Why did North India fog so heavily last week?

January 11, 2024
Posted by: OptimizeIAS Team
Category: DPN Topics

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Why did North India fog so heavily last week?

Subject: Geography

Section: Climatology

Context:

In late December 2023 and early 2024, northern India faced severe winter conditions characterized by low temperatures and dense fog.
Affected regions are: Punjab, Haryana, Chandigarh, Rajasthan, Uttarakhand and Uttar Pradesh, Bihar and Madhya Pradesh.

What is fog?

Fog is the result of small water droplets forming when evaporated water cools and condenses.
Fog is a thick cloud near the earth’s surface, dependent on lower temperatures and abundant surface moisture.
Fog forms when there’s a temperature difference between the ground and the air, common during Indian winters.
High humidity, along with ample moisture, contributes to the creation of foggy conditions.
Mechanisms:
- Infrared Cooling: Occurs during the transition from summer to winter, with warm, moist air coming into contact with cooling processes, leading to rapid condensation and fog formation.
Types of fog:
- Radiation Fog: Prevails after an unseasonably warm day with high humidity, followed by a rapid temperature drop.
- Advectional fog: Fogs formed by condensation of warm air when it moves horizontally over a cold surface, are known as advectional fog. These fogs are thick and persistent. Occurs over warm and cold water mixing zones in oceans.
- Frontal or precipitation fog: It is produced due to convergence of warm and cold air masses where warm air mass is pushed under by the heavier cold air mass.
  - Precipitation in the warm air mass condenses to produce fog at the boundary of the two air masses. These are called frontal or precipitation fog.
Various environmental conditions determine the specific type, duration, and effects of fog, including its impact on snow melting.

Why is northern 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.
Moisture incursion into this region can happen due to Western Disturbance and sometimes Arabian sea.

Other forms of condensation:

1. Dew	When the moisture is deposited in the form of water droplets on cooler surfaces of solid objects (rather than nuclei in air above the surface) such as stones, grass blades and plant leaves, it is known as dew. The ideal conditions for its formation are clear sky, calm air, high relative humidity, and cold and long nights. For the formation of dew, it is necessary that the dew point is above the freezing point.
2. White Frost	Frost forms on cold surfaces when condensation takes place below freezing point (0° C), i.e. the dew point is at or below the freezing point. The excess moisture is deposited in the form of minute ice crystals instead of water droplets. The ideal conditions for the formation of white frost are the same as those for the formation of dew, except that the air temperature must be at or below the freezing point.
3. Mist	The difference between the mist and fog is that mist contains more moisture than fog. In mist each nuclei contains a thicker layer of moisture. Mists are frequent over mountains as the rising warm air up the slopes meets a cold surface. Mist is also formed by water droplets, but with less merging or coalescing. This means mist is less dense and quicker to dissipate. Fogs are drier than mist and they are prevalent where warm currents of air come in contact with cold currents. In mist visibility is more than one kilometer but less than two kilometres.
4. Haze	Haze is traditionally an atmospheric phenomenon where dust, smoke and other dry particles obscure the clarity of the sky (No condensation. Smog is similar to haze but there is condensation in smog). Sources for haze particles include farming (ploughing in dry weather), traffic, industry, and wildfires.