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Old 22nd Jul 2007, 15:44
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Mad (Flt) Scientist
 
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Turbulence is essentially a random phenomenom.

Windshear is, at it's simplest, two layers of air moving at different speeds, hence with a "shear" or tearing layer between them. It can also be a local up or downdraft, and associated in/outflow. Regardless, it's a pseudo-stable condition - if there was a downdraft of strength X 30 seconds ago, it's probably still there, and of similar magnitude.

In practice, one rarely sees windshear without some level of turbulence; the academic windshears used for training and system design therefore comprise both a pure shear model and a turbulence model.

AC120-41 contains some discussion of the modelling approach used.
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