2. 外语
  3. Before 1965 many scientists pictured the circulation of the ocean’s water mass as consisting of large, slow-moving currents, suc

Before 1965 many scientists pictured the circulation of the ocean’s water mass as consisting of large, slow-moving currents, suc

admin2014-12-26  33
问题     Before 1965 many scientists pictured the circulation of the ocean’s water mass as consisting of large, slow-moving currents, such as the Gulf Stream. That view, based on 100 years of observations made around the globe, produced only a rough approximation of the true circulation. But in the 1950’s and the 1960’s, researchers began to employ newly developed techniques and equipment, including subsurface floats that move with ocean currents and emit identification signals, and ocean current meters that record data for months at fixed locations in the ocean. These instruments disclosed an unexpected level of variability in the deep ocean. Rather than being characterized by smooth, large-scale currents that change seasonally(if at all), the seas are dominated by what oceanographers call mesoscale fields: fluctuating, energetic flows whose velocity can reach ten times the mean velocity of the major currents.
    Mesoscale phenomena—the oceanic analogue of weather systems—often extend to distances of 100 kilometers and persist for 100 days(weather systems generally extend about 1,000 kilometers and last 3 to 5 days in any given area). More than 90 percent of the kinetic energy of the entire ocean may be accounted for by mesoscale variability rather than by large scale currents. Mesoscale phenomena may, in fact, play a significant role in oceanic mixing, air-sea interactions, and occasional—but far-reaching—climatic events such as El Nino, the atmospheric-oceanic disturbance in the equatorial Pacific that affects global weather patterns.
    Unfortunately, it is not feasible to use conventional techniques to measure mesoscale fields. To measure them properly, monitoring equipment would have to be laid out on a grid at intervals of at most 50 kilometers, with sensors at each grid point lowered deep in the ocean and kept there for many months. Because using these techniques would be prohibitively expensive and time consuming, it was proposed in 1979 that tomography be adapted to measuring the physical properties of the ocean. In medical tomography X-rays map the human body’s density variations(and hence internal organs); the information from the X-rays, transmitted through the body along many different paths, is recombined to form three-dimensional images of the body’ s interior. It is primarily that this multiplicative increase in data obtained from the multipath transmission of signals that accounts for oceanographers’ attraction to tomography: it allows the measurement of vast areas with relatively few instruments. Researchers reasoned that low-frequency sound waves, because they are so well described mathematically and because even small perturbations in emitted sound waves can be detected, could be transmitted through the ocean over many different paths and that the properties of the ocean’s interior—its temperature, salinity, density, and speed of currents—could be deduced on the basis of how the ocean altered the signals. Their initial trials were highly successful, and ocean acoustic tomography was born.
Which of the following best describes the organization of the third paragraph of the passage?
选项 A、An argument is advanced, then refuted, and an alternative is suggested.
B、Opposing views are presented, elaborated, and then reconciled.
C、A problem is described, then a solution is discussed and its effectiveness is affirmed.
D、A theory is proposed, considered and then amended.
答案C
解析 推断题。文章第三段首先指出现在的问题用常规的技术无法实现紊流的测量，原因是运用这样的技术太过昂贵，而且耗时太长。于是给出解决问题的方法——采用X线断层摄影术，实际上X线断层摄影术在首次尝试中获得成功，也证实了这种技术的可行性，因此海洋声学X线断层摄影术便产生了。因此本段的结构是“先描述问题，然后讨论解决方案，最后肯定方案的有效性”，和选项C的表述一致，所以答案是C。
转载请注明原文地址:https://jikaoti.com/ti/HrOFFFFM
0

大学英语六级

相关试题推荐
随机试题
最新回复(0)