Frost 11763 225977897 2008-07-16T08:30:26Z Constan69 521547 /* Window frost */ Added link. {{refimprove|date=December 2007}} {{otheruses}} [[Image:Frost on black pipes.jpg|thumb|right|Frost on black pipes]] '''Frost''' is the solid [[deposition (meteorology)|deposition]] of [[water vapor]] from [[Saturation (chemistry)|saturated]] air. It is formed when solid surfaces are cooled to below the [[dew point]] of the adjacent air.<ref>{{cite web |url=http://www.weatherquestions.com/What_causes_frost.htm |title=What causes frost? |accessdate=2007-12-05 |format= |work= }}</ref> Frost crystals' size differ depending on time and water vapor available. Frost is also usually [[translucent]] in appearance. There are many types of frost, such as radiation and window frost. Frost causes economic damage when it destroys plants or hanging fruits. It can also damage road surfaces through a process known as [[frost heaving]]. ==Formation== [[Image:Hoarfrost-shadow.jpg|thumb|right|160px|Frost evaporates briskly, when exposed in the [[sunlight]].]] If a solid surface is chilled below the [[dew point]] of the surrounding air and the surface itself is colder than freezing, frost will form on the surface. Frost consists of [[spicule]]s of [[ice]] which grow out from the solid surface. The size of the [[crystal]]s depends on time, temperature, and the amount of [[water vapor]] available. In general, for frost to form the deposition surface must be colder than the surrounding air. For instance frost may be observed around cracks in cold wooden sidewalks when moist air escapes from the ground below. Other objects on which frost tends to form are those with low [[specific heat]] or high [[thermal emissivity]], such as blackened metals; hence the accumulation of frost on the heads of rusty nails. The apparently erratic occurrence of frost in adjacent localities is due partly to differences of elevation, the lower areas becoming colder on calm nights. It is also affected by differences in [[absorptivity]] and specific heat of the ground which in the absence of wind greatly influences the temperature attained by the [[wikt:superincumbent|superincumbent]] air. Because cold air is more dense than warm air, in calm weather cold air pools at ground level. This is known as surface temperature inversion. It explains why frost is more common and extensive in low-lying areas. Areas where frost forms due to cold air trapped against the ground or against a solid barrier such as a wall are known as "frost pockets". The formation of frost is an example of [[deposition (meteorology)|meteorological deposition]]. ==Types of Frost== === Hoar frost === ===='''Radiation frost'''==== '''Radiation frost''' (also called '''hoar frost''' or '''hoarfrost''') refers to the white ice crystals, loosely deposited on the ground or exposed objects, that form on cold clear nights when radiation losses into the open skies cause objects to become colder than the surrounding air. A related effect is '''flood frost''' which occurs when air cooled by ground-level radiation losses travels downhill to form pockets of very cold air in depressions, valleys, and hollows. Hoar frost can form in these areas even when the air temperature a few feet above ground is well above freezing. Nonetheless the frost itself will be at or below the freezing temperature of water. Hoar frost may have different names depending on where it forms. For example, '''air hoar''' is a deposit of hoar frost on objects above the surface, such as tree branches, plant stems, wires; '''surface hoar''' is formed by fernlike [[ice crystals]] directly deposited on snow, ice or already frozen surfaces; '''crevasse hoar''' consists in crystals that form in glacial crevasses where water vapour can accumulate under calm weather conditions; '''depth hoar''' refers to cup shaped, faceted crystals formed within dry snow, beneath the surface. Depth hoar is a common cause of [[avalanche]]s when it forms in air spaces within snow, especially below a snow crust, and subsequent layers of snow fall on top of it. The layer of depth hoar consists of angular crystals that do not bond well to each other or other layers of snow, causing upper layers to slide off under the right conditions, especially when upper layers are well bonded within themselves, as is the case in a slab avalanche. Hoar frost also occurs around man-made environments such as freezers or industrial [[cold storage]] facilities. It occurs in adjacent rooms that are not well insulated against the cold or around entry locations where [[humidity]] and moisture will enter and [[freezing|freeze]] instantly depending on the [[freezer]] [[temperature]]. [[Image:D Hoarfrost 3.jpg|right|thumb|250px|Hoar frost or soft rime on a cold winter day.]] ===='''Advection frost'''==== '''Advection frost''' (also called '''wind frost''') refers to tiny ice spikes forming when there is a very cold wind blowing over branches of trees, poles and other surfaces. It looks like rimming the edge of flowers and leaves and usually it forms against the direction of the wind. It can occur at any hour of day and night. ===='''Window frost'''==== '''Window frost''' (also called '''fern frost''') forms when a glass pane is exposed to very cold air on the outside and moderately moist air on the inside. If the pane is not a good [[insulation|insulator]] (such as a single pane window), water vapour condenses on the glass forming patterns. The glass surface influences the shape of crystals, so imperfections, scratches or dust can modify the way ice [[nucleation|nucleates]]. If the indoor air is very [[relative humidity|humid]], rather than moderately so, water would first [[condensation|condense]] in small droplets and then freeze into [[clear ice]]. ===='''[[Frost flowers]]'''==== '''[[Frost flowers]]''' occur when there is a freezing weather condition but the ground is not already frozen. The water contained in the [[plant stem]] expands and causes long cracks along. Water, via [[capillary action]], goes out from the cracks and freezes on contact with the air. === Rime === [[Hard rime|Rime]] is a type of frost that occurs quickly, often under conditions of heavily saturated air and windy conditions. Ships traveling through Arctic seas may accumulate rime on the rigging. Unlike hoar frost, which has a feathery appearance, rime generally has an icy solid appearance. In contrast to the formation of hoar frost, in which the water vapor condenses slowly and directly into icy feathers, Rime typically goes through a liquid phase where the surface is wet by condensation before freezing. ==Effect on plants== [[Image:Frost on a nettle, Netherlands.jpg|thumb|250px|Frost on a nettle.]] [[Image:Icy LingonBerry.jpg|thumb|250px|Frost on lingon berry leaves.]] Many plants can be damaged or killed by freezing temperatures or frost. This will vary with the type of plant and tissue exposed to low temperatures. Tender plants, like tomatoes, die when they are exposed to frost. Hardy plants, like radish, tolerate lower temperatures. Perennials, such as the hosta plant, die after first frosts and regrow when spring arrives. The entire visible plant may completely turn brown until the spring warmth, or will drop all of its leaves and flowers, leaving the stem and stalk only. Evergreen plants, such as pine trees, will withstand frost although all or most growth stops. Vegetation will not necessarily be damaged when leaf temperatures drop below the freezing point of their cell contents. In the absence of a site nucleating the formation of ice crystals, the leaves remain in a [[supercooled]] liquid state, safely reaching temperatures of &minus;4°C to &minus;12°C. However, once frost forms, the leaf [[cell (biology)|cell]]s may be damaged by sharp ice crystals. Certain [[bacterium|bacteria]], notably ''[[Pseudomonas syringae]]'', are particularly effective at triggering frost formation, raising the nucleation temperature to about &minus;2°C<ref>{{cite journal | author=Maki LR, Galyan EL, Chang-Chien MM, Caldwell DR | title=Ice nucleation induced by pseudomonas syringae | journal=Applied Microbiology | volume=28 | issue=3 | year=1974 | pages=456–459 |pmid=4371331 }}</ref>. Bacteria lacking ice [[nucleation]]-active proteins ([[ice-minus bacteria]]) result in greatly reduced frost damage<ref>{{cite journal | last = Lindow | first = Stephen E. | authorlink = Steven E. Lindow | coauthors = Deane C. Arny, Christen D. Upper | title = Bacterial Ice Nucleation: A Factor in Frost Injury to Plants | journal = Plant Physiology | volume = 70 | issue = 4 | pages = 1084–1089 | date = [[October 1982]] | url = http://www.pubmedcentral.gov/articlerender.fcgi?tool=pubmed&pubmedid=16662618 | pmid = 16662618 | accessdate = 2006-08-08 }}</ref>. The [[Selective Inverted Sink]] <ref>[http://www.rolexawards.com/laureates/laureate-20-guarga.html Selective Inverted Sink] Rolex Awards site (won award in ''Technology and Innovation'' category) 1998.</ref> prevents frost by drawing cold air from the ground and blowing it up through a chimney. It was originally developed to prevent frost damage to [[citrus]] fruits in [[Uruguay]]. ==See also== {{commonscat-inline|Hoar frost}} {{commons-inline|White frost}} {{Wiktionary}} * [[Air frost]] * [[Frostbite]] * [[Frost flowers]] * [[Frost heaving]] * [[Frost line]] * [[Ice-minus bacteria]] * [[Icing (nautical)]] * Rime: [[Soft rime|soft]]/[[Hard rime|hard]] * [[White frost]] ==Notes and references== {{reflist}} ==External links== *[http://www.pbase.com/sdwinsor/jfrost Window Frost Images & Art - Frost] *[http://www.rcn27.dial.pipex.com/cloudsrus/frost.html Clouds R Us - Frost] *[http://www.its.caltech.edu/~atomic/snowcrystals/frost/frost.htm Guide to Frost] *[http://www.bbc.co.uk/weather/features/understanding/frost.shtml BBC Understanding Weather - Frost] *[http://amsglossary.allenpress.com/glossary/search?id=hoarfrost1 American Meteorological Society, ''Glossary of Meteorology'' - Hoarfrost] *[http://www.islandnet.com/~see/weather/whys/frost.htm The Weather Doctor - Weather Whys - Frost] [[Category:Weather]] [[Category:Psychrometrics]] [[Category:Water ice]] [[Category:Precipitation]] [[Category:Forms of water]] [[zh-yue:霜]] [[ar:صقيع]] [[gn:Eláda]] [[ay:Juyphi]] [[ca:Gelada]] [[cs:Mráz]] [[da:Rimfrost]] [[de:Frost]] [[el:Πάχνη]] [[es:Helada (clima)]] [[eo:Frosto]] [[fr:Gelée blanche]] [[it:Brina]] [[he:קרה]] [[la:Pruina]] [[lt:Šerkšnas]] [[nl:Rijp]] [[ja:霜]] [[pl:Szron]] [[pt:Geada]] [[qu:Qasa]] [[ru:Иней]] [[simple:Frost]] [[sl:Slana]] [[sr:Мраз]] [[fi:Kuura]] [[sv:Frost]] [[th:น้ำค้างแข็ง]] [[tr:Kırağı]] [[uk:Іній]] [[bat-smg:Šerkšnos]] [[zh:霜]]