A revaluation of the Kansas mast influence on measurements of stress and cup anemometer overspeeding |
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| Authors: | J Wieringa |
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| Institution: | (1) Royal Netherlands Meteorological Institute, De Bilt, Netherlands |
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| Abstract: | For the 1968 Kansas atmospheric surface-layer experiment, a supplementary analysis is made of the evaluation procedure. Available data on the ratio of wind speeds measured on separate booms show a variation with wind direction which is too large for an open mast. Actually the Kansas mast appears to have carried a bulky array of apparatus at the sonic anemometer levels. It is shown that the air flow interference caused by this obstacle can be satisfactorily estimated by way of potential flow calculations. From these it follows that the sonic anemometer measurements probably have undervalued the free-flow eddy stress by 20% to 30%, which implies that the simultaneous drag plate measurements of stress were generally correct. Also the overestimation of the mean wind speed by the Kansas cup anemometer is found to have been 6% rather than 10%. Some Kansas evaluation results are amended accordingly. The von Kármán constant is found to be 0.41 rather than 0.35, and the near-adiabatic eddy diffusivity ratio K
H
/K
M
becomes 1.0 rather than 1.3. The flux-gradient relations (Businger et al., 1971) after similar revision no longer differ significantly from those obtained elsewhere. |
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