Monday 7 September 2009
Virga
Did you know that rain can evaporate before it hits the ground?
In meteorology, virga is an observable streak or shaft of precipitation that falls from a cloud but evaporates before reaching the ground.
Virga can cause varying weather effects, because as rain is changed from liquid to vapor form, it removes heat from the air due to the high heat of vaporization of water. In some instances, these pockets of colder air can descend rapidly, creating a dry microburst which can be extremely hazardous to aviation. Conversely, precipitation evaporating at high altitude can compressionally heat as it falls, and result in a gusty downburst which may substantially and rapidly warm the surface temperature.
Virga can produce dramatic and beautiful scenes, especially during a red sunset.
The word virga is derived from Latin, twig or branch. A backronym sometimes found in amateur discussions of meteorology is "Variable Intensity Rain Gradient Aloft."
http://en.wikipedia.org/wiki/Virga
See pic in http://imgur.com/gUZof.jpg and details in http://www.reddit.com/r/pics/comments/9h5ei/rain_rain_go_away/
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