WW2010
University of Illinois

WW2010
 
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> online guides
 
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  current weather
 
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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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Cirrostratus Clouds
sheet-like and nearly transparent

Cirrostratus are sheet-like clouds composed of ice crystals. Though cirrostratus can cover the entire sky and be up to several thousand feet deep, they are relatively transparent, as the sun or the moon can be easily seen through them. Sometimes the only indication of their presence is given by an observed halo around the sun or moon Halos result from the refraction of light by the cloud's ice crystals.

[Image: halo through the cirrostratus clouds (58K)] These high level clouds typically form when a broad layer of air is lifted to its Lifting Condensation Level by large-scale convergence. Cirrostratus clouds, however, tend to thicken as a warm front approaches, signifying an increased production of ice crystals. As a result, the halo is no longer seen and the sun (or moon by night) becomes less visible.

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 criss-cross pattern of cirrus streaks is commonly seen before an approaching warm front.

[Image: thickening cirrus and cirrostratus at sunset (65K)] The cirrus streaks were aligned in a southwest to northeast direction, indicative of the advancing warmer air at higher levels. Lower on the horizon, thickening cirrostratus clouds effectively hide the sun, signifying changing weather ahead. With time, these clouds will thicken into altostratus and eventually into the lower and more dense nimbostratus clouds as the warm front gets closer and closer.


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.