臺灣博碩士論文加值系統

本文針對1998年6月4-5日，發生在華南/南海北部的組織性中尺度對流系統，利用NCAR/PSU MM5模式，探討此一地區MCSs的演變及結構。此個案最顯著的外部特徵為伴隨梅雨鋒面的南側，沿著20∘N呈東─西方向排列了三個組織完整的MCS，每個MCS之間相距約400公里。經由模擬的結果顯示，模式大體上能夠掌握諸如鋒面、風切線、槽線及低層噴流（LLJ）等綜觀尺度的系統特徵。對於三個MCS（分別以MCS A、B及C來標示）的模擬上，其中除MCS B的模擬結果生命期較觀測為短，且降水強度稍弱外，其他與觀測結果相近。
模式15公里網格之模擬的結果顯示，MCS A在具有暖濕、氣旋式風切、合流及風速輻合的環境下初始。夜間中南半島陸風的增強，更加強了離岸風在MCS A處之風速輻合的效果。初始前，盛行西南風越過狹長的安南山脈形成背風波。由背風擾動所造成一連串垂直運動中的上升氣流，將850 hPa高相當位溫區的潛在不穩定氣層舉升，是激發MCS A初始前對流活動的重要機制。位於MCS A南方及西南方的底層暖平流，在成長期階段是重要的對流活動強迫項。另外，850 hPa風切線南方的綜觀尺度LLJ在成長期到成熟期階段顯著增強，透過LLJ所帶來的豐沛暖濕空氣，使得位於LLJ左前方的MCS A獲得較強的水汽及質量輻合，產生更強的上升運動。
MCS B形成於華南低層相當位溫脊線附近及風切線南側，伴隨大尺度鋒區之輻合帶並具潛在不穩定的大氣環境內。激發MCS B的強迫機制，包括了：1.此區內的合流及局部風速輻合之效應；2.由熱力因素激發之前一降水系統外流邊界和MCS B初始前降水蒸發冷卻所造成之冷池對氣流的強迫抬升；3.地形對氣流的強迫抬升作用等因素。發展過程中由水汽凝結潛熱釋放所誘發出來的中尺度低壓（低層）及中尺度高壓（高層）也是維持MCS繼續發展的有利條件。而次綜觀環境中底層冷平流的出現，則為模式中MCS B迅速消散的重要因素。
MCS C初始於呂宋島西北方海面上，同樣位於具有850 hPa高相當位溫區，屬於潛在不穩定的環境。低層強西南氣流下風處的風速輻合、合流效應及暖平流，是MCS C初始的可能舉升機制。且在MCS C發展過程中，其中的風速輻合及合流效應幾乎均有伴隨。消散期階段，位於巴士海峽附近的850 hPa相當位溫脊線明顯減弱，MCS C的降水強度亦隨之迅速減弱。

摘要………………………………………………………………………Ⅰ
致謝………………………………………………………………………Ⅲ
目錄………………………………………………………………………IV
圖表目錄…………………………………………………………………VI
第一章 前言…………………………………………………………… 1
第二章 個案介紹……………………………………………………… 5
2-1綜觀天氣形勢………………………………………… 5
2-2衛星雲圖上MCS的發展……………………………… 6
第三章 模式及資料來源………………………………………… 8
第四章 模擬結果與觀測之比較………………………………………10
4-1 綜觀環境之模擬結果………………………………………10
4-2 降水之模擬結果……………………………………………11
第五章 MCS的生成與結構……………………………………………13
5-1 定義MCS之生命階段………………………………………13
5-2 中尺度天氣特徵……………………………………………14
5-3 MCS的垂直結構………………………………………………23
5-4 小結…………………………………………………………29
第六章 討論……………………………………………………………32
6-1 中尺度對流系統的平均結構………………………………32
6-1-1 MCS A…………………………………………………32
6-1-2 MCS B…………………………………………………33
6-1-3 MCS C…………………………………………………34
6-1-4 小結…………………………………………………34
6-2 次綜觀環境對中尺度對流系統的影響與反應……………35
6-2-1 MCS A…………………………………………………36
6-2-2 MCS B…………………………………………………37
6-2-3 MCS C…………………………………………………38
6-2-4 小結…………………………………………………39
6-3華南/南海北部短波槽之角色……………………………39
第七章 結論……………………………………………………………41
參考文獻…………………………………………………………………45
附表………………………………………………………………………50
附圖………………………………………………………………………54

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