摘要
颱風離臺後所伴隨的西南氣流，往往同時伴隨長時間的強降雨，有時甚至比颱風本身造成之降雨更為劇烈。然而並非所有颱風個案皆與西南氣流共伴，為瞭解大尺度環境(包括MJO、QBWO等季內振盪)是否在其中扮演重要角色，本研究選取發生西南氣流共伴之颱風個案，如敏督利(2004)、卡玫基(2008)、鳳凰(2008)、莫拉克(2009)、潭美(2013)，使用WRF模式模擬，並進行系集平均分析。
移除MJO環流後對颱風駛流的改變並不顯著，但臺灣海峽附近之西風、水氣量、水氣通量的輻合均變小，使西南氣流降雨減少。而QBWO對伴隨西南氣流颱風個案最顯著之影響在於路徑與駛流，當移除QBWO後，使颱風路徑改變，颱風環流與南海的豐沛水氣無法互相連結，且西南風不足的情況下無法將對流雨帶推往陸地；亦或是颱風路徑大幅偏離，導致颱風中心遠離臺灣，皆致使大量降雨發生於海面上。而路徑差異較小之個案，移除QBWO後的模擬結果在臺灣海峽之西南氣流強度明顯不如移除MJO之結果，故臺灣西南方的共伴降雨大幅減少。以中尺度之觀點分析，QBWO對颱風伴隨西南氣流的影響明顯大於MJO。歸納上述，季內振盪改變亞洲與西北太平洋地區大尺度環境場，產生有利颱風伴隨西南氣流之條件，進而使共伴降雨增強。關鍵字：颱風，季內振盪，西南氣流，數值模擬

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