What is Atmosphere?

Atmosphere is complex fluidic system surrounding earth and bound to earth by gravity.

This complex fluidic  system consists of physical mixing of

* Gases

* Water Vapours

* Suspended Particulates

What is the composition of Atmosphere?

1- Gases– Atmosphere consists of mixture of gases whose composition remains constant.

a) Nitrogen

b) Oxygen

c) Argon

d) Carbon-di-oxide

2- Water Vapour and Suspended Particulates

Distribution of Water Vapours change from place to place and from time to time. 100% of water Vapour is limited in Troposphere and 50 % of which is limited within 5 k.m of sea level.

Suspended particulates consists of :

* Dust Particles

* Burnt Particles

* Pollen Grains

* Salt Particles etc

These play a role of hygroscopic nuclei ( also called as condensation nuclei ). These retain moisture which help in the formation of clouds.

What is the structure of Atmosphere?

Structure of atmosphere refers to vertical arrangement of concentric layers in atmosphere.

Structure of atmosphere can be differentiated in two ways :

1- Chemical Structure– on the basis of mixing of gases

2- Physical Structure– on the basis of temp, temp change and density with altitude

What is the Chemical Structure of Atmosphere?

On the basis of mixing of gases, two layers are identified:

atmosphere1- Homo-sphere  In this layer gases are uniformly mixed. This layer extends from 0- 90 km from earth surface.

2- Hetero-sphere- here layers are separated on the basis of concentration of particular gas in their molecular and atomic form. It extends beyond 90 k.m from the earth surface.

*  From 90 k.m- 200 k.m there exists layer of Nitrogen in Molecular Form

*  From 200 k.m – 110 k.m there exists layer of Oxygen (O) in atomic form

*  From 1100 k.m – 3500 k.m there exists layer of Helium(He)  in atomic form

* Beyond 3500 k.m there exists layer of Hydrogen (H)  in atomic form

What is the Physical Structure of Atmosphere?

Physical structure of atmosphere can be divided into Major Layers and Transitional Layers.




TROPOSPHERE 0-15 K.M In transition between troposphere &  stratosphereTROPOPAUSE
STRATOSPHERE 20- 50 K.M In transition between  stratosphere & MesophereSTRATOPAUSE
MESOSPHERE 50- 80 K.M In transition between  Mesophere & ThermosphereMESOPAUSE

What is Troposphere?

Its average thickness is 15 k.m. Temperature declines with altitude in troposphere. State of decline of temperature is 6.5 0 C / K.m, which is called as Normal / Environmental Lapse Rate.

Three factors are responsible for decline in temperature in Troposphere.

1- Troposphere is heated by terrestrial radiation of which earth is the source.

2- Density of atmosphere declines with altitude, thus its capacity to absorb terrestrial radiation declines with altitude.

3- Components producing Green House Effect are close to surface of earth in atmosphere.

What is Stratosphere?

It extends from 20- 50 K.M, stratosphere consists Ozone molecule concentrated between 15 k.m to 35 k.m and this part of stratosphere is known as Ozono – sphere.

This layer is non convective in nature as in stratosphere hot and lighter air is placed above cold and denser air. This layer is stratified and stable. Stability is the reason behind use of tropo – pause and Stratosphere in air transport.

What are the characteristics of Mesosphere?

It extends from 50- 90 K.M from earth surface.

Temperature decreases with altitude as Ozone molecules are not found above 50 k.m.

At the top of mesosphere temperature is – 120 0 C

What are the characteristics of Thermosphere?

Here in thermosphere, temperature increases with altitude. Process of ionization is responsible for release in energy which results in increase in temperature with altitude.

Ionization is carried by ionizing radiation coming from sun in the form of solar winds. These ionizing radiations excludes electron from atoms, once electrons are excluded, these electrons further ionize the air by excluding electrons from the atoms.

Due to this property of ionization, radio waves are used for propagation as longer wavelength of Radio Waves get reflected by oscillations of ions and electrons in ionosphere thereby facilitating their propagation.

How can we represent the temperature variations in different layers of atmosphere with the help of a graph?

Temperature variations can be shown by the following graph:




  1. By Shashi sandilya


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