• Earth receives almost all of its energy from sun. The energy in Sun is produced from nuclear reactions (nuclear fission and fusion).
  • The earth in turn radiates back to space the energy received from sun.
  • SOLAR RADIATION: The radiation emitted from sun in form of short wave is called as Solar Radiation.
  • INSOLATION: The energy received by Earth from incoming solar radiation is called as insolation.
  • The amount of insolation received earth surface is around 1.94 or 2 calories per square kilometer per minute.
  • Insolation is measured with the help of
  • Albedo: The ratio between the total solar radiation falling upon a surface and the amount reflected.
  • Represented as %
  • Earth average albedo = 35%
  • Lowest- Dark Soil
  • Highest- Snowfall

Surface            Albedo (%)

Fresh Snow      80-90

Desert               35-45

Grasses              26

Crops                 15

Brick-concrete   10


Processes involved in Heating and Cooling of Atmosphere:

  1. Conduction
  2. Convection
  3. Radiation
  4. Advection


  1. Conduction: (transfer of heat by contact)
  • Conduction is the process of heat transfer from a warmer object to a cooler object when they come in contact with each other.
  • The transfer continues until both bodies maintain the same temperature.
  • The conduction in the atmosphere occurs at the zone of contact between the atmosphere and the earth’s surface.
  • Conduction is important in heating the lower layers of the atmosphere.


  1. Convection: (vertical transfer of heat)
  • Transfer of heat by the movement of a mass or substance from one place to another, generally vertical, is called convection.
  • The air of the lower layers of the atmosphere gets heated either by the earth’s radiation or by conduction. The heating of the air leads to its expansion. Its density decreases and it moves upwards.
  • The continuous ascent of heated air creates a vacuum in the lower layers of the atmosphere. As a consequence, cooler air comes down to fill the vacuum, leading to convection.
  • The cyclic movement associated with the convectional process in the atmosphere transfer heat from the lower layer to the upper layer and heats up the atmosphere.
  • The convection transfer of energy is confined only to the troposphere.


  1. Radiation:
  • Radiation is the form of energy that is transmitted in the form of waves.
  • The energy received from sun is in the form of short wave radiation and the atmosphere emits it in the form of long wave radiation.
  1. Advection: (horizontal transfer of heat)
  • The transfer of heat through horizontal movement of air (wind) is called advection.
  • Winds carry the temperature of one place to another. The temperature of a place will rise if it lies in the path of winds coming from warmer regions.
  • The temperature will fall if the place lies in the path of the winds blowing from cold regions.
  • Horizontal movement of the air is relatively more important than the vertical movement. In the middle latitudes, most of diurnal (day and night) variations in daily weather are caused by advection alone.
  • In tropical regions particularly in northern India during the summer season, local winds called ‘Loo’ is the outcome of advection process.

Factors responsible for difference of Insolation at Surface of Earth:

  1. Rotation of Earth
  2. Inclination of Sun rays
  3. Duration of  the day
  4. Transparency of the atmosphere


  1. Rotation of Earth
  • Rotation refers to movement of Earth around its own axis,which makes an angle of 66.5 with the plane of its orbit around the sun.
  • The rotation of the earth on this inclined axis has a greater influence on the amount of insolation received at different latitudes
  • The part of the Earth facing the sun will receive the maximum insolation as compared to the other side of Earth.


  1. Inclination of Sun rays
  • If rays are vertical, it will cover less area but net energy received and distributed is more heat whereas area which receives oblique rays covers more area but net energy received and distributed is less.


  1. Duration of the day
  • Duration of the day varies from place to place and season to season. It decides the amount of insolation received on the earth’s surface.
  • The longer the duration of the day, the greater is the amount of insolation received. Conversely shorter the duration of the day leads to receive of less insolation.
  1. Transparency of the atmosphere
  • The transparency of the atmosphere depends upon the cloud cover and its thickness, dust particles, water vapour, etc. They reflect, absorb or transmit insolation.
  • Thick cloud hinders the solar radiation to reach the earth’s surface. Similarly, water vapour absorbs solar radiation resulting in less amount of insolation reaching the surface.


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