本研究主要是探討在南海實驗計畫SCSMEX期間利用C-Pol偏極化雷達所觀測到明顯不同的兩個降水系統。分析C-Pol偏極化雷達觀測資料在通過系統時，由於參數本身的特性所產生的變化，藉由這些變化來討論這些參數對於描述降水系統現象的能力。 將這些偏極化雷達參數再經過像是平滑相位差ΦDP與利用垂直觀測資料（vertical pointing data）平移差異反射率ZDR的過程，以及由平滑過的ΦDP計算出差異相位差KDP，了解相位與回波及其他偏極化雷達參數之間的異同，並探討偏極化雷達之參數對降水粒子的統計特性與物理意義。 從雷達參數與降水參數（主要是降雨率R）之間的關係，我們也可以了解這些雷達參數所配置出來的降雨率會有所差異。為了能夠對照地面雨量站之實際觀測，我們再利用5月15日這一天有較長時間的降水系統通過位在C-Pol雷達西南方約45公里處的海面上之聲波雨量站資料來作分析。對照結果發現由KDP所計算出來的降水與地面觀測較為接近。 最後本篇研究也嘗試著利用較適當的降水關係式將5月18日0340 UTC的地面降水粒子做分類，利用不同的降雨率分成大雨、中雨以及小雨三種降水粒子。用統計的方式找出這三種降雨率落在偏極化雷達參數的範圍為何，藉以調整Vivekanandan et. al. （1999）所定義在S-Band偏極化雷達方面對這些降水粒子所界定的範圍，並且討論分類的結果。 During the SCSMEX experiment in 1998, at the Tongsa island a C-Pol radar, ISS ( Integrated Sounding System), and a few disdrometers were deployed. Two cases with obvious precipitation were selected for analysis. The first case was on May 18th near the onset of South China Sea monsoon, the second case was on June 8th . The polarimetric radar data including the ZDR, ΦDP, and KDP and other variables was edited and analyzed for both cases to understand the rainfall characteristics difference between these variables. The hydrometer conditions at the different stages of the systems in these two cases were studied together with ISS and Acoustic Rain Gauge observation. There are wide stratiform areas on both front and rear of the convective region in the symmetric squall line in May 18th case. An asymmetric squall line with a curved convective band as the leading edge was found in June 8th case. The rainfall estimate through the polarimetric variable was carried out within 60 km of the radar site. From these two case studies, we found the KDP variable was quite reasonable and KDP is very sensitive to the structure of the system. KDP field is immune to the attenuation and system calibration error. We use the polarimetric variables to study the hydrometer type with in precipitation system. We also use the relationship between the polarimetric variable and rainfall rate to classify the hydrometer type with the case of May 15th .
