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6. Measuring turbulent structure
A comprehensive review of the use of radar to measure the morphology of the boundary
layer is provided by Gossard (1990), who also provides a review of the use of Doppler radar
to measure turbulent velocity variance and covariance. VAD scans do not produce perfect
sinusoids, and their derived time series are perturbed by random turbulent fluctuations at
scales larger than the radar pulse volume, but much smaller than the diameter of the VAD.
Wilson (1970) and Wilson and Miller (1972) developed a procedure for extracting
quantitatively the variances and covariances of u, v and w. This was developed further by
Kropfli (1984) who measured profiles of vertical momentum flux through the convective
boundary layer as shown in Figure 3.
Fig. 3. Single radar measurement of vertical profile of momentum flux through the
boundary layer by the method of Wilson (1970). Data are from a 100-min period beginning
at 12-3 MDT during the PHOENIX experiment (from Kropfli, 1984)
The radar Doppler spectral width has also been used to extract small-scale turbulence
information from spectral broadening due to wind shear, the radar antenna properties and
the variance of the velocity component in the radial direction due to turbulence. In
particular, the eddy dissipation rate can be measured, the first attempt to do this being by
Gorelik and Mel'nichuk (1963). Table 5 is a summary of the literature on the measurement of
turbulent energy dissipation (ε). Note that both radar and lidar have been used to measure
this quantity.
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