As the temperatures kept plummeting, Delhi once again woke up to chills this morning, engulfed in thick clouds of smog and bringing down visibility to a minimum.
However, as per India Meteorological Department (IMD), the respite lies around the next corner as they predict that temperatures may rise from Wednesday onwards owing to a western disturbance. Fog, according to IMD, will attenuate which would allow more sunlight to hit the surface.
The cold wave spell continued in Delhi and other northern parts of India as the minimum temperature in Delhi was recorded at 7 degrees Celcius on early Tuesday morning.
According to the IMD, a "cold day" is when the minimum temperature is less than 10 degrees Celsius and the maximum is at least 4.5 degrees Celsius below normal.
A "severe" cold day is when the maximum temperature is at least 6.5 notches below normal.
The IMD declares a cold wave in the plains if the minimum temperature dips to 4 degrees Celsius, and also when the minimum temperature is 10 degrees Celsius or below and is 4.5 notches less than normal.
A few places in the capital also reported a cold day on Sunday— when the minimum temperature is less than or equal to 10 degrees Celsius and the maximum temperature is at least 4.5 degrees Celsius below normal. Delhi's primary weather station, Safdarjung observatory, recorded a minimum temperature of 5.3 degrees Celsius -- three notches below normal, and the maximum temperature settled at 16.2 degrees Celsius, five notches below normal and the lowest so far this season.
Moreover, a ‘severe’ cold wave is when the minimum temperature dips to two degrees Celsius or the departure from normal is more than 6.4 degrees Celsius.
What causes the cold wave?
“The winds were west-northwesterly but now they are north-northwesterly, blowing at about 10kmph over Delhi. A layer of upper haze when morning fog hasn’t lifted completely and is also obscuring sunshine during the day giving a feel of biting cold. These conditions will last for a day before temperatures rise gradually," Mahesh Palawat, vice president, climate and meteorology, at Skymet Weather, was quoted saying by several media reports.
A cold wave can result from cloud cover, or more precisely, from a lack of cloud cover. A decrease in cloud cover causes more heat to escape from the Earth's surface, resulting in a cooler surface and lower temperatures because clouds absorb infrared radiation from the planet.
Cold waves also occur because of a weather phenomenon known as La Nia that develops in the Pacific Ocean. Cold water sinks beneath warm water. La Nia is a weather anomaly that causes these warm seas to blow in the direction of Indonesia. This causes cold water to surface and rise as a result. This rise in surface cold water leads to a cooling effect.
Besides, non-seasonal or non-monsoon rainfall is another major cause of cold waves.