COLD WAVE | IAS GYAN

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Context

Cold wave conditions will continue in North India -India Meteorological Department.

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

the minimum temperature is equal to or less than 10 degree Celsius at a weather station in the plains,
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. In this gap of five to six days, the IMD expects strong northwesterly and westerly cold winds over north India.