Water vapour

a. Water vapour

Other important part of the atmosphere is water vapour. The sources of the water vapour in the atmosphere are sea, lakes, rivers, soil, plants, etc. we can get water vapour in the atmosphere up to the height of 7500 m only. The percentage of the water vapour decreases as one moves from the equator towards the poles. Water vapour is the only one source of clouds, rainfall, due, hell stone, etc.

b. Dust Particles

The third important part of the atmosphere is dust particles. Some of these dust particles are visible while others are quite beyond human sight. These dust particles are responsible for such phenomena as sunsets, twilight and haze. There are the nuclei about which condensation takes place. Besides they are effective in absorbing and diffusing solar energy.   

1.3 Extension of the atmosphere

     The earth is surrounded by the gaseous blanket called atmosphere. It is supposed that the atmosphere is extended up to thousands of kilometers from the sea level. 75% of the atmosphere is found up to 11 km from the surface of the earth. 97% of it is found up to the height of 29 km from the surface of the earth. Carbon Dioxide, Nitrogen and Oxygen are the heavier gases which are found in the lower part of the atmosphere.

1.4 Insolation

     The main source of the heat and light to the earth is the sun. The sun is 10 times greater than the earth in diameter and 100000 times larger in the volume. The distance between the earth and the sun is 14,88,00,000 km. It is estimated that the temperature at the surface of the sun is 6,000⁰ Celsius.

Solar heat which is received by the earth is called insolation. Sun is the main source of energy and heat but much of it is lost in its passage through the atmosphere and only a small fraction of it is able to reach the earth.

A.    Factors affecting the Distribution of Insolation

1. Position of the Sun
2. Thickness of the Atmosphere
3. Duration of day and Night
4. Colour of the Surface
5. Distance between the earth and the Sun