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What Is a Cirrus Cloud?


Cirrus clouds are thin, feathery, upper-level clouds. They form at extremely high altitudes, usually 20,000 feet or more.  At this altitude, the temperature is quite low, freezing tiny droplets of water and creating ice crystals. The relative lack of moisture at such high altitudes results in sparse, wispy strands rather than clouds that are more substantial. The weightless quality of these clouds makes them quite mobile.  [1 ]They are the fastest moving clouds, usually traveling from west to east.  [2]

Cirrus Clouds and Climate

Generally, cloudiness has a cooling effect on the climate, but cirrus clouds are unique in that they are more likely to have a warming effect. [3] Occasionally, cirrus clouds are so prevalent they fuse together, forming a continuous sheet. This sheet of cirrus is called cirrostratus. Such a shield can create a significant greenhouse effect. Radiation from the earth is trapped by the sheet of cirrus clouds and not immediately allowed to leave the atmosphere. Cirrus clouds are often cited as a partial cause of global warming due to this effect. Conversely, increased global warming would increase cirrus cloud cover. This would effectively increase temperature and humidity. [4]

Cirrus Clouds and Weather

While cirrus clouds usually develop in fair weather, a large number of these thin clouds often signal an approaching storm or air disturbance of some kind usually meaning rain in the next 24-48 hours. [5]  Thunderstorms may also leave cirrus clouds in their wake, as these clouds are often found in large numbers high above a frontal system. Cirrus clouds do not usually produce precipitation unless they are a product of a dissolving thunderstorm. When precipitation is produced, it is often in the form of large droplets. Afterwards, the clouds will disappear. Cirrus clouds that are not part of a storm system will dissipate on their own. [6]



[1] Northern Michigan University
Cirrus Clouds

Cirrus Clouds

[3]Environmental Research Letter

Modification of cirrus clouds to reduce global warming

[4 ] NASA
Clouds Likely Created Positive Climate Feedback In Past Decade

[5]Paul Fleisher
Vapor, Rain, and Snow: The Science of Precipitation

Lerner Publishing Group. Print

[6] Lee M Grenci
A World of Weather: Fundamentals of Meteorology: a Text Laboratory Manual

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