台灣北部地區長期統計之不同季節與不同降雨型態之雨滴粒徑為物理特徵分析;Microphysical characteristics of raindrop size distribution in different seasons and precipitation type in Northern Taiwan

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Title:	台灣北部地區長期統計之不同季節與不同降雨型態之雨滴粒徑為物理特徵分析;Microphysical characteristics of raindrop size distribution in different seasons and precipitation type in Northern Taiwan
Authors:	李孟澤;Lee,Meng-Tze
Contributors:	大氣科學學系
Keywords:	雨滴粒徑;雷達;雨滴譜儀;Drop size distribution;Radar;JWD
Date:	2016-08-30
Issue Date:	2016-10-13 12:10:19 (UTC+8)
Publisher:	國立中央大學
Abstract:	台灣位於太平洋西側、歐亞大陸東側的熱帶與副熱帶季風地區，春夏季轉換時、梅雨鋒面、夏季的颱風和午後熱對流常常帶來豪大雨，在加上台灣地形陡峭，容易造成水災、土石流，因此準確預估降水對防災有極大的幫助。雷達回波與降雨率的關係廣泛被用來估計降水的方法之一，可以用在大範圍降水估計;缺點則是空間上的雨滴粒徑變化太大，相同的回波值對應的降雨率範圍很廣，兩者並非一對一的關係，因此了解雨滴粒徑分佈的特性將有助於改善降水估計。不同的地區、不同的降水型態，都有可能造成雨滴粒徑分佈不同，以及分析比較降水積分參數有助於了解不同的降水特性。本研究使用的資料來源為中央大學Joss-Waldvogel disdrometer(JWD)觀測資料與中央氣象局(CWB)三維雷達回波合成資料(QPESUMS)，統計的區間為2005年1月至2014年12月間。由標準化的gamma分布顯示,平均直徑Dm (Mass-weighted average diameter)於夏季有最高值，而平均Nw(normalized intercept parameter)最高值則出現在冬季; 透過雷達回波在高度上的變化得知垂直發展影響DSD (drop size distribution)在不同季節的結果。此外，台灣北部降雨率多集中於20mm/hr以下(層狀性降水)，本篇研究使用雷達回波區分對流性與層狀性降雨，移除層狀性降水主導的因素。所有季節的層狀降雨皆有相近的DSD分布結構，但對流降雨的DSD則是偏向海洋型對流; 平均Dm在對流降雨系統有較高值，而平均log10Nw在層狀系統內有較高值，透過 Contoured frequency by altitude diagrams (CFADs)發現垂直發展主導DSD的變異性。 ;Drop size distribution (DSD) is a metric widely used in meteorology and hydrology. Taiwan is located in a subtropical monsoon area in the west Pacific Ocean off the coast of East Asia. Enormous quantities of rainfall during the transition season often cause flooding and mudslides. Accurate rainfall prediction can help to alleviate the effects of such rainfall events. DSD varies with regard to the type of rain as well as its spatial distribution. Radar reflectivity-rate of rainfall (Z-R) relations are strongly dependent on DSD variations, which means that it is important to analyze the DSD in various seasons as well as in various types of rain. Between January 2005 and December 2014, DSD data was collected using a Joss-Waldvogel Disdrometer (JWD) to analyze variations in the Gamma parameters of raindrop spectra at NCU (24°58′6"N 121°11′27"E). The normalized Gamma distribution of DSD revealed that the highest mean Dm (Mass-Weighted Average Diameter) values were in summer, whereas the highest mean log10Nw (normalized intercept parameter) values were in winter. Vertical structures detected in radar reflectivity profiles dominate the results of seasonal DSD. Furthermore, most of the rain falling at less than 20 mm/hr (stratiform precipitation) occurs in Northern Taiwan. In this study, we used radar reflectivity to differentiate between convective and stratiform systems. It was discovered that the mean Dm value is higher in convective systems, whereas the mean log10Nw value is higher in stratiform systems. The structure of DSD in stratiform systems remains constant in all seasons; however, convection is similar to maritime type. Contoured Frequency by Altitude Diagrams (CFADs) revealed that vertical structures dominate DSD in various types of precipitation.
Appears in Collections:	[Department of Atmospheric Sciences and Graduate Institute of Atmospheric Physics ] Department of Earth Sciences

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