Atmosphere, Troposphere, Stratosphere, Mesosphere and Ionosphere

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Layered structure: troposphere, stratosphere, mesosphere, ionosphere, thermosphere-exosphere


  • Most important for life forms
  • Thickness: 8 - 16 km. (low at poles, high at equator) (more in summer, less in winter)
  • Contains of the total molecular mass of the atmosphere.
  • All weather phenomenon occurs here
  • Temperature: Falls with increasing height at rate of 1 degree for every 165 metres (or 6.5 degree per km) . This is called the lapse rate. Lapse rate varies with latitude and altitude. Decreases with altitude. Higher over tropical zone. Hence, the upper limit of troposphere is cooler over the equator than over the poles.


  • Extends up to height of 50 kms. Upper part is also called ozonosphere.
  • Uniformity in horizontal distribution of temperature; however, increase with height.
  • Contains most of atmospheric ozone. Absorbs UV rays.
  • Free from dust particles and atmospheric turbulence. Ideal for flying aircrafts.


  • up to height of 80 km.
  • Temperature decreases with height.
  • Mesopause (the upper boundary of mesosphere) is the coldest atmospheric layer with an average temperature of -85-degree C.


  • up to 600 km
  • Contains electrically charged ions. Used for radio communication.
  • Temperature increases with height.
  • Most meteors burn up here upon entering the atmosphere.

Thermosphere, Exosphere, Magnetosphere

  • Thermosphere: 85 - 400 km. International Space Station orbits in this layer.
  • Exosphere: up to a height of 9600 km. The outermost part of exosphere is called magnetosphere.

Radiation Belts

There are two belts in the upper atmosphere having a high concentration of ionized particles. They are known as Van Allen՚s radiation belts. Lower belt lies at about 2600 km height while the upper belt is about 13000 - 19000 km height.

Composition of Atmosphere

  • Heavier gases concentrated in the lower part while lighter gases are in the upper apart.
  • Nitrogen (78 pc) , Oxygen (21 pc) by volume. They are also called permanent components of the atmosphere.
  • Proportion of other gases like , , water vapour etc varies from place to place. Hence, they are called variable components of the atmosphere.
  • Nitrogen has a moderating influence on temperature and controls combustion. It is also an important nutrient for vegetative growth.
  • Oxygen is important for breathing, decomposition and combustion.
  • Water vapors help in containing temperature.
  • Carbon dioxide and water vapors lead to greenhouse effect preventing the earth from cooling down excessively.
  • Ozone: The maximum concentration of ozone is found in the stratosphere, about 25 - 30 km above the earth՚s surface.
  • Ozone depletion: Ozone depleting at rate of 4 pc per decade since late 70՚s. Ozone has declined by about 33 pc in the Antarctic. This is known as the Ozone hole.
  • Global Warming: According to IPCC, global surface temperature increased 0.74 +- 0.18 degree C during the 20th century.

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