clear-air turbulence (CAT) The variable pattern of up- and down-draughts, or turbulence, sometimes occurring in the absence of any cloud. It is caused by strong wind shear, especially associated with jet streams in the upper troposphere and lower stratosphere. The phenomenon is significant for aircraft.

clear-air turbulence (CAT) The variable pattern of up- and down-draughts, or turbulence, sometimes occurring in the absence of any cloud. It is caused by strong wind shear, especially associated with jet streams in the upper troposphere and lower stratosphere. The phenomenon is significant for aircraft.