

For most of us, fog is simply a murky white-grey-ish cloud that hangs over an area and makes it hard to see. What you may not know, however, unless you’re a pilot, meteorologist, or citizen of an oft-foggy city like London, is just how many “types” of fog there are. Clouds deflect the blowing wind to ground level.Fog lowers visibility, which can make it harder to see where you’re going.The Earth’s surface would have a low temperature on cloudy nights.Clouds reflect back the Earth’s radiation.Clouds absorb the radiation released from the Earth’s surface.Q.2) Why are dewdrops not formed on a cloudy night? (2019) Which of the statements given above is/are correct? (2022) Low clouds have a high absorption of infrared radiation emanating from the Earth’s surface and thus cause warming effect.High clouds primarily reflect solar radiation and cool the surface of the Earth.Advection fog episodes last longer and secondary particulate formation then begins leading to rapid build-up of pollutants.Recently, Delhi recorded a spike in pollution levels with AQI in the ‘severe’ category.This results 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 also falls.

According to the India Meteorological Department (IMD), Delhi being more polluted, records more fog days compared to others.In the absence of western disturbances, local moisture sources like water vapor from rivers and soil moisture can also cause fog.This can result in increased moisture levels over the region.Western disturbances, which are storms that originate in the Mediterranean Sea, bring moisture-bearing winds to northwest India.The fall in temperature along with moisture and light winds over the Indo Gangetic Plain has resulted in dense fog over the region.Cold wave conditions, in which the minimum temperature is significantly lower than normal, have been recorded recently over Punjab, Haryana, and parts of Rajasthan.


It forms when warm, moist air passes over a cool surface, causing water vapour to condense.Advection fog is larger in scale for both area covered and duration.The Indo Gangetic Plain is most vulnerable to fog occurrences, with major, weeks-long spells of dense fog in the months of December and January.Areas near water bodies, for instance, may see denser fog because of the higher humidity.Fog can have “high spatial variability”, and its intensity can depend on factors like humidity, wind, and temperature.The presence of moisture and a fall in the temperature are key factors for the formation of fog.Fog begins to form in the early hours of the morning, when the temperature is at its lowest.Since cooler air cannot hold as much moisture as warm air, the water vapour in the air condenses to form fog.With the land surface cooling down at night, the air close to the surface also cools down.Context: Recently, dense fog has enveloped north-western India, including Delhi, Punjab, Haryana, parts of Uttar Pradesh, and parts of Rajasthan.
