Insolation and Heat Budget

IAS Notes October 26, 2022
Insolation and Heat Budget

Insolation (INcoming SOLar radiATION) -
  • The amount of incoming solar radiation is called as insolation which is equal to two-billionth of solar energy.
  • The amount of insolation received on the surface is equal to 1.92 cal/min/sq. cm, which is known as Solar Constant.
  • The incoming solar radiation is shorter in wavelength and this radiation is absorbed by the Earth's surface and is re-emitted as long wavelength radiation known as Terrestrial radiation.
  • The atmosphere is transparent to incoming solar radiation but is opaque to outgoing terrestrial radiation.
  • The warming of Earth's atmosphere and its surface by the absorption of terrestrial radiation by some of the gases is called Green House Effect and the gases responsible for this effect are called Green House Gases. 
  • Example - Carbon di-oxide, Methane, Nitrous oxide, Perfluorocarbon (PFC), Sulphur hexa-fluoride, HFC, Water Vapour, etc

insolation

Normal Lapse Rate - 
  • Since, the Earth's surface absorbs the incoming solar radiation and emits the Terrestrial radiation, it acts as a source of heat for the Atmosphere.
  • Therefore, temperature decreases with increase in height which is called as Normal Lapse Rate which equals to 6.5℃/KM.

Methods of heat transfer 

1.   Radiation -
  • It involves the transfer of heat in the form of radiant energy.
  • The incoming solar radiation is in the form of electromagnetic radiation.
  • All the objects, hot or cold emits radiation continuously. 
  • Hotter the object, shorter the wavelength is.
2.   Conduction -
  • It involves the transfer of heat through molecular activity at the zone of contact.
  • It occurs at the zone of contact between troposphere and the Earth's surface.
3.   Convection -
  • It involves the transfer of heat by vertical movement of mass/air.
  • Transfer of heat in fluid occurs through convection.
  • Example - Convection currents
4.   Advection -
  • It is the transfer of heat by horizontal movement of wind.
  • Example - Planetary winds and Oceanic currents

Factors affecting insolation -

1.   Angle of incidence -
  • The angle of Incidence which depends on the latitude or altitude of the sun affects the insolation received.
  • The altitude of the sun affects the insolation received per unit area of the surface and the amount of insolation absorbed.
  • When the sun rays are vertical, the sun rays are concentrated in a small area, thus maximum insolation is absorbed.
  • Also, reflection is less in case of perpendicular incidence than oblique incidence.
  • For example - At Tropical and Equatorial region, maximum amount of insolation is received.
  • Whereas when the sun rays are oblique, the sun rays are distributed in a larger area leading to lesser intensity and thus lesser insolation is absorbed. 
  • For example - At Temperate and Polar regions, less amount of insolation is received.
2.   Length of the day - The longer the duration of the day, more insolation will be received on the surface.

3.   Transparency of the Atmosphere -
  • It includes the factors such as Cloud cover, dust particles, water vapour, etc which reduced the transparency of the Atmosphere and thus reduced the amount of insolation received at the surface.
  • Whereas clear and calm condition of the Atmosphere leads to the higher insolation received at the surface.

Heat Budget

heat budget
  • On the global scale, the Earth must re-radiate as much heat back to the space as it receives from the Sun. 
  • This is necessary in order to maintain a uniform temperature by the Earth.
  • The gains and losses in heat by the way of incoming Solar Radiation and outgoing Terrestrial Radiation is known as Heat Budget.
heat budget


Albedo - It is the ratio of the reflected amount of Solar radiation and the total incoming Solar radiation. It is also known as the Reflection coefficient.

Range of Albedo - [0,1]

The average Albedo of the Earth as a whole (surface + Atmosphere) is equal to 0.35 or 35%.

Albedo of various landforms -
  • Fresh Asphalt - 0.04
  • Open ocean - 0.06
  • Worn Asphalt - 0.12
  • Conifer forest - 0.08, 0.09, 0.15
  • Deciduous forest - 0.15-0.18
  • Bare soil - 0.17
  • Green grass - 0.25
  • Desert sand - 0.4
  • New concrete - 0.55
  • Ocean ice - 0.5-0.7
  • Fresh snow - 0.8-0.9

Previous Article - An introduction to Climatology
Next Article - Temperature

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Optional Notes
Note - This is my Vision IAS Notes (Vision IAS Class Notes) and Ashutosh Pandey Sir's Public Administration Class notes. I've also added some of the information on my own. 

Hope! It will help you to achieve your dream of getting selected in Civil Services Examination 👍
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