What caused the recent unprecedented fog in Delhi-NCR? Decoding factors
The intensity and duration of the recent spell of fog was never seen before for many in Delhi-NCR, some of whom took to social media to share visuals.
While fog is not uncommon for Delhi and other parts of the national capital region (NCR) such as Ghaziabad, Noida and Gurugram during this time of the year, the cities witnessed freakishly foggy conditions that peaked on Friday night and continued till Saturday morning.
The intensity and duration of this particular spell of fog was never seen before for many in Delhi-NCR, some of whom took to social media to share visuals of the foggy scenes that showed nothing but ghostly haze that made even the nearest objects hard to see.
In pics | Dense fog blinds Delhi, Ghaziabad, Noida; season's longest zero visibility spell
The zero visibility conditions, which was also the season's longest spell of fog as per the India Meteorological Department (IMD), led to dozens of flights and trains getting affected.
Even though fog and haze is common, what caused such a blinding fog situation in Delhi-NCR this week?
What causes fog?
Fog forms when the air near the ground cools down to a temperature where moisture in the air condenses into tiny water droplets, making the air appear misty or cloudy.
This typically happens during the night when temperatures drop, and the ground cools rapidly, causing moisture to form fog. Several factors can influence fog formation, including temperature, wind speed, moisture content in the air, and topography.
Indo-Gangetic plains most vulnerable to fog
The Indo-Gangetic plains, on which Delhi also lies, are most vulnerable to dense fog. The flat, low-lying topography of the region contributes to poor air circulation, which means that fog can remain trapped for long periods, according to information found through online sources.
The Indo-Gangetic Plains (IGP) of India is made up of five states: Punjab, Haryana, Uttar Pradesh, Bihar, and West Bengal. The northwestern part of the IGP is called the Trans-Gangetic Plains (TGP), includes Delhi, Chandigarh, Punjab, and Haryana.
What caused Delhi's recent blinding fog
Meteorological factors such as temperature drop, low wind speeds and high humidity played a significant role. Another reason for the fog was a western disturbance and its interaction with easterly winds recently caused rainfall and thunderstorms over northwest and central India, including Delhi-NCR.
- Temperature drop: During winter, particularly in the early morning, the surface temperature in the Delhi-NCR region drops significantly. This cooling of the ground air causes moisture to condense, forming fog.
- Low wind speeds: Winds typically help disperse fog, but with calm winds or very light breezes, the fog lingers longer. The lack of wind in Delhi-NCR allowed the dense fog to persist for an extended period and even deteriorated the Air Quality Index (AQI).
Weather scientists cited in a Times of India report attributed no winds, an abundance of moisture near the surface layer, and a highly stable surface boundary layer as the reasons for the fog situation in Delhi-NCR.
Also Read | Delhi fog: City sees season's longest zero visibility spell; 400 flights delayed
- Western disturbance: As mentioned above in this report, Delhi and its adjoining areas received rain recently due the impact of a western disturbance. These disturbances bring moisture to the region, sometimes causing fog when combined with the cold air, although in this case, they may have added moisture without clearing the fog.
- High humidity: The moisture content in the air played a significant role. Following rains and the influx of moisture from the Arabian Sea or Bay of Bengal, the humidity levels in the region were high, contributing to fog formation.
- Pollution: The fog situation got extreme as the meteorological factors were also coupled by poor air quality in Delhi and NCR. Dropping temperatures, calm winds, high humidity along with air pollution-causing factors like vehicle emission and constructions, led to the fog trapping pollutants close to the ground, making the situation worse.
A thick layer of fog enveloped several areas of Delhi for a third consecutive morning, leading to an impact on flight, train and road traffic on Sunday. The Met office said there was zero visibility at Palam between 4 am and 7:30am. On Saturday, Palam had recorded a nine-hour spell of zero visibility.
Also Read: Aerial footage captures Delhi wrapped in a thick blanket of fog: ‘A haunting morning’
Delhi's air quality was in the 'very poor' category, with an Air Quality Index (AQI) reading of 372 at 9 am on Sunday, according to Central Pollution Control Board data.
An AQI between zero and 50 is considered 'good', 51 and 100 'satisfactory', 101 and 200 'moderate', 201 and 300 'poor', 301 and 400 'very poor', and 401 and 500 'severe'.
