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
 
  mechanisms
 
  precip processes
 
> 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 whispy

High level clouds typically form above 20000 feet (6000 meters) and since the temperatures are so cold at such high elevations, these clouds are primarily composed of ice crystals. They are typically thin and white in appearance, however during sunrise and sunset, these clouds can appear in a magnificent array of colors as unscattered components of sunlight (red, yellow, and orange) are reflected by the underside of the clouds.

The most common variation of high level clouds are cirrus clouds. Cirrus are thin, whispy clouds composed of ice crystals that originate from the freezing of supercooled water droplets and exist where temperatures are below -38 degrees Celsius. Cirrus generally occur in fair weather and move from west to east, pointing in the direction of the prevailing winds 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, commonly seen during pleasant weather conditions, to the uniform texture of more extensive cirrus clouds associated with an approaching warm front.

[Image: cirrus fall streaks (83K)]


Fall streaks form when snowflakes and ice crystals fall from cirrus clouds. The change in wind with height and how quickly these ice crystals actually fall determine the shapes and sizes the fall streaks attain. Since ice crystals fall much more slowly than rain drops - about 1 meter per second compared with about 8 meters per second for large raindrops - fall streaks tend to be stretched out horizontally as well as vertically.


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.