Insolation
- The amount of solar energy that the planet receives or absorbs is known as insolation.
- Factors Affecting Insolation – Solar constant, the angle of incidence, the duration of the day, distance from the Sun, and transparency of the atmosphere.
Heat Budget of the Earth
- When 100% of solar radiation reaches the earth’s atmosphere, about 35% is reflected back to space even before reaching the surface of the earth. The reflected amount is called the albedo of the earth. This amount of energy does not heat either the earth or the atmosphere.
- Out of the remaining 65% of the energy, 14% are absorbed by the atmosphere and the rest, 51% by the surface of the earth (34% through direct solar radiation and 17% from scattered radiation).
- 51% of the energy received by the earth is radiated back as terrestrial radiation.
- 17% is radiated back to space directly and the remaining 34% is absorbed by the atmosphere (6% is absorbed directly by the atmosphere, 9% through convection and 19% through latent heat of condensation).
- The total 48% absorbed by the atmosphere (14% from insolation and 34% from terrestrial radiation) are also radiated back to space.
- Thus, the total radiation returning back from the atmosphere and the earth is respectively 48+17=65% which balances the total of 65% received from the sun.
- This is termed the heat balance or heat budget of the earth, and explains how the earth maintains its temperature despite the huge transfer of heat.
