A description of the composition & structure of atmosphere

1. Dr. Meenakshi Prasad
Assistant Professor
P.G. Deptt. of Geography
M.U, Bodh Gaya
Source : google images

2. CONTENTS
• Definition of Atmosphere
• Composition of
Atmosphere
• Structure of Atmosphere
Source : google images

3. Definition
• Atmosphere is a thick gaseous envelope which
surrounds the earth and is attached to the
earth’s surface by gravitational force.
• According to a study of NASA, it extends till a
height of 80,000 km above the earth’s surface
• It is estimated that 97% of the effective
atmosphere is confined upto a height of 29
km above the earth’s surface.

4. COMPOSITION OF THE ATMOSPHERE
The atmosphere is composed of gases, water vapour & gas
particles.
Gases :
• 95% of the total weight of the atmosphere is made by
gases
• By volume dry air contains 78.08% Nitrogen, 20.95%
Oxygen, 0.93% argon, 0.035% of Carbon Dioxide & a small
amount of other gases such as Methane, Hydrogen,
Helium, Krypton, Xenon, Neon, Sulphur Dioxide, etc.
• Thus, Nitrogen & Oxygen are major gases which
constitute almost 99% of the total gaseous composition of
the atmosphere till a height of 25km from the earth’s
surface.

5. Gaseous Composition of the
Atmosphere
Source : google images

6. • This proportion of gases exists till a height of 80 km
beyond which the proportion changes & the amount
of Hydrogen & Helium starts increasing.
• Infact above the height of 80 km separate layers of
different gases are found among which 4 layers are
important :
GASEOUS LAYE HEIGHT
1 Molecular Nitrogen Layer 90-120 km
2 Atomic Oxygen Layer 200-400 km
3 Helium Layer 1100-3500 km
4 Atomic Hydrogen Layer 3500-10,000 km

7. Importance of Different Gases :
• Nitrogen is generally chemically inactive but it
dilutes the oxygen & makes it breathable. It is
also absorbed by the plant in the form of nitrate
& helps in their growth.
• Oxygen makes breathing possible & is also
essential for combustion.
• Carbon dioxide is used by green plants for
photosynthesis & it also regulates the
temperature of the earth through green house
effect.
• At ground level ozone is a pollutant but the ozone
layer of stratosphere protects the earth from the
Ultra Violet radiation of the Sun.

8. Dust Particles :
• The dust particles present in the atmosphere are
divided into two types – terrestrial dust particles
& cosmic dust particles
• Terrestrial dust particles are mainly found upto a
height of 5 km from the earth’s surface.
• They act as hygroscopic nuclei & help in the
formation of clouds
• Cosmic dust particles are found mainly above the
height of 50 km & they originate due to the
disintegration of celestial bodies that enter the
earth’s atmosphere. They help in the formation
of noctilucent clouds.

9. • Dust particles help in the scattering of solar radiation
which adds varied charming colours of red & orange
to sunrise & sunset
ROLE OF DUST PARTICLES
Formation of Clouds Scattering of Solar Radiation
Source : all google images

10. Water Vapour :
• The availability of water vapour is generally
upto a height of 12 km. However, some
amount of water vapour is also found above
the height of 50 km in the middle part of the
atmosphere. The vertical currents of the
atmosphere first carries it to the stratosphere
& then due to an increase in the temperature
of stratosphere it reaches above the height of
50 km. After crossing the ozone layer this
vapour starts condensing & forms noctilucent
clouds.

11. • Three processes are responsible for the
presence of water vapour in the atmosphere.
They are –
(a)Evapoation, (b)Evapo- tranpiration and
(c)Sublimation
• The water vapour is responsible for various
types of weather phenomena that occur in the
atmosphere, such as- formation of clouds,
different forms of precipitation, storms, etc.
• Water vapour also helps in heating the
atmosphere as it absorbs terrestrial radiation

12. STRUCTURE OF THE ATMOSPHERE
As we go up higher in the atmosphere variations
occur in temperature. Based on the
characteristics of temperature the vertical
structure of the atmosphere can be divided into
following 6 concentric layers :
(i)Troposphere
(ii)Stratosphere
(iii)Mesosphere
(iv)Ionosphere or Thermosphere
(v)Exosphere
(vi)Magnetosphere

13. Troposphere :
• Lower most layer of the atmosphere
• Its average height is 8-18 km, i.e. 8 km at the
poles & 18 km at the equator. The reason of
greater height at the equator is the presence of
convectional currents due to which the air rises
up vertically to a greater height.
• All kinds of weather phenomena (e.g. fog, cloud,
dew, frost, rainfall, snowfall, thunder- storms,
lightning, etc.) occur in this layer.
• It is the zone of radiation, conduction &
convection

14. • Temperature decreases
with increasing height
in the troposphere at
the rate of 6.50C per
1000 m. This is called
the normal lapse rate.
• The temperature at the
upper limit of the
troposphere is -600C
• Jet streams are found at
the upper boundary of
this layer
Source : google images

15. Stratosphere:
• It is located just above the troposphere & is
separated from it by a transition belt having a
thickness of 1.5 km which is known as the
tropopause.
• It extends upto a height of 50 km.
• In the lower part of the stratosphere between a
height of 15-35 km, heavy concentration of ozone
gas is found. This is known as the ‘ozone layer’.
• Temperature gradually increases with height in
this layer due to the presence of ozone layer as
ozone absorbs the UV rays coming from the sun.

16. • Temperature at the upper limit of the stratosphere
reaches 00C
• The layer is usually devoid of atmospheric
disturbances
• The Jet streams occur in the lower parts of this layer
as well.
Source: google images

17. Mesosphere:
• Mesosphere extends between a height of 50-80
km
• It is separated from stratosphere by a transitional
belt known as stratopause.
• Temperature decreases with increasing height in
the layer
• At the upper limit of mesosphere the
temperature becomes -850C to -1000C
• This is the coldest layer of the atmosphere
• Noctilucent clouds & cosmic or meteoric dust are
found here

18. Thermosphere or Ionosphere:
• This layer extends upto a height of 500 km
• It is separated from mesosphere by a transition
belt known as ‘mesopause’
• Temperature increases with increasing height in
this belt & at the upper limit of this belt it
becomes +250C
• Ionised particles are present in this layer which
are capable of reflecting back radio waves
• This layer has made radio communication &
telecommunication possible on earth

19. • When the charged
particles coming from the
sun strike against the
ionised particles of this
layer, it creates colourful
lights in the sky which can
been seen from within
the Arctic circle &
Antarctic circle. These
lights are called ‘Auroras’.
When seen from within
Arctic circle they are
called ‘Aurora Borealis’
(Northern Lights) & when
seen from within the
Antarctic circle they are
called ‘aurora Australis’
(Southern Lights)
AURORAS
Source : google images

20. Exosphere :
• Exosphere extends till a height of 2000 km
• In this layer temperature increases rapidly with
increasing height
• At the upper limit of this layer the temperature is
recorded as 10000C
• This layer is dominated by ionised particles
• Molecules & atoms of Oxygen, Hydrogen & Helium
are found in this layer.

21. Magnetosphere:
• This sphere extends beyond the height of 2000 km till a
height of 80,000 km
• Magnetosphere is the region where the temperature
continuously increases with increasing height & where
the effect of earth’s gravitation decreases.
• At the upper limit of this layer temperature becomes
17000C
• This layer is dominated by charged particles, i.e.
electrons & protons. A dense layer of these particles is
found between the height of 3000-16,000 km.
• This layer is affected by cosmic rays, solar flares & solar
storms.
• Studies have shown that solar flares & solar storms
affect the temperature of magnetosphere which inturn
influence the weather changes of troposphere

22. Conclusion
• Thus, it is clear that a lot of variations are
there in the structure of the atmosphere
• Not only that, further researches are required
for the upper layers of the atmosphere
Source : google images

23. References
• Singh, S : Physical Geography, Prayag Pustak
Bhawan, Allahabad, 2012
• Critchfield, Howard J : General Climatology,
McGraw Hill Book Co, New York,1965

24. Source : google images