台灣東北部的宜蘭蘇澳地區(北緯24.9度以南，北緯24.3度以北，雪山山脈以東)，在10月因為受到較強東北季風的影響(Chen and Chen 2003)，而且大氣仍屬於對流不穩定狀態(Chen and Chen 2003)，所以常有不是因為颱風直接侵襲台灣所引起的大雨發生。在此豪大雨的定義為在宜蘭蘇澳地區(共約有34雨量站)，至少有一雨量站的時雨量大於15mm，且日雨量大於50mm (Chen et. al. 2007)，。當台灣東北部發生豪大雨時可能引起重大災情，如：在2010年10月18日到10月20日，雖然強颱「梅姬」登陸呂宋島，颱風半徑沒有直接影響台灣東北部，但這三天在宜蘭地區日累積雨量都達到豪大雨(200mm)的標準，且三天最大累積雨量高達 1195 mm。另外一個災情重大的例子發生在2009年10月11日到10月13日。在這期間「芭瑪」颱風沿著南海移向南海島，雖然沒有直接影響台灣，但在宜蘭地區三天內降下約1202 mm。其中10月11日雨量高達651 mm。從1996年到2009年，未受到鋒面影響下在宜蘭蘇澳地區共有16天日雨量達到200mm的大豪雨事件，其中有11個事件發生在10月上旬。在這16個大豪雨事件的最大日雨量，有5個在海邊、6個在坡度剛開始增加的內陸、5個在500公尺的高山。在台灣西南部夏季季風影響下，豪大雨的研究相對較多，而在東北部，東北季風引起的豪雨研究相對較少。本計畫利用ECMWF、自動雨量站、人造衛星及雷達資料研究未受鋒面影響，且颱風未直接侵襲台灣的東北部豪大雨之環境條件，並利用WRF探討大豪雨的激發、維持機制及地形效應的影響。 After mid-September, the northeasterly monsoon influences Taiwan in Autumn (Chen and Chen 2003). Upper-level westerly wind and low-level easterly wind become evident as season progresses. Low-level moisture is transported into Taiwan. Because of central mountain range (CMR), northeastern Taiwan becomes the windward side of the northeasterly monsoon. Heavy rainfall events are significantly over northeastern Taiwan during Autumn (Chen et al. 2007) when atmosphere is still convectively unstable. From 1979 to 2009, the transport of moisture into northeastern Taiwan becomes significantly in October. From 1996 to 2009, there are 16 torrential rainfall events (the accumulated daily rainfall exceeding 200 mm) over northeast Taiwan computing from 34 rainfall stations. These episodes commence when the front is not present in Taiwan and typhoon is not directly influences Taiwan. Among these 16 cases, five cases of the maximum daily rainfall occurrence are over coastal areas. Six cases are in the interior lowlands where terrain slopes begins to increase. Five cases are over high mountain areas where elevation is over 500 m. During southwesterly monsoon season, the number of study of heavy rainfall events over southwestern Taiwan is relatively higher than that over northeastern Taiwan during northeasterly monsoon season. We propose to use the available data, such as ECMWF, ARMTS (Chen et al. 2007), satellite images and radar reflectivity to investigate the environmental conditions for producing heavy rainfall in northeastern Taiwan. The commencement and maintenance mechanisms and orographic effects for heavy rainfall are examined by using WRF model. 研究期間：10008 ~ 10107
