• Earth does not receive the same amount of insolation everywhere on its surface. Places near the equator receive more insolation than places near poles.
  • There are three main reasons for the variations in the distribution of insolation on the surface of the earth. They are:
  1. Revolution of Earth around Sun
  2. Spherical Shape of Earth and,
  3. Inclined Axis of Earth
  • Earth is divided into three major temperature zones on the basis of insolation received:
  1. Torrid Zone
  2. Temperate Zone and,
  3. Frigid Zone
  • Torrid Zone is the region lying between the Tropic of Cancer and the Tropic of Capricorn. This zone receives maximum insolation.
  • Temperate Zone lies between the latitudes 23½° and 66½° in both the hemispheres.
  • The amount of insolation received in this zone is less than that of Torrid Zone. This reduction in the amount of insolation happens as a result of increase in latitude.
  • Frigid Zone lies between 66½° N and North Pole in the Northern Hemisphere and 66½° S and South Pole in the Southern Hemisphere. The insolation received in this zone is extremely less.
  • The temperature remains highest in the Torrid Zone as it receives the maximum amount of insolation. The temperature remains lowest in the Frigid Zone as it receives the minimum amount of insolation.
  • The temperature changes at various times during the day and night. Temperature during morning, noon, evening and night varies.
  • The temperature of atmosphere varies from season to season. These seasonal changes of temperature during summer and winter repeat themselves year after year.
  • The two factors responsible for temperature differences are latitude and, land and sea contrast.
  • The effects of land and sea contrast are temperature differences in coastal and interior areas and also formation of monsoon winds.
  • The difference in the temperature in the atmosphere gets noticed easily. Meteorologists compile data on the basis of temperature measurement.
  • Mean temperature is calculated by adding the maximum and minimum temperature and dividing it by two. It can be calculated daily, monthly or annually.
  • The difference between the maximum and minimum temperature gives us the ‘range of temperature’.
  • Insolation is important as it is responsible for sustaining the circulation of atmosphere and water. It also determines the type of vegetation in one region.
  • Graphs can be used to show the temperature of a place. Line graphs and bar graphs are used to represent the climatic data commonly.
  • The world distribution of temperature can be shown on an isothermal map by isotherms.
  • Isothermal maps are mostly drawn for the months of January and July, as they represent the highest and the lowest temperatures.

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  • Q1

    Explain the process of terrestrial radiation.


    The Sun’s energy absorbed by the Earth’s surface and radiated out in the space is called terrestrial radiation.

    The Sun heat energy is absorbed by the Earth and its atmosphere during the day. At night, this heat which is absorbed by the Earth and its atmosphere is radiated out by the Earth and its atmosphere.

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  • Q2

    How insolation is received and reflected by the Earth?


    i. The Earth absorbs only about half of the insolation enters the atmosphere. The atmosphere absorbs only 14% of the incoming insolation.
    ii. A large amount of insolation is reflected back into space by clouds, snowfields and oceans.

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  • Q3

    What is electromagnetic radiation? How they are received by the Earth?


    The Sun’s energy travels to the Earth as electromagnetic radiation which can be thought of as energy moving in waves.

    There are short and long waves. The incoming solar radiation is received in the form of short waves.

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  • Q4

    What is insolation?


    The incoming solar energy is intercepted by the Earth is defined as insolation.

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  • Q5

    What is the primary source of heat and light on the Earth?


    Solar radiation is the only primary source of heat and light for the Earth.

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