Dense fog disrupted flights for hours at the Kolkata airport and delayed trains on Monday morning.
A combination of moisture, clouds and light wind contributed to the formation of the dense cover of fog, said a Met official.
The density of the fog was not uniform. Visibility in Dum Dum dipped to 25m early in the morning. During the same time, visibility in Alipore was around 200m, said a Met official. In the Sunderbans, the visibility was up to 20m.
Six incoming flights had to be diverted because poor visibility made it impossible for the planes to land, said officials. The fog disrupted flights between 4.30am and 9am, said the officials.
They said 37 departures and 20 arrivals were delayed.
The airport has Category III B instrumental landing that helps flights to operate at a minimum visibility of 50m. But airport sources said the visibility had dropped to 25m.
IndiGo’s flight from Bangalore was scheduled to land around 6am but could not because of fog. Sources said the pilot told the air traffic control that he would hover till visibility improved.
The plane hovered for more than one-and-a-half hours but the situation did not improve. “The flight's fuel was getting exhausted and so it had to be diverted to Ranchi airport,” said an official.
Five other flights were also diverted to cities like Ranchi, Guwahati and Bhubaneswar, said officials.
The fog also disrupted trains.
“Long-distance trains to and from Howrah and Sealdah were delayed by an hour to 90 minutes,” said an official of Eastern Railway.
“Both long-distance and local trains were delayed but there were no cancellations,” said an official of South Eastern Railway.
“Apart from variation in the moisture content, other factors also determine the intensity of fog in an area. The airport compound is a sprawling and open area. Alipore, in contrast, has many buildings,”said G.K. Das, director, IMD, Calcutta.
A cyclonic circulation over Jharkhand drew moisture from the Bay of Bengal and led to the formation of clouds a day before.
The clouds had triggered rain in several districts of Bengal. Salt Lake, Dum Dum and some other areas in and around Calcutta got a drizzle or two.
“The remaining moisture… led to the formation of the dense fog cover,” said Das.