General Studies: Important Geography Topic Atmosphere and Layers of Atmosphere for UPSC, SSC CGL, Postal Exams

Atmosphere

Atmosphere is thick gaseous envelope surrounding the Earth from all sides and attached to Earth through the force of gravitation. Atmosphere acts as filter because it absorbs the various unwanted radiation, source to various gases. It supports life forms in biosphere. The atmosphere is composed of gases, vapours and particulates. Gases such as Helium, Ozone and Hydrogen etc are present in traces. Ozone gas absorbs the ultraviolet radiations and save the biosphere from its adverse impact.


Layers of Atmosphere

1) Troposphere:

It extend up to 16 km from the Earth's surface. Thickness varies from 8 km at the pole to 16 km at the equator. At every  165 m, there is a drop of 1° (or 6.4°C per km). This is called Normal Lapse Rate of Temperature. Tropopause separates troposphere from stratosphere. This,layer accounts for practically the entire water vapour, all dust particles and most of the Carbon dioxide contained in the atmos-phere. Due to this all weather phenomena such as condensation, precipitation and storms, etc occur in the troposphere only.


2) Stratosphere :

The stratosphere extends up to about 50 km, where stratosphere separates it from the mesosphere. In this layer, the in hight. This phenomenon is known as temperature inversion. The temperature rises in this layer from about -60° C at the tropopause to 0°C at stratopause. The part of the stratosphere, in which there is a concentration of ozone is often called ozonosphere. It absorbs ultraviolet radiation, which is harmful for us. Stratosphere is free from dust particles and also from atmospheric turbulences. Hence, this this layer is considered ideal for flying of jet aircraft's.

3) Mesosphere:

Mesosphere extends above the stratopause up to a height of about 80 km. In this layer, the temperature decreases with height like in the troposphere and it falls from about 0°C at its base to about -100°C at 80 k height. It is considered the coldest layer of the atmosphere. The upper limit of the mesosphere is marked by the mesopause, a transitional layer separating it from the ionosphere.

4) Ionosphere :

Ionosphere is located above the mesosphere and extends up to about 600 km. This layer is also called as Ionosphere because it contains electrically charged ions that reflect the radio waves back to the Earth thus making radio communication possible. Absorption of solar radiation by ionised particles cause an increase in temperature with increasing height in the ionosphere. Due to large concentration of ionised particles in this layer the ionosphere. acts as a protective layers against meteorites, that are burnt in this layer.

5) Thermosphere:

The zone between the 85 km and 400 km above the surface is often called Thermosphere. In this layer, the temperature increases with increasing altitude. The upper limit of the thermosphere, the Thermopause is generally taken at an altitude of about 600 km. The day temperature at 600 km altitude exceed 1400°C while night temperature remains about 225°C. The upper part of the thermosphere contains only the lighter gases like helium and hydrogen.

6) Exosphere and Megnetosphere :

The outermost part of the atmosphere of the Earth is called Exosphere. This zone of the atmosphere extends up to a height of about 900 km. The upper limit of the exosphere is uncertain as this layer acts as a transitional layer between the Earth's atmosphere and the space. The outer part of the exosphere is called Megnetosphere.