WW2010
University of Illinois

WW2010
 
welcome
 
online guides
 
archives
 
educational cd-rom
 
current weather
 
about ww2010
 
index

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

Other Cloud Types
 
contrails
 
billow clouds
 
mammatus
 
orographic
 
pileus

User Interface
 
graphics
text

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Mammatus Clouds
sagging pouch-like structures

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

[Image: example of mammatus (67K)] 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 up 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, but heat energy is required to melt and evaporate the precipitation particles contained within the sinking air. Consequently, 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 downwards.

[Image: ominous looking mammatus (70K)] 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)] 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.


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.