本研究以長期觀測資料分析年代際尺度臺灣秋季（9～10 月）及春季（2～4 月）降雨反相位的關係， 並探索其與太平洋年代際震盪(Pacific Decadal Oscillation, PDO)的密切關聯。PDO 正相位的秋季，除了 中高緯度北太平洋區域的海溫(Sea Surface Temperature)偏低外，赤道東太平洋附近的暖海溫距平引發的 反氣旋距平，正好在臺灣附近，因而抑制了此時期臺灣的降雨；但PDO 正相位的春季，雖然海溫距平 的分布與PDO 正相位的秋季相似，因反氣旋距平的位置在菲律賓海附近（較秋季更為東移），臺灣地區 因更深的槽線而降雨比秋季多。該高海溫距平在春季時比秋季時出現在更東邊，因此誘發的反氣旋距平 也較東邊。至於PDO 負相位時的秋季和春季，其狀況則與正相位相反。總結來說，春季與秋季降雨在 年代際時間尺度反相位的關係，來自於些微的海溫距平於空間分布上的差別，而造成臺灣地區春季及秋 季降雨的多寡。這樣些微的空間差別，卻可造成年代際降雨之不同，說明了PDO 應用在臺灣降雨的分 析上，應該更深入地研究。

This study analyzes the negative correlation between boreal autumn (September and October) and spring (between February to April) rainfall in Taiwan on decadal time scales. With warm sea surface temperature (SST) anomaly near the equatorial eastern Pacific Ocean presenting similar patterns but in little different locations during autumn and spring, the rainfall amount in Taiwan shows different results. The decadal autumn and spring seasonal rainfall fluctuate with Pacific Decadal Oscillation (PDO). In the positive phase of PDO, the warm SST anomaly at the eastern equatorial Pacific Ocean induces an anti-cyclone anomaly just near Taiwan in autumn. As a result, the rainfall is suppressed during this period. However, although the spring SST anomaly displays similar pattern to the positive phase of PDO in autumn, more rainfall in Taiwan is caused by deeper trough anomaly. This is due to the anti-cyclone anomaly near the Philippine Sea which can be seen in spring during the positive phase of PDO. The anti-cyclone anomaly slightly moves eastward along with the warm SST anomaly from autumn to spring. On the other hand, during the negative phase of PDO, the opposite situation occurred in autumn and spring. These little differences on location of warm SST anomaly between autumn and spring lead to different rainfall anomalies in Taiwan in the decadal variations. This implies that it is necessary to carefully apply the effect of the PDO to the location responses such as the rainfall in Taiwan.