Why Did North India Fog So Heavily Last Week?

What’s in Today’s Article?

• Background
• What is Fog?
• Why is North India Prone to Fogging?

Background

• A thick blanket of fog descended on several states of northern India in the last days of 2023 and first of 2024, creating challenging conditions for residents and travelers alike.
• Some places in the country’s north reported low temperatures and dense fog for the last week of December.
• According to weather reports in late December 2023, minimum temperatures in Punjab, Haryana, and the northern reaches of Rajasthan and Uttar Pradesh hovered around 6-9 degrees C.
• In New Delhi, south Rajasthan, and north Madhya Pradesh, some places recorded minimum temperatures in the range of 10-12 degrees C, according to the India Meteorological Department (IMD).
• In the same time, most of North India also experienced a dense fog that reduced visibility in many areas to as little as 50 metres for several days.
• Haryana, including Chandigarh, plus isolated pockets of Uttarakhand, Uttar Pradesh, Bihar, Rajasthan, and Madhya Pradesh reported fog with visibility reduced to under 200 metres.

What is Fog?

• About
  • Fog is a common weather phenomenon.
  • It is a collection of small droplets of water produced when evaporated water has cooled down and condensed.
  • In simple terms, it is nothing but a thick cloud, but very close to the earth’s surface.
    • For a thick fog to form, temperatures should be lower and abundant moisture should be available near the surface.
• Formation
  • Fog materialises whenever there is a temperature disparity between the ground and the air.
    • This happens frequently during Indian winters: the fog is created when the temperature drops at night and in the early morning, condenses on aerosols present in the atmosphere.
  • High humidity, combined with an ample presence of water vapor or moisture, encourages foggy conditions.
  • The process by which it cools plays a pivotal role in the formation of fog.
• Mechanism
  • One primary mechanism contributing to fog formation is called Infrared Cooling.
    • It typically occurs when the weather is transitioning from summer to winter.
    • In the summer, the ground absorbs radiation from the Sun, becomes warmer, and moistens the air passing over it.
  • When cooler weather kicks in, this mass of warm, moist air comes in contact with processes that cool it.
  • The ‘collision’ prompts the water vapor in the air to condense rapidly, giving rise to fog.
• Other types
  • Another type of fog, known as radiation fog, is prevalent and occurs when an unseasonably warm day with high humidity is followed by rapidly dropping temperatures.
  • The specific type of fog, its duration, and its effects are contingent on various environmental conditions.
  • For example, there exists a unique type of fog that encourages snow to melt faster.

Why is North India Prone to Fogging?

• The entire Indo-Gangetic plains are prone to formation of fog during winter season, as all the conditions — low temperatures, low wind speed, moisture availability and plenty of aerosols — are present in this region.
• Winds called the Western Disturbances, originating in the Mediterranean, bring in moisture to Northern India.
  • Sometimes, the Arabian Sea also elevates the moisture content in the northern region.
• Moreover, the Himalayas in the north act as a barrier, preventing the eastward movement of the fog over the plains, leading to its concentration over the Indo-Gangetic region.
• In Delhi’s case, air pollutants such as particulate matter add to the load, creating smog (smoke fog).

Source: Why did North India fog so heavily last week? | Explained | India Today

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