A Comment on “How Well Can We Measure the Vertical Wind Speed? Implications for Fluxes of Energy and Mass” by Kochendorfer et al.
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Kochendorfer et al. (Boundary-Layer Meterol, 145:383–398, 2012) conducted an experiment to evaluate azimuth and angle-of-attack dependent errors of sonic anemometer measurements. Several questions are raised regarding the experimental design and the presented results. The finding that instruments with non-orthogonal sonic paths underestimate fluctuations of vertical wind speed and consequently also scalar fluxes by about 10 % is compared with the results of a hitherto unpublished side-by-side field comparison and other past intercomparison experiments. Scale considerations are presented that raise considerable doubts on the validity of the implicit assumption of Kochendorfer et al. (2012) that the turbulent wind vector is highly correlated across a distance of 1.2 m at a height of 2.5 m over flat grassland, which corresponds to the separation between the sonic anemometers tested in their experiment. Nevertheless, new developments in sonic anemometer design to minimize transducer-shadow effects are desirable.
KeywordsAngle-of-attack error Energy balance closure Field intercomparison Sonic anemometer Transducer-shadow effects
We would like to acknowledge Dr. Ray Desjardins and Dr. Elisabeth Pattey who provided the instruments for the intercomparison experiment. Thanks to Dr. Hans Peter Schmid and Dr. Matthias Zeeman for sharing their thoughts and for valuable discussions.
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