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  • 1
    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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  • 2
    Electronic Resource
    Electronic Resource
    Concentration fluctuation measurements in clouds released from a quasi-instantaneous point source in the atmospheric surface layer (1994)
    Springer
    Boundary layer meteorology 71 (1994), S. 341-373 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract This study is an experimental investigation of the statistical properties of the turbulent concentration field of a cloud (puff) of pollutant dispersing in a near-neutral or slightly convective atmospheric surface layer. Experiments were conducted at ranges between about 25 and 300 m, and involved the quasi-instantaneous release of a tracer from a point source, with the instantaneous concentration field downwind of the source measured with concentration detectors possessing high temporal resolution (i.e, ≈270 Hz at the −6 dB point). Each experiment was accompanied by simultaneous measurements of surface-layer mean wind and turbulence statistics obtained with sonic anemometers. A new description of the statistical structure of a dispersing cloud is presented. This description utilizesL-moments to provide representative measures of cloud concentration in order to minimize the number of realizations required to compile meaningful ensemble averages.L-moments, which are ensemble averages (expectations) of certain linear combinations of order statistics of the concentration data, were used to describe, summarize, and characterize robustly the underlying distributional shape of a number of puff characteristics. In particular, experimental measurements of ensemble-mean concentration time profiles, some higher-orderL-moment (e.g.,L-fluctuation intensity,L-skewness, andL-kurtosis) profiles of instantaneous puff concentration, and variousL-moments of puff duration, maximum instantaneous concentration, and dosage were obtained. In addition, the probability distributions of maximum instantaneous concentration and dosage were studied, and found to be well represented by a gamma distribution. Finally, the downwind development of a number of puff characteristics was examined: maximum ensemble-mean concentration, mean puff duration, variousL-moments of instantaneous puff concentration and dosage, ensemblemean (L-mean) of maximum instantaneous puff concentration,. degree of unmixedness factor, and concentration integral length scale (obtained by evaluating the integral of the autocorrelation function). The downwind variation of most of these puff statistics was well characterized by power-low functional forms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00712175
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  • 3
    Electronic Resource
    Electronic Resource
    Measurements of level-crossing statistics of concentration fluctuations in plumes dispersing in the atmospheric surface layer (1995)
    Springer
    Boundary layer meteorology 73 (1995), S. 53-90 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The statistics of level crossings and local extremes in concentration fluctuations in plumes dispersing in the atmosphere have been investigated. A set of concentration fluctuation tracer experiments has been utilized to measure the statistical propertics of the upcrossing interval (inter-arrival time between consecutive concentration bursts), excursion duration (persistence or width of concentration bursts), and concentration amplitude (difference between the maximum and minimum concentrations between successive upcrossings) with respect to a range of concentration crossing levels. In particular, the effect of downwind distance and atmospheric stratification on the level-crossing statistics has been studied in detail. It is shown that the effect of increasing atmospheric stability on level-crossing statistics is similar to the effect of increasing distance from the source in the sense that level-crossing statistics of concentration fluctuations in stable stratification resemble those in neutral stratification, but at a greater downwind distance. It is also found that the distribution of the interval between consecutive upcrossings of a concentration level, as well as the duration of an excursion across a concentration level, can be approximated by a lognormal distribution, whereas the distribution of the concentration amplitude is best characterized by a gamma distribution. Some implications of these results for the modeling of level-crossing statistics of concentration fluctuations are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00708930
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  • 4
    Electronic Resource
    Electronic Resource
    A Study of Concentration Fluctuations in Instantaneous Clouds Dispersing in the Atmospheric Surface Layer for Relative Turbulent Diffusion: Basic Descriptive Statistics (1998)
    Springer
    Boundary layer meteorology 87 (1998), S. 409-457 
    Details
    ISSN: 1573-1472
    Keywords: Cloud dispersion ; Concentration fluctuations ; Relative diffusion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A series of tracer experiments studying the statistical properties of concentration fluctuations in clouds dispersing in the atmospheric surface layer is described and analyzed. Experiments were conducted at downwind fetches between about 200 and 1200 m, under a wide range of atmospheric conditions ranging from very unstable to moderately stable stratification. The present experiments have addressed basic requirements not met by past field experiments involving instantaneously released clouds; namely, the experiments provided repeat realizations of instantaneously released clouds measured with high-resolution concentration detectors, accompanied by the contemporaneous acquisition of high-quality meteorological and turbulence measurements. Extensive analyses are performed on the cloud concentration data in the framework of relative diffusion. Ensembles of cloud concentration realizations have been constructed. From these ensembles, crosswind and time profiles of the ensemble-mean concentration, concentration variance, ensemble-mean dosage, and dosage variance are obtained. The behaviour of the time profiles of the integral time scale of cloud concentration fluctuations is studied. The use of surface-layer similarity theory for the analysis of the downwind variation of a number of cloud quantities (e.g., cloud size and duration, cloud centre ensemble-mean concentration and dosage, cloud centre concentration and dosage variance, cloud centre integral time scale) is shown to be an effective basis for ordering these quantities. Furthermore, a number of approximate universal relationships describing the behavior of these cloud quantities has been derived. Finally, it is shown that the scaled crosswind and time profiles of ensemble-mean concentration and concentration variance as well as the scaled time profiles of the concentration fluctuation integral time scale exhibit self-similar forms that are independent of atmospheric stratification and downwind fetch.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1001080429083
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  • 5
    Electronic Resource
    Electronic Resource
    Multiscaling properties of concentration fluctuations in dispersing plumes revealed using an orthonormal wavelet decomposition (1996)
    Springer
    Boundary layer meteorology 77 (1996), S. 173-207 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The dynamical characteristics of concentration fluctuations in a dispersing plume over the energetic and inertial-convective range of scales of turbulent motion are studied using a multiscale analysis technique that is based on an orthonormal wavelet representation. It is shown that the Haar wavelet concentration spectrum is similar to the Fourier concentration spectrum in that both spectra exhibit an extensive inertial-convective subrange spanning about two decades in frequency, with a scaling exponent of -5/3. Analysis of the statistical properties (e.g., fluctuation intensity, skewness, and kurtosis) of the concentration wavelet coefficients (i.e., the concentration discrete detailed signal) suggests that the small scales are always more intermittent than the large scales. The degree of intermittency increases monotonically with decreasing scale within the inertial-convective subrange, reaching a plateau at the very small scales associated with the beginning of the near-dissipation subrange. The probability density function (pdf) of the concentration discrete detailed signal displays stretched exponential tails with an intermittency exponent (tail slope) q that increases as Τ a , where Τ is the scale or dilation and a is a power-law exponent that is dependent on downwind distance, plume height, and stratification strength with typical values in the range from about 0.25 to 0.35. It is shown that the concentration variance cascade process requires a phase coherency of eddies between different scales at the small-scale end of the inertial-convective subrange. The variation of the concentration wavelet statistics with height above the ground is investigated. The increased mean shear near the ground smooths the fine-scale plume structure for scales within the inertial-convective subrange, producing a weaker spatiotemporal intermittency in the concentration field compared to that measured higher up in the plume. The pdf of the concentration detailed signal at a fixed scale possesses less elongated tails with decreasing height z. The intermittency exponent q is found to decrease roughly linearly with increasing z. Finally, the results of the wavelet decomposition are combined to provide a conceptual model of the turbulent transport, stirring, and mixing regimes in a dispersing plume. The implications of the results for contaminant texture in a plume are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00119577
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  • 6
    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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  • 7
    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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  • 8
    Electronic Resource
    Electronic Resource
    The vertical structure of concentration fluctuation statistics in plumes dispersing in the atmospheric surface layer (1995)
    Springer
    Boundary layer meteorology 76 (1995), S. 41-67 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract This paper describes a study of the vertical structure of concentration fluctuations in a neutrally buoyant plume from an elevated point source in slightly convective to moderately stable meteorological conditions at ranges of between 12.5 and 100 m for a range of source heights between 1 and 5 m. Observations were made of concentration fluctuations in a dispersing plume using a vertical array of sixteen very fast-response photoionization detectors placed at heights between 0.5 and 16 m. Vertical profiles of a number of concentration statistics were extracted, namely, mean concentration, fluctuation intensity, intermittency factor, peak-to-mean concentration ratio, mean dissipation rate of concentration variance, and various concentration time and length scales of dominant motions in the plume (e.g., integral macro-scale, in-plume mid-scale and Taylor micro-scale). The profiles revealed a similarity to corresponding crosswind profiles for a fully elevated plume, but showed greater and greater departure from the latter shapes once the plume had grown in the vertical so that its lower dege began to interact progressively more strongly with the ground. The evolution of the concentration probability density function at a fixed range, but with decreasing height from the ground, is similar to that obtained at a fixed height but with increasing distance from the source. Concentration power spectra obtained at different heights all had an extensive inertial-convective subrange spanning at least two decades in frequency, but spectra measured near the ground had a greater proportion of the total concentration variance in the lower frequencies (energetic subrange), with a correspondingly smaller proportion in the higher frequencies (inertial-convective subrange). It is believed that these effects result from the increased mean shear near the surface, and blocking by the surface. The effect of enhanced shear-induced molecular diffusion on concentration fluctuations is examined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00710890
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  • 9
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    The vertical structure of concentration fluctuation statistics in plumes dispersing in the atmospheric surface layer (1995)
    Springer
    Details
    Publication Date: 1995-10-01
    Print ISSN: 0006-8314
    Electronic ISSN: 1573-1472
    Topics: Geosciences , Physics
    Published by Springer
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  • 10
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    Concentration fluctuation measurements in clouds released from a quasi-instantaneous point source in the atmospheric surface layer (1994)
    Springer
    Details
    Publication Date: 1994-12-01
    Print ISSN: 0006-8314
    Electronic ISSN: 1573-1472
    Topics: Geosciences , Physics
    Published by Springer
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