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  3. The recent, apparently successful prediction by mathematical models of an appearance of EI Nino—the warm ocean current that peri

The recent, apparently successful prediction by mathematical models of an appearance of EI Nino—the warm ocean current that peri

admin2020-12-14  71
问题     The recent, apparently successful prediction by mathematical models of an appearance of EI Nino—the warm ocean current that periodically develops along 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 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 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 correct, is to be found in the ocean.
    It has long been known that during an El Nino, two conditions exist: unusually warm water extends along the eastern Pacific, principally along the coasts of Ecuador and Peru, and 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 surface water into 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 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 as a negative Rossby wave, a wave of depressed, or negative, sea level, mat moves westward parallel to the equator at 25 to 85 kilometers per day. Taking months to traverse the Pacific, Rossby 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.
    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 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 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 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 return as cold cycle-ending positive Kelvin waves, beginning another warming cycle.
Which of the following, if true, would most seriously undermine the validity of the model El Nino that is presented in the passage?
选项 A、El Nino extends much farther along the coasts of Ecuador and Peru during some years.
B、The rising of cold water in the eastern Pacific depends on the local characters.
C、The variations in the time for Rossby waves to cross the Pacific rely on the wind power.
D、The Pacific irregular western coast hinders most Kelvin waves from heading eastward.
答案D
解析 细节题。根据第二段最后一句即花费数月时间穿越太平洋后，“罗斯比波波浪”来到太平洋盆地的西部边缘——该盆地被模拟成平坦的屏障，但实际上包含很不规则的岛屿群。可知，该模式依据的是太平洋盆地的西部边缘是平坦的。而如果不是这样，则该模式就不正确。通读答案，D选项内容太平洋不规律规则的西部海岸阻碍了大多数开氏波浪流向东部和原文表述一致，所以答案选D。
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