What causes clear air turbulence?

• A. Wind shear, a difference in wind speed or direction, often near jet streams.
• B. Turbulence only associated with thunderstorms.
• C. Mechanical turbulence from terrain.
• D. Wake turbulence.

Answer: (A)

Clear air turbulence happens when there are rapid changes in wind speed or direction at high altitudes, in air that looks clear and has no visible clouds. The main driver is wind shear, especially near jet streams where wind gradients are strong. Those sharp changes twist and shake air parcels as they move, creating turbulence without any visible weather. It’s not caused by thunderstorms (which involve clouds and convective activity), not by mechanical turbulence from terrain (which occurs near the ground due to rough surfaces), and not by wake turbulence (the disturbed air behind another aircraft). So the drop in smoothness comes from wind shear in the upper atmosphere, often associated with jet streams.