题目内容
（请给出正确答案）
A.1～2km
B. 6～8km
C. 10～12km
D. 17～18km
参考答案
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（由简答题聘请的专业题库老师提供的解答）
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更多“对流层（Troposphere）：下界为地面，上界随纬度和季节变化，平均厚度（）”相关的问题
A．plainly
B．repeatedly
C．nearly
D．changeably
Atmosphere
1．The atmosphere is a mixture of several gases. There are about ten chemical elements which remain permanently in gaseous form. in the atmosphere under all natural conditions. Of these permanent gases, oxygen makes up about 21 percent and nitrogen about 78 percent. Several other gases, such as argon (氩), carbon dioxide, hydrogen, neon (氖), krypton (氪), and xenon (氙), comprise the remaining one percent of the volume of dry air. The amount of water vapor, and its variations in amount and distribution is of extraordinary importance in weather changes. Atmospheric gases hold in suspension (悬浮) great quantities of dust, pollen (花粉), smoke, and other impurities which are always present in considerable, hut variable amounts.
2．The atmosphere has no definite upper limits but gradually thins until it becomes imperceptible (感觉不到的). Until recently it was assumed that the air above the first few miles gradually grew thinner and colder at a constant rate. It was also assumed that upper air had little influence on weather changes. Recent studies of the upper atmosphere, currently being conducted by earth satellites and missile probings, have shown these assumptions to be incorrect. The atmosphere has three well-defined strata (layers).
3．The layer of the air next to the earth, which extends upward for about ten miles, is known as the tropophere (对流层). On the whole, it makes up about 75 per cent of all the weight of the atmosphere. It is the warmest part of the atmosphere because most of the solar radiation is absorbed by the earth's surface which warms the air immediately surrounding it. A steady decrease of temperature with increasing elevation is a most striking characteristic. The upper layers are colder because of their greater distance from the earth's surface and rapid radiation of heat into space. The temperatures within the troposphere decrease about 3.5 degrees per 1,000 feet increase in altitude (海拔高度). Within the troposphere, winds and air currents distribute heat and moisture. Strong winds, called jet streams, are located at the upper levels of the troposphere. These jet streams are both complex and widespread in occurrence. They normally show a waveshaped pattern and move from west to east at velocities (速度) of 150 mph, but velocities as high as 400 mph have been noted. The influences of changing locations and strengths of jet streams upon weather conditions and patterns are no doubt considerable. Current intensive research may eventually rebel their true significance.
4．Above the troposphere to a height of about 50 miles is a zone called the stratosphere (高温层). The stratosphere is separated from the troposphere by a zone of uniform. temperatures called the tropopause (对流层顶). Within the lower portions of the stratosphere is a layer of ozone (臭氧) gases which filters (过滤) out most of the ultraviolet rays from the sun. The ozone layer varies with air pressure. If this zone were not there, the full blast of the sun's ultraviolet light would burn out skins, blind our eyes, and eventually result in our destruction. Within the stratosphere, the temperature and atmospheric composition are relatively uniform.
5．The layer upward of about 50 miles is the most fascinating but the least known of the three strata. It is called the ionosphere (电离层) because it consists of electrically charged particles called ions, thrown from the sun. The northern lights (aurora borealis) originates within this highly charged portion of the atmosphere. Its effect upon weather conditions if any, is as yet, unknown.
A New finding about the upper atmosphere
B Stratosphere
C Ionosphere
D The composition of the permanent gases in the atmosphere.
E The suspension of dust
F Tropophere
Paragraph 2 ______
Although it may sound funny to call scientists weather-watchers, there's【B3】funny about what they do. Specifically, weather-watchers are meteorologists(气象学者)【B4】work for the United States Weather Bureau. They study the ocean of【B5】that surrounds the earth and, with the information they get, predict our weather.
The atmosphere【B6】in height from 300 to 700 miles above the earth and is divided into a series of layers or shells. The layer that is most interesting【B7】the meteorologist is the troposphere(对流层) or the layer closest to the earth.【B8】is in the troposphere that all our weather is formed.
【B9】causes our weather is really a very simple process. Endless streams of hot air push up from the earth. As they rise, they are【B10】by the freezing temperatures of the【B11】troposphere. Once it has become cold and heavy, the air【B12】back toward the earth, but it【B13】move down because of the rising hot air. In the meantime, planetary winds, which blow around the earth, or air currents keep both the cold air mass as well as the hot air mass in【B14】.
There are two additional factors that influence these moving air masses.【B15】is water vapor that the rising hot air soaks up like a sponge. The other is temperature Which, by cooling the hot air, forces it to【B16】out its water vapor in the form. of rain, snow, or sleet(雨夹雪).
These air masses【B17】push against each other with tremendous pressure. When a high-pressure mass of air succeeds【B18】pushing out a low-pressure air mass, we have clearing conditions and【B19】weather. When a low-pressure air mass forces out a high-pressure mass of air, stormy weather can be【B20】.
【B1】
A．when
B．as
C．while
D．if
A．Y
B．N
C．NG
A．Y
B．N
C．NG
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