What is a cold wave?
- Wind chill factor is taken into account while declaring the cold wave situation. Wind chill factor is a measure of the rate of heat loss from skin that is exposed to the air.
- The wind chill effective minimum temperature (WCTn) is defined as the effective minimum temperature due to wind flow. For eg: when the minimum temperature is 15 degree Celcius and the wind speed is 10 mph, WCTn will be 10.5 degree celsius.
- Departure of WCTn from normal minimum temperature is from –5° C to –6° C where normal minimum temperature above 10 degree Celsius and from –4 degree Celsius to –5 degree Celsius elsewhere, Cold Wave is declared.
- For declaring cold wave WCTn only is used and when it is below 10 degree Celsius only, cold wave is considered (this criteria does not hold for coastal stations).
- Cold wave is declared when WCTn is below 0 degree celsius irrespective of the normal minimum temperature for those stations.
- Indian Meteorological Department (IMD) declares a cold wave in India.
Why in the news?
- Since the minimum temperatures touched 10 degree celsius in Delhi and NCR region, the IMD was about to declare that the region was under the cold wave.