西北太平洋副熱帶高壓(以下簡稱副高)為影響東亞地區夏季環流變化的主要系統之一，其影響主要來自西側邊緣西伸東退的變化。過去研究指出，副高西伸東退與季風槽消長造成的環流變化，有影響西北太平洋熱帶氣旋移動路徑的作用，但對於副高西伸時熱帶氣旋總生成個數減少的情形，仍未有一套完整的物理解釋，且副高對熱帶氣旋發展強度的影響也還不清楚。本研究目的在於了解西北太平洋副高西伸東退的行為，對西北太平洋熱帶氣旋移動路徑外的影響，如熱帶氣旋的總生成個數及強度的氣候特性等。 研究結果指出，在副高西伸年時，西北太平洋地區反氣旋式環流的東風距平，抑制了季風槽平均流的正壓轉換過程，使西北太平洋地區的環境紊流動能減少，造成熱帶氣旋的擾動較難生成，因而TC總生成個數有明顯減少的情形。同時，在西伸年環境渦度減小的影響下，熱帶氣旋的發展強度有較弱的現象。副高西伸的行為也使得季風槽有向低緯地區移動的情形，並帶動TC生成位置向南發展，增加了熱帶氣旋侵襲菲律賓與南海地區的頻率，也使得颱風從南部侵襲台灣的機會增加。東退年時，西北太平洋熱帶氣旋的活動則呈現較為活躍的情形，在氣旋式環流西風距平的影響下，季風槽提供了西北太平洋地區較多的正壓轉換能量，使熱帶擾動的生成個數增多，且在渦度場增強的影響下，強氣旋的生成個數有增加的情形。此外，季風槽北移也使得熱帶氣旋生成位置偏北，使日本與東海地區熱帶氣旋的出現頻率有上升的趨勢，同時造成侵台颱風有較多的機會從北部西行及東部北轉影響台灣。 Western North Pacific subtropical high(WNPSH) is one of the most important systems in East Asia particularly in summer. The circulation anomaly caused by zonal variation of WNPSH affects the track of tropical cyclones. But the relationship between WNPSH and other tropical cyclone characteristics, such as population and intensity, are not well studied. The purpose of this study is to find out the effect of zonal variation of WNPSH on tropical cyclone climatology characteristics, for example, the population and intensity of tropical cyclones. In WNPSH westward (eastward) year, anticyclonic (cyclonic) circulation anomaly occurred in western Pacific. The energy due to barotropic conversion from mean flow is suppressed (enhanced) by easterly (westerly) anomaly, reduced (increased) the amount of eddy kinetic energy in western Pacific. The results show significant decreasing (increasing) of tropical cyclone population caused by change of eddy kinetic energy in western Pacific. And the intensity of tropical cyclone weakened (strengthened) due to reduce (increase) of low-level vorticity in westward (eastward) year. On the other hand, the genesis location of tropical cyclone shifted southward (northward) through the meridional shift of monsoon trough, caused the increasing occurrence frequency of tropical cyclone in Philippines and South China Sea (Japan and East China sea). And also increase the probability of passage of typhoon through south (north and east) of Taiwan.
