Friction slows the wind and changes its direction. This effect can cause turbulence in winds near the surface or boundaries between areas with different surface roughnesses. Turbulence mixes the lower part of the atmosphere, stabilizing the temperature. Turbulence causes eddies in the atmosphere, which are swirls of wind responsible for wind gusts and bumpy plane rides.
Why do I care? Friction and turbulence mix the air and are responsible for air motions in the lower atmosphere. They are the main cause of wind gusts.
Figure A: Eddy Created By Airplane Wing. (Image from NASA).
Friction is a force that acts on moving objects to slow them down. It always acts opposite the direction of motion as a result of resistance between rough surfaces, although friction can also act between regions of the atmosphere that are moving at different speeds.
Friction slows the wind down at the surface or in areas with winds of different speeds (wind shear). When the wind is blowing near the surface, the ground creates friction that makes the wind blow slower. Friction doesn’t just slow the wind down, it breaks up the flow of the wind, making it blow in different directions at different speeds. This creates turbulence.
Turbulence is created when the smooth flow of the wind is broken up and changed by the ground, buildings or other objects. Turbulence can also be created by daytime heating when differences in air temperature cause rising and sinking air. Turbulence causes eddies, which are swirling areas of the air. These eddies are responsible for wind gusts and mixing of the air in the atmosphere. You can sometimes see these eddies when dust or leaves get mixed into the air and follow the swirling winds around.