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Daily News Analysis

COLD WAVE          

18th December, 2021 Geography


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  • The India Meteorological Department (IMD) has predicted a cold wave in parts of Punjab, Haryana, Chandigarh, Gujarat, Rajasthan and Uttar Pradesh over the next few days.

What is a cold wave?

  • The IMD defines a cold wave qualitatively as “a condition of air temperature which becomes fatal to the human body when exposed.”
  • The IMD records a cold wave when
  1. the minimum temperature is equal to or less than 10 degree Celsius at a weather station in the plains,
  2. and the min temperature is 4.5 degrees to 6.4 degrees below the normal temperature for that period.
  • A cold wave may also be recorded at a station in the plains when the minimum temperature is less than or equal to 4 degree Celsius.
  • For hilly regions, a cold wave is declared when the minimum temperature is less than or equal to 0 degree Celsius and the minimum temperature is 4.5 degrees to 6.4 degrees below the normal.
  • The ‘normal’ temperature is calculated for every five days by taking the average temperature for these days over the past 30 years.


Cause of this cold wave

  • Cold waves usually occur from mid-December to the end of February.
  • According to the IMD, the factors that bring cold waves to India include the movement of cold air masses brought about by upper-level winds.
  • They can be triggered by strong westerly winds approaching northwest India and transporting cold air towards the southeast direction.
  • Build up of an extended area of relatively high pressure over northwest Asia can also bring cold waves.


Western Disturbance and cold wave

  • A western disturbance as a cyclonic circulation lies over north Pakistan and adjoining Jammu and Kashmir.
  • Western disturbances are storms that originate in the Mediterranean region and bring winter rainfall to northwest India.
  • After this western disturbance moves, there is a brief gap. The next western disturbance will set in only on December 22 night.
  • In this gap of five to six days, the IMD expects strong northwesterly and westerly cold winds over north India.