Wind shear is a form of atmospheric turbulence, defined as the rate of change of wind speed and/or direction over a given distance. The shearing of the wind creates forces that can produce eddies.
When the wind encounters a solid object, a whirl of air (called an eddy) forms off the leeward side of the object.
Eddies can form near the surface or aloft, and the size and shape of the eddy depend on the speed of the wind, combined with the size and shape of the object.
Eddies with a violent vertical motion that produce extreme turbulence are called rotors (or roll eddies). These particular eddies are typically produced by winds moving over a mountain range and can be extremely dangerous for Aviation. If these eddies form in the clear air, it is known as clear air turbulence.
Eddies create small areas of high air density can sometimes produce sound (described as howling) as compressions cause the molecules to push on one another.