本篇論文主要是利用經驗正交模分析法（Empirical Normal Mode Analysis；ENMA），分析實際觀測的月平均資料，試圖找出具有物理意義的時空一致性結構，並了解其影響範圍、因子及其時空的演變。
本文所使用的資料為美國國家環境預報中心重新分析資料（National Centers for Environmental Prediction/NCAR reanalysis），資料時間自1950年1月至2003年12月共計54年的月平均資料，水平解析度為2.5°（lat.）×5°（long.），分別範圍為60°S~60°N。分析所用資料包括溫度場（K）、重力位高度場（gpm）、比濕（kg/kg）、緯向風場（m/s）、流函數（m2/s）、速度位（m2/s）及垂直運動場（Pa/s）等七個變數場。其中除比濕場垂直空間層高度只到300hPa，採用1000、850、500及300hPa四層標準氣壓層外，其餘六個變數場垂直空間層則使用1000、850、500及250hPa四層標準氣壓層。
本文所使用的方法是李在2004年發展出的經驗正交模分析(ENMA)，此方法結合MSSA的線性特徵與POP(Principal Oscillation Pattern)的波動特徵，從觀測資料中獲得動力系統的正交模震盪，並計算其波譜值與確認波動的傳播和變化的分布。
在熱帶地區最明顯的氣候訊號就是聖嬰現象 (ENSO)，週期大約2至7年，其源地和發展機制至今仍是一個謎，因此本文希望藉由ENMA的分析方法，進一步去探討各種氣象因子所造成的影響，分析結果顯示ENSO現象是由兩個明顯的波動所組成，一個波的週期約是59個月，起源於赤道中太平洋並且向東傳播。另一個波是有43個月的週期，產生在南美洲沿岸，有向西傳遞的趨勢。

ENMA

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