STRUCTURE OF THE ATMOSPHERE

STRUCTURE OF THE ATMOSPHERE

The atmosphere is an integral part of the earth. It surrounds the earth from all
sides. Generally it extends up to about 1600 kilo meters from the earths surface. 97
percent of the total amount of weight of the atmosphere is limited up to the height
of about 30 kilo meters. The atmosphere can be divided into five layers according
to the diversity of temperature and density.
(a) Troposphere (d) Ionosphere
(b) Stratosphere (e) Exosphere
(c) Mesosphere

(a) TROPOSPHERE :-

(i) This is the lowest layer of the atmosphere.
(ii) The height of this layer is about 18 km on the equator and 8 km on the
poles. The main reason of higher height at the equator is due to presence of
hot convection currents that push the gases upward. 

(iii) This is the most important layer of the atmosphere because all kinds of weather
changes take place only in this layer. Due to these changes development of
living world take place on the earth. The air never remains static in this layer.
Therefore this layer is called changing sphere or troposphere.
(iv) The environmental temperature decreases with increasing height of
atmosphere. It decreases at the rate of 10C at the height of 165 metre. This
is called Normal lapse rate.
(v) The upper limit of the troposphere is called tropopause. This is a transitional
zone. In this zone characteristics of both the troposphere and ionosphere are
found.

(b) STRATOSPHERE

(i) This layer is above the troposphere.
(ii) This layer is spread upto the height of 50 kms from the Earth’s surface. Its
average extent 40 kms.
(iii) The temperature remains almost the same in the lower part of this layer upto
the height of 20 kms. After this the temperature increases slowly with the
increase in the height. The temperature increases due to the presence of
ozone gas in the upper part of this layer.
(iv) Weather related incidents do not take place in this layer. The air blows
horizontally here. Therefore this layer is considered ideal for flying of aircrafts.
(c) MESOSPHERE
(i) It is the third layer of the atmosphere spreading over stratosphere.
(ii) It spreads upto the height of 80 kms. from the surface of the earth. It’s extent
is 30 kms.
(iii) Temperature goes on decreasing and drops upto – 1000C.
(iv) ‘Meteors’ or falling stars occur in this layer.

(d) IONOSPHERE

(i) This is the fourth layer of the atmosphere. It is located above the mesosphere.
(ii) This layer spreads upto the height of 400 kms. from the surface of the earth.
The width of this layer is about 300 kms.
(iii) The temperature starts increasing again with increasing height in this layer.
(iv) Electrically charged currents flows in the air in this sphere. Radio waves are
reflected back on the earth from this sphere and due to this radio broadcasting
has become possible.

(e) EXOSPHERE

(i) This is the last layer of the atmosphere located above ionosphere and extends
to beyond 400 km above the earth.
(ii) Gases are very sparse in this sphere due to the lack of gravitational force.
Therefore, the density of air is very less here. MORE