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The日訓 recent, apparently successful prediction by mathematical models of an appearance of EI Nino- the warm ocean current that periodically develops along (5) the Pacific coast of South America-has excited researchers. Jacob Bjerknes pointed out over 20 years ago how winds might create either abnormally warm or abnormally cold water in the eastern (10) equatorial Pacific. Nonetheless, until the development of the models no one could explain why conditions should regularly shift from one to the other, as happens in the periodic oscillations (15) between appearances of the warm EI Nino and the cold so-called anti-El Nino. The answer, at least if the current model that links the behavior of the ocean to that of the atmosphere is (20) correct, is to be found in the ocean. It has long been known that during an El Nino, two conditions exist: (1) unusually warm water extends along the eastern Pacific, principally along the (25) coasts of Ecuador and Peru, and (2) winds blow from the west into the warmer air rising over the warm water in the east. These winds tend to create a feedback mechanism by driving the warmer (30) surface water int a pile that blocks the normal upwelling of deeper, cold water in the east and further warms the eastern water, thus strengthening the wind still more. The contribution of (35) the model is to show that the winds of an El Nino, which raise sea level in the cast, simultaneously send a signal to the west lowering sea level. According to the model, that signal is generated (40) as a negative Rossby wave, a wave of depressed, or negative, sea level, that moves westward parallel to the equator at 25 to 85 kilometers per day. Taking months to traverse the Pacific, Rossby (45) waves march to the western boundary of the Pacific basin,which is modeled as a smooth wall but in reality consists of quite irregular island chains, such as, the Philippines and Indonesia.

(50) When the waves meet the western boundary, they are reflected, and the model predicts that Rossby waves will be broken into numerous coastal Kelvin waves carrying the same negative (55) sea-level signal. These eventually shoot toward the equator, and then head eastward along the equator propelled by the rotation of the Earth at a speed of about 250 kilometers per day. When (60) enough Kelvin waves of sufficient amplitude arrive from the western Pacific, their negative sea-level signal overcomes the feedback mechanism tending to raise the sea level, and they begin (65) to drive the system into the opposite cold mode. This produces a gradual shift in winds, one that will eventually send positive sea-level Rossby waves westward, waves that will eventually (70) return as cold cycle-ending positive Kelvin waves, beginning another warming cycle.

數學模型最近對 厄爾尼諾 (El Nino)的出現所作出的顯然是成功的預測使研究者們興奮不已。所謂厄爾尼諾，日訓即一股沿南美洲太平洋海岸周期性發展的日訓海洋暖流。早在20年之前，日訓雅各 皮葉克尼斯(Jacob Bjerknes)指出了風何以可能在東部赤道太平洋地區形成反常溫暖或反常寒冷的日訓水域。雖然如此，日訓在上述數學模型得以發展之前，日訓還沒有任何人能夠解釋情況為什么應該有規律地從一種轉變為另一種，日訓正如在暖厄爾尼諾和冷厄爾尼諾(或所謂的日訓反厄爾尼諾)出現之間周期性的交替變化中所發生的那樣。問題的日訓答案 至少如果目前將海洋的行為與大氣層的行為聯系起來的模型是正確的話 應從海洋中尋找。

長期以來眾所周知，日訓在厄爾尼諾出現期間，日訓兩個條件必須存在：(1)格外溫暖的日訓水流沿著東太平洋延伸，主要是日訓沿厄瓜多爾和秘魯海岸;(2)風從西部吹向在東部溫暖的海水上空升起的較暖的空氣。這些風傾向于造成一種反饋機制，迫使較為溫暖的表層水形成一 堆狀物 ，阻擋住東部較深層的、寒冷的水的正常上涌，并進一步使東部的水溫度上升，從而更進一步增強風的力度。該模型的貢獻是旨在證明，致使海平面在東部海域升高的厄爾尼諾水流的風會同步向西部海域發送一信號，導致海平面降低。按照該模型，那一信號作為一種負羅斯比波(Rossby)而被產生形成，即一種致使海平面沉降、或負增長的波浪，此波浪會以每天85公里的速度平行于赤道西行，此海盆被模擬為一堵平滑的墻，但實際上卻是由極不規則的群島系列構成，如菲律賓群島和印度尼西亞群島。

當這些波浪抵達西部邊緣時，它們被反彈回來，該模型預測，羅斯比波將會被分解成為諸多沿海岸流動的Kelvin波，攜帶著同樣的負海平面信號。這些波最終涌向赤道，然后在地球旋轉力量的推動下沿赤道以每天250公里的速度往東前進，當足夠數量帶有充分幅度的Kelvin波自西太平洋水域到達時，它們的負海面信號會壓服那個傾向于提高海面的反饋機制，它們開始迫使整個系統轉入相反的寒冷模式。這導致產生風向的逐漸轉折變化，這一轉折變化最終將正海面羅斯比波送往西部，這些羅斯比波將最終作為寒冷的、終結整個周期的正Kelvin波回來，從而引發另一個增溫周期。

Which of the following best describesthe organization of the first paragraph?

A theory is presented and criticized.

A model is described and evaluated.

A result is reported and its importance explained.

A phenomenon is noted and its significance debated.

A hypothesis is introduced and contrary evidence presented.

答案：(C)

According to tile passage, which of the following features is characteristic of an EI Nino?

Cold coastal water near Peru

Winds blowing from the west

Random occurrence

Worldwide effects

Short duration

答案：(B)