COLD WAVE          

 

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Context

• 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.

 

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