NCERT Class 11 Geography Chapter 8: Composition and Structure of Atmosphere YouTube Lecture Handouts

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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

Image of Constituent And Its Formula

Image of Constituent and Its Formula

Image of Constituent And Its Formula

: 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

Image of Structure of Atmosphere

Image of Structure of Atmosphere

Image of Structure of Atmosphere

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