Study of Space and Time Distribution of Precipitation in Tropics by Doppler Radars

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Using Chiang Mai Radar of TMD and Om Koi Radar of BRRAA in Thailand, radar echo intensity in monsoon rainy seasons in 1998-2000 was analyzed. It was shown that the total echo area observed by both radars had a significant diurnal variation: it rapidly increased before noon, reached its maximum at 15-16 LT and slowly decreased through the night In May-July, almost all echoes moved from south or southwest as the lower tropospheric wind. In the early October, the both direction of echo movement and wind reversed. By dividing radar observation area of Om Koi into 11 stripes parallel to the main mountain range, the diurnal variation in the each stripe was investigated. The results showed that in May-July the diurnal variation in stripes in the lee-side of mountains had clear trends towards later maxima leeward (eastward) from the mountainous region. In the early October, the diurnal variation in stripes in the leeside (western side) of the mountains showed the same leeward phase shifts.Using a numerical cloud-resolving model, it was concluded that eastward movement of squall lines governed the diurnal variation of precipitation over the Indo-China Peninsula. Above results by radar data analysis proved this conclusion by he numerical.By using a regional climate model, effects of deforestation in northeastern part of Thailand were evaluated. It was shown that monthly averaged precipitation decreased in September over the deforested area, because the monsoon wind and thus the horizontal vapor transport were week in September.Using rain gages and IR data of GMS, the diurnal variation of precipitation over Bangladesh and whole Indo-China Peninsula was studied in detail. It was shown by the analysis that not only the difference of the diurnal variation of precipitation between the land and the sea but the difference between plain areas and mountainous areas were clearly indicated.