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- Significance of atmosphere –
- Acts as a filter as it absorbs the various unwanted radiation.
- Supports life form in biosphere.
- Extent of atmosphere –
- Almost 97% of effective atmosphere confines within 29 km of the earth’s surface.
- Distribution is not uniform and even not homogeneous.
- It extends to 16-29,000 km from the sea level.
- Atmosphere = gases + vapours + particulates
- Layers of atmosphere –
- Troposphere.
- Thickness varies from 8 km at poles to 18 km at equator.
- Normal lapse rate of temperature, 10C drops at every 165 m (or 6.40C / km).
- Accounts for practically the entire water vapour, all dust particles and most of the CO2.
- All weather phenomenons such as condensation, precipitation and storms etc. occurs in this layer.
- Tropopause.
- Separates troposphere from stratosphere.
- Stratosphere.
- Temperature increases with height. (temperature inversion)
- Temperature range, -600C at tropopause to 00C at stratopause.
- Free from dust particles and atmospheric turbulences, thus ideal for jet aircrafts.
- Stratopause.
- Separates stratosphere and mesosphere.
- Mesosphere.
- Temperature decreases with height, 00C to -1000C.
- Coldest layer of atmosphere.
- Mesopause.
- Transitional layer between mesosphere and ionosphere.
- Ionosphere.
- Contains electrically charged ions which reflects radio waves back.
- Absorption of solar radiations causes temperature increase with height.
- Due to ion concentration it acts as a protective layer against meteorites that are burnt in this layer.
- Thermosphere.
- Zone between 85 km to 400 km above the surface.
- Temperature rises with altitude.
- Thermopause.
- It is the upper limit of thermosphere.
- At an altitude of about 600 km.
- Day temperature exceeds 14000C while night 2250C.
- Contains lighter gases like hydrogen and helium.
- Exosphere.
- Outer most part of the atmosphere.
- Upper limit acts as transitional layer between atmosphere and space.
- Magnetosphere.
- Outer part of the exosphere.
- Presence of air is extremely rare.
- Insolation –
- Solar radiation that is intercepted by earth.
- Amount of insolation depends on:
- Area and nature of surface.
- Inclination of the rays of the sun.
- Distance between earth and the sun.
- Transparency of the atmosphere.
- Albedo – Portion of solar radiation reflected from the surface.
- Heat budget of the earth / Heat balance – Mechanism of maintaining the same temperature by the atmosphere.
- Terrestrial radiation – Process in which heated surface of the earth radiates energy in the form of long waves.
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