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01 Climate

Weather refers to the state of the atmosphere over an area at any point of time. Weather conditions may fluctuate often. Climate refers to the sum total of weather conditions and variations over a large area for a long period of time (over 30 years). The elements of weather and climate are: temperature, atmospheric pressure, wind, humidity and precipitation.

Climatic conditions in India:

  • In India, we have the ‘monsoon’ type of climate which refers to the seasonal reversal in the wind direction during a year.

Climatic Controls

Climate is controlled by six major factors. They are Latitude, Altitude, Pressure and wind system, Distance from the sea, Ocean currents and Relief features.

Factors Affecting India’s climate

Pressure and wind

  • Major atmospheric conditions that govern the Indian climate and its associated weather conditions are:
    • Pressure & surface winds;
    • Upper air circulation;
    • Western Cyclonic disturbances; and
    • Tropical cyclones.

The Indian Monsoon

  • The following facts help understand the mechanism of monsoon
    • Differential heating and cooling of land and water
    • Shift of the position of Inter Tropical Convergence Zone (ITCZ)
    • Presence of high pressure area, east of Madagascar
    • Intense heating of the Tibetan plateau
    • The movement of the westerly Jet Stream
    • Southern Oscillation (SO)
    • El Nino

The Onset of the Monsoon and Withdrawal

  • As monsoon arrives, the normal rainfall increases suddenly and continues constantly for several days. This is known as the ‘burst’ of the monsoon.

Withdrawal or the retreat of the monsoon

  • By early September, monsoon starts to withdraw from the north-western states.
  • It withdraws completely from the northern peninsula by mid-October.
  • The rest of the country stops experiencing monsoon by early December.

The Seasons

  • In India, there are 4 main seasons the cold weather season, the hot weather season, the advancing monsoon and the retreating monsoon.

Winter: The Cold Weather Season

  • In northern India, the cold weather season is experienced from mid-November and till February.

Summer: The hot weather season

  • In India, this season lasts from March to May.
  • Summer is characterized by rising temperature and falling air pressure in the northern part of the country.

Rainy Season: Advancing monsoon

  • The south east trade winds originate over the warm subtropical areas of the southern oceans and enter the peninsula as south west monsoon after they cross the equator and blow south westerly.
  • The trough and its axis keep on moving northward or southward, which determines the spatial distribution of rainfall.
  • The frequency and intensity of tropical depressions too, determine the amount and duration of monsoon rains.

Transition Season: Retreating/ Post Monsoon

  • The monsoon or low pressure weakens in the northern plain and is replaced by a high pressure system.
  • The trough moves towards the south with the apparent movement of the sun during October-November.

Distribution of Rainfall

  • Due to the nature of monsoons, annual rainfall varies from year to year.

Monsoon as a Unifying Bond

  • The Himalayas act as a barrier and protect India from the cold winds of central Asia.
  • Due to moderating influences of the sea, the peninsular plateau has moderate temperature.
  • Due to seasonal alterations of the wind systems and associated weather conditions, a rhythmic cycle of seasons exist.

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