WW2010
University of Illinois

WW2010
 
welcome
 
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Online Guides
 
introduction
 
meteorology
 
remote sensing
 
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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

Severe Storms
 
introduction
 
dangers of t-storms
 
types of t-storms
 
tstorm components
 
tornadoes
 
modeling

Modeling
 
introduction
 
supercells
 
convective lines
 
forecasting

Forecasting
 
introduction
 
forecast matrix
 
parameters
 
ncsa access article

Parameters
 
stability
 
wind shear
 
cape

User Interface
 
graphics
text

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Wind Shear

The environmental wind field is also very important in determining what type of a thunderstorm could develop. Severe weather usually occurs when the change in horizontal winds (wind shear) is significant. This includes the change in wind direction (directional shear) or speed (speed shear).

Speed Shear
In speed shear, the wind increases in speed from the surface to the upper levels, as shown in this diagram by the arrows. This vertical shear creates horizontal rotation which can best be visualized by placing a paddle wheel in the environment. Besides the rotation, the change in wind speed with height lets the updraft separate from the downdraft, allowing the storm to survive longer and even become stronger.

[Embedded Object: Shear Movie (1.20MB)]


Illustration of vertical speed shear (arrows)
(paddlewheel inserted to demonstrate local vorticity)
The original source of this image is the Cooperative Program for Operational Meteorology, Education and Training (COMET®) of the University Corporation for Atmospheric Research. Copyright © 1996 University Corporation for Atmospheric Research. All Rights Reserved

Directional Shear
Directional shear refers to a change in the direction of the wind with height. Notice in this image there is both speed and directional shear as both the angle and the length of the wind vectors are changing with height. Two viewpoints are shown in the following figure. The length of the arrows represents the wind speed. The arrows point in the direction that the wind is blowing and are located at different heights in the column of air shown. Both speed and directional changes occur from one level to another.

[Image: (45K)]
Illustration of both directional and speed shear
Image by Bramer

Modelers run experiments with storms developing in different amounts of wind shear. Differing amounts of wind shear can determine whether a storm remains small or becomes a supercell.



stability
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.

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