If we place a block in continuous, steadily flowing water, some periodic eddy currents will appear behind it. In my report, I would like to introduce a new way to explain how the periodical movement of eddy currents would help to triggering El Nino. According to my experiment, these eddy currents have a certain life cycle, and the eddy current give a force, which drag water form the area they just went by. It will cause water level became lowest for a period of time. These phenomena are also shown in the real data of “Sea Surface Height Anomaly”, it is a quiescence period, and then changes into the highest one it is interesting that highest one always follows by the starting of El Nino. Another important result from my experiment is that, in the same fluid, the frequency of eddy currents is controlled by 2 variables: Size of the block and velocity of the flow, From this result, then get the frequency of eddy current-occur every 3.2 years. It is just correspond with frequency of historical data the El Nino from the 70’s to the present.
本報告嘗試以南極繞極環流在南美洲南端產生週期性渦流脫離的現象來解釋聖嬰的發生根據水槽實驗的結果,水流在通過障礙物後渦流脫離瞬間,會形成一水位低的空區,之後在周圍的水大量湧入,水位突然升高,並有一段時間的振盪。另外,實驗結果也顯示,渦流形成和脫離頻率大致上和注水流速成正比,且和障礙物的大小成反比。根據此結果,對照實驗結果,我認為1993 年3-4 月,1996 年1-6 月及2001 年7-10 月三個「海平面高度異常」的最低值密集帶,此極可能是渦流脫離的時段。且對照「海平面高度異常」實際資料後,發現「海平面高度異常」的「最低值密集帶」後均伴隨水面「寧靜期」,接著就出現周圍暖水流大量湧入的「最高值密集帶」,此時南美洲東南側海水溫度驟增,接著馬上接續著聖嬰的到來。「海平面高度異常」分析的結果,指示渦流脫離的「最低值密集帶」和顯示著聖嬰到來的「最高密值密集帶」間約間隔半年左右。我們推算水的史托爾數約為1,以這個值代入實際南極繞極環流通過南美洲南端,得到渦流脫離的頻率約每3.2 年一次,和長期聖嬰發生的平均頻率非常接近。
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