西北太平洋暖季熱帶氣旋生成受年際變化與季內振盪影響之分析

本研究分析西北太平洋(Western north Pacific, WNP)2000年至2009年暖季（五月至九月）熱帶氣旋生成(tropical cyclone genesis, TCG)受到年際變化(interannual variation)的ENSO(El Nino-southernoscillation)、季內尺度(intraseasonal scale)的MJO(Madden and Julian oscillation)的影響。利用3-8天濾波之相對渦度找出479個熱帶擾動，其中有165個有發展成命名的TC (TCd)，其餘314個為未發展熱帶擾動(TCn)，定義熱帶氣旋生成機率[PTCG = TCd/(TCd+TCn)]，並輔以生成潛勢指標(genesis potential index,GPI)與合成分析，探討當中相關的機制。暖年、正常年與冷年的每百天生成機率分別為40%、33%、30%，機率差異主要來自TCn 數量在暖年較少、冷年較多。GPI 分析顯示WNP 季風槽在暖年（冷年）受西風距平（東風距平）而增強東伸（減弱西退）為最大的變化；擾動中心合成分析，TCd 組比TCn組有更好的發展條件，但冷年的TCd有最高的GPI值（來自最高平均相對渦度與平均緯度），反映出冷年時WNP 低緯度洋面背景渦度較低、擾動發展要較高自身強度及較高行星渦度幫助的特徵。MJO對流活躍期比對流不活躍期有利於颱風生成（PTCG為41%比30%），但總擾動數近似相等（每百天32與31 個）；大尺度850hPa相對渦度與700hPa相對溼度距平在MJO中呈現南北對比，擾動中心合成結果與年際變化的擾動中心合成結果相似。結合年際變化與MJO，當WNP大尺度低頻背景場為暖年或MJO對流活躍期就能將PTCG提升至40%以上。冷年MJO對流不活躍期時季風槽近乎消失，PTCG只有23%，結果顯示MJO 期在冷年背景下對TCd數量及PTCG有顯著對比，在暖年背景下則較不顯著。

關鍵字

熱帶氣旋生成；有發展擾動；未發展擾動；熱帶氣旋生成機率；合成分析

並列摘要

In this research, 165 developed tropical disturbances (TCd) and 314 non-developed tropical disturbances (TCn) and genesis potential index (GPI) are used to study how El Nino-Southern Oscillation (ENSO) and Madden-Julian oscillation (MJO) affect Western north Pacific (WNP) tropical cyclone genesis (TCG) during warm seasons (May to September) from 2000 to 2009 from aspect of tropical cyclone genesis probability [PTCG, TCd/(TCd+TCn)]. After normalized to per 100 days, PTCG in warm years, normal years and cold years are 40%, 33% and 30%, respectively. More (less) TCn in cold (warm) years caused different PTCG. GPI analysis showed that eastward extended (westward retreated) monsoon trough in warm (cold) years due to westerly anomaly (easterly anomaly) over WNP were the most significant change. Composite from disturbance centers showed TCd groups had better conditions than TCn groups. TCd in cold years also had highest GPI due to highest mean relative vorticity and mean latitude. That means disturbances need higher strength and higher planetary vorticity due to lower background vorticity over WNP in cold years. MJO convection active phase is more favorable for TCG than MJO convection inactive phase (PTCG 41% V.S. 30%), but total number of disturbances per 100 days remains nearly unchanged (32 V.S. 31). MJO composite results are similar to ENSO results, except large scale vorticity and humidity anomaly showed northsouth reversed change. Combine ENSO and MJO together, results suggested that PTCG would up to 40% if the background of WNP is warm years or MJO convection active phase. TCd numbers and PTCG contrast between MJO phases under cold year condition is more clear than under warm year condition.

並列關鍵字

Tropical cyclone Genesis ； ENSO ； MJO ； Developed and Nondeveloped disturbances ； Probability of TCG ； Composite analysis

國際替代計量

西北太平洋暖季熱帶氣旋生成受年際變化與季內振盪影響之分析

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