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Ch-4 | Climate of India | NCERT Class 9

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SUMMARY

  • Climate refers to the sum total of weather conditions and variations over a large area for a long period of time (more than thirty years).
  • Weather refers to the state of the atmosphere over an area at any point of time.
  • The elements of weather and climate are the same, i.e. temperature, atmospheric pressure, wind, humidity and precipitation.
  • The climate of India is described as the ‘monsoon’ type. In Asia, this type of climate is found mainly in the south and the southeast.

CLIMATE CONTROL

There are six major controls of the climate of any place. They are:

  • Latitude: Due to the curvature of the earth, the amount of solar energy received varies according to latitude. As a result, air temperature generally decreases from the equator towards the poles.
  • Altitude: As one goes from the surface of the earth to higher altitudes, the atmosphere becomes less dense and temperature decreases. The hills are therefore cooler during summers.
  • Pressure and wind system: The pressure and wind system of any area depend on the latitude and altitude of the place. Thus it influences the temperature and rainfall pattern.
  • Distance from the sea (continentality): The sea exerts a moderating influence on climate: As the distance from the sea increases, its moderating influence decreases and the people experience extreme weather conditions. This condition is known as continentality (i.e. very hot during summers and very cold during winters).
  • Ocean currents: Ocean currents along with onshore winds affect the climate of the coastal areas, For example, any coastal area with warm or cold currents flowing past it, will be warmed or cooled if the winds are onshore.
  • Relief features: relief too plays a major role in determining the climate of a place. High mountains act as barriers for cold or hot winds; they may also cause precipitation if they are high enough and lie in the path of rain-bearing winds. The leeward side of mountains remains relatively dry.

FACTORS AFFECTING INDIA’S CLIMATE

  • Altitude: The Himalayas prevent the cold winds from Central Asia from entering the subcontinent. It is because of these mountains that this subcontinent experiences comparatively milder winters as compared to central Asia.
  • Pressure & Winds: The climate and associated weather conditions in India are governed by the following atmospheric conditions:
    • Pressure and Surface Winds.
    • Upper Air Circulation.
    • Western Cyclonic Disturbances and Tropical Cyclones.

INDIAN MONSOON

  • The word monsoon is derived from the Arabic word ‘mausim’ which literally means season.
  • ‘Monsoon’ refers to the seasonal reversal in the wind direction during a year.
  • In summer, a low-pressure area develops over interior Asia as well as over northwestern India.
  • This causes a complete reversal of the direction of winds during summer.
  • Air moves from the high-pressure area over the southern Indian Ocean, in a south-easterly direction, crosses the equator, and turns right towards the low-pressure areas over the Indian subcontinent. These are known as the Southwest Monsoon winds.
  • These winds blow over the warm oceans, gather moisture and bring widespread rainfall over the mainland of India.
  • Jet Streams important for South-West Monsoon: Sub-Tropical Easterly JetStream
    Jet Streams important for North-East Monsoon: Sub-Tropical Westerly JetStream
  • The monsoons all over the world are experienced in the tropical area only, roughly between 20° N and 20° S.

Note: The Process of Monsoon & other concepts such as El Nino, La Nina, ENSO & Indian Ocean Dipole have been discussed in separate Video Lectures.

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