摘要
本研究採用CDC分析1979~1998年之每日垂直積分外逸長波輻射資料（OLR），CMAP之每侯降水資料，NCEP重新分析之每日水平風場、垂直速度場、溫度場及1982~1998年每7日之平均海表面溫度資料（SST）。並選擇在頻率域及時間域皆可維持良好區域特性的小波轉換進行資料濾波（Daubechies,1988），過濾出30~60天的波動。接著透過計算南海地區110~120E˚，7.5~17.5˚N 各年之對流變異量的區域平均值及百分比異常值，並選擇個案年份，通過t-test的檢驗，以分類出對流活躍年與對流不活躍年。經分析後發現，SST、低層熱通量與30~60天對流活動在南海地區產生顯著的差異。其中在阿拉伯海－印度洋－孟加拉灣－南海以及台灣以北、日本以南等海域，30~60天OLR變異量的年際變化與SST的年際變化，有良好的對應關係。而南海30~60天OLR變異量的年際變化與當地低層熱通量的年際變化，雖在數值大小上無直接相關，然透過水平空間分布差異的比較，可發現南海地區仍為低層熱通量的加熱區，與30~60天對流活動相互對應。因此SST與低層熱通量等低層熱力因素為影響南海30~60天對流年際變化的關鍵。
本文進一步採用相位合成（phase composite）方法，來探討影響季內對流年際變化的因子在時空演變上的特性。首先發現，來自印度洋的季內對流先經孟加拉灣，再向東移至南海，與赤道西太平洋季內對流系統匯合於南海地區。在東移的過程中，SST一直領先對流發展約2個phase；低層熱通量出現在對流的偏北側，不僅與850mb靜力穩定度出現的位置一致，且兩者演進時間亦為同步。在低層環流場方面，首先是東西風輻合於對流區的西北邊，渦度中心、輻合中心均位於對流中心的西北側；之後，東西風場漸為西風所取代，輻合增強，作用範圍涵蓋整個對流區，渦度亦增強；最後，當對流抵達南海時，西風風場、低層渦度與輻合均達到最強，並且渦度中心位置仍位於對流西北側。
由於季內對流移行與前緣850mb低層渦度場存在正向回饋關係，並且具有領先對流發展的特徵。於是我們運用尺度分析方法（Charney,1963）推導三維流線函數趨勢方程式，將實際資料代入計算，求得渦度平流、溫度平流、靜力穩定度與非絕熱加熱等大氣作用力對渦度趨勢的貢獻，進而獲知大氣作用力對季內對流移行的貢獻。結果發現，SST正距平、非絕熱加熱所造成的正渦度趨勢及東移之30~60天對流，彼此具有良好的先後順序，前者均領先後者1/4個phase。靜力穩定度的貢獻則與非絕熱加熱相反；渦度平流則是促進熱帶西北太平洋30~60天對流向西北方移行，在南海30~60天對流東移則無明顯的作用。非絕熱加熱造成的正渦度趨勢，是導致30~60天對流東移的主要機制。

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