NCERT Class 11 Geography Chapter 8: Composition and Structure of Atmosphere YouTube Lecture Handouts
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NCERT Class 11 Geography Part 1 Chapter 8: Structure and Composition of Atmosphere
Frequency: (hence air is crucial)
99% of mass of atmosphere is confined in 32 km from earth՚s surface
Air is colorless & odorless and felt only when it blows as wind
Composition of Atmosphere
- Oxygen would be negligible beyond 120 km
- not found beyond 90 km
: Interesting Gas
- Transparent to incoming solar radiation but opaque to outgoing terrestrial radiation
- Absorbs a part of terrestrial radiation and reflects back some part of it towards the earth՚s surface
- Responsible for greenhouse effect
- Volume increasing due to burning of fossil fuels
- Leads to rise of temperature
Ozone
- Lies between 10 to 50 km
- Act as filter and absorbs ultra-violet rays
Water Vapor
- Varies in atmosphere
- Decreases with altitude
- Account for 4% by volume (warm & tropical area) & 1% by volume (in cold desert and polar areas)
- Decreases from equator to poles
- Absorbs insolation and act as blanket
- Contributes to stability and instability of air
Dust Particles
- Concentrated in lower layers
- Convectional air currents transport them to more heights
- High concentration in subtropical and temperate regions due to dry wind as compared to equatorial and polar regions
- Act as hygroscopic nuclei around which water vapor condenses to produce clouds
Structure of Atmosphere
Density decreases with altitude
Troposphere
- Lowermost layer with average height of 13 km (8 km at poles and 18 km at equator)
- Maximum thickness at equator as heat transported by convection currents
- Temperature fall of for every 165 meters
- Major layer for biological activities
Tropopause
- Separates troposphere and stratosphere
- Ranges from at equator to at poles
- Temperature is constant
Stratosphere
- Height upto 50 km
- Has ozone layer – absorbs UV rays
Mesosphere
- Upto 80 km
- Temperature decreases with height and reach at 80 km
Ionosphere
- Between 80 to 400 km
- Electrically charged particles as ions
- Reflects radio waves
- Temperature increases with height
Exosphere
- Outermost layer
- Extremely rarified
Elements of Climate
- Temperature
- Pressure
- Winds
- Humidity
- Clouds
- Precipitation
✍ Manishika