WW2010
University of Illinois

WW2010
 
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> online guides
 
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Online Guides
 
  introduction
 
> meteorology
 
  remote sensing
 
  reading maps
 
  projects, activities

Meteorology
 
  introduction
 
  air masses, fronts
 
> clouds, precipitation
 
  el nino
 
  forces, winds
 
  hurricanes
 
  hydrologic cycle
 
  light, optics
 
  midlatitude cyclones
 
  severe storms
 
  weather forecasting

Clouds, Precipitation
 
  introduction
 
  development
 
> cloud types
 
  precipitation

Cloud Types
 
  introduction
 
> high-level clouds
 
  mid-level clouds
 
  low-level clouds
 
  vertically developed
 
  other cloud types

High-Level Clouds
 
> cirrus
 
  cirrostratus

User Interface
 
  graphics
> text

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Cirrus Clouds
thin and wispy

The most common form of high-level clouds are thin and often wispy cirrus clouds. Typically found at heights greater than 20,000 feet (6,000 meters), cirrus clouds are composed of ice crystals that originate from the freezing of supercooled water droplets. Cirrus generally occur in fair weather and point in the direction of air movement at their elevation.

[Image: more cirrus clouds (76K)]

Cirrus can form from almost any cloud that has undergone glaciation and can be observed in a variety of shapes and sizes. Possibilities range from the "finger-like" appearance of cirrus fall streaks to the uniform texture of more extensive cirrus clouds associated with an approaching warm front.

[Image: cirrus fall streaks (83K)]
Photograph by: Holle

Fall streaks form when snowflakes and ice crystals fall from cirrus clouds. The change in wind with height and how quickly these ice crystals fall determine the shapes and sizes the fall streaks attain. Since ice crystals fall much more slowly than raindrops, fall streaks tend to be stretched out horizontally as well as vertically. Cirrus streaks may be nearly straight, shaped like a comma, or seemingly all tangled together.

Similar to fall streaks is virga, which appears as streamers suspended in the air beneath the base of precipitating clouds. Virga develops when precipitation falls through a layer of dry air and evaporates before reaching the ground.



Cloud Types
Terms for using data resources. CD-ROM available.
Credits and Acknowledgments for WW2010.
Department of Atmospheric Sciences (DAS) at
the University of Illinois at Urbana-Champaign.

cirrostratus