Ground Frost
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Ground frost refers to the various coverings of
ice Ice is water that is frozen into a solid state, typically forming at or below temperatures of 0 ° C, 32 ° F, or 273.15 K. It occurs naturally on Earth, on other planets, in Oort cloud objects, and as interstellar ice. As a naturally oc ...
produced by the direct deposition of
water vapor Water vapor, water vapour, or aqueous vapor is the gaseous phase of Properties of water, water. It is one Phase (matter), state of water within the hydrosphere. Water vapor can be produced from the evaporation or boiling of liquid water or from th ...
on objects and trees, whose surfaces have a temperature below the
freezing point The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state of matter, state from solid to liquid. At the melting point the solid and liquid phase (matter), phase exist in Thermodynamic equilib ...
of water (0 °C, 32 °F).


Types

The three main types of ground frost are radiation frost ( hoar frost), advection frost ( advection hoar frost) and evaporation frost. The latter is a rare type which occurs when surface moisture evaporates into drier air causing its temperature at the surface to fall at or under the freezing point of water. Rime (both soft and hard) is technically not a type of ground frost.


Alternative definition

Ground frost may also refer to the condition when the temperature of the upper layer of the soil falls below the freezing point of water.


In England

From 1906 to 1960 the
Met Office The Met Office, until November 2000 officially the Meteorological Office, is the United Kingdom's national weather and climate service. It is an executive agency and trading fund of the Department for Science, Innovation and Technology and ...
practice was to base the number of days of ground frost on this criterion: a day with a minimum temperature reaching 30 °F (−1 °C), probably because 32 °F (0 °C) was not considered enough cold to cause damage to growing plants. Since 1961 the statistics have referred to the ''number of days with grass minimum temperature below 0°C''. Occasionally, the term ground frost can still be seen, but it means simply a minimum temperature below 0 °C.


In Finland

Typical depth of frost in Finland is 0–200 cm in winter. If the frost does not melt completely during the summer, it is called
permafrost Permafrost () is soil or underwater sediment which continuously remains below for two years or more; the oldest permafrost has been continuously frozen for around 700,000 years. Whilst the shallowest permafrost has a vertical extent of below ...
.


See also

*
Frost Frost is a thin layer of ice on a solid surface, which forms from water vapor that deposits onto a freezing surface. Frost forms when the air contains more water vapor than it can normally hold at a specific temperature. The process is simila ...
* Frost (temperature)


References

{{Authority control Snow or ice weather phenomena