Measurements of Air Motion in Regions of Clear Air Turbulence using High-power Doppler Radar

IT is widely accepted that the primary cause of clear air turbulence (CAT) in the free atmosphere is Kelvin-Helmholtz (K-H) instability 1 . This appears as amplifying waves (billows), with amplitudes ranging from one metre to hundreds of metres, which often break into turbulence on a range of smaller scales. The intensity of the turbulence depends on the billow amplitude and on the magnitude of the vertical shear of the wind across their depth before they break.