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

利用泰国TMD的清迈雷达和泰国BRRAA的Om Koi雷达，分析了1998-2000年季风雨季的雷达回波强度。结果表明，两台雷达观测到的总回波面积有明显的日变化：中午前回波总面积迅速增大，在15-16LT达到最大值，5-7月夜间回波面积缓慢减小，几乎所有回波都以对流层低层风的形式从南方或西南方向移动。10月初，回波运动和风向都发生了逆转。通过将观测区划分为11条平行于主要山脉的条带，研究了各条带的日变化。结果表明，在5-7月期间，背风面条纹的日变化具有明显的从山区向最大值偏东方向移动的趋势。10月上旬，山脉背风面(西侧)的条纹日变化也表现出同样的背风相移。利用数值云解模式，得出以下结论：印度支那-中国半岛降水的日变化主要受广场东移的影响。雷达数据分析的上述结果用数值方法证明了这一结论。利用区域气候模式，评估了泰国东北部森林砍伐的影响。结果表明，由于9月季风风和水汽水平输送较弱，森林砍伐区的月平均降水量在9月减少。利用GMS的雨量计和红外资料，详细分析了孟加拉国和整个印度支那-中国半岛降水的日变化。分析表明，不仅明确了陆地和海洋降水日变化的差异，而且明确了平原地区和山区的差异。

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.