Time series analyses of concentration and wind fluctuations |
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Authors: | Steven R Hanna Elizabeth M Insley |
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Institution: | (1) Sigma Research Corporation, 234 Littleton Road, Suite 2E, 01886 Westford, MA, USA |
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Abstract: | Analyses of concentration fluctuation (C) spectra from boundary-layer smoke plume experiments at six separate locations show that the spectra from these experiments generally exhibit an inertial subrange at high frequencies with a slope of -5/3 and indicate peak energy at a time period of about 50 to 100 s. These periods of peak energy are a factor of two to five less than those for the peak of the wind speed fluctuation (u or v) spectra. A general spectral formula fits normalized spectra from the U.S. and Australia, where the frequency, n, is made dimensionless by multiplying by the plume dispersion parameter,
y
, and dividing by the wind speed, u. Peak energy occurs at a dimensionless frequency of n
y/u equal to about 0.15. The Kolmogorov constant in the inertial subrange is estimated from a set of averaged spectra. Cross-spectra indicate little relation between concentration and wind fluctuations. However, most of the correlation that exists is due to periods larger than about 10 or 20 s. |
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