Virga
Virga is precipitation that falls from a cloud but evaporates before reaching the ground. At high altitudes the precipitation falls mainly as ice crystals, before melting and finally evaporating. Virga can cause very interesting weather effects, because as the rain changes from liquid to vapour form it takes a lot of heat out of the air due to the high heat of vaporization of water. These small pockets of extremely cold air then descend rapidly, creating a microburst which can be extremely hazardous to aviation. Virga also has a role in seeding storm cells, where light particles from one cloud are blown into neigbouring supersaturated air and act as nucleation particles for the next thunderhead cloud to begin forming. Virga can produce dramatic and beautiful scenes, especialy during a red sunset. The red light can is caught by the streamers of falling precipitation, while aloft winds push the bottom ends of the virga so it falls at an angle, making the clouds appear to have commas attached.
See also Fall streaks Aviation safety
External links National Science Digital Library - Virga
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