NAME =  Mikiko FUJITA  
ORGANIZATION =  Institute of Observational Research for Global Change, Japan Agency for Marine-Earth Science and Technology  
ADDRESS =  2-15 Natsushima-cho, Yokosuka, Kanagawa, 237-0061  
COUNTRY =  Japan  
PHONE =  81-46-867-9839  
FAX =  81-46-867-9835  
E-MAIL =  fmiki@jamstec.go.jp  
POSTER_ONLY =  yes  
THEME =  T3  
DATE =  09-Aug-04-15:10:03  
ABSID = T3MF09Aug04151003 
TITLE = Diurnal variation of precipitable water vapor observed with GPS in Thailand 
AUTHOR_1 = Mikiko FUJITA 
INSTITUTION_1 = IORGC, JAMSTEC 
PRESENTER = AUTHOR_1 
AUTHOR_2 = Fujio KIMURA 
INSTITUTION_2 = Institute of Geoscience, University of Tsukuba / FRCGC, JAMSTEC 
AUTHOR_3 = Mikio SATOMURA 
INSTITUTION_3 = Faculty of Science, Shizuoka University 
AUTHOR_4 = Teruyuki KATO 
INSTITUTION_4 = Earthquake Research Institute, University of Tokyo 
ABSTRACT = Observation using GPS receiver was performed to obtain PWV (Precipitable Water Vapor) with high time resolution at six stations in Thailand by GAME-T (GEWEX Asian Monsoon Experiment -Tropics). Diurnal variation of PWV was examined using GPS data obtained during 1998-1999. The results show that the diurnal variation is weak both in the dry season (from January to April, November, and December) and the wet season (from May to October) over Thailand. At Bangkok, the amplitude of diurnal variation is less than 1mm. Precipitable water vapor decreases in the morning showing minimum, but its peak is unclear. And PWV at Bangkok have especially clear diurnal variations in April 1998 and March 1999. The amplitude of PWV is about 5mm, its maxima appear around early morning and minimum appear in evening. In these periods, westerly wind at 850hPa is significantly weaker than those in other months. On the other hand, prominent seasonal variation can be observed in PWV over Thailand. There is clear difference in change of PWV between dry and wet season. At Bangkok, variation of about 10-15 days cycle is prominent in PWV with large amplitude of about 40mm in the dry season. In case of the wet season, however, variation of PWV is smaller than that in the dry season, and mean PWV keeps high value of between 50mm to 60mm. In general, the diurnal variation of PWV in the dry season is clearer than that in the wet season.  Variation of water vapor is small in the wet season because of nearly saturated water vapor in the atmosphere as the result of continuous supply by monsoon. In case of Thailand, however, the diurnal variation of PWV is not clear even in the dry season, and the clear diurnal variations of PWV appear before monsoon onset at Bangkok.