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  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

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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.
The author mentions EL Nino primarily in order to emphasize______.
选项 A、the difficulty of measuring the ocean’ s large scale currents
B、the variability of mesoscale phenomena
C、the brief duration of weather patterns
D、the possible impact of mesoscale fields on weather conditions
答案D
解析 细节题。根据“El Nino”定位到文章第二段Mesoscale phenomena may，infact，play a significant role in oceanic mixing，air-sea interactions，and occasional--butfar—reaching--climatic events such as El Nino．the atmospheric-oceanic disturbance inthe equatorial Pacific that affects global weather patterns．“事实上，紊流现象可能在空气和海洋的互相影响中扮演重要角色，也在一些偶尔发生但却影响深远的气候现象中扮演重要角色，比如厄尔尼诺就是这样一种在赤道太平洋地区通过大气和海洋的相互干扰来影响全球气候的现象。”可知作者提到厄尔尼诺主要是为了强调紊流现象对于气象造成的影响。和选项D表述一致，所以D为正确答案。
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