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  • 1
    Electronic Resource
    Electronic Resource
    Fractal characteristics of isoconcentration surfaces in plumes dispersing in the atmospheric surface layer (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 7 (1995), S. 2715-2724 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The geometrical properties of isoconcentration surfaces in a plume dispersing in the atmospheric surface layer are studied using a generalized box-counting method applied to a limited random point set. This method yields the hierarchy of generalized dimensions Dq that can be used to characterize the fractal nature of the plume concentration level sets. The dimension spectra for the concentration level sets are computed from one-dimensional cuts of the concentration field. The concentration level sets are found to be monofractals that can be characterized by one scaling exponent or fractal dimension. The fractal dimension of the level sets is independent of the concentration threshold over a wide range of threshold values. The evolution of the fractal dimension of plume concentration level sets with distance x downwind from the source, cross-wind distance y from the lateral mean-plume centerline, and vertical height z above the ground is examined. At a fixed plume height, the fractal dimension is essentially independent of either x or y. The fractal dimension of the plume isoconcentration surface decreases roughly linearly from a value of 0.7±0.05 near the surface (z(approximately-less-than)1 m) to 0.45±0.05 higher up in the plume (z(approximately-greater-than)8 m). The increased wrinkling of the plume isoconcentration surface near the ground is most likely the result of the increased mean velocity shear and blocking by the surface. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.868718
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  • 2
    Electronic Resource
    Electronic Resource
    Recurrence statistics of concentration fluctuations in plumes within a near-neutral atmospheric surface layer (1993)
    Springer
    Boundary layer meteorology 66 (1993), S. 127-153 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract This study examines the statistical properties of the concentration derivative, χ′, for a dispersing plume in a near-neutrally stratified atmospheric surface layer. Towards this goal, the probability density function (pdf) of χ′, and the conditional pdf of χ′ given a fixed concentration level, χ, 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, x′2, 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 χ and χ′, 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 χ and χ′ must be explicitly incorporated if good estimates of the upcrossing intensity are to be obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00705463
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  • 3
    Electronic Resource
    Electronic Resource
    Application of nonlinear dynamical systems analysis to conditionally sampled concentration fluctuations of a passive scalar in the atmospheric boundary layer (1991)
    Springer
    Boundary layer meteorology 57 (1991), S. 49-78 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Time series and nonlinear dynamical systems analysis have been applied to the characterization of conditionally sampled concentration fluctuations (viz., zero concentration intervals censored) of a passive scalar from a unipolar ion plume experiment in an atmospheric boundary layer. The statistical characteristics of the scalar fluctuations are summarized in terms of basic descriptive statistics (e.g., mean concentration, fluctuation intensity, skewness, kurtosis, etc.), the concentration probability density function and the power spectral density function (or, equivalently, the autocorrelation function). In order to determine the origins for the variability and seemingly random behavior in concentration, new nonlinear dynamical systems-theoretical methods have been utilized for the analysis of concentration fluctuations. The concentration attractor, which is responsible for the temporal evolution of the observed concentration time series, has been reconstructed using phase-space techniques. The results provide compelling evidence for the existence of a strange attractor with an intriguingly low fractional correlation dimension of about 5.6. Furthermore, the spectra of generalized dimensions and of singularities have been determined for the concentration attractor and these results provide indications of the inhomogeneous, multifractal nature of the attractor. Finally, the most significant Lyapunov exponents have been extracted for the system and these exponents provide evidence that the nature of the dynamics is chaotic.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00119713
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  • 4
    Electronic Resource
    Electronic Resource
    Reply to the ‘comments on: The PDF of concentration fluctuations’ by Kenneth R. Mylne (1992)
    Springer
    Boundary layer meteorology 61 (1992), S. 195-204 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02034002
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  • 5
    Electronic Resource
    Electronic Resource
    Statistical characteristics of concentration fluctuations in dispersing plumes in the atmospheric surface layer (1993)
    Springer
    Boundary layer meteorology 65 (1993), S. 69-109 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Measurements have been made of concentration fluctuations in a dispersing plume from an elevated point source in the atmospheric surface layer using a recently developed fast-response photoionization detector. This detector, which has a frequency response (−6 dB point) of about 100 Hz, is shown to be capable of resolving the fluctuation variance contributed by the energetic subrange and most of the inertial-convective subrange, with a reduction in the fluctuation variance due to instrument smoothing of the finest scales present in the plume of at most 4%. Concentration time series have been analyzed to obtain the statistical characteristics of both the amplitude and temporal structure of the dispersing plume. We present alongwind and crosswind concentration fluctuation profiles of statistics of amplitude structure such as total and conditional fluctuation intensity, skewness and kurtosis, and of temporal structure such as intermittency factor, burst frequency, and mean burst persistence time. Comparisons of empirical concentration probability distributions with a number of model distributions show that our near-neutral data are best represented by the lognormal distribution at shorter ranges, where both plume meandering and fine-scale in-plume mixing are equally important (turbulent-convective regime), and by the gamma distribution at longer ranges, where internal structure or spottiness is becoming dominant (turbulent-diffusive regime). The gamma distribution provides the best model of the concentration pdf over all downwind fetches for data measured under stable stratification. A physical model is developed to explain the mechanism-induced probabilistic schemes in the alongwind development of a dispersing plume, that lead to the observed probability distributions of concentration. Probability distributions of concentration burst length and burst return period have been extracted and are shown to be modelled well with a powerlaw distribution. Power spectra of concentration fluctuations are presented. These spectra exhibit a significant inertial-convective subrange, with the frequency at the spectral peak decreasing with increasing downwind fetch. The Kolmogorov constant for the inertial-convective subrange has been determined from the measured spectra to be 0.17±0.03.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00708819
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  • 6
    Electronic Resource
    Electronic Resource
    Incorporation of internal fluctuations in a meandering plume model of concentration fluctuations (1994)
    Springer
    Boundary layer meteorology 67 (1994), S. 11-39 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A meandering plume model that explicitly incorporates the effects of small-scale structure in the instantaneous plume has been formulated. The model requires the specification of two physically based input parameters; namely, the meander ratio,M, which is dependent on the ratio of the meandering plume dispersion to the instantaneous relative plume dispersion and, a relative in-plume fluctuation measure,k, that is related inversely to the fluctuation intensity in relative coordinates. Simple analytical expressions for crosswind profiles of the higher moments (including the important shape parameters such as fluctuation intensity, skewness, and kurtosis) and for the concentration pdf have been derived from the model. The model has been tested against some field data sets, indicating that it can reproduce many key aspects of the observed behavior of concentration fluctuations, particularly with respect to modeling the change in shape of the concentration pdf in the crosswind direction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00705506
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  • 7
    Electronic Resource
    Electronic Resource
    On the moments approximation method for constructing a Lagrangian Stochastic model (1994)
    Springer
    Boundary layer meteorology 70 (1994), S. 273-292 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The exact Eulerian velocity probability density function (pdf) of a turbulent field is generally unknown, and one normally has available only partial information in the form of low order moments. We compare two alternative Lagrangian Stochastic (LS) approaches formed from this partial information, (i) the “moments approximation” approach (Kaplan and Dinar, 1993); and (ii) the well-mixed model (Thomson, 1987) that corresponds to the “maximum missing information” pdf formed from the available information. We show that the moments approximation model does not in general satisfy the well-mixed constraint, and can give an inferior prediction of dispersion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00709122
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  • 8
    Electronic Resource
    Electronic Resource
    The shape of the probability density function of short-term concentration fluctuations of plumes in the atmospheric boundary layer (1990)
    Springer
    Boundary layer meteorology 51 (1990), S. 269-298 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The shape of the probability distribution of a set of high-resolution concentration fluctuation measurements from an ion plume is studied using order statistics and certain selected quantiles derived from them. A number of graphical techniques based on the order statistics are shown to be useful for the assessment of the symmetry and tailweight of the underlying distribution of concentration. These graphical techniques are applied, from both a descriptive and a computational point of view, to elucidate the underlying distributional shape of concentration and to assess the characterization efficacy of the probability distributions that have been proposed as models for concentration fluctuations. In this respect, a new probability distribution, namely, the g and h distribution, is introduced for describing concentration fluctuations and it is shown that this distribution is superior to the more commonly used models, namely, the log-normal, the exponential, and the clipped-normal distributions utilized by previous investigators. Except for the g and h distribution, it is found that none of the commonly used models for the concentration probability distribution is able to characterize accurately the extreme upper end of the concentration frequency distribution (i.e., the end of the distribution that is critical for the prediction of the probability of exposure to peak levels). However, the clipped-normal distribution is shown to provide a reasonably conservative model for the prediction of the exceedances of critical concentration levels. Finally, it is noted that the g and h distribution yields a bimodal form for the total probability density function for concentration whereas the clipped-normal distribution provides a unimodal form. It is shown that the bimodal form of the total concentration probability density function is consistent with both the data and certain theoretical results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00122141
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  • 9
    Electronic Resource
    Electronic Resource
    COMMENTS ON ’’RELATIONSHIPS BETWEEN HIGHER MOMENTS OF CONCENTRATION AND OF DOSE IN TURBULENT DISPERSION‘‘ (1997)
    Springer
    Boundary layer meteorology 82 (1997), S. 341-351 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1000254829126
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  • 10
    Electronic Resource
    Electronic Resource
    Probability distributions of concentration fluctuations of a weakly diffusive passive plume in a turbulent boundary layer (1993)
    Springer
    Boundary layer meteorology 64 (1993), S. 321-354 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Results are presented from an experimental investigation of turbulent dispersion of a saline plume of large Schmidt number (Sc=830) in a turbulent boundary-layer shear flow simulated in a laboratory water channel. The dispersion measurements are obtained in a neutrally buoyant plume from an elevated point source over a range of downstream distances, where both plume meandering and fine-structure variations in the instantaneous plume are important. High-resolution measurements of the scalar fluctuations in the plume are made with a rake of conductivity probes from which probability distributions of concentration at various points throught the plume are extracted from the time series. Seven candidate probability distributions were tested, namely, the exponential, lognormal, clipped normal, gamma, Weibull, conjugate beta, andK-distributions. Using the measured values of the conditional mean concentration, $$\overline {\chi _p } $$ , and the conditional fluctuation intensity,i p , the Weibull distribution provided the best match to the skewness and kurtosis over all downstream fetches. The skewness and kurtosis were always overpredicted by the lognormal probability density function (pdf), and underpredicted by the gamma pdf. The conjugate beta distribution for which the model parameters are determined using a method of moments based on the fluctuation intensity,i p , and skewness,S p , was capable of modeling the distribution of scalar concentration over a wide range of positions in the plume.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00711704
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