Heavy dew on grass amid sunlight and a bit of frost

Dew on some leaves

Some dew on a wildflower in Sequoia National Park

Dew on a spider web

Dew on grass

A spider in a dew-covered web near Orosí, Costa Rica. Orosi is a town in the Cartago Province in Costa Rica, about 30 kilometers south of the capital San José.

Morning dew on a blade of grass

Dew is water in the form of droplets that appears on thin, exposed objects in the morning or evening. As the exposed surface cools by radiating its heat, atmospheric moisture condenses at a rate greater than that of which it can evaporate, resulting in the formation of water droplets. Thermal radiation is Electromagnetic radiation emitted from the surface of an object which is due to the object's Temperature. Condensation is the change of the physical state of aggregation (or simply state of matter from gaseous phase into liquid phase Evaporation is the process by which Molecules in a Liquid state (e

When temperatures are low enough, dew takes the form of ice; this form is called frost. Frost is the solid deposition of Water vapor from saturated air

Because dew is related to the temperature of surfaces, in late summer it is formed most easily on surfaces which are not warmed by conducted heat from deep ground, such as: grass, leaves, railings, car roofs, and bridges.

Dew should not be confused with guttation, which is the process by which plants release excess water from the tips of their leaves. Guttation is the appearance of drops of Xylem sap on the tips or edges of leaves of some Vascular plants such as Grasses At night Transpiration

Formation

Water will condense into droplets depending on the temperature. The temperature at which droplets can form is called the Dew Point. Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature The dew point (sometimes spelled dewpoint) is the Temperature to which a given parcel of Air must be cooled at constant Barometric pressure, 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 are formed directly in air cooling to its dew point (typically around condensation nuclei) such as fog or clouds. In Meteorology, precipitation (also known as one class of hydrometeors, which are atmospheric water phenomena is any product of the condensation of atmospheric Cloud condensation nuclei or CCN s (also known as cloud seeds) are small particles (typically 0 Fog is a cloud that is in contact with the ground Stratus clouds are usually the only clouds that touch the ground A cloud is a visible mass of droplets or frozen crystals floating in the atmosphere above the surface of the Earth or another Planetary body The thermodynamic principles of formation, however, are virtually the same.

Occurrence

Sufficient 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. Infrared ( IR) radiation is Electromagnetic radiation whose Wavelength is longer than that of Visible light, but shorter than that of Radiation, as in Physics, is Energy in the form of waves or moving Subatomic particles emitted by an atom or other body as it changes from a higher energy As another important point, poor thermal conductivity restricts the replacement of such losses from deeper ground layers which are typically warmer at night. In Physics, thermal conductivity, k is the property of a material that indicates its ability to conduct Heat. Preferred objects of dew formation are thus poor conducting or well isolated from the ground, and non-metallic or coated as shiny metal 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 to be calm because the wind transports (nocturnally) warmer air from higher levels to the cold surface. But, if the atmosphere is the major source of moisture (this part of dew 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. If the wet soil beneath is the major source of vapor, however (this part of dew is called distillation), wind always seems to be adverse. Distillation is a method of separating Mixtures based on differences in their volatilities in a boiling liquid mixture

The principles of dew formation do not strictly constrict 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. Condensation is the change of the physical state of aggregation (or simply state of matter from gaseous phase into liquid phase

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. A lysimeter is a measuring device which can be used to measure the amount of actual Evapotranspiration which is released by plants usually crops or trees 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. It has to be kept in mind that some of these methods include guttation, while others only measure dewfall and/or distillation. Guttation is the appearance of drops of Xylem sap on the tips or edges of leaves of some Vascular plants such as Grasses At night Transpiration Distillation is a method of separating Mixtures based on differences in their volatilities in a boiling liquid mixture

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 exceeding 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 Desert and Namib desert, however, is mostly attributed to fog water. Atacama redirects here for the political-administrative region of Chile, see Atacama Region. The Namib Desert is a Desert in Namibia and southwest Angola which forms part of the Namib-Naukluft National Park. Fog is a cloud that is in contact with the ground Stratus clouds are usually the only clouds that touch the ground

Another effect of dew on plants is its role as a habitat for pathogens such as the fungus Phytophthora infestans which infects potato plants. A habitat (which is Latin for "it inhabits" is an Ecological or environmental area that is inhabited by a particular Species. A pathogen (from Greek πάθος pathos "suffering passion" and γἰγνομαι (γεν- gignomai (gen- "I give birth to" infectious Phytophthora infestans is an Oomycete that causes the serious Potato disease known as late blight or potato blight.

In Greek mythology, Ersa is the goddess of dew. In Greek mythology, Ersa (or Herse; English translation: dew is the daughter of Zeus and Eos.

Artificial harvesting

Main article: Fog collection

Several man-made devices such as antique, big stone piles in the Ukraine, medieval "dew ponds" in southern England, or 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. Fog collection refers to the collection of water from fog using large pieces of vertical canvas to make the fog condense into droplets Ukraine (Україна Ukrayina, /ukrɑˈjinɑ/ is a country in Eastern Europe. Dew pond west leakejpg|thumb|Dew pond on hill above West Leake Nottinghamshire England is a Country which is part of the United Kingdom. Its inhabitants account for more than 83% of the total UK population whilst its mainland Lanzarote, a Spanish Island, is the easternmost of the Canary Islands, in the Atlantic Ocean, approximately 125 km off the coast of Africa At present, the International Organization for Dew Utilization is working on effective, foil-based condensers for regions where rain or fog cannot cover water needs throughout the year. An interesting strategy for harvesting dew on large scale for drinking water was proposed in 1980. ^[1]

Large scale dew harvesting systems have been made by Indian Institute of Management Ahmedabad (IIMA) at coastal semi arid region Kutch. The Indian Institute of Management Ahmedabad (IIM Ahmedabad also known as IIMA is considered to be the premier institute of management education in India Kachchh (also spelled as Kutch) is a District of Gujarat state in western India. These condensers can harvest more than 200 litres (on average) of dew water per night for about 90 nights in the dew season October-May. The research lab of IIMA has shown that dew can serve as a supplementary source of water in coastal arid areas.

References

External links

• OPUR (International Organisation for Dew Utilization)
• International Conference on Fog, Fog Collection and Dew