CLIMATOLOGY

ATMOSPHERE COMPOSITION AND STRUCTURE

Origin of the Atmosphere
     Initially Earth is a red hot ball like structure slowly it got cooled, as it is rotating on its own axis the centrifugal forces acted upon and made the material to segregate according to their densities, this is why the denser material like Nickel and Ferrous are their in the Core of the Earth, the less dense material like Aluminium is located at the periphery and the intermediate material like Magnesium is located in the intermediate level between these two, apart from these minerals there are certain very less density minerals like Hydrogen, Helium, Nitrogen, etc., because of their less dense nature they are thrown out of the earth, this is the process of De-gassing.  These gases have enveloped the earth and are held to the earth due to the gravity.
Composition of Atmosphere
Gravity of the Earth plays a major role in the distribution of gases according to their densities.  The following picture reveals that the density is more near the surface of the earth and reduces with the altitude

  It is said that 97 percent of the atmospheric mass is upto the height of 25 kms.  The major gases like Nitrogen and Oxygen accounts for 99 percent of the gases and all other gases like Argon, Carbon dioxide, Neon, Helium, Hydrogen, Krypton, Xenon accounts just one percent.
Structure of the Atmosphere
The Earth's atmosphere is a layered structure, basing on temperature and pressure these layers can be divided into two, one Homosphere and other Heterosphere.  Homosphere consists of three layers namely, Troposphere, Stratosphere and Mesosphere.  The Heterosphere consists of two layers, namely Ionosphere and Exosohere.
Troposphere:
Tropos means Turbulence, since all the turbulence of the atmosphere is restricted in this layer alone.
This layer consists 99 percent of water vapour.
This layer consists 75 percent of Atmospheric mass.
Temperature decreases with height in this layer this phenomenon is called Normal Lapse Rate, for every 165 meters of assent 1 degree temperature will reduce, or for every one kilometer of assent 6.5 degrees of temperature will get reduces.