STRUCTURE OF ATMOSPHERE

1. TROPOSPHERE: The lowermost layer of the atmosphere is known as Troposphere and is the most important layer because almost all of the weather phenomena is occurred in this layer. E.g., Fog, cloud. Thunder, lightning, etc., occurs in this layer. It extends roughly to a height of eight kilometers near the poles and about 18 kilometers at the Equator. The thickness of the troposphere at the equator is the greater heights by strong conventional currents. Temperature decreases with increasing height at the rate of 6.5 C per 1000m. This rate of decrease of temperature is called normal lapse rate. This layer contains dust particles and over 90% of the earth’s water vapour. The upper limit of the tropopause is called troposphere which is about 1.5km. Thick. Temperature ceases to fall with the air temperature at the troposphere is about-80 C over the equator and about -45 covers the poles. The word troposphere literally means zone or region of mixing whereas the word tropopause means where the mixing stops.

2. STRATOSPHERE:  The Stratosphere begins at the tropopause which forms its lower boundary. The lower stratosphere is isothermal in character, i.e, the temperature in the lower part of this layer does not change with altitude. The stratosphere extends up to a height of 50 km. Afterwards it gradually increases up to a height of 50 km because of the presence of ozone layer which absorbs the Sun’s Ultra-Violet Rays. Clouds are almost absent and there is very little dust or water Vapours. The air movement is almost horizontal. The upper boundary of the stratosphere is called Statopause. Above this level there is a steep rise in temperature.

3. MESOSPHERE: Over the stratopause there exists the third layer known as mesosphere. It extends up to a height of 80 kms. Temperature decreases with height again and reaches up to – 100 C at the height of 80 kms.

4. IONOSPHERE: Ionosphere is located between 80 km to 400 kms. It is electrically charged layer. Radio waves transmitted from the earth are reflected back to the earth by this layer. Temperature again starts increasing with height because of radiation from the sun. The ionosphere consists of the following ionized layers:

5. EXOSPHERE: The outermost layer of the earth’s atmosphere is known as the exosphere which lies between 400 and 1000kms. The atmosphere in this region is so rarefied that it resembles a nebula-hydrogen and helium gases predominates in this outermost region. The temperature becomes 5568 C at its outer limit but this temperature is entirely different from the air temperature of the earth’s surface.