On the basis of the characteristics of temperature and air pressure, earth’s environmental envelop is divided into 5 layers. They are
- Ionosphere and
- Troposphere layer is the lowermost and most important layer of the atmosphere, as almost all the weather phenomena occur in this layer.
- Troposphere layer extends from earth surface upto 7 kms over pole and 16 kms over equator it means, Troposphere is thick over equator that over pole. The first 1.5 to 2 km height of troposphere is called friction layer.
- At the end of troposphere, tropopause is located. Temperature at tropopause is – 45°C over pole and – 80°C over equator.
- In this layer temperature decreases with increasing altitude at the rate of 1°C/165m or 6.5°C/1000m. This average rate of decrease in temperature is called Normal lapse rate.
- About 75% mass of environmental gases and about 99% mass of water vapour and dust particles is located within this layer. It means, Troposphere contains most of the clouds.
Troposphere is not suitable for flying aircrafts, because bumpy air pockets are present in this layer.
- Stratosphere layer extends from tropopause upto 50 kms of height. It is extremely dry region and almost no clouds are present in it except cirrus and mother of pearl clouds.
- Temperature remains stable at the beginning of this layer but it suddenly starts changing after the height of 20 km. This sudden change in temperature is due to the presence of Ozone layer (30 to 50 km) in the upper layer of stratosphere, which absorbs the ultraviolet radiations present in the solar radiation. at the end of stratosphere, temperature becomes 0° C.
- Stratosphere layer is suitable for flying aircrafts because this layer is almost free from weather disturebances.
- Mesosphere extends from 50 km to 80 km of height.
- In Mesosphere layer, temperature decreases with height and at the end of this layer temperature becomes -100° C, which is the minimum temperature of the atmosphere.
- Ionosphere layer extends from 80 km to 500 km height and it is the thickest among above all layers. Ionosphere is divided into various layers such as D, E, F1, F2, etc. Upper part of ionosphere is called as Thermosphere.
- Temperature in this layer and subsequent layers over it constantly rises with height and becomes 1000° C at the end of this layer.
- In this layer, most of the gases are present in ionised state and electrical conductivity is responsible for reflecting the radio waves and other electromagnetic reflecting the radio waves and other electromagnetic waves back to the earth surface.
- Most of the heavenly bodies such as meteorites when enter into earth’s surface get burnt in this layer due to ionized friction.
- Exosphere layer beyond 400 km of height, Upper part of exosphere is called magnetosphere.
- The temperature keeps on rising constantly at high rate.
- Practically earth environment extends up to 36000 kms, when earth looses its gravity effect.