艾利颱風（2016）期間臺灣東部強降雨之研究

2016年10月5日，艾利颱風於臺灣東南方約580公里的海面上生成。10月7日至8日，當艾利颱風（2016）移至臺灣西南方海面上、與臺灣相距500至600公里時，臺灣東部發生強降雨事件，並引發嚴重災情。本研究分析此雨事件的原因，並探討艾利颱風在此中所扮演的角色。觀測資料與WRF模擬結果顯示，強降雨期間颱風周圍的大低壓帶明此低壓流場與太平洋高在臺灣東部輻合，形成東南風；東南風受地形舉升並與地形繞流輻合，而產生強烈對降雨集中於臺灣東部山區側及南側。臺灣東部對流不穩定的環境，亦有利於對流之維持。採用片段位渦反演方法移除颱風的實驗結果顯示，位於南海大低壓帶仍然明顯，與高流場的合流仍位於臺灣東部。此大低壓帶仍提供臺灣周圍的暖濕空氣，維持強降雨區的對流不穩定，有利於對流的生成及維持。移除颱風僅改變對流生成的位置，降雨強度並未改變期間的累積量化不大。移除臺灣地形實驗結果顯示，由於地形舉升及繞流的機制消失累積雨量減少約40%，且降雨空間分布亦改變，強降雨並未集中於東部而是整個南臺灣。綜上所述此雨事件應為綜觀環境主導，臺灣地形產生舉升及繞流機制而增加降雨量，颱風則僅扮演改變對流位置的角色。

關鍵字

颱風；颱風遠距降雨；強降雨；臺灣地形

並列摘要

Heavy rainfalls occurred over the southeastern Taiwan during 7-8 October when Typhoon Aere (2016) was located at northern South China Sea, or about 500~600 km away from Taiwan. Purpose of this study is to analyze the synoptic environment and the triggering mechanism of this heavy rainfall event. The numerical simulation using the Advanced Research version of the Weather Research and Forecast (ARW-WRF) model is used to reproduce the heavy rainfall event in Taiwan. The synoptic analyses and the control experiment show that an anticyclone was located to the east of Taiwan, accompanied by a large-scale cyclonic circulation surrounding Typhoon Aere. Humid and strong southeasterlies due to the large-scale cyclonic circulation is observed in the southeastern Taiwan. A convergent zone, due to the northerly winds and the offshore flow caused by the blocking of the topography, was observed over where convections occurred. In the sensitivity experiments the typhoon is removed by the piecewise potential vorticity inversion (PPVI) method. The no-typhoon experiments show that the spatial distribution of convection and the heavy rainfall zone shift. However, the accumulated precipitation is as much as the control experiment because the large-scale cyclonic circulation and the anticyclone still exist. The impact of topography is also tested by the sensitivity experiment that change the altitude over Taiwan area. Results show that the spatial distribution of precipitation changes when the Taiwan topography is removed. To sum up, the heavy rainfall event is associated with synoptic-scale patterns that would have produced rainfall whether Typhoon Aere existed or not.