Spectra of concentration fluctuations: The two time scales of a meandering plume |
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| Institution: | 1. Institute of Psychology, University of Wroclaw, Poland;2. Neag School of Education, Department of Educational Psychology, University of Connecticut, United States;3. Department of Educational Sciences, The Maria Grzegorzewska University, Warsaw, Poland;4. Department of Applied Social Sciences, The Maria Grzegorzewska University, Warsaw, Poland |
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| Abstract: | The integral time scale, TC, of the concentration fluctuations in a narrow, meandering (intermittent) plume can be much less than the time scale, TE, of the turbulence in which the plume is immersed, and is generally of the same order of magnitude as the time required for the plume to pass once over a receptor. However the total concentration fluctuation variance is equally strongly influenced by the larger time scale, TE, associated with meandering caused by ambient turbulence. It is shown that observed energy spectra of concentration fluctuations can be fitted by a linear combination of two Markov spectra, one with the time scale of the meandering motions and another with the time scale of the small scale plume motions. The two components are weighted by I and 1 − I, respectively, where I is the intermittency or fraction of time that non-zero concentrations occur. |
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