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1.
Observations of the dispersion of a contaminant plume in the atmospheric boundary layer, obtained using a Lidar, are analysed in the coordinate frame relative to the instantaneous centre of mass of the plume, as well as the absolute (or fixed) coordinate frame. The study extends the work presented in a previous article, which analysed the structure of the probability density function (pdf) of concentration within the relative coordinate frame. Firstly, the plume displacement component, or plume meander, is analysed and a simple parametric form for the pdf of the plume centreline position is suggested. This is then used to analyse the accuracy and applicability of absolute framework statistical quantities obtained by a convolution of the relative frame statistical quantity with the plume centreline pdf. 相似文献
2.
Ralph M. Gailis Alexander Hill Eugene Yee Trevor Hilderman 《Boundary-Layer Meteorology》2007,122(3):577-607
Fluctuating plume models provide a useful conceptual paradigm in the understanding of plume dispersion in a turbulent flow.
In particular, these models have enabled analytical predictions of higher-order concentration moments, and the form of the
one-point concentration probability density function (PDF). In this paper, we extend the traditional formalism of these models,
grounded in the theory of homogeneous and isotropic turbulent flow, to two cases: namely, a simple sheared boundary layer
and a large array of regular obstacles. Some very high-resolution measurements of plume dispersion in a water channel, obtained
using laser-induced fluorescence (LIF) line-scan techniques are utilised. These data enable us to extract time series of plume
centroid position (plume meander) and dispersion in the relative frame of reference in unprecedented detail. Consequently,
experimentally extracted PDFs are able to be directly compared with various theoretical forms proposed in the literature.
This includes the PDF of plume centroid motion, the PDF of concentration in the relative frame, and a variety of concentration
moments in the absolute and relative frames of reference. The analysis confirms the accuracy of some previously proposed functional
forms of model components used in fluctuating plume models, as well as suggesting some new forms necessary to deal with the
complex boundary conditions in the spatial domain. 相似文献
3.
4.
北京秋季一次降雪前污染天气的激光雷达观测研究 总被引：1，自引：0，他引：1
以2009年11月5~8日北京地区发生的一次特殊天气形势下的重污染天气过程为例,研究分析本次污染特点和大气边界层结构特征以及此天气过程的大气温度和相对湿度结构特点。激光雷达是探测大气边界层及气溶胶的一个高效工具,利用ALS300激光雷达系统测量信号,应用Fernald方法反演大气消光系数,根据反演的气溶胶消光系数的最大突变,即最大递减率的高度来确定大气边界层的高度。利用其观测的退偏比分析大气污染物特性。利用微波辐射计数据,确定大气温度和湿度时空特征。研究结果表明:在本次污染天气下,大气具有很强的逆温结构,逆温最大可达近1 K(100 m)-1,500 m以上的大气相对湿度很低,在这种天气特征下的大气边界层高度在400 m左右,非常稳定。污染结束降雪开始前,大气逆温结构消失,大气湿度大幅度增加,接近饱和。根据lidar(light detection and ranging)退偏比的分析,本次污染天气是一次典型的烟尘类颗粒物的污染,污染具有区域性特点。PM2.5(空气动力学当量直径小于等于2.5μm的颗粒物)与AOT(Aerosol Optical Thickness)之间有明显的线性关系,相关系数达到0.72。该lidar系统能够反演出秋季降雪前本次污染天气背景下北京城区上空的大气污染特性和大气边界层高度。 相似文献
5.
Observations from aircraft, an island station, and tworesearch vessels are used to investigate the development of an elevated mixed layeror land plume over the Arabian sea during the Indian Ocean Experiment Intensive FieldPhase 1999 (INDOEX) through air mass modification. Much of the transport of aerosolsand gases occurs in this plume located above a well-mixed convective marine boundary layerwith a depth of 800–1000 m. The depth of the land plume isapproximately 2000 m with the peak ozone concentrations occurring near the centre of this land plume.Significant latitudinal variations in the concentration of ozone occur in the marineboundary layer and in the plume. Mean ozone concentrations in the land plume decreasedwith distance from the Indian coastline. 相似文献
6.
Eugene Yee P. R. Kosteniuk C. A. Biltoft J. F. Bowers 《Boundary-Layer Meteorology》1998,87(3):409-457
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. 相似文献
7.
A meandering plume model that explicitly incorporatesinternal fluctuations has been developed and used to model the evolutionof concentration fluctuations in point-source plumes in grid turbulenceobtained from a detailed water-channel simulation. This fluctuating plumemodel includes three physical parameters: the mean plume spread in fixedcoordinates, which represents the outer plume length scale; the meaninstantaneous plume spread in coordinates attached to the instantaneousplume centroid, which represents the inner plume length scale; and, theconcentration fluctuation intensity in the meandering reference frame,which represents the in-plume fluctuation scale. These parameters arespecified in terms of a set of coupled dynamical equations that modeltheir development with downstream distance from the source. Explicitexpressions for the concentration moments of arbitrary integral orderand the concentration probability density function have been obtainedfrom the fluctuating plume model. Detailed comparisons of model predictionsagainst water-channel measurements for the first four concentrationmoments and the concentration probability distributions generally showvery good overall quantitative agreement. Exact quantitative conditions,expressed in terms of the physical parameters of the fluctuating plumemodel, have been derived for the emergence of off-centreline peaks inthe concentration variance profile. These quantitative conditions havebeen illustrated in terms of a diagram of states of the dispersing plume,and the qualitatively different regimes of plume concentration variancebehaviour on this state diagram have been identified and characterized. 相似文献
8.
By D. MÜLLER B. HEINOLD M. TESCHE I. TEGEN D. ALTHAUSEN L. ALADOS ARBOLEDAS V. AMIRIDIS A. AMODEO A. ANSMANN D. BALIS A. COMERON G. D'AMICO E. GERASOPOULOS J. L. GUERRERO-RASCADO V. FREUDENTHALER E. GIANNAKAKI B. HEESE M. IARLORI P. KNIPPERTZ R. E. MAMOURI L. MONA A. PAPAYANNIS G. PAPPALARDO R.-M. PERRONE G. PISANI V. RIZI M. SICARD N. SPINELLI A. TAFURO M. WIEGNER 《Tellus. Series B, Chemical and physical meteorology》2009,61(1):325-339
We observed a long-range transport event of mineral dust from North Africa to South Europe during the Saharan Mineral Dust Experiment (SAMUM) 2006. Geometrical and optical properties of that dust plume were determined with Sun photometer of the Aerosol Robotic Network (AERONET) and Raman lidar near the North African source region, and with Sun photometers of AERONET and lidars of the European Aerosol Research Lidar Network (EARLINET) in the far field in Europe. Extinction-to-backscatter ratios of the dust plume over Morocco and Southern Europe do not differ. Ångström exponents increase with distance from Morocco. We simulated the transport, and geometrical and optical properties of the dust plume with a dust transport model. The model results and the experimental data show similar times regarding the appearance of the dust plume over each EARLINET site. Dust optical depth from the model agrees in most cases to particle optical depth measured with the Sun photometers. The vertical distribution of the mineral dust could be satisfactorily reproduced, if we use as benchmark the extinction profiles measured with lidar. In some cases we find differences. We assume that insufficient vertical resolution of the dust plume in the model calculations is one reason for these deviations. 相似文献
9.
Umberto Rizza Massimo Cassiani Umberto Giostra Cristina Mangia 《Boundary-Layer Meteorology》2000,95(2):319-339
An advanced model aimed at describing the problem of dispersion in theconvective boundary layer is proposed. The pollutant particles are groupedin clusters and modelled as Gaussian puffs. The expansion of each puff ismodelled according to the concept of relative dispersion and expressed interms of the spectral properties of the energy containing eddies of the turbulent field. The centre of mass of each puff is moved along a stochastic trajectory, obtained using a Lagrangian stochastic model and filtering the velocity with a recursive Kalman filter. At any instant, a filtering procedure, depending both on travel time and on puff size, acts to select spectral components involved in the expansion and in the meandering of the puff. Such an approach requires only a moderate number of puff releases, so that the proposed model is faster to run than a standard Lagrangian model. On the other hand, unlike the traditional puff model, it allows us to simulate both expansion and meandering of the puff. Therefore, it is well suited to simulate dispersion when the turbulent structures are larger thanthe plume dimensions, as for example in convective conditions. Being based onspectral formulations in both Eulerian and Lagrangian parts, the model is consistent in all the turbulent parameterizations utilised. Comparisons with a standard Lagrangian particle model as well as with a classical convective experimental dataset show good performance of the proposed model. 相似文献
10.
11.
Eugene Yee Ralph M. Gailis Alexander Hill Trevor Hilderman Darwin Kiel 《Boundary-Layer Meteorology》2006,121(3):389-432
We report on measurements of the near-field dispersion of contaminant plumes in a large array of building-like obstacles at three scales; namely, at full-scale in a field experiment, at 1:50 scale in a wind-tunnel simulation, and at 1:205 scale in a water-channel simulation. Plume concentration statistics extracted from the physical modelling in the wind-tunnel and water-channel simulations are compared to those obtained from a field experiment. The modification of the detailed structure of the plume as it interacts with the obstacles is investigated. To this purpose, measurements of the evolution of the mean concentration, concentration fluctuation intensity, concentration probability density function, and integral time scale of concentration fluctuations in the array plume obtained from the field experiment and the scaled wind-tunnel and water-channel experiments are reported and compared, as well as measurements of upwind and within-array velocity spectra. Generally, the wind-tunnel and water-channel results on the modification of the detailed plume structure by the obstacles were qualitatively similar to those observed in the field experiments. However, with the appropriate scaling, the water-channel simulations were able to reproduce quantitatively the results of the full-scale field experiments better than the wind-tunnel simulations. 相似文献
12.
The higher-order correlation functions for the concentrationfluctuations arising from a two-point-source configuration have beencalculated analytically within the context of the phenomenology of afluctuating plume model (viz., a meandering plume model that explicitlyincorporates internal fluctuations). Explicit expressions for thesecond-, third-, and fourth-order correlationfunctions between the concentrationfluctuations produced by two point sources are given in terms of the sourceseparation d and the five physically based parameters that define thegeneralized fluctuating plume model: namely, the absolute plume dispersion,a, which determines the outer plume length scale; the relative plume dispersion, r, which determines the inner plume length scale; the fluctuation intensity, ir, in relative coordinates, which determines the internal concentration fluctuation level; the correlation coefficient, r,between the positions of the centroids of the two interfering plumes; and,the correlation coefficient, r*, between the concentration fluctuationsof the two plumes in relative coordinates, which determines the degree ofinternal mixing of the two scalars. Furthermore, the form of the totalconcentration probability density function arising from the interferenceproduced by two point sources is presented. Predictions for the second-ordercorrelation function, , and for the total concentration probabilitydensity function have been compared with some new experimental data fora two-point-source configuration in grid turbulence generated in awater-channel simulation. These results are in good agreement with the dataand suggest that the analytical model for the second-order correlationfunction and the total concentration probability density function canreproduce many qualitative trends in the interaction of plumes from twosources. 相似文献
13.
Summary Extreme values of the ground level concentration of air pollutants were evaluated as a function of plume rise Δh, and wind speed in two cases. Firstly, when a plume rise depends on the downwind distance x, and secondly, with a constant plume rise (i.e., independent on x). Also, the extreme values for the effective stack height were evaluated for different stability classes. The maximum value
of the ground level concentration was obtained in unstable stability when plume rise depends on x and in the neutral stability when plume rise independent on x. Also, in stable case, the extreme values of the ground level concentration of air pollutants showed similar values in the
two cases when plume rise depends on x, and with constant plume rise. Finally, it was found that the extreme value of the ground level concentration occurred near
the stack and after that it was decreases in all stabilities. 相似文献
14.
The effects of source size on plume behaviour have been examined in a 1.2 m wind tunnel boundary layer for isokinetic sources with diameters from 3 to 35 mm at source heights of 230 mm and at ground level. Experimental measurements of mean concentration and the variance, intermittency and probability density functions of the concentration fluctuations were obtained. In addition, a fluctuating Gaussian plume model is presented which reproduces many of the observed features of the elevated emission. The mean plume width becomes independent of source size much more rapidly than the instantaneous plume width. Since it is the meandering of the instantaneous plume which generates most of the concentration fluctuations near the source, these are also dependent on source size. The flux of variance in the plume reaches a maximum, whose value is greatest for the smallest source size, close to the source and thereafter is monotonically decreasing. The intermittency factor reaches a minimum, whose value is lowest for the smallest source, and increases back towards one. Concentration fluctuations for the ground-level source are much less dependent on source size due to the effects of the surface. 相似文献
15.
The SF6 gas tracer observations for puffs released near the ground during the Joint Urban 2003 (JU2003) urban dispersion experiment
in Oklahoma City have been analysed. The JU2003 observations, at distances of about 100–1,100 m from the source, show that,
at small times, when the puff is still within the built-up downtown domain, the standard deviation of the concentration time
series, σt, is influenced by the initial puff spread due to buildings near the source and by hold-up in the wakes of large buildings
at the sampler locations. This effect is parameterised by assuming an initial σto of about 42 s, leading to a comprehensive similarity formula: σt = 42 + 0.1t. The second term, 0.1t, is consistent with an earlier similarity relation, σt = 0.1t, derived from puff observations in many experiments over rural terrain. The along-wind dispersion coefficient, σx, is assumed to equal σt
u, in which u is the puff speed calculated as the distance from the source to the sampler, x, divided by the time after the release that the maximum concentration is observed at the sampler. σx can be expressed as σx = σxo + 0.14x, with the initial σxo of 45 m. This initial σxo agrees with the suggestion of an initial plume spread of about 40 m, made by McElroy and Pooler from analysis of the 1960s’
St. Louis urban dispersion experiment. The puff speeds, u, are initially only about 20% of the observed wind speed, averaged over about 80 street-level and rooftop anemometers in
the city, but approach the mean observed wind speed as the puffs grow vertically. The scatter in the σt data is about ± a factor of two or three at any given travel time. The maximum σt is about 250 s, and the maximum duration of the puff over the sampler, Dt, sometimes called the retention time, is about
1,100 s or 18 min for these puffs and distances. 相似文献
16.
Plume meandering and averaging time effects were measured directly using a high spatial resolution, high frequency, linescan
laser-induced fluorescence (LIF) technique for measuring scalar concentrations in a plume dispersing in a water channel. Post-processing
of the collected data removed time dependent background dye levels and corrected for attenuation across the laser beam to
produce accurate measurements over long sample times in both a rough surface boundary-layer shear flow and shear free grid-generated
turbulent flow. The data were used to verify the applicability of a meandering plume model for predicting the properties of
mean and fluctuating concentrations. The centroid position of the crosswind concentration profile was found to have a Gaussian
probability density function and the instantaneous plume spread about the centroid fluctuated log-normally. A modified travel-time
power law model for averaging time adjustment was developed and compared to the widely used, but much less accurate, 0.2 power-law
model. 相似文献
17.
Wind tunnel experiments were performed to examine the behavior of suddenly released volumes of dense gas in a turbulent shear layer. Instantaneous concentrations were measured with hot-wire katherometers. Multiple replications of each cloud volume, density, and velocity combination produced statistics for plume arrival time, arrival of maximum concentration time, plume departure time, and maximum concentrations. Probability distributions and standard deviations of each plume property permit prediction of hazard risks. 相似文献
18.
An analysis of wind tunnel data of dispersion from elevated point sources over a flat floor and gently sloping, 2-D hills is performed. (The data were obtained by Khurshudyan et al., 1981.) Formulas for the mixing lengths and the Lagrangian time scales are tested, suitable for use in various dispersion models. Some expressions for the vertical first moments of the plume concentration distribution suitable for shear flow (Hunt, 1985) are also tested.Then, a normalization is suggested, based on the source mean flow and turbulence parameters, for the ground-level concentration maximum value and position along the plume centerline. Using this normalization, the maximum position is almost constant, regardless of source height variation and of whether the hill is present or not, at least for source positions upstream or over the top.The maximum values allow the determination of normalized terrain amplification factors TAFN, which are shown to be in most cases closer to one than the corresponding TAF obtained without normalization. 相似文献
19.
The effects of a pressure jump and a following internal gravity wave on turbulence and plume diffusion in the stable planetary
boundary layer are examined. The pressure jump was accompanied by a sudden increase in turbulence and plume dispersion. The
effects of wave perturbations on turbulence statistics are analysed by calculating fluxes and variances with and without the
wave signal for averaging times ranging from 1 to 30 min. The wave signals are obtained using a band-pass filter. It is shown
that second-order turbulence quantities calculated without first subtracting the wave perturbations from the time are greater
than those calculated when the wave signal is separated from the turbulence. Estimates of the vertical dispersion of an elevated
tracer plume in the stable boundary layer are made using an elastic backscatter lidar. Plume dispersion observed 25 m downwind
of the source increases rapidly with the arrival of the flow disturbances. Measured plume dispersion and plume centreline
height correlate with the standard deviation of the vertical velocity but not with the wave signal. 相似文献