摘要
在快頻年循環(fast annual cycles)與天氣鐘(weather clocks)等創新概念下，從四月初到八月亞洲夏季季風的演進得到新的詮釋。利用在北半球夏季六個特徵區域濾波後所得的平均長波外逸輻射(OLR)，確認了一系列相位鎖結(phase-lock)在時間上的天氣事件。研究顯示在上述時段內的快頻年循環有著明顯的雙重結構(bimodal structure) 。據此，17年的資料被分類為正常年(normal (NM) onset years)與延遲年(delayed (DL) onset years)兩組。在正常年中，五月中旬的前汛期(pre-flood period)獨立存在，而在延遲年中，於同時期南海處於無雨的狀態。延遲的南海肇始一直到六月中旬才發生，幾乎與整個季風槽(monsoon trough)的對流活動同時。在兩組不同的年中，太平洋副熱帶高壓(subtropical high)的行為明顯相異。
造成快頻年循環延遲的原因據推測與四月初赤道印度洋東經60度到80度海平面溫度(SST)升高的時間有密切關連。高的海平面溫度引發了由赤道印度洋北上的對流系統。但此時孟加拉灣的邊界狀況尚未成熟，因而於延遲年中，提前於四月初在赤道印度洋的海溫升高並無法引發南海的肇始。

ABSTRACT
The evolution of Asian Summer Monsoon from early April to August is described under the innovative ideas of fast annual cycles and weather clocks. By using mean filtered OLR over six key areas during the boreal summer, a series of weather events that are phase-locked in time and Julian calendar have been identified. It is found that the fast annual cycles of above period manifest strong bimodal structure, the 17-year data can be divided into NM (normal onset) and DL (delayed onset) years. Only in NM years an independent pre-flood period in mid-May can be observed. In DL years, the SCS region experiences a dry condition on the same period, and the delayed onset will not happen until middle June, almost spontaneously with the convective surge of the whole monsoon trough. The subtropical high clearly behaves differently between these two modes.
Causes of the delayed fast annual cycle is speculated closely related to the timing of warm SST over the equatorial Indian Ocean between 60~80E one month earlier, the warm SST induces convective system northward from tropical Indian Ocean. However, the thermal capacity over the Bay of Bengal seems to be less then ready. The pre-mature warming of a hot patch in the equatorial Indian Ocean early April has cost a failed attempt to trigger SCS onset in the DL years.

TABLE OF CONTENTS
Page
ACKNOWLEDGEMENTS誌謝iii
ABSTRACTiv
LIST OF FIGURESvi
LIST OF TABLESX
SECTION 1: BASIC IDEAS1
SECTION 2: FAST ANNUAL CYCLE AND WEATHER CLOCKS4
SECTION 3: BIMODALITY OF FAST ANNUAL CYCLES8
SECTION 4: COMPOSITE OF TWIN FAST ANNUAL CYCLES11
SECTION 5: EOF ANALYSIS13
SECTION 6: CAUSES AND IMPACTS OF DELAYED ANNUAL CYCLE15
SECTION 7: CONCLUSION AND DISCUSSION18
FIGURES20
TABLES50
APPENDIX A: DATA53
APPENDIX B: FILTER54
REFERENCE55

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