COMPOSITION AND STRUCTURE OF ATMOSPHERE NTA UGC NET GEOGRAPHY
Composition of Atmosphere
Introduction
- The envelope of gases surrounding the Earth or planet is Atmosphere.
- Earth’s atmosphere is a dynamic mixture of various gases and aerosols.
- The atmosphere is composed of gases, water vapor and dust particles.
- About 99% of mass of atmosphere is confined in 32 km from earth surface.
Vertical Profile of Major Atmospheric Gases:
Carbon dioxide (Co2), Water Vapour (H2O): < 90 Km
Nitrogen (N2): 100-200 Km
Oxygen (O2): 200-1100 Km
Helium (He): 1100-3500 Km
Hydrogen (H2): 3500 Km & above
Permanent Gases of the Atmosphere:
Constituent Formula Percentage by Volume
Nitrogen N2 78.08
Oxygen O2 20.95
Argon Ar 0.93
Carbon dioxide CO2 0.03
Neaon Ne 0.002
Helium He 0.0005
Krypto Kr 0.0001
Xenon Xe 0.00009
Hydrogen H2 0.00005
Composition of Atmosphere:
The Earth’s atmosphere is consists of a mixture of various gases, water vapour and dust particles etc.
Gases:
Carbon dioxide / CO2:
- Ability to absorb heat & helps in rising lower atmosphere temperature.
- Volume of CO2 increases due to burning of fossil fuels.
- Responsible for Greenhouse effect.
- Green plants utilizes carbon dioxide in the process of photosynthesis from the atmosphere converting it with water into solid hydrocarbons.
Ozone:
- Actually a type of oxygen molecule consisting of three atoms O3.
- Lies between 20 to 30 km.
- Act as filter & absorbs harmful ultraviolet radiation coming from the Sun.
Water Vapour:
- Varies in atmosphere.
- Decrease with altitude
- Accounts for 4% by volume in warm and tropical regions
& 1% by volume in cold and polar regions.
- Decreases from Equator to Pole
- Absorbs insolation & act as blanket
- Contributes in stability and instability.
Dust Particles:
- Concentrated in lower atmosphere.
- Convectional air currents transport them to more heights.
- High Concentration in subtropical and temperate regtions due to dry wind as compared to equatorial & polar regions
- Act as hydroscopic nuclei around which water vapour condense and produce clouds.
Structure of the Atmosphere:
Consists of many layers with different density and temperature.
Each layer having its own peculiar characteristics.
Maximum Density- Near the surface of the Earth
Lowest/low Density- Increases Height decreases density.
Troposphere:
It means the regions of mixing
Lowermost layer of atmosphere
Height/Altitude: 8km at the poles and 18 km at the equator.
Temperature and pressure both decreases with increasing height, at the rate of 6.50c per 1000 meter. (6.50c/1000m) (Normal Lapse Rate)
This layer consists of different gases, dust particles and water vapour.
It is meteorologically the most significant zone because all the weather phenomena like rainfall, fog, hailstorm, cyclone, anticyclone storm occur here.
The upper boundary is called ‘Tropopause’ means where the mixing stops.
Tropopause between- Troposphere and Stratosphere.
Stratosphere:
It lies after troposphere, at the height of 18 km – 50 km.
It contains Ozone layer is between 20km-30km, called ozonosphere.
Temperature remains constant/same for some distant (lower stratosphere) but then temperature rises 00c at 50 km altitude.
Temperature increases with increasing height due to presence of ozone layer.
Almost free from water vapor, clouds, dust particles etc. and this condition ideal for flying aeroplanes.
The upper boundary is called ‘stratopause’
Stratopause between- Stratosphere and Mesosphere.
Mesosphere
It lies after stratosphere, at the height of 50km to 80km.
Rise of temperature stop near stratopause.
Temperature decreases with increasing height, reaches -1000c at 80 km height
Absence of Greenhouse gas.
The upper limit is called Mesopause
Mesopause between Mesosphere and Thermosphere
Thermosphere:
It lies after Mesosphere, at the height of 80km to 400km.
Ionosphere is part of Thermosphere.
Temperature rises very rapidly with increasing height, reaches 17000C.
People could not feel warm due to extremely low pressure and thin air.
Aurora’s are observed in lower parts of this layer.
Aurora Borealis- Northern Hemisphere
Aurora Australis- Southern Hemisphere.
Ionosphere:
Located between 80km to 400km.
It is an electrically charged layer.
This layer is characterized by ionization of atoms
Ionization of molecules and atoms occurs mainly for the UV Rays, X Rays & Gama Rays.
Use in radio-communication.
Exosphere:
The uppermost layer of the atmosphere, beyond ionosphere, above height of about 400 km
Air is extremely thin.
Temperature gradually increases.
Light gases like helium and hydrogen float into space from here.
This layer meet with space