Model Answer

Fog is a meteorological phenomenon in which microscopic water droplets or ice crystals remain suspended near the Earth’s surface, reducing horizontal visibility to less than 1 kilometre. It occurs when air becomes saturated either due to cooling to the dew point or increase in moisture content. During winter, northern India frequently experiences dense fog owing to favourable atmospheric conditions.

Formation of Fog

Fog forms through multiple physical processes:

1. Radiational cooling during long winter nights lowers surface temperatures.
2. Advection of warm, moist air over colder surfaces leads to condensation.
3. Evaporation and mixing increase moisture levels to saturation.
4. Orographic uplift cools rising air along slopes.
5. Temperature inversions and calm winds trap cold, moist air near the surface. High humidity, weak wind conditions, and stable atmospheric layers are crucial enabling factors.

Major Types of Fog

a. Radiation Fog Forms on clear, calm winter nights when the ground loses heat rapidly. Common over northern plains and usually dissipates after sunrise. b. Valley Fog A denser and more persistent form of radiation fog where cold air drains into valleys and remains trapped. c. Advection Fog Occurs when moist air moves horizontally over colder land or ocean surfaces and may persist even during daytime. d. Freezing Fog Consists of supercooled droplets that freeze on contact, creating icy surfaces and posing severe safety hazards. e. Evaporation (Mixing) Fog Develops when warm water vapour mixes with colder air, commonly seen over water bodies or during rainfall.

Impacts on Weather and Society

• Transport Disruptions: Near-zero visibility leads to delays and accidents in road, rail, and aviation sectors.
• Prolonged Cold Conditions: Fog suppresses solar radiation, delaying daytime warming.
• Air Quality Deterioration: Fog traps pollutants, intensifying smog and increasing respiratory illnesses.
• Economic Losses: Delays in logistics, agriculture operations, and urban mobility affect productivity.
• Administrative Challenges: Requires timely weather forecasting, public advisories, and disaster preparedness by agencies like IMD.

Fog is not merely a weather inconvenience but a complex atmospheric phenomenon with significant socio-economic consequences. Improved forecasting, integrated air-quality management, and adaptive urban planning are essential to mitigate its growing impacts in a changing climate.