| 摘要: | 2008年5月~6月的梅雨季期間，台灣與美國合作在台灣南部地區進行西南氣流觀測實驗（SoWMEX/TiMREX）該實驗除了美國的S-Pol雷達以及中大/國科會Team-R雷達分別布署在屏東新園堤防以及九如堤防進行觀測之外，另外也架設一部光學式雨滴譜儀（2DVD）以及五部撞擊式雨滴議儀（JWD）在廣興、瑪家、關福、繁華、青山等站進行雨滴粒徑之觀測，本研究即利用這些觀測資料進行梅雨季台灣南部地區的降雨型態分類以及雨滴粒徑特性分析。 本研究針對2008年5月16日至6月30日之降水事件，首先利用不同方法來區分降水型態並進行雨滴粒徑分佈特性討論。研究結果發現，無論是利用何種方法區分降水型態，平均而言，對流降水雨滴濃度較層狀降水大了一個數量級，另外對流降水之雨滴粒徑分佈能夠延伸至較大粒徑的部份。若以降雨率20 mm/hr來區別層狀與對流降水型態時，本研究發現，粒徑2.0 mm是一個重要的分界，平均來說粒徑大於2.0 mm時對流降水的雨滴濃度高於層狀降水，而粒徑小於2.0 mm時對流降水的雨滴濃度則低於層狀降水。對照Bringi et. al（2003）之Dm-Nw的關係，台灣南部地區層狀降水之分佈特性與過去實驗結果相似，但是對流降水則比較接近海洋性對流降水的特性，此結果與台灣北部地區雨滴分佈特性差異不大。 以廣興站二維光學式雨滴譜儀（2DVD）分析2008年梅雨季之降雨特性，發現雨滴譜儀記錄的總降雨時間為8383分鐘，其中層狀降水發生時間為5523分鐘，對流降水為2580分鐘，分別占了總降雨時間的65％及34%；觀測期間總降雨量為987 mm，其中層狀降水貢獻190.11 mm，對流降水為794.14mm，分別占總降雨量之19%及80%，顯示雖然梅雨季是由綿綿細雨占據大部分的降雨時間，但在總降雨量主要來自短時刻對流性降水的貢獻。平均而言，雨滴粒徑分佈參數斜率參數Λ、標準化截距參數Nw、平均粒徑Dm、液態水含量LWC、回波強度dBZ皆是在對流降水時會大於層狀降水，而形狀參數μ則是對流降水時小於層狀降水。但是利用N0-R關係式的區分方法，則形狀參數μ的部份會與其他分類方法相反，即在對流降水時μ值會大於層狀降水。因此，使用不同方法在參數統計上仍有一些差異，值得進一步研究。 In 2008,a joint field experiment named SoWMEX/TiMREX was conducted in southern Taiwan.Most previous studies of the DSD in Taiwan focus on the north, and therefore this experiment is expected to help analyze the DSD in the south. Six disdrometers located in Quan-Xin,Ma-Ja,Quan-Fu,Fan-Hua,and Chin-San were utilized. This study analyzes precipitation events from May 16 to June 30 and discusses the properties of the DSD for different precipitation types. No matter what distinguishing precipitation types method used,the result shows the drop number concentration of convective precipitation is an order of magnitude larger than that of stratiform rain, and the range of the convective DSD is larger as well. When these two types are distinguished with 20 mm/hr as a rain rate boundary, the drop number concentration of convective rainfall is more than that of stratiform rain for drop sizes more than 2.0 mm, and less for drop sizes smaller than 2.0 mm. In addition, the rainfall and D_m observed in Chin-San are larger than the others because of its higher altitude. Compared with the Dm-Nw relation deduced by Bringi et al.(2003),there are similar results with the stratiform rainfall in southern Taiwan, while the convective rain is maritime-like and close to that observed in northern Taiwan. The rainfall properties of the Mei-yu season in 2008 is analyzed using an 2DVD located in Quan-Xin. The total rainfall duration is 8383 minutes, within which the stratiform rain is 5523 minutes(65%) and the convective rain is 2500 minutes(34%).The total rainfall accumulation is 987 mm, within which the stratiform one is 190.11mm(19%) and the convective one is 794.14 mm(80%). Therefore it’s shown that, in the Mei-yu season, the statiform rain is the major contribution to the rainfall duration while the short-time convective rainfall contributed to the most accumulation rainfall . DSD parameter statistics shows, slope parameterΛ, mean mass diameter Dm, liquid water content LWC and reflectivity dBZ are all larger in the convective rain than in the stratiform one, but the event frequency and shape parameter μ of the stratiform rainfall is larger instead.But the results derived from N0-R relation method has converse with the others while in convective type. |
