| Schoolchildren in Chandigarh beat the chill as they wait for their bus. (Reuters)
New Delhi, Jan. 24: The wet New Year’s eve across north India may not have dampened the revelry, but weather scientists are blaming the low pressure “system” that triggered the rain that day for the intense cold wave.
The “western disturbance” — the weather scientists’ term for the low pressure zones that move into India from western Asia — had triggered widespread rain in north India. As a result, the atmosphere above the northern plains was laden with moisture.
The cold winter winds from the north-west combined with this moisture to spark the cold wave and the fog, pushing temperatures 8-14 degrees below normal.
Another strong western disturbance might have broken that cold spell, and a fresh wave did not turn up until early this week.
Though day temperatures have now started rising in Delhi and neighbouring northern regions, the cold wave persists across much of Uttar Pradesh and Bihar.
The maximum day temperature was 14 degrees below normal in Lucknow and 10 degrees below normal in Benares, Indian Meteorological Department (IMD) officials said. The minimum temperatures in several cities have stayed 6-8 degrees below normal.
The officials said there was nothing unusual about the fog this year. In recent years, Delhi has had fog for 21-30 days in January.
“This year, we have had fog for 22 days so far, which is well within weather variability,” said Suresh Kumar Srivastava, IMD additional director-general.
But meteorologists conceded that pollution in cities may be helping the fog persist long past sunrise.
“Pure fog lifts within a couple of hours after sunrise, but fog mixed with dust particles and other pollutants blocks solar radiation, prevents ground heating and persists much longer,” said Govind Ballabh Pant, director, Indian Institute of Tropical Meteorology, Pune.
According to Pant, the pollution slows the ground heating process that keeps the maximum day temperature relatively close to the minimum temperature. As a result, such days are unusually cold.
Scientists said it is impossible to link the cold weather this year with climate change. “Climate change is a reality that can’t be ignored. But no one can yet authentically claim that climate change is influencing such regional weather phenomenon,” Srivastava said.