Insolation and Heat Balance of the Earth

In the previous article, we have discussed the composition and structure of the earth’s atmosphere. The atmosphere is essential for the survival of plant and animal life. They also require the optimum temperature to keep themselves warm and grow. In this article, we are going to discuss in details about some of the topics like insolation, terrestrial radiation, heat budget of the earth, albedo, etc.

Insolation or Incoming Solar Radiation

  • As we all know, the sun is the primary source of energy for the earth. The sun radiates its energy in all directions into space in short wavelengths, which is known as solar radiation.
  • The earth’s surface receives only a part of this radiated energy (2 units out of 1,00,00,00,000 units of energy radiated by the sun).
  • The energy received by the earth’s surface in the form of short waves is termed as Incoming Solar Radiation or Insolation.
  • The amount of insolation received on the earth’s surface is far less than that is radiated from the sun because of the small size of the earth and its distance from the sun.
    Moreover, water vapour, dust particles, ozone and other gases present in the atmosphere absorb a small amount of solar radiation.
    The solar radiation received at the top of the atmosphere varies slightly in a year due to the variations in the distance between the earth and the sun.
    During the earth’s revolution around the sun, the earth is farthest from the sun on 4th July. This position of the earth is called aphelion. On 3rd January, the earth is nearest to the sun. This position is called perihelion.
    Due to this variation in the distance between the earth and the sun, the annual insolation received by the earth on 3rd January is slightly more than the amount received on 4th July.
    However, the effect of this variation is masked by some other factors like the distribution of land and sea and the atmospheric circulation. Hence the variation does not have a greater effect on daily weather changes on the surface of the earth.

    Factors influencing Insolation

    The amount of insolation received on the earth’s surface is not uniform everywhere. It varies according to the place and time. When the tropical regions receive maximum annual insolation, it gradually decreases towards the poles. Insolation is more in summers and less in winters. The major factors which influence the amount of insolation received are:

    1. Rotation of the earth on its axis
    2. The angle of incidence of the sun’s rays
    3. Duration of the day
    4. Transparency of the atmosphere

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