Shear

Wind shear is the change in the direction and/or magnitude of wind with height. If the wind shear is large enough, turbulence is produced. A rapid change in wind speed or direction allows eddies to split away from the general flow. Shears are often formed due to friction with the rough surface of the earth. This allows slower winds near the surface and faster wind aloft. Thus, a shear is created. The more rough a surface, the greater the wind shear. In the diagram to the right, notice the exponential curve that connects the wind vector tips. This shows the dramatic increase in wind velocity near the surface. However, further up, the wind speed does not increase rapidly with height. Therefore, the greatest shear is created near the surface.