The two turbulence indicators in use are the variance of vertical wind speed and the eddy-dissipation rate. In order to obtain physically meaningful measures of turbulence from the cloud radar, a thorough analysis of potential sources of error in the Doppler wind retrieval has proved essential. For instance, the pulse-volume averaging effect of the radar beam, the contamination of radial Doppler velocity by the horizontal wind due to changes in aircraft attitude, and the possible misalignment of the fixed radar beam need to be taken into account. The uncertainty resulting from these error sources limits the minimum detectable turbulence signal to approximately 0.16 m2 s-2 and 0.002 m2 s-3 for the variance of vertical wind speed and eddy-dissipation rate, respectively. As a consequence, only qualitative estimates of turbulence intensity can be obtained away from the most turbulent regions, while better than 20% accuracy can be achieved in regions of severe turbulence in the lee of the mountain.
Inspired by numerous historic and contemporary studies of lee-side lower turbulent zones associated with mountain gravity waves, our study provides new measures of turbulence intensity at unprecedented spatial resolution and accuracy. In good agreement with past investigations, severe turbulence (up to 15 m2 s-2 or 0.16 m2 s-3) is observed in the interior of an atmospheric rotor, and moderate-to-severe turbulence (up to 2.6 m2 s-2 or 0.023 m2 s-3) is encountered in a wave-breaking region at flight level.
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