第二篇
Forecasting Methods
There are several different methods that can be used to create a forecast (预测). The method a forecaster chooses depends upon the experience of the forecaster, the amount of information available to the forecaster, the level of difficulty that the forecast situation presents, and the degree of accuracy or confidence needed in the forecast.
The first of these methods is the persistence method; the simplest way of producing a forecast. The persistence (坚持) method assumes that the conditions at the time of the forecast will not change. For example, if it is sunny and 87 degree today, the persistence method predicts that it will be sunny and 87 degree tomorrow. If two inches of rain fell today, the persistence method would predict two inches of rain for tomorrow. However, if weather conditions change significantly from day to day, the persistence method usually breaks down and is not the best forecasting method to use.
The trends method involves determining the speed and direction of movement for fronts, high and low pressure centers, and areas of clouds and precipitation. Using this information, the forecaster can predict where he or she expects those features to be at some future time. For example, if a storm system is 1000 miles west of your location and moving to the east at 250 miles per day, using the trends method you would predict it to arrive in your area in 4 days. The trends (趋势) method works well when systems continue to move at the same speed in the same direction for a long period of time. If they slow down, speed up, change intensity, or change direction, the trends forecast will probably not work as well.
The climatology method is another simple way of producing a forecast. This method involves averaging weather statistics accumulated over many years to make the forecast. For example, if you were using the climatology method to predict the weather for New York City on July 4th, you would go through all the weather data that has been recorded for every July 4th and take an average. The climatology method only works well when the weather pattern is similar to that expected for the chosen time of year. If the pattern is quite unusual for the given time of year, the climatology method will often fail.
The analog method is a slightly more complicated method of producing a forecast. It involves examining today’s forecast scenario and remembering a day in the past when the weather scenario (推测) looked very similar (an analog). The forecaster would predict that the weather in this forecast will behave the same as it did in the past. The analog method is difficult to use because it is virtually impossible to find a predict analog. Various weather features rarely align themselves in the same locations they were in the previous time. Even small differences between the current time and the analog can lead to very different results.
36. What factor is NOT mentioned in choosing a forecasting method?
A. Imagination of the forecaster.
B. Necessary amount of information.
C. Practical knowledge of the forecaster.
D. Degree of difficulty involved in forecasting.
37. Persistence method will work well
A. if weather conditions change greatly from day to day.
B. if weather conditions do not change much.
C. on sunny days.
D. on rainy days.
38. The limitation of the trends method is the same as the persistence method in that
A. it makes predictions about weather.
B. it makes predictions about precipitation.
C. the weather features need to be well defined.
D. the weather features need to be constant for a long period of time.
39. Which method may involve historical weather data?
A. The trends method.
B. The analog method.
C. Both climatology method and analog method.
D. The trends method and the persistence method.
40. It will be impossible to make weather forecast using the analog method
A. when the current weather scenario differs from the analog.
B. when the current weather scenario is the same as the analog.
C. when the analog is over ten years old.
D. when the analog is a simple repetition of the current weather scenario.
第三篇
Ants Have Big Impact on Environment as “Ecosystem Engineers”
Research by the University of Exeter has revealed that ants have a big impact on their local environment as a result of their activity as “ecosystem engineers” and predators. The study, published in the Journal of Animal Ecology, found that ants have two distinct effects on their local environment.
Firstly, through moving of soil by nest building activity and by collecting food they affect the level of nutrients in the soil. This can indirectly impact the local populations of many animal groups, from decomposers to species much higher up the food chain.
Secondly, they prey on a wide range of other animals, including larger prey which can be attacked by vast numbers of ant workers.
Dirk Sanders, an author of the study from the university’s Centre for Ecology and Conservation, said: “Ants are very effective predators which thrive in huge numbers. They’re also very territorial and very aggressive, defending their resources and territory against other predators. All of this means they have a strong influence on their surrounding area.”
“In this research, we studied for the first time how big this impact is and the subtleties of it. What we found is that despite being predators, their presence can also lead to an increase in density and diversity of other animal groups. They genuinely play a key role in the local environment, having a big influence on the grassland food web,” Sanders said.
The study, carried out in Germany, studied the impact of the presence of different combinations and densities of black garden ants and common red ants, both species which can be found across Europe, including in the UK. It found that a low density of ants in an area increased the diversity and density of other animals in the local area, particularly the density of herbivores and decomposers. At higher densities ants had no or the opposite effect, showing that predation is counteracting the positive influence.
Dr Frank van Veen, another author on the study, said: “What we find is that the impact of ants on soil nutrient levels has a positive effect on animal groups at low levels, but as the number of ants increases, their predatory impacts have the bigger effect—thereby counteracting the positive influence via ecosystem engineering.”
Ants are important components of ecosystems not only because they constitute a great part of the animal biomass but also because they act as ecosystem engineers. Ant biodiversity is incredibly high and these organisms are highly responsive to human impact, which obviously reduces its richness. However, it is not clear how such disturbance damages the maintenance of ant services to the ecosystem. Ants are important in below ground processes through the alteration of the physical and chemical environment and through their effects on plants, microorganisms, and other soil organisms.
41 .Why are ants compared to ecosystem engineers?
A. Because they build their own nests.
B. Because they collect food.
C. Because their activity affects the environment.
D. Because they are predators.
42. As predators, ants
A. prey on small as well as large animals.
B. collect nutritious food from the soil
C. collect food as decomposers.
D. prey on species much higher up the food chain.
43. Dir Sanders’ study centered on how ants
A. can manage to thrive in huge numbers.
B. defend their resources and territory against other predators.
C. attack those invading animals for survival.
D. produce such a big impact on the environment.
44. What does paragraph 6 tell us?
A. Ants bring about a negative influence to an area when their population is small.
B. Ants bring about a positive influence to an area when their population is small.
C. Ants’ predation counteracts the positive influence they may have on an area.
D. At higher density, ants produce a positive influence on an area.
45. What still remains unclear about ants, according to the last paragraph?
A. What roles do ants play in the ecosystem in which they live?
B. How do ants affect the animal diversity in a given ecosystem?
C. How do human activities affect ants’ influence on a given ecosystem?
D. How do ants alter the physical and chemical environment?
