Dew

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A drop of dew in the middle of a clover A drop of dew on a clover.jpg
A drop of dew in the middle of a clover
Dew formed on the surface of strawberry leaves Dew Formed on the Surface of Strawberry Leafs.jpg
Dew formed on the surface of strawberry leaves
A drop of dew on a Colocasia leaf at the Garden Society of Gothenburg Dew drop.jpg
A drop of dew on a Colocasia leaf at the Garden Society of Gothenburg
Dew drops on a flower Chrysantheme rot tautropfen -20191024-RM-102058.jpg
Dew drops on a flower
Dense dew on grass Dense dew on grass.jpg
Dense dew on grass
Under cold temperatures, dew may freeze and form a layer of ice over plants and objects. Slovenia (12248224706).jpg
Under cold temperatures, dew may freeze and form a layer of ice over plants and objects.

Dew is water in the form of droplets that appears on thin, exposed objects in the morning or evening due to condensation. [1] As the exposed surface cools by radiating its heat, atmospheric moisture condenses at a rate greater than that at which it can evaporate, resulting in the formation of water droplets. [2]

Contents

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.

Formation

Water vapor will condense into droplets depending on the temperature. The temperature at which droplets form 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. [3] 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 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. [4]

Occurrence

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 the replacement of such losses from deeper ground layers, which are typically warmer at night. [3] 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 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 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.

Measurement

A classical device for dew measurement 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 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.

Significance

Due to its dependence on radiation balance, dew amounts can reach 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, 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 . [5]

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. [6]

Historic

The book On 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". [7]

In Greek mythology, Ersa is the goddess and personification of dew. Also, according to the myth, the dew in 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 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. [8] "Dewy" or "my father is the morning dew" are approximate etymologies of the Hebrew given name, Avital. [9] [10]

In the Biblical Torah or Old Testament, dew is used symbolically in Deuteronomy 32:2: "My doctrine shall drop as the rain, my speech shall distill as the dew, as the small rain upon the tender herb, and as the showers upon the grass." [11]

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 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.[ citation needed ]

Artificial harvesting

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 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 the participation of OPUR in the coastal, semiarid region of Kutch [12] .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 the seashore. These condense dew and fog to supply clean drinking water. [13] Other, more recent, studies display possible roof integration for dew harvesting devices. [14]

Related Research Articles

<span class="mw-page-title-main">Frost</span> Coating or deposit of ice

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 similar to the formation of dew, except it occurs below the freezing point of water typically without crossing through a liquid state.

<span class="mw-page-title-main">Condensation</span> Change of state of matter from a gas phase into a liquid phase

Condensation is the change of the state of matter from the gas phase into the liquid phase, and is the reverse of vaporization. The word most often refers to the water cycle. It can also be defined as the change in the state of water vapor to liquid water when in contact with a liquid or solid surface or cloud condensation nuclei within the atmosphere. When the transition happens from the gaseous phase into the solid phase directly, the change is called deposition.

<span class="mw-page-title-main">Humidity</span> Concentration of water vapour in the air

Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present.

<span class="mw-page-title-main">Dew point</span> Temperature at which air becomes saturated with water vapour during a cooling process

The dew point of a given body of air is the temperature to which it must be cooled to become saturated with water vapor. This temperature depends on the pressure and water content of the air. When the air is cooled below the dew point, its moisture capacity is reduced and airborne water vapor will condense to form liquid water known as dew. When this occurs through the air's contact with a colder surface, dew will form on that surface.

<span class="mw-page-title-main">Fog</span> Atmospheric phenomenon

Fog is a visible aerosol consisting of tiny water droplets or ice crystals suspended in the air at or near the Earth's surface. Fog can be considered a type of low-lying cloud usually resembling stratus, and is heavily influenced by nearby bodies of water, topography, and wind conditions. In turn, fog affects many human activities, such as shipping, travel, and warfare.

Water vapor, water vapour or aqueous vapor is the gaseous phase of water. It is one state of water within the hydrosphere. Water vapor can be produced from the evaporation or boiling of liquid water or from the sublimation of ice. Water vapor is transparent, like most constituents of the atmosphere. Under typical atmospheric conditions, water vapor is continuously generated by evaporation and removed by condensation. It is less dense than most of the other constituents of air and triggers convection currents that can lead to clouds and fog.

<span class="mw-page-title-main">Mist</span> Phenomenon caused by small droplets of water suspended in air

Mist is a phenomenon caused by small droplets of water suspended in the cold air, usually by condensation. Physically, it is an example of a dispersion. It is most commonly seen where water vapor in warm, moist air meets sudden cooling, such as in exhaled air in the winter, or when throwing water onto the hot stove of a sauna. It can be created artificially with aerosol canisters if the humidity and temperature conditions are right. It can also occur as part of natural weather, when humid air cools rapidly, notably when the air comes into contact with surfaces that are much cooler than the air.

<span class="mw-page-title-main">Dehumidifier</span> Device which reduces humidity

A dehumidifier is an air conditioning device which reduces and maintains the level of humidity in the air. This is done usually for health or thermal comfort reasons or to eliminate musty odor and to prevent the growth of mildew by extracting water from the air. It can be used for household, commercial, or industrial applications. Large dehumidifiers are used in commercial buildings such as indoor ice rinks and swimming pools, as well as manufacturing plants or storage warehouses. Typical air conditioning systems combine dehumidification with cooling, by operating cooling coils below the dewpoint and draining away the water that condenses.

<span class="mw-page-title-main">Mushroom cloud</span> Cloud of debris and smoke from a large explosion

A mushroom cloud is a distinctive mushroom-shaped flammagenitus cloud of debris, smoke, and usually condensed water vapour resulting from a large explosion. The effect is most commonly associated with a nuclear explosion, but any sufficiently energetic detonation or deflagration will produce a similar effect. They can be caused by powerful conventional weapons, including thermobaric weapons such as the ATBIP and GBU-43/B MOAB. Some volcanic eruptions and impact events can produce natural mushroom clouds.

<span class="mw-page-title-main">Cloud chamber</span> Particle detector for visualizing ionizing radiation

A cloud chamber, also known as a Wilson chamber, is a particle detector used for visualizing the passage of ionizing radiation.

<span class="mw-page-title-main">Cloud physics</span> Study of the physical processes in atmospheric clouds

Cloud physics is the study of the physical processes that lead to the formation, growth and precipitation of atmospheric clouds. These aerosols are found in the troposphere, stratosphere, and mesosphere, which collectively make up the greatest part of the homosphere. Clouds consist of microscopic droplets of liquid water, tiny crystals of ice, or both, along with microscopic particles of dust, smoke, or other matter, known as condensation nuclei. Cloud droplets initially form by the condensation of water vapor onto condensation nuclei when the supersaturation of air exceeds a critical value according to Köhler theory. Cloud condensation nuclei are necessary for cloud droplets formation because of the Kelvin effect, which describes the change in saturation vapor pressure due to a curved surface. At small radii, the amount of supersaturation needed for condensation to occur is so large, that it does not happen naturally. Raoult's law describes how the vapor pressure is dependent on the amount of solute in a solution. At high concentrations, when the cloud droplets are small, the supersaturation required is smaller than without the presence of a nucleus.

<span class="mw-page-title-main">Rime ice</span> Granular whitish deposit of ice formed by freezing fog

Rime ice forms when supercooled water droplets freeze onto surfaces. In the atmosphere, there are three basic types of rime ice:

An atmospheric water generator (AWG), is a device that extracts water from humid ambient air, producing potable water. Water vapor in the air can be extracted either by condensation - cooling the air below its dew point, exposing the air to desiccants, using membranes that only pass water vapor, collecting fog, or pressurizing the air. AWGs are useful where potable water is difficult to obtain, because water is always present in ambient air.

Moisture analysis covers a variety of methods for measuring the moisture content in solids, liquids, or gases. For example, moisture is a common specification in commercial food production. There are many applications where trace moisture measurements are necessary for manufacturing and process quality assurance. Trace moisture in solids must be known in processes involving plastics, pharmaceuticals and heat treatment. Fields that require moisture measurement in gasses or liquids include hydrocarbon processing, pure semiconductor gases, bulk pure or mixed gases, dielectric gases such as those in transformers and power plants, and natural gas pipeline transport. Moisture content measurements can be reported in multiple units, such as: parts per million, pounds of water per million standard cubic feet of gas, mass of water vapor per unit volume or mass of water vapor per unit mass of dry gas.

<span class="mw-page-title-main">Condenser (laboratory)</span> Laboratory apparatus used to condense vapors

In chemistry, a condenser is laboratory apparatus used to condense vapors – that is, turn them into liquids – by cooling them down.

<span class="mw-page-title-main">Air well (condenser)</span> A building or device used to collect water by condensing the water vapor present in the air

An air well or aerial well is a structure or device that collects water by promoting the condensation of moisture from air. Designs for air wells are many and varied, but the simplest designs are completely passive, require no external energy source and have few, if any, moving parts.

<span class="mw-page-title-main">Fog collection</span> Mechanical harvesting of water from fog

Fog collection is the harvesting of water from fog using large pieces of vertical mesh netting to induce the fog-droplets to flow down towards a trough below. The setup is known as a fog fence, fog collector or fog net. Through condensation, atmospheric water vapour from the air condenses on cold surfaces into droplets of liquid water known as dew. The phenomenon is most observable on thin, flat, exposed objects including plant leaves and blades of grass. As the exposed surface cools by radiating its heat to the sky, atmospheric moisture condenses at a rate greater than that of which it can evaporate, resulting in the formation of water droplets.

Interstitial condensation is a type of condensation that may occur within an enclosed wall, roof or floor cavity structure, which can create dampening.

<span class="mw-page-title-main">Breath-figure self-assembly</span>

Breath-figure self-assembly is the self-assembly process of the formation of honeycomb micro-scaled polymer patterns by the condensation of water droplets. "Breath-figure" refers to the fog that forms when water vapor contacts a cold surface. In the modern era systematic study of the process of breath-figures water condensation was carried out by Aitken and Rayleigh, among others. Half a century later the interest in the breath-figure formation was revived in a view of study of atmospheric processes, and in particular the extended study of a dew formation which turned out to be a complicated physical process. The experimental and theoretical study of dew formation has been carried out by Beysens. Thermodynamic and kinetic aspects of dew formation, which are crucial for understanding of formation of breath-figures inspired polymer patterns will be addressed further in detail.

Compressed air dryers are special types of filter systems that are specifically designed to remove the water that is inherent in compressed air. The compression of air raises its temperature and concentrates atmospheric contaminants, primarily water vapor, as resulting in air with elevated temperature and 100% relative humidity. As the compressed air cools down, water vapor condenses into the tank(s), pipes, hoses and tools connected downstream from the compressor which may be damaging. Therefore water vapor is removed from compressed air to prevent condensation from occurring and to prevent moisture from interfering in sensitive industrial processes.

References

  1. ↑ "dew". Merriam-Webster.com Dictionary . Merriam-Webster.
  2. ↑ "dew". The Columbia Encyclopedia (6th ed.). Retrieved 18 May 2013.
  3. 1 2 "Dew and Frost Development". ZHU Training Page. National Weather Service, NOAA. Retrieved 2021-10-21.
  4. ↑ Leopold, L.B. (1952). "Dew as a source of plant moisture" (PDF). Pac Sci. 6 (3): 259–261. hdl:10125/8818/.
  5. ↑ Hill, Amber (2015). "The Role of Dew in Negev Desert plants". Oecologia. 178 (2): 317–327. Bibcode:2015Oecol.178..317H. doi:10.1007/s00442-015-3287-5. PMID   25783489. S2CID   18134058.
  6. ↑ "Late Blight in Potato — Publications". www.ag.ndsu.edu. 5 May 2017. Retrieved 2021-10-21.
  7. ↑ Aristotle; Forster, E. S.; Dobson, J. F. (1914). De Mundo. p. End of chapter 3.
  8. ↑ "Resurrection". Jewish Encyclopedia . Retrieved 21 Dec 2008.
  9. ↑ Hanks, Patrick; Hardcastle, Kate; Hodges, Flavia (2006). A Dictionary of First Names. Oxford paperback reference. Oxford University Press. p. 42. ISBN   978-0-19-861060-1 . Retrieved 2018-11-17.
  10. ↑ "Abital" . Retrieved 2013-06-27.
  11. ↑ Deuteronomy 32: King James Version, accessed 22 September 2019
  12. ↑ Sharan, G.; Clus, O.; Singh, S.; Muselli, M.; Beysens, D. (2011-07-01). "A very large dew and rain ridge collector in the Kutch area (Gujarat, India)". Journal of Hydrology. 405 (1–2): 171–181. Bibcode:2011JHyd..405..171S. doi:10.1016/j.jhydrol.2011.05.019. ISSN   0022-1694.
  13. ↑ Rajvanshi, Anil K. (March 1981). "Large Scale Dew Collection as a Source of Fresh Water Supply". Desalination. 36 (3): 299–306. Bibcode:1981Desal..36..299R. CiteSeerX   10.1.1.730.5055 . doi:10.1016/S0011-9164(00)88647-6.
  14. ↑ Carvajal, Danilo; Minonzio, Jean-Gabriel; Casanga, Elvira; Muñoz, Jorge; Aracena, Alvaro; Montecinos, Sonia; Beysens, Daniel (2018-05-15). "Roof-integrated dew water harvesting in Combarbalá, Chile". Journal of Water Supply: Research and Technology-Aqua. 67 (4): 357–374. doi: 10.2166/aqua.2018.174 .
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