Displaced-Beam Small Aperture Scintillometer Test. Part I: The Wintex Data-Set |
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Authors: | H. A. R. De Bruin W. M. L. Meijninger Ann-Sofi Smedman Mikael Magnusson |
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Affiliation: | (1) Meteorology and Air Quality Group, Wageningen University, Duivendaal 2, 6701 AP Wageningen, The Netherlands;(2) Department of Earth Sciences, Meteorology, University of Uppsala, Uppsala, Sweden |
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Abstract: | The friction velocity (u*) and the sensible heat flux density (H) determined with a displaced-beam small aperture scintillometer (DBSAS) and a hot-film eddy correlation system are compared. Random errors in the DBSAS are relatively small, compared to scatter found with two eddy-correlation systems. Assuming that the hot-film system yields the true fluxes, theDBSAS appears to overestimate u* when u* is less than 0.2 m s-1 and to underestimate u* at high wind speeds. This implies that the DBSAS measurements of theinner scale length of turbulence, l0, a direct measure for the dissipation rate of kinetic turbulent energy, are biased. Possible causes for these results are discussedin detail. A correction procedure is presented to account for effects of random noise and of so-called inactive turbulence or sensor vibrations. The errors in u* cause errors in the DBSAS measurements of the structure parameter of temperature CT2. The derived H appears to be less sensitive to errors in l0 and CT2, because errors in these quantities tend to cancel out. |
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Keywords: | Dissipation rate Friction velocity Inner scale length Laser scintillometry Sensible heat flux Structure parameter of temperature |
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