Distribution of the Insolation (Factors)

 Factors Affecting the Distribution of Insolation:

          The amount of the Insolation received at the Earth's surface varies significantly or say decreases from equator towards the poles due to certain astronomical and geographical factors viz-

             

        (i) Angle of the Sun's Rays,

        (ii) Length of Day

       (iii) Distance between Earth and Sun                (iv)  Sunspot

        ( v) Effect of the Atmosphere.

(i) Angle of the Sun's Rays:

                The Sun's rays are vertical at equator and become oblique as we moves towards the poles . So more amount of Insolation is received at equator than at poles because- 

*Vertical rays are concentrated on a minimum areas and the energy received per unit area increases, where oblique rays are spread over large area. So amount of energy decline.

    * Oblique rays travel largest distance in the atmosphere than vertical rays. Thus amount of solar Insolation is lost due to reflection, scattering etc. In the case of oblique rays and they lose more energy as compared to vertical rays.

(i) Length of Day:

                During a equinox, when sun is over head at equator, both the hemispheres receive equal amount of insolation. The length of day is 12 hours at the equator but increase towards the poles equally in both hemispheres.

                During summer solstice, when sun is over head at Tropic of Cancer, the length of the day increases from equator to poles in the Northern hemisphere. The length of the day decreases from equator to poles in the Southern hemisphere.

                During a winter solstice, when Sun is at the Tropic of the Capricorn, the length of the day decreases from equator to poles in Northern hemisphere. The length of the day increases from equator to poles in the Southern hemisphere.

 (iii) Distance between Earth and Sun:

               The distance between the Earth and Sun changes during the course of year because the earth revolves around the sun in elliptical orbit. When the earth is at perihelion nearest to sun, it receives maximum Insolation. While at aphelion, when earth is farthest from sun, it receives minimum Insolation. In January,  when Earth is at perihelion, there is winter season in Northern hemisphere and in July, when Earth is at aphelion, there is summer in Northern hemisphere.

            There is summer in Southern hemisphere , when earth is at perihelion and winter, when Earth is at aphelion. Winter are 7% less severe in January in Northern hemisphere and summer are 7% more severe in Southern hemisphere due to more amount of solar Insolation received during perihelion.

         Summer are 7% less intense in July in Northern hemisphere and winter is 7% more severe in Southern hemisphere due to less amount of solar Insolation received during aphelion.

(iv) Sunspot:

         Sunspots are created in the

Solar outer surface due to periodic disturbances and explosions. The energy radiated from the Sun increases when the number of Sunspots increases and therefore, the amount of insolation received at the earth's surface when the number of Sunspots increases and therefore, the amount of insolation received at the earth's surface also increases. On the other hand if the number of Sunspots decreases then the insolation received also decreases.

(v) Effect of the Atmosphere:

       The electro magnetic solar radiation or the incoming short wave solar radiation has to pass through thick layer of the earth's atmosphere and hence it is partly absorbed, partly reflected and partly scattered by the atmosphere and partly transmitted to the earth's surface. It also affects up to some extent the amount of insolation.