芭瑪(Parma)颱風於2009年10月3-7日通過呂宋島北方，颱風中心與台灣南端最近距離雖達250 km，仍在宜蘭以及花蓮地區造成超大豪雨。為了解降水機制，本研究利用數值模式(WRF)進行模擬，以探討東部地區強降水之成因，並針對颱風環流，與東北季風的共伴效應，以及台灣地形進行敏感度分析。
　　當颱風環流的暖溼空氣通過台灣東側，與東北方冷乾空氣輻合後西移，輻合氣流受地形抬升後舉升凝結，使對流發展旺盛而降下豪雨。其中宜蘭地區於颱風開始南移後有共伴效應加強水氣傳送，使降水持續。花蓮地區由於山脈緊鄰海岸且夫如數較宜蘭地區小，氣流不易被舉升，使降水量少且集中於外海。此外，芭瑪颱風移速緩慢，使對流系統通過台灣東側的時間加長，也是造成超大豪雨的原因之ㄧ。
本研究也利用改變地形高度、環流強弱等因素進行測試，發現
當地形降低時，於東岸低層氣流輻合減弱，同時氣流被舉升形成的對流胞亦減弱；當地形高度增加時，雖輻合強度增加，但此時夫如數僅0.4，低層氣流因不易被舉升而轉為繞山，使降水量減少。當環流減弱時，台灣東側之輻合強度、風速以及水氣混合比皆相對減弱，此時颱風內對流系統以及共伴效應所產生之對流胞強度亦較弱。同時，東北季風受地形舉升為東北部帶來持續且穩定的降水，經移除地形或移除芭瑪颱風的敏感度實驗，在宜蘭地區降水皆僅剩原本的1/3左右，顯示宜蘭地區之強降水主要是由地形與共伴效應交互作用而形成，芭瑪颱風外圍環流的對流系統對此區影響相對較小。

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