TPO43阅读文本及答案解析

3.El Nirio

The cold Humboldt Current of the Pacific Ocean flows toward theequator along the coasts of Ecuador and Peru in South America. When the currentapproaches the equator, the westward-flowing trade winds cause nutrient-richcold water along the coast to rise from deeper depths to more shallow ones.This upwelling of water has economic repercussions. Fishing, especially foranchovies, is a major local industry.

Every year during the months of December and January, a weak, warmcountercurrent replaces the normally cold coastal waters. Without the upwellingof nutrients from below to feed the fish, fishing comes to a standstill.Fishers in this region have known the phenomenon for hundreds of years. Infact, this is the time of year they traditionally set aside to tend to theirequipment and await the return of cold water. The residents of the region havegiven this phenomenon the name of El  Nifio，,which is Spanish for "the child," because it occurs atabout the time of the celebration of birth of the Christ child.

While the warm-water countercurrent usually lasts for two months orless, there are occasions when the disruption to the normal flow lasts for manymonths. In these situations, water temperatures are raised not just along thecoast, but for thousands of kilometers offshore. Over the last few decades, theterm El  Nifio has come to be used todescribe these exceptionally strong episodes and not the annual event. Duringthe past 60 years, at least ten El Nifios have been observed Not only do ElNiftos affect the temperature of the equatorial Pacific, but the strongest ofthem impact global weather.

The processes that interact to produce an El  Nifio involve conditions all across thePacific, not just in the waters off South America. Over 60 years ago, SirGilbert Walker, a British scientist, discovered a connection between surfacepressure readings at weather stations on the eastern and western sides of thePacific. He noted that a rise in atmospheric pressure in the eastern Pacific isusually accompanied by a fall in pressure in the western Pacific and viceversa. He called this seesaw pattern the Southern Oscillation. It was laterrealized that there is a close link between El Nino and the SouthernOscillation. In fact, the link between the two is so great that they are oftenreferred to jointly as ENSO (El Nino-Southern Oscillation).

During a typical year, the eastern Pacific has a higher pressurethan the western Pacific does. This east-to-west pressure gradient enhances thetrade winds over the equatorial waters. This results in a warm surface currentthat moves east to west at the equator. The western Pacific develops a thick,warm layer of water while the eastern Pacific has the cold Humboldt Currentenhanced by upwelling. However, in other years the Southern Oscillation, forunknown reasons, swings in the opposite direction, dramatically changing theusual conditions described above, with pressure increasing in the western.Pacific and decreasing in the eastern Pacific. This change in the pressuregradient causes the trade winds to weaken or, in some cases, to reverse. Thisthen causes the warm water in the western Pacific to flow eastward, increasingsea-surface temperatures in the central and eastern Pacific. The eastward shiftsignals the beginning of an El  Nifio.

Scientists try to document as many past El Nino events as possibleby piecing together bits of historical evidence, such as sea-surfacetemperature records, daily observations of atmospheric pressure and rainfall,fisheries’ records from South America, and the writings of Spanish colonistsdating back to the fifteenth century. From such historical evidence we knowthat El Nirtos have occurred as far back as records go. ■ It would seem that they are becoming more frequent. ■Records indicate that during the sixteenth century, an El Ninooccurred on average every six years. ■ Evidencegathered over the past few decades indicates that El Ninos are now occurring onaverage a little over every two years. ■Even morealarming is the fact that they appear to be getting stronger. The 1997-1998 El  Nifio brought copious and damaging rainfall tothe southern United States, from California to Florida. Snowstorms in thenortheast portion of the United States were more frequent and intense than inmost years.

The word "approaches" in the passage is closest in meaningto

O nears

O crosses

O travels along

O leaves

2. According to paragraph 1, what happens when the Humboldt Currentinteracts with westward flowing trade winds?

O Anchovies from southern waters are carried northward.

O Cold water from lower depths is brought closer to the surface.

O The Humboldt Current stops flowing toward the equator.

O The Humboldt Current begins to flow closer to the coasts ofEcuador and Peru.

3.Which of the following questions about the El Nino phenomenon isNOT answered in paragraph 2 ?

O Why is the El Niflo phenomenon called El Nirto?

O How do fishers spend their time during the El Nifio season?

O How do coastal fish obtain enough nutrients during the El Nifioseason?

O Is the temperature of coastal waters different during the El Nifloseason than it is the rest of the year?

4. The word "exceptionally"，in thepassage is closest in meaning to

O obviously

O unusually

O relatively

O occasionally

5. Paragraph 3 supports which of the following statements about ElNinos, as that term is now used?

O El Nifios can originate in areas other than the Pacific Ocean.

O El Nifios can arise when warm currents last for two months orless.

O El Nifios affect water temperatures long distances from the SouthAmerican coast.

O Multiple El Niflos can arise within a single calendar year.

6. The phrase "is usually accompanied by” in the passage isclosest in meaning to

O usually develops before

O usually occurs together with

O is usually indicated by

O is usually caused by

7. The word "jointly" in the passage is closest in meaningto

O together

O therefore

O rightfully

O simply

8. According to paragraph 4, what did Sir Gilbert Walker discover?

O There is a close link between El Nifio and the Southern Oscillation.

O Surface pressure readings all across the Pacific first rise andthen fall before an El Nifio occurs.

O Surface pressure on one side of the Pacific tends to fall whenpressure rises on the opposite side.

O The formation of an El Nirto depends on conditions all across thePacific, not just in the waters off of South America.

9. According to paragraph 5, what is the end result of theeast-to-west pressure gradient in the eastern Pacific during a typical year?

O The formation of a thick, warm layer of water in the westernPacific

O The reversal of the pressure gradient to west-to-east by the endof the year

O A change in the direction of the Southern Oscillation

O The eastward flow of warm water from the western Pacific

10. According to paragraph 5, all of the following changes occur inthe Pacific before an El Nifio begins EXCEPT:

O Pressure increases in the western Pacific and decreases in theeastern Pacific.

O The trade winds decrease in intensity or reverse in the direction.

O Surface temperatures increase in the central and eastern Pacific.

O Ocean currents speed up as they move eastward.

11. What can be inferred about El Ninos from the historical evidencementioned in paragraph 6 ?

O They have often brought damaging weather to parts of the UnitedStates.

O They have been occurring since at least the fifteenth century.

O They occurred less frequently in the sixteenth century than in thefifteenth.

O They have had stronger weather effects on the United States inrecent decades than on other locations.

12. Why does the author include the information that in 1997-1998"Snowstorms in the northeast portion of the United States were morefrequent and intense than in most years"?

O To provide evidence supporting the claim that El Nifios aregetting stronger

O To explain why the southern United States experienced copious anddamaging rainfall in 1997-1998

O To show that traditional methods are not adequate for documentingthe effects of El Niftos

O To identify a consequence of the fact that El Niflos are nowoccurring a little over once every two years

13. Look at the four squares [■] thatindicate where the following sentence could be added to the passage.

There is clear support for this view in the available documents.

Where would the sentence best fit? Click on a square [■] to add the sentence to the passage.

14. Directions: An introductory sentence for a brief summary of thepassage is provided below. Complete the summary by selecting the THREE answerchoices that express the most important ideas in the passage. Some sentences donot belong in the summary because they express ideas that are not presented inthe passage or are minor ideas in the passage. This question is worth 2 points.

Drag your answer choices to the spaces where they belong To removean answer choice, click on it.

To review the passage, click VIEW TEXT

As it is currently used, the term El Nirio refers to a strong andlengthy disruption to the normal pattern of ocean currents, water temperatures,and winds in the Pacific.

Answer Choices

An El Nino typically begins when the Humboldt Current causesupwelling as it travels toward the equator along the coast of Peru and Ecuador.

El Nirlos are preceded by the reversal of the usual east-to- westpressure gradient in the Pacific, the weakening or reversal of the trade winds,and the movement of warm water eastward.

Comparisons of historical records with recent past events show thatEl Ninos are becoming more frequent and stronger.

In an El Nino, warm surface currents replace the Humboldt Currentfor many months, raising ocean temperatures far from the coast.

Scientists discovered the Southern Oscillation by takingsurface-pressure readings at weather stations on both sides of the Pacific.

In recent decades, El Nifios have begun to occur north of theequator and thereby affect weather conditions in the United States.

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