915MHz的UHF雷達對降水粒子很敏感，並且在垂直方向上有很好的空間、時間解析度，是良好的降水研究觀測儀器。本篇論文針對南海季風觀測實驗計畫期間的降水個案，利用UHF雷達在東沙島的觀測資料進行研究。本研究主要分成三個部份，一是針對辨識降水，區別雨、冰晶、融冰、空氣回波的探測；二是對流降水雲系系統垂直結構隨時間變性的討論；三是分析雨滴粒徑分布特性以及雨滴譜儀和UHF雷達整合觀測研究的初探。在辨識槳水的部份，UHF雷達波譜動差資料中的回波功率S(dB)和垂直速度V(m/s)的相關圖確實可以幫助我們辨識降水。看出不同回波來源的分群現象。不同降水型態垂直速度值分布範圍會有所不同：層狀降水的個案，可見明顯的融冰分布(45~55dB，-2~-5m/s)，雨滴速度分佈(-5~-8m/s)比對流降水(-2~-8m/s)要來得窄；而對流降水的冰晶速度分布範圍較大(0~-3.5m/s)。波譜寬特性和降水形式也有關：層狀降水雨滴資料點的波譜寬小於2m/s，對流降水則有波譜寬超過2~3m/s的雨滴資料點。利用不同S區間速度數量分布圖可彌補S-V相關圖的不足，更清楚定義門檻值，並評估出使用速度門檻區別降水、空氣造成的誤差。冰晶和空氣資料點分布疊合的情形最明顯，特別是在25~30dB這個回波強度區間時，選出的最佳門檻，特別是在25~30dB這個回波區間時，選出的最佳門檻為0.2m/s(6月7日)、0.1m/s(5月20日)；雨滴波形遠離速度0值處，跟空氣回波有很好的分離。
在對流降水雲系垂直結構的分析方面，根據回波功率密度之速度-高度剖面統計不同降水型態的發生率，發現東沙島關到的第一波降水期間(1998年5月15日~5月20日)之雲雨系統多處於對流轉層狀降水的轉變期，第二波降水期間(1998年5月30日~6月8日)則多處於發展階段。雨滴粒徑分布特性方面：南海季風肇始前後東沙島雨滴粒徑分部眾數多為0.9mm，但在小雨滴處數量有突增現象，沒有強降水的日子，眾數即轉為0.35mm。2-D雨滴譜儀可作為UHF雷達反演雨滴粒徑的驗證工具，另外對地面降水特性方面所提供的雨滴粒徑分布
、垂直下降速度、扁圓率分布等資訊，甚有助於我們了解過去一些相關經驗式的適用性由台灣中壢2D-雨滴譜儀觀測到的個案發現，使用M-P關係估計雨滴粒徑分布可能會在強降水時產生很大的誤差，而小雨滴的扁圓率、垂直下降速度特性也出現了一些過去經驗式所無法掌握的散點，值得進一步研究。

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