WW2010
University of Illinois

WW2010
 
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Online Guides
 
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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

Other Cloud Types
 
  contrails
 
  billow clouds
 
> mammatus
 
  orographic
 
  pileus

User Interface
 
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> text

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Mammatus Clouds
sagging pouch-like structures

Mammatus are pouch-like cloud structures and a rare example of clouds in sinking air.

[Image: example of mammatus (67K)]
Photograph by: Manikin
Sometimes very ominous in appearance, mammatus clouds are harmless and do not mean that a tornado is about to form; a commonly held misconception. In fact, mammatus are usually seen after the worst of a thunderstorm has passed.

As updrafts carry precipitation enriched air to the cloud top, upward momentum is lost and the air begins to spread out horizontally, becoming a part of the anvil cloud. Because of its high concentration of precipitation particles (ice crystals and water droplets), the saturated air is heavier than the surrounding air and sinks back towards the earth.

The temperature of the subsiding air increases as it descends. However, since heat energy is required to melt and evaporate the precipitation particles contained within the sinking air, the warming produced by the sinking motion is quickly used up in the evaporation of precipitation particles. If more energy is required for evaporation than is generated by the subsidence, the sinking air will be cooler than its surroundings and will continue to sink downward.

[Image: ominous looking mammatus (70K)]
Photograph by: NOAA
The subsiding air eventually appears below the cloud base as rounded pouch-like structures called mammatus clouds.

Mammatus are long lived if the sinking air contains large drops and snow crystals since larger particles require greater amounts of energy for evaporation to occur. Over time, the cloud droplets do eventually evaporate and the mammatus dissolve.

[Image: sunlit mammatus beneath a thunderstorm (102K)]
Photograph by: NOAA
Mammatus typically develop on the underside of a thunderstorm's anvil and can be a remarkable sight, especially when sunlight is reflected off of them.



billow clouds
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Credits and Acknowledgments for WW2010.
Department of Atmospheric Sciences (DAS) at
the University of Illinois at Urbana-Champaign.

orographic