NAME =  Kimpei Ichiyanagi  
ORGANIZATION =  Institute of Observational Research for Global Change  
ADDRESS =  3183-25 Showa-machi, Kanazawa-ku, Yokohama 236-0001  
COUNTRY =  Japan  
PHONE =  81-45-778-5637  
FAX =  81-45-778-5706  
E-MAIL =  kimpei@jamstec.go.jp  
POSTER_ONLY =  yes  
THEME =  T3  
DATE =  02-Aug-04-10:55:16  
ABSID = T3KI02Aug04105516 
TITLE = Stable Isotopic Composition of Rainfall in Thailand Depend on the Convection System 
AUTHOR_1 = Kimpei Ichiyanagi 
INSTITUTION_1 = IORGC 
PRESENTER = AUTHOR_1 
AUTHOR_2 = Kei Yoshimura 
INSTITUTION_2 = Univ. Tokyo 
AUTHOR_3 = Manabu D. Yamanaka 
INSTITUTION_3 = IORGC/Kobe Univ. 
ABSTRACT = Past precipitation studies on stable isotopes and the amount effect largely used monthly data, only a few studies incorporated daily observation data. The daily rainfall samples were collected at Bangkok and Phuket, Thailand, between August and November in 2001. Isotopic composition and rainfall amount at both stations revealed similar trend of monthly variability, while different trends of daily variability. The relation between Oxygen-18 and rainfall amount was not obvious at Bangkok. They clearly correlated at Phuket when daily rainfall was less than 30 mm, while no relation was evident when daily rainfall exceeded 30 mm. To determine the diurnal variations, composite of 3-hourly rainfall and relative humidity data for light (>30 mm/day) and heavy rain (< 30 mm/day) events were analyzed. There were two rainfall peaks in the early morning and evening at Bangkok, while rainfall was continuously high throughout the days except early morning at Phuket. Also, there exist large diurnal variation of relative humidity during both light and heavy rain events at Bangkok. At Phuket, the relative humidity at daytime for heavy rain events is much higher than those for light rain events. Composite maps of convective activity were also analyzed using black-body temperature (TBB) data from the Geostationary Meteorological Satellite (GMS-5). For periods of light rain at both stations, clouds developed only along the coastal region during the evening. These clouds had marked diurnal variation. During periods of heavy rain, the cloud often extended from the Indian Ocean to the Indochina Peninsula only in the evening at Bangkok and throughout the day at Phuket. From these results, local- and large-scale cloud systems forced light and heavy rainfalls, respectively. Therefore, the convective system may have an important role in determining the isotopic composition of rainfall.