台灣北部初秋豪雨個案之降雨特性研究

The precipitation characteristics of autumn torrential rainfall event in northern Taiwan.

馮雅茜(Ya-Chien Feng)

指導教授 ： 廖宇慶 ； 陳台琦

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

本文主要探討2006年9月10日北台灣初秋豪雨個案之降雨特性，當日最大累積雨量為竹子湖測站的556 mm/day(已達超大豪雨)，降雨主要集中在06-12 UTC。研究中利用中央大學雙偏極化雷達和五分山雷達進行中尺度分析，討論降雨之時空分布特徵、可能機制與微物理特性。
綜觀天氣主要受到大陸性高壓與台灣南方外海之低壓產生的共伴環流所影響，大陸性高壓出海與高層轉為西風，屬於初秋的氣候特性。
中尺度水平方向的雷達回波具有多種樣貌，系統自東向西移動，並由南北走向聚集後轉為東西走向。統計結果顯示強回波主要集中於三區：台灣東北部外海、大屯山區以及淡水河口附近，此三區皆存在有利的環境因子，分別為：綜觀環境高、低壓的風場輻合，地形上坡增強，穿過台北盆地之東風與環境東北風的輻合。
雙偏極化雷達顯示降水系統主要由層狀和發展不深的對流組成，而這些淺對流被嵌於層狀系統之間，利用雙偏極化雷達反演雨滴粒徑再配合風場資訊整理出一個雲物理的概念模式，長時間存在的層狀區持續提供融解後的水滴給低層，地形迎風坡或對流區有較大的上升速度，利於凝結使得小雨滴個數增多，可能有類似種雲餵雲的加強機制，且大ZDR集中在低層，降水可能以碰撞結合為主。

關鍵字

豪雨 ； 雙偏極化雷達

並列摘要

Precipitation characteristics of the torrential rainfall event on 10th Sep. 2006 in northern Taiwan will be discussed in this thesis. The maximum daily accumulated rainfall was 556 mm at Zhuzihu. The heavist rainfall took place during 06-12UTC. The data collected by NCU dual-polarimetric radar and RCWF radar are mainly used to analyze mesoscale features, such as space-time distribution of precipitation, possible mechanisms, as well as microphysics characteristics.
In synoptic scale, a continental high in China and a low locating on Bashi Channel influenced Taiwan. They caused a low level convergent zone in the north-eastern area of Taiwan. Because the continental high moved out of China and it turned to westerly on high level, the climate character was categorized to early autumn.
The horizontal reflectivity patterns were diverse. Convections moved from east to west. Statistic result shows that the strong reflectivity dispersed to three areas, northeastern sea of Taiwan, Mt. Datun and Tamsui River estuary. The environment provided favorable conditions for these precipitation systems, such as convergence and terrain upslope enhancement.
From dual-polarization data, shallow convections were embedded in large and long-lasting stratiform system. ZDR was increasing as height decreasing. Within near saturated environment, the bigger drops in lower level indicated that precipitation may be enhanced by collision and coalescence. Using dual-polarization radar data to retrieve raindrop size distribution, and combing kinematics analysis, we could prescribe a simple microphysics conceptual model. The long-lasting stratiform system continuously provided droplets to low level convections in a wide spread region. Wherever there is more upward motion, more vapor would condense. A wider spread of DSD set up the stage of seeder-feeder mechanism.

並列關鍵字

dual-polarimetric radar ； torrential rain

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