Tropical Cyclone- and Monsoon-Induced Rainfall Variability in Taiwan
Tropical Cyclone- and Monsoon-Induced Rainfall Variability in Taiwan
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DOI：
10.1175/2010jcli3355.1
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发表时间：
2010-08-01
影响因子：
4.9
通讯作者：
Shih, Ching-Feng
中科院分区：
文献类型：
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作者：
Chen, Jau-Ming;Li, Tim;Shih, Ching-Feng
摘要本研究探讨1950-2002年期间台湾热带气旋（TC）与季风（P）所引发降雨的年际变化。为了探讨热带气旋与季风的相对影响，本研究将台湾地区的雨量分为热带气旋雨量（P（TC））与季性季风雨量（P（SM））。前者是TC通过台湾引起的，后者是大尺度季风环流引起的，从气候上看，P（TC）和P（SM）分别占台湾总降雨量的47.5%和52.5%，贡献相当。在年际时间尺度上，P（TC）和P（SM）异常倾向于反向变化。台湾地区的降水变化主要有两种类型：P（TC）增强P（SM）抑制型（T+S-）和P（TC）抑制P（SM）增强型（T-S+）。T+S型以低层异常气旋及台湾东南方向上升运动增强为特征。这种有利的环境条件导致该地区更多的TC形成。TC进一步被平均东南风流转向台湾，以增加P（TC）（T+）。由于台湾位于异常气旋的西边界，异常的东北风水汽通量阻碍了南海向台湾的水汽供应，导致P（SM）（S-）降低。T-S+型与台湾上空的异常气旋同时出现。它的中心增强上升运动和水汽通量从南海进入台湾，产生增加P（SM）（S+）。同时，台湾东南部出现较弱的相对涡度异常，抑制了该地区的TC生成。平均偏南转向流倾向于将更多的TC推向日本和北太平洋，导致台湾（T-）的TC频率和P（TC）降低。本方法通过将降雨分为TC和季风引起的降雨子分量，而不是仅仅着眼于总降雨，为研究和预测年际降雨变率提供了一个新的视角。结果显示，台湾地区总降雨量有两种显著增加的方式（T+S-和T-S+），但只有一种显著减少的方式（T-S-）。基于两种降水指数的环流异常组合比基于总降水指数的环流异常组合具有更显著、更连贯的动力学型。
This study investigates the interannual variability of tropical cyclone (TC)- and monsoon-induced rainfall (P) in Taiwan during July September for the period 1950-2002. To examine the relative effects of TCs and monsoons, local rainfall in Taiwan is separated into two subcomponents: TC rainfall (P(TC)) and seasonal monsoon rainfall (P(SM)). The former is induced by TC passage across Taiwan, while the later is caused by large-scale monsoon circulation.Climatologically, P(TC) and P(SM) accounts for 47.5% and 52.5% of total rainfall in Taiwan, respectively, showing a comparable contribution. On an interannual time scale, P(TC) and P(SM) anomalies tend to vary inversely. Two dominant rainfall variability types are found in Taiwan: enhanced P(TC) but suppressed P(SM) (T+S-) and suppressed P(TC) but enhanced P(SM) (T-S+). The T+S- type features a low-level anomalous cyclone and enhanced upward motion southeast of Taiwan. This favorable environmental condition leads to more TC formation in the region. TCs are further steered by mean southeasterly flows toward Taiwan to increase P(TC) (T+). As Taiwan is located in the western boundary of the anomalous cyclone, anomalous northeasterly water vapor fluxes hinder moisture supplies from the South China Sea into Taiwan, resulting in decreased P(SM) (S-). The T-S+ type concurs with an anomalous cyclone over Taiwan. Its center enhances upward motion and moisture fluxes from the South China Sea into Taiwan, yielding increased P(SM) (S+). Meanwhile, weak relative vorticity anomalies occur to the southeast of Taiwan, suppressing TC formation in the region. Mean southerly steering flows tend to drive more TCs toward Japan and the North Pacific, resulting in decreased TC frequency and P(TC) in Taiwan (T-).The present approach provides a new perspective for studying and predicting interannual rainfall variability via the separation of rainfall into TC- and monsoon-induced rainfall subcomponents, rather than looking solely at total rainfall. The result shows that there are two ways to significantly increase total rainfall in Taiwan (T+S- and T-S+), but there is only one way to decrease it (T-S-). The composites of circulation anomalies based on two rainfall indexes have more significant and coherent dynamic patterns than those sorted based on the total rainfall index.