台灣北部地區層狀與對流降水的雨滴粒徑分布特性

毛又玉(You-Yu Mao)

指導教授 ： 林沛練

國立中央大學/地球科學學院/大氣物理研究所/碩士(2007年)

摘要

層狀與對流降水的形成原因與垂直的熱力結構皆有所不同，造成雨滴粒徑分布特性的差異，同時也對雲模式的參數化有影響。雨滴粒徑分布可決定回波強度、降雨率、液態水含量等降雨積分參數，因此研究層狀與對流降水型態下的雨滴粒徑分布能對降水特性有更多的了解。本研究使用位於中央大學的光學式雨滴譜儀，及五個撞擊式雨滴譜儀：中央、石門、南港、翡翠、霞雲等站，分析2005~2006年大雨事件中，層狀與對流降水的雨滴粒徑分布特性。
本研究使用Tokay and Short (1996)的N0-R關係式區分層狀與對流降水。研究結果顯示，經過標準化後的雨滴粒徑分布能明顯的看出層狀與對流降水的差異，層狀降水的雨滴粒徑分布較接近指數型態，小雨滴的數量比較多；對流降水在小雨滴數量的部份則比層狀降水減少許多。而在降雨率相同的情況下，層狀降水的雨滴粒徑大於對流降水。兩種降水在雨滴粒徑分布上的差異進而影響到各雨滴粒徑分布參數及降雨積分參數的不同。整體而言，對流降水的μ、Λ、N0、Dm、Nw等參數都比層狀降水來得大。將各站的層狀與對流降水的Nw-Dm關係與Bringi et al. (2003)做的統計相比較，發現台灣北部地區的對流降水分布偏向海洋性對流降水，但降雨率大於20 mm/hr時則介於海洋性對流及大陸性對流之間，而北部地區的層狀降水分布則與國外的層狀分類一致。Z-R關係式中的係數A、b在經過標準化後，b可定義為一個常數，而A與降雨率R幾乎為一對一的關係。
分析颱風與梅雨個案後發現，不論是哪種天氣型態，在分類層狀及對流降水後的μ、Λ、Dm、Nw等參數的變化很類似。但在對流降水時，颱風個案的各參數值的變化又比梅雨個案的參數變化幅度來得大。而兩個個案的層狀降水時的各種參數變化則很穩定。

關鍵字

雨滴粒徑分布

並列摘要

The formation mechanism and vertical thermal structure of stratiform and convective precipitation are different. It affects not only the characteristics of drop size distribution (DSD), but also the parameterization of cloud model. The DSD can be used to determine rainfall integer parameters including rainfall rate, liquid water content, and reflectivity factor, etc. This study used DSD data collected with five Joss-Waldvogel disdrometers (i.e. NCU, Feitsui, Nankang, Suiman, Shiyun), and a 2D-Video disdrometer in NCU, to investigate heavy rain events occurred during 2005 to 2006. And then use the intercept parameter N0 and rainfall rate to classify precipitation type into two categories: stratiform and convective.
The normalized DSDs are distinct difference between stratiform and convective. The shape of DSD in stratiform is near exponential, and have more small raindrops, but there are less small raindrops in convective. At the same rainfall rate, stratiform has larger drop spectrum than convective. The DSD parameters and integral rainfall parameters are also different in these two rainfall types. Overall, the parameters of μ, Λ, N0, Nw, and Dm in convective type rainfall are greater then those of stratiform. Having compared Nw-Dm of stratiform and convective precipitation with the statistic results of Bringi et al. (2003), we found that the pattern of stratiform in northern Taiwan agreed well. The pattern of convective type is near the maritime-like cluster, but when rainfall rate is greater than 20 mm/hr, the pattern is between maritime and continental-like cluster. After normalized, the b parameters of Z-R relation can be defined as constant, and parameter A almost has one-to-one relation with rainfall rate R.
Case study on Typhoon and Mei-yu, we found that no matter what type it is, the variation of parameters (i.e. μ, Λ, Dm , Nw) are similar when rainfall are classified to stratiform and convective types. In convective precipitation, the variation of parameters of Typhoon case is greater than Mei-yu case. However, the variations of stratiform parameters in both cases are stable.

並列關鍵字

drop size distribution

參考文獻

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