Layers of Atmosphere: The atmosphere consists of four spheres (layers) extending from the surface of the earth upwards. The concentration of the components gases decreases gradually upwards, which results in a gradual decrease in pressure. But the temperature of the atmosphere does not change in a gradual way. It varies in a complex way.
Depending upon the temperature variation, the atmosphere is divided into four regions. Temperature decreases from 170C to -580C regularly in the lowest layer extending up to 12 km. this layer of the atmosphere is called the troposphere. Above this layer lies the stratosphere that extends up to 50 km.
in this layer, the temperature rises up to 20C. Beyond the stratosphere lies the mesosphere, covering up to 85 km. in this region again temperature decreases down to -930C. Beyond 85 km lies the thermosphere, in which temperature goes on increasing upwards.
Characteristics of four regions of atmospheric regions:
|Name of regions||Height above the earth’s surface||Temperature range and trend|
|Troposphere||0 —– 12 km||170C —– -580C (decreases)|
|Stratosphere||12 —– 50 km||-580C —- 20C (increases)|
|Mesosphere||50 —– 85 km||20C —– -930C (decreases)|
|Thermosphere||85 —– 120 km||˃ -930C (increases)|
Reasons for variations of temperature and other phenomena in troposphere and stratosphere:
The major constituents of the troposphere are nitrogen and oxygen gases. These two gases comprise 99% of the volume of the earth’s atmosphere.
Although the concentration of carbon dioxide and water vapors is negligible in the atmosphere, yet they play a significant role in maintaining the temperature of the atmosphere. Both of these gases allow visible light to pass through but absorbs infrared radiations emitted by the earth’s surface.
Therefore, these gases absorb much of the outgoing radiation and warm the atmosphere. As the concentration of gases decreases gradually with the increase of altitude, correspondingly temperature also decreases at the rate of 60C per kilometer.
This is the region where all whether occur. Almost all aircraft fly in this region.
This region is next to the troposphere and extends up to 50 km. in this region, the temperature rises gradually up to 20C. The presence of ozone (due to absorption of radiation) in this region is responsible for the rise of temperature in the stratosphere.
Within this region, temperature increases as altitude increases, such as lower layer temperature are about -580C and the upper layer are about 20C.
Thus, the upper layer absorbs high energy ultraviolet radiations from the sun, it breaks down into monoatomic (O) and diatomic oxygen (O2).
O3 → O2(g) + O(g)
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