The atmosphere may be defined as a transparent gaseous envelope surrounding the Earth. The vertical profile of the atmosphere shows several concentric layers. These layers vary in density, temperature, composition, and properties. The density is highest near the earth’s surface and decreases with altitude.
The thin layer from the surface of the earth upwards is:
- Troposphere
- Stratosphere
- Mesosphere
- Thermosphere
- Exosphere
(i) Troposphere
This is the region up to 8-16 km—height from the earth’s surface. Therefore wind clouds, dust particles, spores, pollen, and more than 90% of gases of the atmosphere are present here.
Temperature decreases with increasing height up to tropopause (Top of the troposphere).
The temperature average 15ºC near the soil surface and lower down to –57ºC at the tropopause, which makes the transition to the stratosphere.
(ii) Stratosphere
The region lies up to 16-50 km. from the earth above the troposphere. There is the absence of large convectional currents (wind) so it is an excellent region for air travel.
The ozone layer is present in the stratosphere, protecting us from the harmful U.V. radiation from the sun.
Stratopause is the transit layer between the stratosphere and the mesosphere.
(iii) Mesosphere
The region lies up to 50-80 km. from the earth above the stratosphere. It shows a decrease in temperature with height.
(iv) Thermosphere
This region lies up to 80-150 km. From the earth above the mesosphere is the thermosphere, which contains free electrons and ions. All the communication, satellites are launched only in this layer because ions and electrons transmit or reflect radio waves (Signals) from the surface of the earth.
(v) Exosphere
The outer fringe of the atmosphere known as the exosphere is highly rarefied and gradually merges with outer space. So above the thermosphere is the exosphere.
