本文以JTWC颱風資料和NCEP/NCAR大氣資料分析西北太平洋地區颱風活動氣候分布，並藉由量化的颱風活躍度指標來分析颱風活躍年和不活躍年颱風活動區域差異，以及伴隨之大氣環流變化，以提供未來颱風季颱風活躍度預報之參考。利用一個新定義的颱風活躍度指數選出5個颱風活躍年和8個不活躍年，並比較二者間差異以及伴隨之大氣環流變化。
研究結果顯示，旋轉風分量是影響西北太平洋颱風活躍度之關鍵。在活躍年時，氣旋式環流槽線由中太平洋延伸至東海以及菲律賓東方海面，提供颱風發展有利之氣候條件，並與該區颱風活躍度驟增趨勢一致。反之，在不活躍年反氣旋式環流脊線由中太平洋延伸至菲律賓和台灣東部海面上，抑制該區颱風活動。輻散（合）風分量無論從強度和位置都顯示和颱風活躍度關係不大，並不足以顯著地影響西北太平洋地區颱風活躍度之變化。
In this paper, JTWC typhoon data and NCEP/NCAR reanalysis data of atmosphere are used to investigate the climatic distribution of Western North Pacific (WNP) Typhoon activity. Through a newly-defined Typhoon activity index (TAI) to examine the difference between active and inactive years, and the associated change of atmospheric circulation, to provide a reference for future Typhoon activity forecast. 5 active years and 7 inactive years are selected to examine the difference.
Our results indicate that the rotational wind component is the key factor affecting Typhoon activity in the WNP. In WNP Typhoon active years a cyclonic anomaly extends from central Pacific to the East China Sea and to the east of Philippine, providing a favorable environment for Typhoon development. The region of cyclonic anomaly coincides with the enhanced activity of WNP Typhoons during active years. On the other hand, in WNP Typhoon inactive years, an anti-cyclonic anomaly extends form central Pacific to the east of Taiwan and Philippine, prohibiting the development of WP Typhoons. The divergent wind component shows a modest impact on the WNP Typhoon activity change.
