What is a cold wave and why northwest India is shivering

Subject: Geography

Context:

In Delhi, the Safdarjung weather station has recorded cold wave conditions for five consecutive days so far this month, making it the longest such spell in a decade.

Details:

The lowest minimum temperature recorded this month was 1.9 degrees Celsius on January 8, the second-lowest minimum temperature in January in 15 years.
Fog and low cloud coverage brought severe cold day conditions to the region when temperatures remained below normal over parts of Delhi, Punjab, Haryana, Chandigarh, Himachal Pradesh, Rajasthan, Uttar Pradesh and Madhya Pradesh.

What is a cold wave?

The IMD marks a cold wave in terms of minimum temperatures – when the minimum temperat5ure in the plains is 4 degrees or less or when the minimum temperature is less than 10 degrees and 4.5 to 6.4 degrees below the normal.

Major factors:

Large-scale fog cover:
- Preventing sunlight from reaching the surface and affecting the radiation balance.
- Light winds and high moisture near the land surface have been contributing to the formation of a blanket of fog over large swathes of the Indo-Gangetic plains.
Western disturbances:
- Western disturbances, which are storms from the Mediterranean region, are associated with a change in wind direction, bringing easterly winds to northwest India.
- Cold north-westerly winds have also been contributing to low temperatures.