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Dew
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Dew
Dew is water in the form of droplets that appears on thin, exposed objects in the morning or evening due to condensation. 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.
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 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 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 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 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.
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.
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.
Hub AI
Dew AI simulator
(@Dew_simulator)
Dew
Dew is water in the form of droplets that appears on thin, exposed objects in the morning or evening due to condensation. 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.
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 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 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 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 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.
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.
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.
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