FOGGING 

Fog forms when the air reaches a point of saturation, meaning it can no longer hold all the water vapour it contains. This happens when either the temperature drops, causing the air to hold less moisture or the amount of moisture in the air increases. There are several ways this can occur:

• As the ground loses heat to the night sky, the air close to the surface cools down. If it reaches the dew point, the excess moisture condenses into tiny water droplets, forming a radiation fog. This is the most common type, often seen in valleys and open fields.
• When warm, moist air moves over a cold surface, such as a body of water or snow-covered land, it cools down and condenses, forming advection fog. This type is frequently seen near coastlines and mountains.
• When two air masses with different temperatures and moisture content mix, the resulting mixture can become saturated, leading to the formation of mixing fog. This type is common near fronts, where warm and cold air masses collide.

Fog's Characteristics and Features

Once formed, fog exhibits a variety of characteristics and features:

• Fog can range from wispy and ethereal to thick and impenetrable, depending on the amount of moisture present and the size of the water droplets.
•  Dense fog can significantly reduce visibility, creating hazardous conditions for transportation and other activities.
• Fog affects how light travels, scattering and diffusing it. This can create a sense of mystery and can also make colours appear muted or washed out.
• Fog acts as a natural sound absorber, muffling sounds and creating a sense of tranquillity.
• Fog provides moisture for plants and can be a vital source of water in arid regions. It can also affect the behaviour of animals, providing cover and influencing migration patterns.

4. Types of Fog 

1. Radiation fog: An update from the SAFAR forecasting system on Monday categorised the fog episode in Delhi on Monday as "radiation fog". Radiation fog (or ground fog) episodes last for a few mornings on account of calm winds and western disturbances, resulting in localised fog formation.
2. Advection fog: Advection fog is larger in scale both in terms of the area covered and duration.
   Advection fog forms when warm, moist air passes over a cool surface, causing water vapour to condense. Advection fog mostly occurs where warm, tropical air meets cooler ocean water. If the wind blows in the right direction, sea fog can be transported over coastal land areas.
3. Valley fog: It is the result of mountains preventing dense air from escaping, in which the fog is trapped in the bowl of the valley and can last for several days.
4. Freezing fog: It is the result of liquid droplets freezing on solid surfaces.  Cloud-covered mountain tops often see freezing fog. These do not apply to the Indo-Gangetic Plain.

5. Impacts of the Fog 

Fog, a mesmerizing blanket of tiny droplets suspended in the air, can transform landscapes and shroud mornings in an ethereal glow. But beneath its beauty lies a complex web of impacts, affecting the environment and society in diverse and often surprising ways. 

Positive Effects

• In dry regions, fog acts as a natural humidifier, delivering vital moisture to parched landscapes and vegetation. This can support plant growth, prevent desertification, and replenish groundwater reserves.
• Fog reflects sunlight back into space, contributing to a cooling effect on the Earth's surface. This role becomes particularly important in mitigating the impacts of climate change.
• Fog droplets can act as tiny air filters, trapping dust, pollutants, and allergens, leading to improved air quality, especially in urban areas.
• Fog provides a unique habitat for specialized plants and animals, supporting biodiversity and ecological balance in certain ecosystems.
• Fog has woven itself into the fabric of human cultures across the world, inspiring folklore, art, and literature. Its ethereal presence often holds symbolic meaning, fostering a sense of mystery and introspection.

Negative Effects

• Dense fog can significantly reduce visibility, leading to delays, accidents, and disruptions in air, sea, and road travel. This can have economic consequences, impacting tourism, trade, and transportation industries.
• Fog can trap air pollutants close to the ground, leading to respiratory problems and exacerbating existing conditions like asthma. This is particularly concerning for vulnerable populations, such as children and the elderly.
• Fog can hinder agricultural activities by delaying planting and harvesting, reducing crop yields, and hindering the movement of farm machinery.
• Dense fog can be a major safety hazard for aircraft, leading to runway closures, delays, and cancellations. This can have significant economic and logistical consequences.
•  Fog can affect the efficiency of solar and wind power generation by reducing the amount of sunlight and wind that reaches the turbines. This can strain energy grids and contribute to reliance on fossil fuels.

• The dense fog that cloaked North India in late December 2023 wasn't just an inconvenience it brought air travel and train schedules to a near standstill.
• Delhi's Indira Gandhi International Airport bore the brunt of the disruption. On December 27, a suffocating fog layer led to the delay or cancellation of nearly 450 flights, leaving passengers stranded and travel plans in disarray.
• The following days offered little respite, with almost 100 and 80 flights delayed on December 29 and 30, respectively.
• The fog's reach extended beyond the skies, impacting rail travel as well. On December 29, several Delhi-bound trains experienced delays due to poor visibility.
• The disruption was so severe that at least eight trains scheduled to arrive in the national capital the night before never made it, while others scheduled for the morning faced delays of several hours.