利用HHT之EMD方法分析SSM/I資料估算之客觀指數與颱風強度年際變化關係

Using the Empirical Mode Decomposition of Hilbert-Huang Transform to analyse the relationship between the annual typhoon intensity and Objective Potential Index estimated by SSM/I data.

藍嘉偉(Chia-Wei Lan)

指導教授 ： 劉振榮

國立中央大學/地球科學學院/大氣物理研究所/碩士(2006年)

摘要

台灣每年所遭受的天然災害中最嚴重的就為颱風的侵襲，大多數颱風帶來的災害不是風所造成，而是颱風所夾帶的大量降雨引發土石流及水災。儘管政府每年投資大筆經費進行颱風的各項研究與天然災害的預防，但極少數的研究是針對颱風年際強度問題來探討，因此本研究將針對南海與西北太平洋地區颱風年際強度變化來加以研究並找出其與海洋間的相互關係。
本研究利用Huang and Coauthors（1998）所提出的希伯特-黃轉換中的經驗模態分解法來分析Liu, Liu, and Kuo（2002）提出的海氣參數及估算出來的客觀指數，首先針對兼具颱風強度與生命期的颱風破壞潛勢（HDP）進行經驗模態分解法分析，接著針對能夠代表海氣交互能量的各海氣參數與客觀指數進行經驗模態分解法分析，最後建立客觀指數經過經驗模態分解法分析後的各內建模態函數（IMF）與HDP的線性相關性。
結果顯示在南海地區的颱風強度年際變化均值趨勢與西北太平洋地區是不相同的，但西北太平洋的年際變化均值趨勢則與Emanuel（2005）相同。而各海氣參數與客觀指數的經驗模態分解法分析後，具有明顯的年變化週期，其餘的內建模態函數則尚未發現其與大氣間的相關性。不管在南海或西北太平洋地區，皆可發現從前年的十月至當年的三至四月中，客觀指數的第四個內建模態函數與當年的颶風破壞潛勢有相對於其他月分與其他內建模態函數來的高，在西北太平洋地區最高的R^2值甚至可以高達0.7左右。且OPI的第四個Mode與Southern Oscillation Index（SOI）有些許反相位的關係，所以當SOI為負值（聖嬰事件）時OPI則有較大的值，表示海洋提供較多能量至大氣中以致於颱風發展較強，因而造成較大的HDP值。
在未來累積一定資料量後，此研究的線性關係結果可以做為未來估算當年颱風強度的一個依據或指標。

關鍵字

HHT/EMD ； 客觀潛力指數 ； SSM/I

並列摘要

Taiwan was attacked by many typhoons every year before. Most damages were not caused by gust wind. Instead, they were caused by the landslides and flood which were leaded by heavy rain. Although our government invested much money in studies about typhoon and disaster protection, there were few scientists aimed at studying annual typhoon intensity. Therefore, our study is about annual typhoon intensity. Meanwhile, we want to find out the relationship between annual typhoon intensity and the air-sea interaction in South China Sea and Western North Pacific Ocean.
In our study, we use Empirical Mode Decomposition (EMD) which is one part of Hilbert-Huang Transform (HHT) suggested by Huang and Coauthors in 1998, to analyze Objective Potential Index (OPI) suggested by Liu et al. in 2002. At first, we analyze the Hurricane Destruction Potential (HDP) which combines the life of typhoon and typhoon intensity by using EMD. Secondly, EMD is also used to analyze the air-sea parameters and OPI. At last, we establish the linear correlation between each Intrinsic Mode Function (IMF) of OPI and HDP.
The results show the mean trend of annual typhoon intensity in Western North Pacific Ocean is the same as the mean trend suggested by Emanuel in 2005, but in South China Sea, we have the contrary results. After each parameter and OPI were separated by using EMD, we can see the annual cycle observably, but it is not easy to understand the atmospheric properties of other IMFs. Whether in South China Sea or in Pacific Ocean region, we could find higher R^2 between OPI in IMF4 and HDP. And R^2 was higher in the months from the last October to that April. Even the value in Western North Pacific Ocean could be as high as more than 0.7. Moreover, we find that the southern oscillation index (SOI) show an slightly antiphase with OPI in IMF4. Therefore, the negative SOI value shows that higher OPI value, and means that ocean supplies more energy into atmosphere and results in stronger typhoons.
In the future, if more data is recorded, the results of this study could be an index to estimate typhoon intensity that year.

並列關鍵字

Objective Potential Index ； HHT/EMD ； SSM/I

參考文獻

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