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radiation fog[‚rād·ē′ā·shən ‚fäg]
A major type of fog, produced over a land area when radiational cooling reduces the air temperature to or below its dew point; thus, strictly, a nighttime occurrence, although the fog may begin to form by evening twilight and often does not dissipate until after sunrise.
A type of fog formed by the cooling of the earth's surface at night, which, in turn, cools the adjoining layer of air above it rapidly to an extent that the dew point is reached. This type of fog may occur even when the relative humidity has not reached 100%. It is the result of the presence of hygroscopic nuclei, especially smoke particles, in the atmosphere. A very slight wind, a clear night, and low temperatures are prerequisites for the formation of radiation fog. Radiation fog is a common feature after the passage of cold fronts. Also known as ground fog