Atmosphere

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  • Huge blanket of air called atmosphere.
  • 99 per cent of the total mass of the atmosphere is confined to the height of 32 km from the earth’s surface
Composition of the Atmosphere
  • Composed of gases, water vapour and dust particles
  • Oxygen will be almost in negligible quantity at the height of 120 km.
  • Carbon dioxide and water vapour are found only up to 90 km from the surface of the earth.
Dust Particle
  • Dust, Pollen grains, Pollutants, Volcanic ash, sea salts, fine soil, smoke-soot, ash and disintegrated particles of meteors.
  • Present in lower layer, convectional air currents may transport them to great heights.
  • Found in subtropical and temperate regions due to dry wind.
  • Dust and salt particles act as hygroscopic nuclei around which water vapour condenses to produce clouds.
Liquid (Water Vapour)
  • Decreases with altitude.
  • Warm and wet tropics - four per cent of the air by volume.
  • Dry and cold areas of desert and polar regions - less than one per cent.
  • Decreases from the equator towards the poles.
  • Water vapour also contributes to the stability and instability in the air.
Gases
  • N2, O2, Ar, CO2, He, Ne…
  • Carbon dioxide (Greenhouse gas)
    • Transparent to the incoming solar radiation but opaque to the outgoing terrestrial radiation.
    • Absorbs a part of terrestrial radiation and reflects back some part of it towards the earth’s surface. It is largely responsible for the Greenhouse effect
    • Increased volume of carbon dioxide is affecting the earth’s weather and climate. Due to factory smoke or car fumes, fossil fuels, the heat retained increases the temperature – Global Warming
Structure of atmosphere
  • Density - Near the surface < Increase in Altitude.
  • Troposphere
    • Average height is 13 km (Roughly 8km at Poles & 13km at the Equator [because of strong conventional current]). Zone of Mixing air & Cloud.
    • Weather phenomena like rainfall, fog and hailstorm occur in this layer.
    • 90% water vapour limited at 5km.
    • Temperature decrease 1o C every 165m of height.
    • Tropopause – Between troposphere & Startosphere.
      • Temperature nearly constant -80 o at Equator & -45 o C at Poles
  • Stratosphere
    • Height of 50 km. free from clouds and associated weather phenomenon making conditions most ideal for flying Aeroplanes.
    • Ozonosphere – Lower Stratospheric Layer. (UV-B rays more harmful).
    • Stratopause – Between Statosphere & Mesosphere.
  • Mesosphere
    • Up to the height of 80 km. Meteorites burn up in this layer on entering from the space.
    • Temperature starts decreasing with the increase in altitude and reaches up to minus 100°C at the height of 80 km.
    • Mesopause – between Mesosphere & Thermosphere.
  • Thermosphere
    • Has part of layer called Ionosphere [(80 – 400 km) – above the mesopause] - Presence of Charged Particle (Ionic character of Layer) for Radio transmission.
    • Temperature here starts increasing with height.
  • Exosphere
    • Merges with the outer space.
    • Layer of very thin air. Helium & Hydrogen.
Weather & Climate
  • Weather - Hour-to-hour, day to day condition of the atmosphere.
  • Climate - The average weather condition of a place for a longer period of time.
Temperature
  • The degree of hotness and coldness of the air.
  • Insolation is the incoming solar energy intercepted by the Earth.
  • Insolation decreases from the equator towards the Poles.
Altitude vs Temperature
Air Pressure
  • The pressure exerted by the weight of air on the earth’s surface.
  • Pressure is highest at sea level and decreases with height.
  • Horizontally the distribution of air pressure is influenced by temperature of air at a given place.
  • Low pressure area - Temperature is high the air gets heated and rises create low pressure area. Associate with cloudy skies and wet weather.
  • High Pressure area – lower temperature, the air is cold became heavy. Heavy air sinks and creates a high pressure area, Associate with clear and sunny skies.
Wind
  • Movement of air from high pressure area to low pressure areas is called wind
  • Types of wind.
    1. Permanent winds – The trade winds, westerlies and easterlies are the permanent winds. These blow constantly throughout the year in a particular direction.
    2. Seasonal winds – These winds change their direction in different seasons.
      • For example, monsoons in India.
    3. Local winds – These blow only during a particular period of the day or year in a small area.
      • For example, land and sea breeze. Do you recall the hot and dry local wind of northern plains of India it is called loo.
Moisture
  • Water evaporates from land and different water bodies, it becomes water vapour.
  • Moisture in the air at any time, is known as humidity.
  • Water vapour condenses causing formation of droplets of water. Clouds are just masses of such water droplets. these droplets of water become too heavy to float in air, then they come down as precipitation
  • Three types of rainfall:
    • The convectional rainfall.
    • The orographic rainfall and
    • The cyclonic rainfall.

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