Geography

Geography - Atmosphere

 

Atmosphere is the mixture of gases surrounding a planet. The major components of atmosphere are Nitrogen (around 78%), Oxygen (around 20%), Argon (around 0.9%). The other components of the atmosphere are Carbon dioxide, Neon, Helium, Krypton, Hydrogen and Ozone. Oxygen and carbon dioxide decreases at higher altitudes. Carbon dioxide is responsible for greenhouse effect. Ozone absorbs the ultra-violet rays preventing them from reaching earth’s surface.

Layers of Atmosphere
• Troposphere
 Lowermost layer of atmosphere
 Weather changes occur here
 Temperature decreases by 1 degree Celsius for every 165 meters of height
 It extends on average about 12 Km from earth. It is higher at equator and lower at poles

• Stratosphere
 It is above troposphere
 It is at about 12 to 50 Km of height above earth’s surface
 Temperature increases with height due to presence of ozone layer
 Aeroplanes fly here as air disturbance is less here

• Mesosphere
 It is above stratosphere
 It is about 50 to 80 Km of height above earth’s surface
 Temperature decreases with increase of height
 Meteors burn in this layer

• Thermosphere
 It is above mesosphere
 It is about 80 to 600 Km of height above earth’s surface
 It is known as ionosphere as it contains ions, the electrically charged particles
 Temperature increases with height
 Helps in Radio communications
 Aurora borealis is seen here
 International Space Station orbits here

• Exosphere
 It is above thermosphere
 It is the outermost layer of earth’s atmosphere
 It is about 600 to 10000 Km of height above earth’s surface
 The particles escape into space

Classification of Winds
• Primary winds (Prevailing winds or Planetary winds)
   Constantly blow in a particular direction throughout the year
   Types of Primary winds
       Trade winds (tropical easterlies)
             They blow from northeast in northern hemisphere and from                                southeast in southern hemisphere
              Used by sailing ships
    Westerlies
         They blow from high pressure areas of 30 degrees north and south                of the equator towards the poles
     Polar easterlies
           They are dry, cold winds that blow at the high-pressure areas of                       the poles
            They are weak and irregular  

• Secondary winds (Seasonal winds or Periodic winds)
      Change direction according to seasons
      Monsoon wind is a seasonal wind that reverses direction between                    summer and winter
• Tertiary winds (Local winds)
      Blow during a particular period in a particular area
      Blow due to difference in air pressure or temperature of a location
      Wind that blows from land to sea is known as land breeze and from                  sea to land sea breeze
       Mountain slopes get cooled in the night and the dense air that blows               into the valley is mountain breeze
       Mountain slopes get warmed up in the day and the wind that blows                 upslope is valley breeze