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56-407: When temperatures are low enough, dew takes the form of ice, called frost . Because dew is related to the temperature of surfaces, in late summer it forms most easily on surfaces that are not warmed by conducted heat from deep ground, such as grass, leaves, railings, car roofs, and bridges. Water vapor will condense into droplets depending on the temperature. The temperature at which droplets form

112-467: A "hard frost" below −2 °C (28 °F). Plants likely to be damaged even by a light frost include vines—such as beans, grapes, squashes, melons—along with nightshades such as tomatoes, eggplants, and peppers. Plants that may tolerate (or even benefit from) frosts include: Even those plants that tolerate frost may be damaged once temperatures drop even lower (below −4 °C or 25 °F). Hardy perennials, such as Hosta , become dormant after

168-479: A balance with their surface at the same height and in the same surroundings as would occur naturally, thus providing a small lysimeter . Further methods include estimation by means of comparing the droplets to standardized photographs or volumetric measurement of the amount of water wiped from the surface. Some of these methods include guttation , while others only measure dewfall and/or distillation . Due to its dependence on radiation balance , dew amounts can reach

224-515: A freezing window. In the atmosphere, it more often occurs when both the air and the surface are below freezing, when the air experiences a drop in temperature bringing it below its dew point, for example, when the temperature falls after the Sun sets. In temperate climates , it most commonly appears on surfaces near the ground as fragile white crystals ; in cold climates, it occurs in a greater variety of forms. The propagation of crystal formation occurs by

280-438: A glass pane is exposed to very cold air on the outside and warmer, moderately moist air on the inside. If the pane is a bad insulator (for example, if it is a single-pane window), water vapour condenses on the glass, forming frost patterns. With very low temperatures outside, frost can appear on the bottom of the window even with double-pane energy-efficient windows because the air convection between two panes of glass ensures that

336-475: A heavy coating of hoar frost with big, interlocking crystals, usually needle-shaped. Rime is a type of ice deposition that occurs quickly, often under heavily humid and windy conditions. Technically speaking, it is not a type of frost, since usually supercooled water drops are involved, in contrast to the formation of hoar frost, in which water vapour desublimates slowly and directly. Ships travelling through Arctic seas may accumulate large quantities of rime on

392-542: A mass of frost crystals scatters light in all directions, the coating of frost appears white. Types of frost include crystalline frost ( hoar frost or radiation frost) from deposition of water vapor from air of low humidity, white frost in humid conditions, window frost on glass surfaces, advection frost from cold wind over cold surfaces, black frost without visible ice at low temperatures and very low humidity, and rime under supercooled wet conditions. Plants that have evolved in warmer climates suffer damage when

448-600: A plant becomes tolerant to low temperatures. See also Cryobiology . Certain bacteria , notably Pseudomonas syringae , are particularly effective at triggering frost formation, raising the nucleation temperature to about −2 °C (28 °F). Bacteria lacking ice nucleation-active proteins ( ice-minus bacteria ) result in greatly reduced frost damage. Typical measures to prevent frost or reduce its severity include one or more of: Such measures need to be applied with discretion, because they may do more harm than good; for example, spraying crops with water can cause damage if

504-479: A process similar to the formation of dust bunnies and similar structures. Hoar frost and white frost also occur in man-made environments such as in freezers or industrial cold-storage facilities. If such cold spaces or the pipes serving them are not well insulated and are exposed to ambient humidity, the moisture will freeze instantly depending on the freezer temperature. The frost may coat pipes thickly, partly insulating them, but such inefficient insulation still

560-455: A theoretical maximum of about 0.8 mm per night; measured values, however, rarely exceed 0.5 mm. In most climates of the world, the annual average is too small to compete with rain. In regions with considerable dry seasons, adapted plants like lichen or pine seedlings benefit from dew. Large-scale, natural irrigation without rainfall, such as in the Atacama and Namib deserts, however,

616-520: Is a consequence of the nucleation process being constrained to unfold in two dimensions, unlike a snowflake, which is shaped by a similar process, but forms in three dimensions and has a fractal dimension greater than two. If the indoor air is very humid, rather than moderately so, water first condenses in small droplets, and then freezes into clear ice . Similar patterns of freezing may occur on other smooth vertical surfaces, but they seldom are as obvious or spectacular as on clear glass. White frost

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672-431: Is a solid deposition of ice that forms directly from water vapour contained in air. White frost forms when relative humidity is above 90% and the temperature below −8 °C (18 °F), and it grows against the wind direction, since air arriving from windward has a higher humidity than leeward air, but the wind must not be strong, else it damages the delicate icy structures as they begin to form. White frost resembles

728-413: Is a source of heat loss. Advection frost (also called wind frost ) refers to tiny ice spikes that form when very cold wind is blowing over tree branches, poles, and other surfaces. It looks like rimming on the edges of flowers and leaves, and usually forms against the direction of the wind . It can occur at any hour, day or night. Window frost (also called fern frost or ice flowers ) forms when

784-406: Is called "killing frost" because white frost tends to be less cold, partly because the latent heat of freezing of the water reduces the temperature drop. Many plants can be damaged or killed by freezing temperatures or frost. This varies with the type of plant, the tissue exposed, and how low temperatures get; a "light frost" of −2 to 0 °C (28 to 32 °F) damages fewer types of plants than

840-451: Is called the dew point . When surface temperature drops, eventually reaching the dew point, atmospheric water vapor condenses to form small droplets on the surface. This process distinguishes dew from those hydrometeors (meteorological occurrences of water), which form directly in air that has cooled to its dew point (typically around condensation nuclei ), such as fog or clouds . The thermodynamic principles of formation, however, are

896-633: Is due partly to differences of elevation, the lower areas becoming colder on calm nights. Where static air settles above an area of ground in the absence of wind, the absorptivity and specific heat of the ground strongly influence the temperature that the trapped air attains. Hoar frost , also hoarfrost , radiation frost , or pruina , refers to white ice crystals deposited on the ground or loosely attached to exposed objects, such as wires or leaves. They form on cold, clear nights when conditions are such that heat radiates into outer space faster than it can be replaced from nearby warm objects or brought in by

952-571: Is mostly attributed to fog water. In the Negev Desert in Israel, dew has been found to account for almost half of the water found in three dominant desert species: Salsola inermis , Artemisia sieberi and Haloxylon scoparium . Another effect of dew is its hydration of fungal substrates and the mycelia of species such as pleated inkcaps , often found on lawns, and Phytophthora infestans which causes blight on potato plants. The book On

1008-411: Is not necessarily 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 −4 to −12 °C (25 to 10 °F). However, once frost forms, the leaf cells may be damaged by sharp ice crystals. Hardening is the process by which

1064-553: Is personified in Russian culture as Ded Moroz . Indigenous peoples of Russia such as the Mordvins have their own traditions of frost deities. English folklore tradition holds that Jack Frost , an elfish creature, is responsible for feathery patterns of frost found on windows on cold mornings. In 2024, two European Space Agency spacecraft, Exomars TGO and Mars Express , discovered a thin but very wide layer of water frost on

1120-423: Is similar to the formation of dew , except it occurs below the freezing point of water typically without crossing through a liquid state. Air always contains a certain amount of water vapor, depending on temperature. Warmer air can hold more than colder air. When the atmosphere contains more water than it can hold at a specific temperature, its relative humidity rises above 100% becoming supersaturated , and

1176-502: Is the drosometer . A small (artificial) condenser surface is suspended from an arm attached to a pointer or a pen that records the weight changes of the condenser on a drum. Besides being very wind sensitive, however, this, like all artificial surface devices, only provides a measure of the meteorological potential for dew formation. The actual amount of dew in a specific place is strongly dependent on surface properties. For its measurement, plants, leaves, or whole soil columns are placed on

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1232-540: The contiguous United States , southern Florida around Miami Beach and the Florida Keys are the only reliably frost-free areas, as well as the Channel Islands off the coast of California . The hardiness zones in these regions are 11a and 11b. Permafrost is a layer of frozen earth underground which never heats above freezing even during summer months, remaining frozen year round. Although not frost in

1288-418: The liquid phase . The air must be humid, but not sufficiently humid to permit the condensation of liquid water, or icing will result instead of desublimation. The size of the crystals depends largely on the temperature, the amount of water vapor available, and how long they have been growing undisturbed. As a rule, except in conditions where supercooled droplets are present in the air, frost will form only if

1344-706: The Body and Blood of our Lord Jesus Christ.’ The idea that the Holy Spirit enters the world and our lives in a quiet, undramatic way, ‘like the dewfall’, has great appeal for many Christians. The harvesting of dew potentially allows water availability in areas where supporting weather conditions, such as rain, are lacking. Several man-made devices such as antique big stone piles in Ukraine , medieval dew ponds in Southern England , and volcanic stone covers on

1400-537: The Earth to reach deep enough to thaw the permafrost layer. The permafrost may begin from the surface of the ground or many meters beneath it, and may extend from just a meter to over a thousand meters in thickness. Permafrost contains a significant portion of the Earth's water and carbon, and prevents surface water from penetrating very deep into the ground, making it responsible in part for the typical taiga and spruce bog environments common in northern latitudes. Frost

1456-460: The Universe ( De Mundo ) (composed before 250 BC or between 350 and 200 BC) stated: "Dew is moisture minute in composition falling from a clear sky; ice is water congealed in a condensed form from a clear sky; hoar-frost is congealed dew, and 'dew-frost' is dew which is half congealed". In Greek mythology, Ersa is the goddess and personification of dew. Also, according to the myth, the dew in

1512-452: The air near the ground. Typical dew nights are classically considered calm, because the wind transports (nocturnally) warmer air from higher levels to the cold surface. However, if the atmosphere is the major source of moisture (this type is called dewfall), a certain amount of ventilation is needed to replace the vapor that is already condensed. The highest optimum wind speeds could be found on arid islands. Wind always seems adverse, however, if

1568-462: The air temperature a few feet above ground is well above freezing. The word "hoar" comes from an Old English adjective that means "showing signs of old age". In this context, it refers to the frost that makes trees and bushes look like white hair. Hoar frost may have different names depending on where it forms: When surface hoar covers sloping snowbanks, the layer of frost crystals may create an avalanche risk; when heavy layers of new snow cover

1624-465: The atmospheric sense, it consists of dirt, soil, sand, rocks, clay, or organic matter (peat) bound firmly together by ice crystals, making the material very hard and difficult to penetrate. Permafrost exists in the colder climates of the Arctic and Antarctic, such as Russia, Canada, Alaska, Norway, Greenland, or Antarctica, where the warmer conditions of summer are insufficient to penetrate the insulation of

1680-399: The bottom part of the glazing unit is colder than the top part. On unheated motor vehicles, the frost usually forms on the outside surface of the glass first. The glass surface influences the shape of crystals, so imperfections, scratches, or dust can modify the way ice nucleates . The patterns in window frost form a fractal with a fractal dimension greater than one, but less than two. This

1736-452: The deposition surface is colder than the surrounding air. For instance, frost may be observed around cracks in cold wooden sidewalks when humid air escapes from the warmer ground beneath. Other objects on which frost commonly forms 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

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1792-428: The excess water vapor is forced to deposit onto any nearby surface, forming seed crystals . The temperature at which frost will form is called the dew point , and depends on the humidity of the air. When the temperature of the air drops below its dew point, excess water vapor is forced out of solution, resulting in a phase change directly from water vapor (a gas ) to ice (a solid). As more water molecules are added to

1848-573: The fields of Lanzarote have been thought to be dew-catching devices, but could be shown to work on other principles. At present, the International Organization for Dew Utilization (OPUR) is working on effective, foil-based condensers for regions where rain or fog cannot cover water needs throughout the year. Large-scale dew harvesting systems have been made by the Indian Institute of Management Ahmedabad (IIMA) with

1904-407: The first frosts and regrow when spring arrives. The entire visible plant may turn completely brown until the spring warmth, or may drop all of its leaves and flowers, leaving the stem and stalk only. Evergreen plants, such as pine trees, withstand frost although all or most growth stops. Frost crack is a bark defect caused by a combination of low temperatures and heat from the winter sun. Vegetation

1960-414: The frosty surface, furry crystals standing out from the old snow hold off the falling flakes, forming a layer of voids that prevents the new snow layers from bonding strongly to the old snow beneath. Ideal conditions for hoarfrost to form on snow are cold, clear nights, with very light, cold air currents conveying humidity at the right rate for growth of frost crystals. Wind that is too strong or warm destroys

2016-405: The furry crystals, and thereby may permit a stronger bond between the old and new snow layers. However, if the winds are strong enough and cold enough to lay the crystals flat and dry, carpeting the snow with cold, loose crystals without removing or destroying them or letting them warm up and become sticky, then the frost interface between the snow layers may still present an avalanche danger, because

2072-412: The level of supersaturation. For example, water vapor adsorbs to glass very well, so automobile windows will often frost before the paint, and large hoar-frost crystals can grow very rapidly when the air is very cold, calm, and heavily saturated, such as during an ice fog . Frost may occur when warm, moist air comes into contact with a cold surface, cooling it below its dew point, such as warm breath on

2128-527: The lowland tropics, where they cover almost all land except at altitudes above about 3,000 metres or 9,800 feet near the equator and around 2,000 metres or 6,600 feet in the semiarid areas in tropical regions. Some areas on the oceanic margins of the subtropics are also frost-free, as are highly oceanic areas near windward coasts. The most poleward frost-free areas are the lower altitudes of the Azores , Île Amsterdam , Île Saint-Paul , and Tristan da Cunha . In

2184-580: The morning was created when Eos (Ersa's aunt), goddess of the dawn, cried for her son 's death, although later he received immortality. Dew, known in Hebrew as טל ( tal ), is significant in the Jewish religion for agricultural and theological purposes. On the first day of Passover , the Chazan , dressed in a white kittel , leads a service in which he prays for dew between that point and Sukkot . During

2240-538: The participation of OPUR in the coastal, semiarid region of Kutch .These condensers can harvest more than 200 liters (on average) of dew water per night for about 90 nights in the October-to-May dew season. The IIMA research laboratory has shown that dew can serve as a supplementary source of water in coastal arid areas. A large-scale dew harvesting scheme envisages circulating cold sea water in EPDM collectors near

2296-479: The peak of Olympus Mons , the highest mountain on Mars . This layer of frost appears for a few hours around sunrise, and then evaporates into the atmosphere for the rest of the Martian day. This was the first instance of frost discovered in the equatorial region of Mars. Haloxylon scoparium Haloxylon scoparium (syns. Arthrophytum scoparium and Hammada scoparia ) is a species of flowering plant in

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2352-466: The plants become overburdened with ice. An effective, low cost method for small crop farms and plant nurseries, exploits the latent heat of freezing . A pulsed irrigation timer delivers water through existing overhead sprinklers at a low volumes to combat frosts down to −5 °C (23 °F). If the water freezes, it gives off its latent heat, preventing the temperature of the foliage from falling much below zero. Frost-free areas are found mainly in

2408-490: The process of nucleation , in specific, water nucleation , which is the same phenomenon responsible for the formation of clouds, fog, snow, rain and other meteorological phenomena. The ice crystals of frost form as the result of fractal process development. The depth of frost crystals varies depending on the amount of time they have been accumulating, and the concentration of the water vapor ( humidity ). Frost crystals may be invisible (black), clear ( translucent ), or, if

2464-659: The rain, my speech shall distill as the dew, as the small rain upon the tender herb, and as the showers upon the grass." In the Catholic Mass in the Western Rite, whenever the Second Eucharistic Prayer is used, the priest prays over bread and wine, to God the Father; ‘Make holy, therefore, these gifts, we pray, by sending down your Spirit upon them like the dewfall, so that they may become for us

2520-675: The rainy season between December and Passover there are also additions in the Amidah for blessed dew to come together with rain. There are many midrashim that refer to dew as being the tool for ultimate resurrection. "Dewy" or "my father is the morning dew" are approximate etymologies of the Hebrew given name, Avital . In the Biblical Torah or Old Testament , dew is used symbolically in Deuteronomy 32:2 : "My doctrine shall drop as

2576-436: The replacement of such losses from deeper ground layers, which are typically warmer at night. Preferred objects of dew formation are thus poor conducting or well isolated from the ground, and non-metallic, while shiny metal coated surfaces are poor infrared radiators. Preferred weather conditions include the absence of clouds and little water vapor in the higher atmosphere to minimize greenhouse effects and sufficient humidity of

2632-411: The rigging. Unlike hoar frost, which has a feathery appearance, rime generally has an icy, solid appearance. Black frost (or "killing frost") is not strictly speaking frost at all, because it is the condition seen in crops when the humidity is too low for frost to form, but the temperature falls so low that plant tissues freeze and die, becoming blackened, hence the term "black frost". Black frost often

2688-455: The same. Dew is commonly formed during select times of the day. Nights, early mornings, and early evenings are all times during which dew is likely to be found. Adequate cooling of the surface typically takes place when it loses more energy by infrared radiation than it receives as solar radiation from the Sun , which is especially the case on clear nights. Poor thermal conductivity restricts

2744-425: The seashore. These condense dew and fog to supply clean drinking water. Other, more recent, studies display possible roof integration for dew harvesting devices. 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

2800-546: The seeds, crystal growth occurs, forming ice crystals . Crystals may vary in size and shape, from an even layer of numerous microscopic-seeds to fewer but much larger crystals, ranging from long dendritic crystals (tree-like) growing across a surface, acicular crystals (needle-like) growing outward from the surface, snowflake-shaped crystals, or even large, knifelike blades of ice covering an object, which depends on many factors such as temperature, air pressure, air motion and turbulence, surface roughness and wettability , and

2856-432: The solid surface on which they grow. The main difference between the ice coatings and frost spicules arises because the crystalline spicules grow directly from desublimation of water vapour from air, and desublimation is not a factor in icing of freezing surfaces. For desublimation to proceed, the surface must be below the frost point of the air, meaning that it is sufficiently cold for ice to form without passing through

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2912-407: The surface itself is colder than freezing, ice will form on it. If the water deposits as a liquid that then freezes, it forms a coating that may look glassy, opaque, or crystalline, depending on its type. Depending on context, that process may also be called atmospheric icing . The ice it produces differs in some ways from crystalline frost, which consists of spicules of ice that typically project from

2968-421: The temperature falls low enough to freeze the water in the cells that make up the plant tissue . The tissue damage resulting from this process is known as "frost damage". Farmers in those regions where frost damage has been known to affect their crops often invest in substantial means to protect their crops from such damage. If a solid surface is chilled below the dew point of the surrounding humid air, and

3024-489: The texture of the frost crystals differs from the snow texture, and the dry crystals will not stick to fresh snow. Such conditions still prevent a strong bond between the snow layers. In very low temperatures where fluffy surface hoar crystals form without subsequently being covered with snow, strong winds may break them off, forming a dust of ice particles and blowing them over the surface. The ice dust then may form yukimarimo , as has been observed in parts of Antarctica, in

3080-399: The wet soil beneath is the major source of vapor (in which case dew is said to form by distillation ). The processes of dew formation do not restrict its occurrence to the night and the outdoors. They are also working when eyeglasses get steamy in a warm, wet room or in industrial processes. However, the term condensation is preferred in these cases. A classical device for dew measurement

3136-428: The wind. Under suitable circumstances, objects cool to below the frost point of the surrounding air, well below the freezing point of water. Such freezing may be promoted by effects such as flood frost or frost pocket . These occur when ground-level radiation cools air until it flows downhill and accumulates in pockets of very cold air in valleys and hollows. Hoar frost may freeze in such low-lying cold air even when

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