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  • Thick gaseous envelope around the Earth and is attached to the Earth’s surface by gravitational force.
  • 97% of the atmosphere is estimated to be upto the height of 29 km even though it extends to thousands of kilometres.
  • It is composed of – gases, vapour and particulates.
  • Nitrogen (78%), Oxygen (20.9%), Argon (0.93%), Carbon Dioxide (0.03%) and trace amounts of neon, helium, ozone etc.
  • Vapour content varies between 0-5% by volume. It decreases from the equator poleward.
  • Solid particles such as dust, pollen, soot, volcanic ash etc.




  • Lowermost layer. Almost all weather phenomena occur in this layer i.e. fog, cloud, dew, frost, rainfall etc.
  • Temperature in the troposphere decreases with increasing altitude at the rate of 6.5 degree celsius per 1000 m. This is called normal lapse rate.
  • Average height of troposphere is about 16 km over the equator and 6 km above the poles – due to rotation and heating
  • Tropopause is about 1.5 km thick and it is at a height of 17 km over equator and 9 -10 km above poles.
  • Troposphere – zone or region of mixing


  • Average upper limit at 80 km.
  • Temperature gradually rises upwards and reaches 0 degrees celsius near the stratopause.
  • Few cirrus clouds are formed in the lower stratosphere.
  • In the winter polar stratospheric clouds are formed near the poles called nacreous clouds.
  • Lower part of the layer has the ozone layer which is important for life forms in the biosphere.



Ozone Layer

  • Ozone layer is located at a height of 15-30 km
  • Lower portion of stratosphere having maximum concentration of ozone is called ozonosphere.






  • Mesosphere extends between 50-80 km.
  • Temperature again decreases with height.
  • At uppermost limit of mesosphere temperature becomes – 80 degrees celsius.
  • Cloud formation happens here in the high latitudes. The clouds formed here are called noctilucent clouds.
  • The layer         in which most meteors   burn up    after entering Earth’s atmosphere and before reaching Earth’s surface





  • It extends from 80 km – 640 km.
  • There are a number of different layers within it – D, E,F, G.
  • This layer reflects radio waves back to the Earth.




  • It extends beyond 640 km height from the sea level.
  • Density is extremely low and the atmosphere is highly rarefied.
  • The temperature reaches up to 5568 degrees celsius at the outer limit but this temperature is entirely different from the air temperature of the Earth’s surface.


Homosphere and Heterosphere


  • Lower Portion Extends up to 90 km.
  • Called homosphere because of the homogeneity in the proportion of various gases.
  • Layers are troposphere, stratosphere and mesosphere.
  • Upper Portion
  • Extends from 90 km onward
  • Different layers in this sphere have different chemical and physical properties.
  • Layers are – Molecular nitrogen, atomic oxygen layer, helium layer and atomic hydrogen layer.


Insolation and Heat Budget Insolation


  • The solar energy received at the Earth’s surface is called insolation
  • On an average, the amount of insolation received at the Earth’s surface decreases from the equator towards the poles but there is also temporal variation of insolation received at different latitudes at different times of the year.
  • The poles receive only 40% of the insolation received at the equator.



Factors affecting distribution of insolation

Angle of the sun’s rays

  • Spread over larger area
  • Oblique rays have to pass through thicker portion of the


Factors affecting distribution of Insolation

Length of the Day

  • Length of day varies due to inclination of the Earth
  • But angle of the sun’s rays controls the amount of insolation received more effectively than the length of the day e.g. six months day at the poles.


Factors affecting distribution of insolation

Distance between the Earth and the Sun

  • Perihelion (Jan 3) – Earth is nearest to the Sun at 147 mil km.
  • Aphelion (Jul 4) – Earth is furthest from the Sun at 152 mil km.
  • Causes winters to be be 7% less severe in January in NH. Summers to be 7% more intense in SH.



Factors affecting distribution of insolation


  • Sunspots follow a 11 year cycle.
  • The energy radiated from the sun increases when the number of sunspots increase and therefore insolation also increases.





Factors affecting distribution of insolation 

Effects of the Atmosphere

  • Absorption
  • Scattering
  • Reflection

Heat Budget of the Earth

On an average, there is supposed to exist heat balance between the amount of solar radiation received by the earth’s surface and its atmosphere and the heat lost by the outgoing terrestrial longwave radiation from the Earth’s surface

Incoming shortwave radiation = radiation from the sun

Outgoing longwave radiation = radiation from the Earth.











Incoming Radiation

Incoming Shortwave Radiation 100%
Amount lost to space through scattering and reflection

●      Reflected by the clouds

●      Reflected by the ground

●      Scattered energy lost into space


●      27%

●      2%

●      6%

Heat Budget of the Earth

●      Received through direct radiation

●      Received as diffused daylight


●      34%

●      17%

Heat Budget of the Atmosphere

●      Absorption of incoming solar radiation

●      Received from outgoing terrestrial radiation


●     14% ●     34%

Outgoing Radiation

Terrestrial Heat Balance

●      Energy lost due to radiation

●      Energy lost due to convection and turbulence

●      Energy lost due to Evaporation


●        23% ●     9%

●        19%

Atmospheric heat Balance ● Energy lost to space 48%



Heat Budget   

Incoming Radiation = 100%

  • Outgoing radiation = 35% (amount lost to space through scattering and reflection) + 48% (radiation from the atmosphere) + 17% (radiation from the Earth)
  • Radiation from Earth lost to space = Radiation from Earth – Radiation from Earth absorbed by the Atmosphere = 51 – 34 = 17%

Distribution of Temperatures

Factors Controlling Distribution of Temperature:

  • Latitudes
  • Altitude
  • Distance from the Coast
  • Nature of Land and Water
  • Nature of Ground Surface (Albedo)
  • Nature of Ground Slope
  • Prevailing Winds
  • Ocean Currents


Inversion of Temperature   

Temperature inversion, a reversal of the normal behaviour of temperature in the troposphere (the region of the atmosphere nearest the Earth’s surface), in which a layer of cool air at the surface is overlain by a layer of warmer air.










Types of Temperature Inversion

Non-advectional Inversion

  • Ground Surface Inversion/ radiation inversion
  • Upper Air Inversion

Advectional Inversion

  • Frontal Inversion
  • Valley Inversion
  • Surface Inversion Mechanical Inversion


Significance of Inversion

  • Frost
  • Fog
  • Stability of atmosphere

Air Pressure and Atmospheric Circulation Horizontal Distribution of Air Pressure

  • Horizontal distribution of air pressure is seen on the basis of isobars
  • Air pressure – High air pressure or Low air pressure
  • The distribution of pressure belts is not regular due to unequal distribution of land and water.
  • Pressure Belts can be Thermally induced or Dynamically induced.




Pressure Belts

  • Thermally induced – Equatorial Low, Polar High
  • Dynamically induced – Subtropical high, Subpolar low

Subtropical high is caused due to rotation of the Earth and sinking and settling down of winds

Subpolar low is caused due to spreading out of surface air due to rotation of the Earth.


Tricellular Meridional Circulation



Shifting of Pressure Belts




Questions for the Day        

  • Analyse why does the temperature of the Earth not rise continuously even as it is regularly exposed to solar radiation. (250 words)
  • Explain tricellular meridional circulation of air in the Earth’s atmosphere. (250 words)
  • What is temperature inversion? How does valley inversion occur? (150 words)