西南氣流實驗之雨滴譜分析研究

Abstract

利用雨量筒測量或者是雷達所計算之相同降雨強度，其雨滴譜可以有很大的不同，因此透過本研究在西南氣流實驗期間微觀特性之瞭解，試圖推導出巨觀之特性。造成層狀與對流降水原因與垂直上的熱力、動力結構皆有不同，故其雨滴粒徑特徵都有顯著的不同，因此探討層狀與對流降水型態下的雨滴譜不僅能對降水特性有更多的瞭解，還可以更進一步知道微物理過程以微觀歸納巨觀，以巨觀演繹微觀。 北部觀測實驗結果顯示，撞擊式雨滴譜儀的雨滴譜呈現Gamma分布，隨著回波的增加小雨滴數量會有明顯之低估；降雨感應系統則是M-P分布，隨著回波的增加雨滴譜從M-P轉變成Gamma分布。另外撞擊式雨滴譜儀在0.6mm到3.0mm觀測到的雨滴數量比降雨感應系統的雨滴數量多，故前者所計算出來的降雨強度以及回波強度都比降雨感應系統為高。 南部觀測實驗則是利用屏東機場探空區分四個不同大氣環境場，並且用Bringi et al. (2003)區分出對流與層狀降水，結果顯示出層狀降水的雨滴譜與亮帶有很大的關係，有觀測到亮帶之階段，平均之平均粒徑(Dm)會比其他階段還要大。對流降水與層狀降水前者在雨滴大小較後者大，也較後者為多。 若與Bringi et al. (2003)統計資料做比較，發現北部與南部的層狀降水與國外的層狀降水分類一致，截距參數(Nw)與中值體積直徑(Do)分布近似線性，且斜率是負值；對流降水在北部的觀測結果趨近於海洋性降水，而南部的對流降水則是介於海洋性與大陸性對流之間。另外分析發現，平均中值體積直徑(Do)大的階段，會觀測到較多的中型雨滴，也就是說中型雨滴可能在降雨積分參數中扮演重要角色。

The rain gauges or radar estimate the same rainfall intensity, raindrop size distribution (DSD) may have very big difference. The present study is trying to understand characteristic of microscopic, and attempt characteristic of macroscopic. The formation mechanism and vertical thermal and dynamic structure of stratiform and convective precipitation are different, therefore the characteristic of DSD will have remarkable difference. The stratiform and convective of DSD not can only understand characteristic of precipitation but also the microphysical processes. The northern observation experimental result showed that DSD of Joss-Waldvogel Distrometer (JWD) is near Gamma distribution. The small drops underestimate when the reflectivity increased. The shape of DSD of Precipitation Occurrence Sensor system (POSS) is near exponential distribution. The M-P pattern changed into the Gamma pattern when the reflectivity increased. The number of DSD of JWD between 0.6mm and 3.0mm is more than POSS, therefore the former rainfall intensity and reflectivity are higher than latter. It separated four regimes from Pingtung sounding during the south observation experiment, and discriminated between stratiform and convective types on Bringi el al.(2003). The study showed the result of relation to the DSD of stratiform and bring band. The convective of DSD have big raindrops and quantity of raindrops are large. The stratiform of DSD is a straight line with negative slope during all the experiment. The north of convective precipitation of DSD is near maritime-like type, but the south of convective type of DSD is between maritime and continental cluster. Otherwise, it’s could important the middle size raindrops in the integral rainfall parameters.