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Frost   [ Meteorology  ]

Dictionary of botanic terminology - index of names

  1) Deposition of ice on the earth's surface when the temperature falls below freezing  
  2) Freeze: weather cold enough to cause freezing  
  3) Plant damage damage by frost;  
  The formation of  ice crystals on a land surface or on exposed objects like tree branches, plant stems, leaves, wires, etc. when the temperature of the frosted object fall below freezing.
Frost, like snow, is the result of sublimation (conversion of water vapour directly to ice in saturated air). If solid surfaces in contact with the air are chilled below the deposition point (see freezing point), then spicules of ice grow out from the solid surface. The size of the crystals is a matter of time and the amount of water vapour available. Frost develops under conditions similar to dew, except that the temperature is 0C degrees or lower. There are frequently questions as to how frost can occur when the reported temperature is in the mid or even upper 1C. This is because the official thermometers are always about 1,50 m above the ground suface. On clear, calm nights, the temperature at the ground can be several degrees lower, thus allowing the formation of frost.
Tender plants will suffer extensive damage or die when exposed to frost.
Frost can be light or heavy and may occur in a variety of forms. When thick enough to produce marked whitening of vegetation (especially grass), it is called hoar frost.

Frost is also used to describe the icy deposits of water vapour that form on such surfaces as windows and windshields, which are colder than the surrounding air and which have a temperature below freezing





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