High moisture, no wind caused worst fog spell

This January, the capital witnessed one of the worst and most unusual spells of dense fog.

This January, the capital witnessed one of the worst and most unusual spells of dense fog. However, the worst is now over and though Delhi will witness more fog days, you wouldn’t have to drive in zero visibility or face major flight delays.

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“The winter season is in the recovering phase now. There could be dense fog in the morning but the duration will be shorter,” said R.K. Jenamani, director-in-charge, met unit, Indira Gandhi International Airport. “February is expected to see just five to six days of dense fog.”

Though things are looking up, January saw the worst fog in the last 12 years. This month, the airport witnessed 172 hours of dense fog, breaking the record of 168 hours of dense fog in January 2003.

What was unusual about fog this winter is that while Dec 2009 saw only a couple of hours of dense fog, the fog in January has been unusually long and disruptive.

“This month, there was no strong wind movement to blow away the fog and moisture was present persistently, leading to dense fog,” he said.

Did pollution lead to this unusual spell of fog?

The met department thinks otherwise. Jenamani said when moisture clings to pollutants, it results in haze or shallow fog but never dense fog.

“Pollution doesn’t cause the formation of dense fog,” said B.P. Yadav, Director, IMD. “Pollution was present in December and during winter last year, but we didn’t witness such a spell of fog.”

“The persistent spell of dense fog was caused by stable weather conditions,” he said.

Dense fog would set in, in the evenings and would continue till late in the morning.

“There was slight rain on two occasions which provided moisture. When the temperature dipped, water vapour got condensed and fog formed,” he said.

Unusually, it was the maximum temperature that saw a dip.

“The minimum temperature never went below normal. While the minimum didn’t dip below 5 degree Celsius, the maximum hovered around 13 degree Celsius,” he said.