![]() Variability: According to IMD, fog episodes over Delhi are highly variable.Mist forms when the warm, moist air suddenly cools because of cold temperatures.Its intensity can depend on factors like humidity, wind, and temperature,.These foggy spells are linked to wind and temperature patterns.Indo Gangetic Plain is most vulnerable to fog occurrences, with major, weeks-long spells of dense fog in the months of December and January.According to the India Meteorological Department (IMD), fall in temperature along with moisture and light winds over the Indo Gangetic Plain has resulted in dense fog over the region.Whereas, 501 metres to 1,000 metres of visibility is present in shallow fog conditions and 1,000 shallow.Moderate fog is identified with a visibility of 201 to 500.Visibility between 51 and 200 metres identifies fog as dense.Fog is categorised as very dense when visibility is between 0 to 50 metres.Once the temperature increases during the day, the fog dissipates.This result in fog formation and particulate matter hangs on the boundary layer, increasing pollution levels.The inversion layer comes down and vertical mixing reduces. As temperature declines, local wind speed falls.Pollution levels and Fog: Delhi being more polluted, records more fog days compared to others.Other Sources: Local moisture sources like water vapour from rivers and soil moisture can also cause fog.However, WD’s has not yet brought much moisture and did not lead to any significant fog formation until December 19.WD’s are the storms that originate in the Mediterranean Sea and bring moisture-bearing winds to northwest India.Western Disturbances (WD): It can result in increased moisture levels over the region.Prevalence of Cold Wave: Cold wave conditions, in which the minimum temperature is significantly lower than normal, have been recorded recently over Punjab, Haryana, and parts of Rajasthan.Types of Fog Fog Episode in North-Western India As the freezing fog lifts, the ground, the trees, and even objects like spider webs, are blanketed by a layer of frost.Mountain tops that are covered by clouds are often covered in freezing fog.Freezing Fog: It happens when the liquid fog droplets freeze to solid surfaces.The fog is trapped in the bowl of the valley. It develops when mountains prevent the dense air from escaping.Valley Fog: It forms in mountain valleys, usually during winter.Advection fog shows up mostly in places where warm, tropical air meets cooler ocean water.When the moist, warm air makes contact with the cooler surface air, water vapor condenses to create fog.Advection Fog: It forms when warm, moist air passes over a cool surface.According to SAFAR forecasting system, fog episode in Delhi is categorised as “radiation fogâ€.Fog that is said to “burn off†in the morning sun is radiation fog.As heat is transferred from the ground to the air, water droplets form. ![]()
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