Structure of the Atmosphere


The atmosphere is an integral part of the earth.

  • It surrounds the earth from all sides.
  • It extends upto about 1600 kilometres from the earths surface.
  • 97 percent of the total amount of weight of the atmosphere is limited upto the height of about 30 kilometres.

The atmosphere can be divided into five layers according to the diversity of temperature and density.

  • (a) Troposphere
  • (b) Stratosphere
  • (c) Mesosphere
  • (d) Ionosphere
  • (e) Exosphere

39

TROPOSPHERE

  • (i) This is the lowest layer of the atmosphere.
  • (ii) The height of this layer is about 18 kms on the equator and 8 kms on the poles. The main reason of higher height at the equator is due to presence of hot convection currents that push the gases upward.
  • (iii) This is the most important layer of the atmosphere because all kinds of weather changes take place only in this layer. Due to these changes development of living world take place on the earth. The air never remains static in this layer. Therefore this layer is called changing sphere or troposphere.
  • (iv) The environmental temperature decreases with increasing height of atmosphere. It decreases at the rate of 10C at the height of 165 metre. This is called Normal lapse rate.
  • (v) The upper limit of the troposphere is called tropopause. This is a transitional zone. In this zone characteristics of both the troposphere and ionosphere are found.

STRATOSPHERE

  • (i) This layer is above the troposphere.
  • (ii) This layer is spread upto the height of 50 kms from the Earth’s surface. Its average extent is 40 kms.
  • (iii) The temperature remains almost the same in the lower part of this layer upto the height of 20 kms. After this the temperature increases slowly with the increase in the height. The temperature increases due to the presence of ozone gas in the upper part of this layer.
  • (iv) Weather related incidents do not take place in this layer. The air blows horizontally here. Therefore this layer is considered ideal for flying of aircrafts.

MESOSPHERE

  • (i) It is the third layer of the atmosphere spreading over stratosphere.
  • (ii) It spreads upto the height of 80 kms. from the surface of the earth. It’s extent
    is 30 kms.
  • (iii) Temperature goes on decreasing and drops upto – 1000C.
  • (iv) ‘Meteors’ or falling stars occur in this layer.

IONOSPHERE

  • (i) This is the fourth layer of the atmosphere. It is located above the mesosphere.
  • (ii) This layer spreads upto the height of 400 kms. from the surface of the earth. The width of this layer is about 300 kms.
  • (iii) The temperature starts increasing again with increasing height in this layer.
  • (iv) Electrically charged currents flows in the air in this sphere. Radio waves are reflected back on the earth from this sphere and due to this radio broadcasting has become possible.

EXOSPHERE

  • (i) This is the last layer of the atmosphere located above ionosphere and extends to beyond 400 km above the earth.
  • (ii) Gases are very sparse in this sphere due to the lack of gravitational force. Therefore, the density of air is very less here.

.

  • Change of weather take place only in troposphere.
  • Change of weather conditions donot take polace in stratosphere. This is an ideal layer for flying aeroplanes.
  • Ions are found in abundance in ionosphere. Ionosphere reflects back the radio waves to the earth and make possible the communication system.
  • Density of air is the least in the exosphere.

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Bibliography : NIOS Geography Book
Reference : http://www.nios.ac.in

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