Fog

Formation:

• The air near the surface cools at night as a result of the land surface cooling.
• Fog forms when water vapour in the air condenses because cooler air cannot hold as much moisture as warmer air.
• Early in the morning, when the temperature is at its lowest, fog starts to form.

Favourable Conditions:

• Two of the most important conditions for the formation of fog are moisture content and a drop in temperature.
• There can be “high spatial variability” in fog, and temperature, wind, and humidity can all affect how thick the fog is.
• Because of the increased humidity, areas close to bodies of water, for example, may experience denser fog.
• The months of December and January see significant, weeks-long periods of heavy fog, with the Indo Gangetic Plain being most susceptible to these occurrences.

Types of fog

Advection fog

• The area covered and duration of advection fog are larger.
• It originates from the condensation of water vapour on a cool surface by warm, humid air.
• It happens at the interface of cool ocean water and warm tropical air.
• When the wind blows in the proper direction, sea fog spreads across coastal regions.

Valley fog

• is the result of mountains blocking the escape of dense air.
• For several days, fog is trapped at the valley’s bottom.

Freezing fog

• is result of liquid droplets freezing on solid surfaces.
• On cloud-covered mountaintops, it happens.
• The Indo Gangetic Plain does not contain them.

Conditions Favouring Fog over North-western India

Decreasing Temperature:

• In northwest India, the temperature has started to drop.
• Six degrees Celsius is the lowest minimum temperature Delhi has seen this season.
• Recent reports of extremely low minimum temperatures over Punjab, Haryana, and portions of Rajasthan indicate the presence of cold wave conditions.

Dense Fog:

• There is a lot of fog over the Indo Gangetic Plain as a result of the temperature dropping, moisture, and light winds.

Effect of Western disturbances:

• Winds carrying moisture are brought to northwest India by western disturbances, which are storms that originate in the Mediterranean Sea.
• This may cause the region’s moisture content to rise.
• Local moisture sources such as soil moisture and river water vapour can also produce fog in the absence of western disturbances.