GRE阅读背景材料：厄尔尼诺现象_GRE阅读

GRE阅读背景材料：厄尔尼诺现象

　　新gre阅读之厄尔尼诺。下面为大家搜索整理的新gre阅读之厄尔尼诺，对于新gre 阅读考试，考生除了采取题海战术，其实更应该做的就是总结。今天带来的gre 阅读neirong希望对同学们的gre 考试有所帮助，下面一起来看看吧：

　　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 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 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, that 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.