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Dew and Frost

Page history last edited by yuliya_yakunina 14 years, 7 months ago

 Dew & Frost by Yuliya Yakunina


Clouds and fog are the most meteorologically important forms of condensation. Dew and white frost must be considered minor by comparison. Dew and frost result from radiation cooling on clear, cool nights.


Dew- the water droplets formed by condensation of water vapor on a relatively cold surface of an object.

Dew is the condensation of water vapor on objects that have radiated sufficient heat to lower their temperature below the dew point of the surrounding air. Because different objects radiate heat at different rates, dew may form on some surfaces but not on others. For example, an automobile may be covered with dew shortly after sunset, whereas the concrete driveway surrounding the car remains free of condensation throughout the night. 


Dew is usually seen in the early mornings. Dew is more frequent on grass because the transpiranion of water vapor by the blades raises the relative humidity to higher levels directly above the grass. Therefore, only modest radiation cooling may be necessary to bring about saturation and condensation. 


At night the ground will cool. If there is enough moisture in the air and the cooling is great enough then condensation will occur on the ground. The formation of the condensation is the same process that occurs when you leave a glass of ice water out when there is moisture in the air.


In some arid regions, plant life depends on dew in order to survive. This moisture is available mainly during the dry summer months when plants are experiencing the greatest stress.





Frost- the ice crystals formed by deposition of water vapor on a relatively cold surface of an object.

White frost is not frozen dew. White frost forms when the dew point of the air is delow freezing. Frost forms when water vapor changes directly from a gas into a solid (ice), without entering the liquid state. Such process is called deposition, produces delicate patterns of ice crystals that frequently decorate windows in northern winters.


Frost is a very important factor for the growing agricultural products. Several methods have been developed to protect crops from freezing: locating on hillslopes, spraying a fine water mist, covering with plastic hot caps, circulating the warm air aloft down the ground with a motor-driven fan.


You can tell the difference between frost and frozen dew by looking at them. Frost looks more feathery, brighter and you can see the crystal formations. Frozen dew is solid and does not have quite the white appearance as frost.







Text Book- "The Atmosphere" by Frederick K. Lutgens & Edward J. Tarbuck.



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