2012年4月22日托福阅读文章来自2010年3月6日的北美考试，无忧托福网为大家带来北京新东方托福研发组葛旭老师对本次托福考试阅读文章的复现。
【2010.3.6NA】
TOPIC 厄尔尼诺
>>考生回忆
厄尔尼诺的起因，形成和影响。大概讲道冷暖洋流的运动，对经济，渔业，气候的影响。
厄尔尼诺定义
El Nino is defined by prolonged differences in Pacific Ocean surface temperatures when compared with the average value. The accepted definition is a warming or cooling of at least 0.5 °C (0.9 °F) averaged over the east-central tropical Pacific Ocean. Typically, this anomaly happens at irregular intervals of 3-7 years and lasts nine months to two years. The average period length is 5 years. When this warming or cooling occurs for only seven to nine months, it is classified as El Nino/La Nina "conditions"; when it occurs for more than that period, it is classified as El Nino/La Nina "episodes".
The first signs of an El Nino are:
·Rise in surface pressure over the Indian Ocean, Indonesia, and Australia
·Fall in air pressure over Tahiti and the rest of the central and eastern Pacific Ocean
·Trade winds in the south Pacific weaken or head east
·Warm air rises near Peru, causing rain in the northern Peruvian deserts
·Warm water spreads from the west Pacific and the Indian Ocean to the east Pacific. It takes the rain with it, causing extensive drought in the western Pacific and rainfall in the normally dry eastern Pacific.
El Nino's warm rush of nutrient-poor tropical water, heated by its eastward passage in the Equatorial Current, replaces the cold, nutrient-rich surface water of the Humboldt Current. When El Nino conditions last for many months, extensive ocean warming and the reduction in Easterly Trade winds limits upwelling of cold nutrient-rich deep water and its economic impact to local fishing for an international market can be serious.
对渔业的影响
The Effects of El Nino on Marine Life
Overview
Fishermen along the coasts of Peru and Ecuador have observed the phenomenon of El Nino for centuries. They noticed a warm ocean current that flowed along their coast every year during the months of December and January and during this interval fish would be less abundant. However, every few years fish in these coastal waters would virtually vanish causing a halt to their fishing businesses. The fisherman used the term El Nino, which is Spanish for the little boy, because of its tendency to arrive around Christmas time. It has since been used to describe the more severe intervals that appear every 2-7 years, with varying intensity.
Once thought to affect only a narrow strip of water off Peru, El Nino was soon recognized as a large-scale oceanic warming that affects most of the Tropical Pacific. It then became clear that El Nino was normally accompanied by a change in atmospheric circulation called the Southern Oscillation, and that the Peruvian event was just the first noticeable occurrence of an event of much wider significance. Together, the effects from El Nino-Southern Oscillation (ENSO) have an impact on fisheries and marine life, as well as climatic conditions around the globe.
The key element of the El Nino phenomenon is the interaction between the sea surface and winds (the ocean-atmosphere system). Normally, the trade winds blow east to west across the Tropical Pacific. These winds push the top layer of water along with it and pile up warm surface water in the western Pacific. This results in a sea surface that is about 0.5 m higher at Indonesia than at Ecuador and a sea surface temperature that is about 8° C higher in the west. As the surface water moves away from the coast of South America, colder, nutrient-rich water comes up from below to replace it, a phenomenon known as upwelling. As the trade winds continue to blow westward, the thermocline, the boundary between the warm surface water and deep cold water, is raised almost completely up to the surface in the east and is depressed in the west. This nutrient-rich deep water mixes with the surface water that supports the high level of primary productivity responsible for the diverse marine ecosystems and major fisheries found in the area.
During El Nino the trade winds weaken and warm water moves back east in a slow wave. This leads to a depression of the thermocline in the eastern Pacific and an elevation of the thermocline in the west. Coastal upwelling along South America is no longer able to tap into the cold, nutrient-rich water from beneath it, thus reducing the supply of chemical nutrients to the euphotic zone. As a result of this decrease in nutrients, there is a drastic decline in phytoplankton production, which in turn adversely affects all the creatures at higher levels of the marine food chain.
The weakening of the easterly trade winds during El Nino also affects the climate. As the upwelling slows, the sea surface temperature rises and warms the moist air above the ocean. Rainfall follows the warm water eastward and results in flooding in Peru and drought in Indonesia and Australia. These climatic aberrations are called teleconnections because statistical correlations have been found between these atypical weather events and El Nino. The eastward displacement of the atmospheric heat source changes the global atmospheric circulation. This in turn forces changes in weather in regions far removed from the Tropical Pacific.
The greatest biological impact of El Nino is upon the fisheries in the coastal regions of the eastern Pacific. But the effects of El Nino have been observed in a wide variety of marine life and even as far south as Antarctica, more than 6,000 km away. The decline in coastal upwelling causes a reduction in primary production, which in turn decreases the food available to the natural fish population. These combined with an increasing sea surface temperature during El Nino encourages fish located in coastal areas to migrate north and south in search of cooler waters and food. Migrating fish tend to find themselves in waters much to cold for them to survive. The fish that do not leave the region move from the surface waters deeper into the water column, becoming inaccessible to predators, such as birds and to fishing trawlers using existing fishing gear. Fish unable to migrate die from lack of food or intolerable temperature elevations.
Another factor of El Nino that alters coastal fish populations is the increase in rainfall along the South American coast. This results in an increase in turbidity and a decrease in salinity from an enhanced river discharge which brings with it large amounts of sediment and fresh water. The fish either leave their coastal habitat or die from unendurable water conditions.
It is often reported that the collapse of the Peruvian anchovy industry in the early 1970s was a direct result of the El Nino of 1972-73. During this El Nino, the anchovy population dropped from 20 million to 2 million. Not only did this collapse the industry that was based on this resource, but it also reduced the population of marine birds that fed on the anchovy and allowed sardines and jack mackerel to move into the area which created a multispecific pelagic ecosystem. The 1982-83 El Nino, which was considered the strongest El Nino thus far this century, affected all of the main pelagic resources leading the Peruvian fishery to its lowest record of catches.
In its long-range effects upon fisheries, the 1982-83 El Nino is thought to have been responsible for mackerel migrating further north than usual and preying on juvenile salmon stocks off the coast of North America. It has also been linked to variations in the migration pattern of sockeye salmon in British Columbia, which resulted in increased predation upon the species. In contrast to reduced catches, Alaskan salmon fisherman in the North Pacific Ocean reported bountiful catches. In the western Pacific, increased amounts of phytoplankton in the East China Sea moved the central fishing grounds toward the coast increasing the sardine catch 10 times higher than the average.
The changes in distribution patterns of the fisheries have an outcome on other marine life. In the Weddell seal population in Antarctica, researchers noticed that the number of births decline every four to six years, coinciding with El Nino events. They believe that the seal population decline may result from changes in the fish populations caused by shifts in ocean currents. Following the 1982-83 El Nino, a dramatic reduction in the number of California sea lions occurred at Santa Catalina Island, California. Another change in cetacean population was a decline in pilot whale numbers followed by an increase in abundance of Risso's dolphins. The limited food source in the area resulted in competitive displacement, which prevented co-occurrence of these species in a restricted geographic area.
The 1982-83 El Nino was responsible for many ecological effects on other marine resources. The eastern Pacific region suffered massive coral bleaching, events and mortalities that have tragic results for the coral reef community. The increased sea surface temperatures and the rainfall-induced salinity changes in the water are believed to be the underlying causes for the incidents of coral death in the eastern Pacific. In the western Pacific, the decrease in sea level was responsible for exposing and destroying the upper layers of the coral reefs that surround many islands.
During the 1982-83 El Nino it is estimated that up to 85% of the sea bird population in Peru was killed. The causes of this mortality are difficult to determine because the information available is preliminary and limited. However, some factors which may contribute negatively to the sea bird population are: flooding of nesting sites, changing atmospheric circulation patterns, increasing sea surface temperatures, and migration of their primary food source, fish.
In spite of the destructive nature of El Nino, some marine creatures do benefit form the disturbances brought upon by the phenomenon. As a result of the 1982-83 El Nino, scallops accelerated their growth and reached enormous densities. Purple snails and octopuses became more common and the shrimp fishery reached its highest level. This is most likely the result of increased run-off from the rivers, due to increased rainfall, which provided a greater abundance of nutrients and decreased predation from a dispersed fish population.
The ability to anticipate how climate will change from one year to the next will lead to better management of fisheries, water supplies, agriculture, and other resources. Scientists are now producing numerical prediction models to indicate how the ocean-atmosphere system might evolve over the next few seasons or years. By incorporating climate predictions into management decisions, humankind is becoming better adapted to the irregular rhythms of climate. While the forecasts of El Nino are clearly of direct value to fisheries in the productive regions of Ecuador, Peru, and Chile, more accurate prediction of El Nino will also be very valuable for countries located outside the tropics, such as Japan and the United States. A reduction of the fish population reduces the amount of fishmeal produced and exported (by local industry) to other countries for feeding poultry and livestock. If the world's fishmeal supply decreases, more expensive alternative feed sources must be used, resulting in an increase in poultry and cattle prices worldwide. The foreknowledge of probabilities of anchovy catches would allow, for example, more stable pricing strategies for world supplies of cattle protein and would forgo the type of rapid rise of cattle protein prices after the 1982-83 El Nino.
El Nino forecasts in fisheries management could help coastal ecosystem managers to distinguish between changes in populations due to anthropogenic factors or changes from natural conditions. Although intense fishing pressure remains a major reason many fisheries ultimately become unproductive and uneconomical, fishing is usually neither the sole, nor necessarily even the primary force behind the fluctuations of the marine resource populations affected by El Nino.
Regardless, population collapse and the inability of the fishing industry to recover would certainly be accelerated by further exploitation. More accurate predictions of El Nino could help ecosystem managers to mitigate the cyclic event and prevent increased ecological disturbances. To respond to the impact of an unexpected El Nino by using measures such as closing the fishing season after the population has declined, will continue to be ineffectual and costly.
Recent predictions report that the 1997-98 El Nino is shaping up to be one of the biggest in 50 years. It will provide scientists with a natural laboratory to increase our understanding of El Nino and its aftermath. With widespread distribution of current forecast results and unprecedented levels of mainstream media attention, it is safe to say that the 1997-98 El Nino will be the most closely watched event by scientists and decision-makers alike.
TOPIC 月球表面成因
>>考生回忆
·星球撞击说
·火山爆发说
The face of the Moon turned toward us is termed the near side. It is divided into light areas called the Lunar Highlands and darker areas called Maria (literally, "seas"; the singular is Mare). The Maria are lower in altitude than the Highlands, but there is no water on the Moon so they are not literally seas. The dark material filling the Maria is actually dark, solidified lava from earlier periods of Lunar volcanism. Both the Maria and the Highlands exhibit large craters that are the result of meteor impacts. There are many more such impact craters in the Highlands.
The side of the Moon unseen from the Earth is called the far side. One of the discoveries of the first Lunar orbiters is that the far side has a very different appearance than the near side. In particular, there are almost no Maria on the far side, but a number of meteor impact craters.
The amount of cratering is usually an indication of the age of a geological surface: the more craters, the older the surface, because if the surface is young there hasn't been time for many craters to form. Thus, the Earth has a relatively young surface because it has few craters. This is because the Earth is geologically active, with plate tectonics and erosion having obliterated most craters from an earlier epoch. In contrast the surface of the Moon is much older, with much more cratering. Further, different parts of the surface of the Moon exhibit different amounts of cratering and therefore are of different ages: the Maria are younger than the highlands, because they have fewer craters.
The oldest surfaces in the Solar System are characterized by maximal cratering density. This means that one cannot increase the density of craters because there are so many craters that, on average, any new crater that is formed by a meteor impact will obliterate a previous crater, leaving the total number unchanged. Some regions of the moon exhibit near maximal cratering density, indicating that they are very old.
TOPIC 观众效应
Audience Effect
The audience effect is the impact that a passive audience has on a subject performing a task. It was first formally noted in various psychology studies in the early 20th century. During some studies the presence of a passive audience facilitated the better performance of a simple task; while other studies show the presence of a passive audience inhibited the performance of a more difficult task.
In 1965, Robert Zajonc proposed Drive theory as an explanation of the audience effect.
Drive Theory in Social Psychology
In social psychology, drive theory was used by Robert Zajonc in 1965 as an explanation of the phenomenon of social facilitation. The audience effect notes that in some cases the presence of a passive audience will facilitate the better performance of a task, while in other cases the presence of an audience will inhibit the performance of a task. Zajonc's drive theory suggests that the variable determining direction of performance is whether the task is composed of a correct dominant response (that is, the task is perceived as being subjectively easy to the individual) or an incorrect dominant response (perceived as being subjectively difficult).
In the presence of a passive audience, an individual is in a heightened state of arousal. Increased arousal, or stress, causes the individual to enact behaviours that form dominant responses, since an individual's dominant response is the most likely response, given the skills which are available. If the dominant response is correct, then social presence enhances performance of the task. However, if the dominant response is incorrect, social presence produces an impaired performance.
