Satellite Pic Shows Fog Cloaking North India Except Delhi Because...

A satellite image of North India that shows dense fog covering much of the region in a thick blanket of white had a stand-out patch of uncovered land - New Delhi.

According to geo-analytics expert Raj Bhagat Palanichamy, who posted the image on social media, the curious gap in the blanket of fog was caused by something called the Urban Heat Island Effect.

Taken at 9:15 am on Wednesday, the image demonstrates how Delhi's urban sprawl, and the resultant heat retention, has created an island of residual warmth, thus clearing out the fog.

However, amid low temperatures, high moisture and still winds, a layer of dense to very dense fog persisted over Punjab, Haryana, northwest Rajasthan, Uttar Pradesh, Bihar and parts of Uttarakhand, according to the India Meteorological Department.

Delhi reported its first foggy morning of the season on Monday, but the haze was milder than in other parts of North India through the week.

While some trains and flights have been affected because of it, the fog has generally cleared out from over much of the city's metropolitan area long before midday.

The biting cold and dense fog led to a vehicle pile-up in Uttar Pradesh on Wednesday while the harshest winter period known as 'Chilla-i-Kalan' set in Kashmir, freezing fringes of many water bodies.

At least 11 people were injured in the pile-up involving several vehicles on the Lucknow-Gorakhpur National Highway on Wednesday morning because of reduced visibility.

At 5:30 am, visibility stood at zero in Bhatinda; 25 m in Ganganagar, Amritsar and Bareilly, and 50 m in Varanasi, Bahraich and Ambala.

Conversely, only a moderate fog cloaked Delhi where 18 trains were reported late by a few hours and operations at the airport remained normal.

Three flights were returned or diverted to the Delhi airport due to bad weather in Chandigarh, Varanasi and Lucknow on Tuesday night.

The Safdarjung Observatory, the primary weather station in Delhi, recorded a minimum temperature of 7.1 degrees Celsius, a notch below normal.

The maximum temperature settled at 21.2 degrees Celsius, the lowest so far this season.

The minimum and maximum temperatures are likely to drop to 5 degrees Celsius and 20 degrees Celsius in the next few days.