摘要
隨著理論和雷達觀測技術的進步，人們對颮線系統的生成原因與組成結構已有相當瞭解。颮線之所以能較一般積雲對流胞有更長生命期，是因為其內部特殊的環流結構-前側向上傾斜的front-to-rear氣流，其主要作用為提供前緣低層暖濕空氣進入對流降水區，並可將對流區頂層的冰晶粒子傳送到系統後方，再透過冰相微物理過程轉換成廣大的層狀雲區。另一由颮線系統後側向下傾斜的rear-to-front氣流，可將後方中層較乾冷的空氣帶到系統低層，加強此處冷卻作用，有利於地面冷池維持。
處於副熱帶地區的台灣，每年梅雨期間、滯留鋒面前緣常有颮線生成。1998年6月，南海北側至巴士海峽之間有許多中尺度強對流系統生成。其中6月4日有一疑似颮線個案生成，由雷達回波圖中可區分其不同生命期，並配合上各種觀測資料，可看出當時環境大氣為適合對流系統生成的狀況。
隨著模式發展，已具備模擬許多中尺度氣象系統的能力，本論文欲使用第五代中尺度數值模式(簡稱MM5)，模擬颮線系統各種特徵環境場，並使用高解析度的網格，模擬其內部的氣流結構。最後由水平動量方程執行尺度分析後，討論颮線移動時的主要作用力項。
使用MM5模式進行模擬後也成功地模擬出颮線系統的部分特徵氣象場。其中模式對各個生命期颮線降水型態有不錯的模擬結果。初生期和系統成熟期主要由對流降水主導，且有較強降水強度；在系統衰退至消散期則改由廣大層狀降水區主導，模式成功得到此一降水趨勢。在其內部氣流模擬上，在颮線成熟期模式模擬到上層(200-300hPa)front-to-rear和低層(700-850hPa)rear-to-front特徵氣流，和Houze(1977)依據雷達回波剖面圖，所提出的概念模式中高低層不同的氣流走向極為相似。

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