Recurrence statistics of concentration fluctuations in plumes within a near-neutral atmospheric surface layer |
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| Authors: | Eugene Yee P R Kosteniuk G M Chandler C A Biltoft J F Bowers |
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| Institution: | (1) Defence Research Establishment Suffield, Box 4000, T1A 8K6 Medicine Hat, Alberta, Canada;(2) Kosteniuk Consulting Ltd, 1301 Cumberland Ave, S7H 2L9 S. Saskatoon, Saskatchewan, Canada;(3) S & J Engineering, Inc., 3447 Kennedy Rd, Suite 6, M1V 3S1 Scarborough, Ontario, Canada;(4) Meteorology Division, Materiel Test Directorate U.S. Army Dugway Proving Ground, 84022-5000 Dugway, Utah, USA |
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| Abstract: | This study examines the statistical properties of the concentration derivative,   , for a dispersing plume in a near-neutrally stratified atmospheric surface layer. Towards this goal, the probability density function (pdf) of , and the conditional pdf of given a fixed concentration level, , have been measured. These pdfs are found to be modeled well by a generalizedq-Gaussian (gqG) distribution with intermittency exponent,q, equal to 0.3 and 3/4, respectively. These results highlight the strong intermittency effect (patchiness) of the small-scale concentration eddy structures in the plume. The distribution of time intervals between successive high peaks in the squared derivative process, x2, is found to be well approximated by a power-law distribution, implying that occurrences of these high peaks are much more clustered than would be predicted by a Poisson or shot-noise process. The results are used to improve models for the joint pdf of and , and for the expected number of upcrossings per unit time interval of a fixed concentration level that have been proposed by Kristensenet al. (1989). The predictions of the improved models are in accord with observations, and suggest that the intercorrelation between and must be explicitly incorporated if good estimates of the upcrossing intensity are to be obtained. |
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