NCERT Notes: Geography - Air

 

COMPOSITION OF THE ATMOSPHERE

• Nitrogen-is the most plentiful gas in the air.
• Plants need nitrogen for their survival.
• Oxygen- is the second most abundant gas in the air.
• Humans and animals take oxygen from the air as they inhale.
• Carbon dioxide- is another most important gas.
• Green plants use carbon dioxide to make their food and release oxygen.
• Argon

STRUCTURE OF THE ATMOSPHERE

Our atmosphere is divided into five layers starting from the earth’s surface.

• Troposphere-the most important layer of the atmosphere. Its average height is 13 km. The air we inhale exists here. Most weather phenomena like rainfall, hailstorm, etc. occur in this layer.
• Stratosphere- just above the troposphere lies the stratosphere. It extends up to a height of 50 km. Being free from associated weather phenomenon, this layer is most ideal for flying aeroplanes. Contains ozone.
• Mesosphere-: This is the next & third layer of the atmosphere. It lies above the stratosphere. It extends up to a height of 80 km.
• Thermosphere -In thermosphere temperature rises very rapidly with increasing height. The ionosphere is a part of this sphere. It extends between80-400 km. This layer helps in radio communications.
• Exosphere-The last & upper most layer of the atmosphere is known as exosphere.

WEATHER AND CLIMATE

• Weather is 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.
• Temperature-The degree of hotness and coldness of the air (body) is known as temperature.
• Air Pressure-is defined as the pressure exerted by the weight of air on the earth’s surface.
• Wind-The movement of air from the high-pressure area to low-pressure areas is called wind.
• Winds can be broadly divided into three types
  • Permanent winds – The trade winds, easterlies and westerlies are the permanent winds. They blow throughout the year constantly in a particular direction.
  • Seasonal winds – These winds change their direction in different seasons- example monsoon winds in India.
  • Local winds – These winds blow only during a certain period of the day or year in a small area. For example, land breeze and sea breeze. – Ex-hot and dry local wind of northern plains of India is called loo.