8．The recent，apparently successful，prediction by mathematical models of an appearance of El Nino-the warm ocean How that periodically develops along the Pacific coast of South America has excited researchers．Jacob Bjerknes pointed out years ago how winds might create either abnormally warm or abnormally cold water in the eastern equatorial （赤道附近的） Pacific．Nevertheless，before the creation of the models，no one could explain why conditions should regularly change between appearances of the warm El Nino and the 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 and winds blow from the west into the warmer air rising over the warm water in the east．The contribution of the model is to show that the winds of an El Nino，which raise sea level in the east，send a signal to the west lowering sea level at the same time．According to the model，that signal is created as a negative （負(fù)的） Rossby wave，a wave of lower sea level，that moves westward parallel to the equator at 25 to 85 kilometers per day．Taking months to move across the Pacific，Rossby waves march to the western boundary of the Pacific basin，which is modeled as a smootli wall but in reality consists of quite irregular island chains．
When the waves meet the western boundary，they are reflected，and the model predicts that Rossby waves will be broken into many coastal Kelvin waves carrying the same negative sea-level signal．These eventually shoot toward the equator，and then head eastward along the equator drove by the earth at a．speed of about．250 kilometers per day．When enough Kelvin waves of adequate amplitude （振幅） arrive from the western Pacific，their negative sea-level signal overcomes the feedback mechanism，raising the sea level，and they begin to drive the system into the opposite cold mode．This produces a gradual change 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．
67．What is the passage mainly about？D
A．How Rossby waves are found．
B．Where El Nino is formed．
C．What the models predict．
D．How the models work．
68．Where does El Nino often appear？B
A．Along the western coast of the USA．
B．In the Pacific in the south，of the equator．
C．In the Pacific in the north of the equator．
D．Along the southern coast of South America．
69．What is right according to the passage？A
A．Rossby waves and Kelvin waves move in opposite directions along the equator．
B．People could explain El Nino before the creation of the mathematical models．
C．Adequate sea-level waves can produce westward positive cold cycle．
D．The speed of Rossby waves is faster than that of Kelvin waves．
70．What does the underlined word"waves"in Paragraph 3 refer to？D
A．Kelvin waves． B．Sea-level signals．C．Coastal waves． D．Rossby waves．
分析 本文主要講述了厄爾尼諾現(xiàn)象的情況，科學(xué)家創(chuàng)立的數(shù)學(xué)模型較為成功的解釋了其發(fā)展，以及在其過程中的可能的各種影響因素．
解答 67．D 主旨概括題．根據(jù)文章內(nèi)容，主要講述了厄爾尼諾現(xiàn)象的形成，發(fā)展和可能會(huì)引起的各種情況，再結(jié)合選項(xiàng)，故答案為D．
68．B 細(xì)節(jié)理解題．根據(jù)文章第一段an appearance of El Nino-the warm ocean How that periodically develops along the Pacific coast of South America has excited researchers．可知，厄爾尼諾經(jīng)常發(fā)生在赤道周邊的南太平洋海域，結(jié)合選項(xiàng)，故答案為B．
69．A 細(xì)節(jié)理解題．根據(jù)文章最后一段的內(nèi)容This produces a gradual change 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．可知，Rossby waves 和 Kelvin waves 二條洋流的方向是相反的，故答案為A．
70．D 詞義猜測題． 根據(jù)劃線單詞的上一段最后一句話Taking months to move across the Pacific，Rossby waves march to the western boundary of the Pacific basin…該句提到了Rossby waves，劃線單詞的所在段落起到承上啟下的作用，聯(lián)系前后句，可知?jiǎng)澗�單詞指代的是Rossby waves，故答案為D．
點(diǎn)評 本文是人文地理類閱讀理解．做這類題材閱讀理解時(shí)要求考生對文章通讀一遍，做題時(shí)結(jié)合原文和題目有針對性的找出相關(guān)語句進(jìn)行仔細(xì)分析，結(jié)合選項(xiàng)選出正確答案．推理判斷題也是要在抓住關(guān)鍵句子的基礎(chǔ)上合理的分析才能得出正確答案，切忌胡亂猜測，一定要做到有理有據(jù)．
