Abstract
Analysis of the velocity filed measured by ballon-borne anemometers through a clear air turbulent patch is presented. It is shown that, except in the case where the ballon altitude is constant, the vertical wind shear related to nonturbulent motions may create a contamination above the outer scale of the turbulent field. The results is typical of all turbulence measurements obtained along non-constant altitude trajectories: it may explain some intriguing characteristics of the gust velocity spectra measured by instrumented aircraft.
