Abstract
Cross-spectra between horizontal wind components at different levels of the Boulder Atmospheric Observatory (BAO) tower lead to the following conclusions:
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(1)
Davenport's hypothesis is satisfied that coherence decays exponentially with the ratio of vertical separation to horizontal wave length, at least to very small values of coherence.
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(2)
The decay coefficients increase with z/L for z/L < 0.5. For larger stabilities, irregular fluctuations with periods of order 10–20 min have considerable vertical coherence. Results at BAO are quite consistent with those elsewhere.
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(3)
Eddy slopes in vertical planes increase with wind shear up to a point where the slope (horizontal delay over vertical separation) is just above 2. Beyond that point, the systematic increase of slopes with shear ceases. Since wind shear decreases upward, slopes tend to decrease upward. Slopes for lateral components are significantly larger than those for u-components.
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References
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Soucy, R., Woodward, R. & Panofsky, H.A. Vertical cross-spectra of horizontal velocity components at the Boulder observatory. Boundary-Layer Meteorol 24, 57–66 (1982). https://doi.org/10.1007/BF00121799
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DOI: https://doi.org/10.1007/BF00121799