Asian monsoon hydrological cycle to different global propagating modes behave in completely different and complicated ways: a.The diurnal variation of rainfall and XQ undergoes a clockwise rotation around the Asian continent in response to the westward propagation of the global diurnal XQ mode. b.The 10-24 day monsoon mode propagates northwestward along the Southeast Asia-western tropical Pacific monsoon trough to East China. The eastward propagation of cold fronts before the East Asian summer monsoon break is regulated by this intraseasonal mode, while the tropical cyclone (TC)/tropical depression (TD) activity in East/Southeast Asia is modulated by this intraseasonal mode after the East Asian monsoon break. Because fronts and TCs/TDs are major rainfall producers, the East/Southeast Asian summer monsoon rainfall is affected by the global 10-24 day mode through this downscale process. c.The East Asian monsoon life cycle (onset-active-break-revival) is basically established by the northward migration of the 30-60 day monsoon trough/ridge from the Equator in response to the global 30-60 day mode. Monsoon rain is primarily generated by fronts along the Meiyu-Baiu rainbelt before the monsoon break, and by TCs/TDs after the break. The modulation of the global 30-60 day mode on the East/Southeast Asian monsoon rainfall is accomplished through the effect of the 30-60 day monsoon mode on the frontal and TC/TD activity. Impacts of the global diurnal and intraseasonal modes on the Asian monsoon rainfall are established through downscale processes described above. On the other hand, the contribution of the Asian monsoon to the global hydrological cycle is reflected by the coherent variations between the global and monsoon-hemispheric precipitation, and the variation in the water vapor flux exchange between the monsoon- and extra-monsoon hemisphere.
Submittal Information
Name :
Date :
Tsing-Chang (Mike) Chen
28-Jul-04-18:56:40
Organization :
Theme :
Department of Geological and Atmospheric Sciences, Iowa State University
Theme 3
Address :
Presentation :
Atmospheric Science Program, Department of Geological and Atmospheric Sciences, 3010 Agronomy Hall, Iowa State University, Ames, IA, 50011, USA