Ch – 4 Air

  • Our earth is surrounded by a huge blanket of air called atmosphere.
  • Nitrogen (78%) and oxygen (21%) are two gases which make up the bulk of the atmosphere.
  • Carbon dioxide, helium, ozone, argon and hydrogen are found in lesser quantities.
  • Carbon dioxide released in the atmosphere creates a green house effect by trapping the heat radiated from the earth. It is therefore called a greenhouse gas
  • Atmosphere has 5 layers. They are:
    • Troposphere
    • Most important layer
    • Average height is 13 km
    • Weather phenomena occurs here
    • Stratosphere
    • Extends up to 50 km
    • Ideal for flying aeroplanes
    • Contains ozone layer
    • Mesosphere
    • Extends up to 80 km
    • Meteorites burn in this layer
    • Thermosphere
    • Extends between 80-400 km
    • Temperature increases with height
    • Helps in radio transmission
    • Exosphere
    • Light gases like helium and hydrogen float here
  • Weather is this hour-to-hour, day to day condition of the atmosphere.
  • The average weather condition of a place for a longer period of time represents the climate of a place.
  • The degree of hotness and coldness of the air is known as temperature.
  • Insolation is the incoming solar energy intercepted by the earth.
  • Air pressure is defined as the pressure exerted by the weight of air on the earth’s surface.
  • The air always moves from high pressure areas to low pressure areas.
  • The movement of air from high pressure area to low pressure areas is called wind.
  • Winds are of three types:
    • Permanent Winds
    • Blow throughout the year
    • Blow in a particular direction
    • Trade winds, westerlies and easterlies are permanent winds
    • Seasonal winds
    • Change direction in different seasons
    • Local winds
    • Blow only during a particular period
    • Eg: loo
  • Moisture in the air at any time, is known as humidity.
  • Precipitation that comes down to the earth in liquid form is called rain.
  • On the basis of mechanism, there are three types of rainfall: the convectional rainfall, the orographic rainfall and the cyclonic rainfall.
  • Other forms of precipitation are snow, sleet, and hail.

Published by Priya Prakash

In the midst of winter, i found there was within me an invincible summer ~ Albert Camus

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