- The atmosphere is a mixture of a layer of gases enveloping the Earth, held to it by gravitational force, Almost all the atmosphere (97 per cent) lies within 29 km of the Earth surface.
- Up to about 50 km the atmosphere is composed of :-
Nitrogen . 78%
Oxygen . 20.95 %
Argon . 0.93%
Carbon dioxide. 0.03 %
(Other are Neon, Helium, Ozone, Hydrogen, etc)
- Water vapour besides being the immediate cause of Condensation and precipitation, absorb the insolation coming from the Sun, reducing the amount reaching the Earth''s surface.
- Carbon dioxide is important for absorption of heat from the sun as well as from the Earth. A high concentration of carbon dioxide leads to Green house effect.
- Dust particles scatter and diffuse insolation and also act as hygroscopic nuclie for condensation (for the formation of clouds).
Layers of Atmosphere
Troposphere :-
- Layer nearesr to Earth''s surface. Thickness varies from 8 km at the poles to 18 km at the Equator. All weather phenomenon occur here.
- Densest at all contains water Vapour, mousmois and dust. Dust oartipart present in this layer hold the water vapour and contribute to the occurrence of twilight and the red colors of sunlight and sunset.
- In this, at every 165 m there is a drop of °C ( or 6.4° c per km). This is called Normal Lapse Rate of Temperature.
- Tropopause sep troposphere from stratosphere.
Stratosphere :-
- Extend from 20 km to 50 km height. The temperature ceases for fall with the increase of height in this layer. Little weather is generated here as there is very little water vapour and virtually no dust present.
- Stratosphere provides ideal condition for flying large airplanes.
- Contains ozone ( 20 - 40 km from Earth's surface), region being called Ozonosphere. It absorb the ultra violet Ray's from the sun. This layer has a comparatively higher temperature due to the absorption of ultraviolet radiation from the sun (temperature increase as we go up).
