共查询到20条相似文献，搜索用时 46 毫秒
1.
Eugene Yee R. Chan P. R. Kosteniuk G. M. Chandler C. A. Biltoft J. F. Bowers 《Boundary-Layer Meteorology》1994,67(1-2):11-39
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.List of Symbols
C
Mean concentration in absolute coordinates
-
C
r
Mean concentration in relative coordinates
- C0
Centerline mean concentration in absolute coordinates
- C
r,0
Centerline mean concentration in relative coordinates
-
f
Probability density function of concentration in absolute coordinates
-
f
c
Probability density function of plume centroid position
-
f
r
Probability density function of concentration in relative coordinates
-
i
Absolute concentration fluctuation intensity (standard deviation to mean ratio)
-
i
r
Relative concentration fluctuation intensity (standard deviation to mean ratio)
-
k
Relative in-plume fluctuation measure:k=1/i
r
2
-
K
Concentration fluctuation kurtosis
-
M
Meander ratio of meandering plume variance to relative plume variance
-
S
Concentration fluctuation skewness
-
x
Downwind distance from source
-
y
Crosswind distance from mean-plume centerline
-
z
Vertical distance above ground
-
Instantaneous (random) concentration
-
Crosswind dispersion ofnth concentration moment about zero
-
ny
Mean-plume crosswind (absolute) dispersion
-
y
Plume centroid (meandering) dispersion in crosswind direction
-
y,c
Instantaneous plume crosswind (relative) dispersion
-
Normalized mean concentration in absolute coordinates:C/C
0
-
Particular value taken on by instantaneous concentration, 相似文献
2.
Siri Jodha Singh Khalsa 《Boundary-Layer Meteorology》1980,19(1):3-17
The indirect dissipation technique is used to estimate 1-min averages of friction velocity u
*in the surface layer over the tropical ocean. These estimates are compared to estimates of u
*obtained using a drag coefficient and the relative difference between the two is examined in relation to stability and averaging time. Plumes and downdrafts are found to be responsible for an anomalous behavior of the drag coefficient estimates. Certain factors relating to plume properties, derived using conditional sampling as described in Khalsa (1980), are shown to be related to the variance between the two estimates of friction velocity. An investigation into the effects of increasing the averaging time reveals that plume spacing, which is dependent on stability, and the mean wind speed determine the minimum time for smoothing the influence of plumes and downdrafts.Department of Atmospheric Sciences contribution number 513. 相似文献
3.
Vertical velocity field in the convective boundary layer as observed with an acoustic Doppler sodar 总被引：1，自引：0，他引：1
The morning development of the daytime convective boundary layer (CBL) during fine weather has been observed with an acoustic Doppler sodar of the C.R.P.E. In particular, the vertical profile of the vertical velocity third-order statistic W*
3 has been obtained. This quantity is a maximum near 0.3z
I where z
I, is the height of the CBL. The histogram of vertical velocity in the CBL shows a relationship between W
3 and the convective velocity W
* and is useful for convective plume determination. 相似文献
4.
5.
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
6.
Eugene Yee R. Chan P. R. Kosteniuk C. A. Biltoft J. F. Bowers 《Boundary-Layer Meteorology》1996,77(2):173-207
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
a
, where 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. 相似文献
7.
J. M. Quinault A. B. Mayhoub G. Deville Cavelin 《Theoretical and Applied Climatology》1997,58(1-2):113-127
Summary A dispersion model is proposed to predict the continuous vertical variation of the dispersion parameters
y
and
z
in case of hot pollutant release to the atmosphere. In such a case, the plume rises far above the ground and is subject to varying levels of turbulence. The framework in this paper can be divided into three approaches: (1) determination of the eddy diffusivitiesK
y
(z,
y
) andK
z
(z,
z
) as functions of height above ground and plume dimensions, (2) determination of both the plume rise and its vertical velocity using a modified version of Brigg's formula, and (3) numerical solution of actual problems with buoyant plumes at each time step. The model results have been applied to a case of pollutant release from fire destruction of a chemical storehouse roof.With 15 Figures 相似文献
8.
Analyses of concentration fluctuation (C) spectra from boundary-layer smoke plume experiments at six separate locations show that the spectra from these experiments generally exhibit an inertial subrange at high frequencies with a slope of -5/3 and indicate peak energy at a time period of about 50 to 100 s. These periods of peak energy are a factor of two to five less than those for the peak of the wind speed fluctuation (u or v) spectra. A general spectral formula fits normalized spectra from the U.S. and Australia, where the frequency, n, is made dimensionless by multiplying by the plume dispersion parameter,
y
, and dividing by the wind speed, u. Peak energy occurs at a dimensionless frequency of n
y/u equal to about 0.15. The Kolmogorov constant in the inertial subrange is estimated from a set of averaged spectra. Cross-spectra indicate little relation between concentration and wind fluctuations. However, most of the correlation that exists is due to periods larger than about 10 or 20 s. 相似文献
9.
Water-tunnel measurements of velocity, turbulence and scalar concentration for three model urban canopies with aspect ratios A r of building height-to-width of 0.25, 1 and 3 are presented. The measurements for the canopies with A r = 1 and 3 are new, while the measurements for A r = 0.25 were previously published. A passive scalar was continuously released from a near-ground point source, and the concentration was measured at several distances from the source and at different heights above the ground. Plume spreads, concentration and distance from the source were non-dimensionalized using length, time and velocity scales reflecting the geometry of the buildings. The scaling collapses the data for all aspect ratios and is valid when the vertical extent of the plume is smaller than the canopy height. The observed plume spreads are compared with analytical relations, which predict linear growth in both transverse and vertical directions. The observed mean concentration is compared with a Gaussian dispersion model that predicts a ?2 power-law decay with distance from the source. 相似文献
10.
Andr Ehrlich Manfred Wendisch Eike Bierwirth Andreas Herber Alfons Schwarzenbck 《Atmospheric Research》2008,88(3-4):266-276
Based on 1-year cloud measurements with radar and microwave radiometer broadband solar radiative transfer simulations were performed to quantify the impact of different ice crystal shapes of Arctic mixed-phase clouds on their radiative properties (reflectance, transmittance and absorptance). The ice crystal shape effects were investigated as a function of microphysical cloud properties (ice volume fraction fi, ice and liquid water content IWC and LWC, mean particle diameter DmI and DmW of ice/water particle number size distributions, NSDs).The required NSDs were statistically derived from radar data. The NSD was composed of a liquid and a solid mode defined by LWC, DmW (water mode) and IWC, DmI (ice mode). It was found that the ratio of DmI and DmW determines the magnitude of the shape effect. For mixed-phase clouds with DmI ≤ 27 μm a significant shape effect was obtained. The shape effect was almost insensitive with regard to the solar zenith angle, but highly sensitive to the ice volume fraction of the mixed-phase cloud. For mixed-phase clouds containing small ice crystals (DmI ≤ 27 μm) and high ice volume fractions (fi > 0.5) crystal shape is crucial. The largest shape effects were observed assuming aggregates and columns. If the IWC was conserved the shape effect reaches values up to 0.23 in cloud reflectance and transmittance. If the ice mode NSD was kept constant only a small shape effect was quantified (≤ 0.04). 相似文献
11.
Probability distributions of concentration fluctuations of a weakly diffusive passive plume in a turbulent boundary layer 总被引：4，自引：0，他引：4
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,
, 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. 相似文献
12.
A method for optimum modelling of the earth's topography, corresponding to differing meteorological phenomena, is presented.The optimum averaging scale for mountains in terms of orographic cyclo- and anti-cyclogenesis is shown to be of the order of 150 km. The use of larger or smaller averaging scales decreases the correlation between the degree of cyclo- and anti-cyclogenesis and the parameters which describe the orography.A quantitative relation between orographic cyclo- and anti-cyclogenesis and the form of orography determined by the Laplacian 2
Z
0 of the terrain function Z
0 = Z
0(x, y) is presented. 相似文献
13.
Concentration probability density functions (pdfs) calculated according to fluctuating plume models in one- and two-dimensions, representing the limiting cases of one-dimensional dispersion from a line source or a point source in strongly anisotropic turbulence and of axisymmetric dispersion from a point source in isotropic turbulence, are discussed and analyzed in terms of the location of the sampling point within the mean plume and of the ratio, s/m, of the standard deviations for relative dispersion and meandering.In both cases, the pdfs cover the finite concentration range from zero to C
0, the centreline concentration of the instantaneous plume. The main difference between them is that whereas the 2-D pdf is always unimodal, the 1-D pdf has a singularity at C
0 which under some circumstances results in a bimodal form. However, the probability associated with this singularity is not always significant. Differences of practical importance in the shape of the pdfs occur mainly for centreline or near-centreline sampling locations when meandering is not too much larger than relative dispersion (1 < m
2/s2 < 10) and for sampling locations a distance of order s from the centreline when relative dispersion is not too much larger than meandering (1 < s
2/m2 < 5).Comparison against wind tunnel measurements not too far downstream of a line source in grid turbulence shows that the 1-D model reproduces the essential features and trends of the measurements. Under appropriate circumstances the measurements show the bimodal pdf predicted by the 1-D model (but not by the 2-D model) confirming that the effect of the anisotropy in the source distribution is observable.Present address: School of Mechanical Engineering, Aristotle University, Thessaloniki, 54006 Thessaloniki, Greece. 相似文献
14.
Ronald B. Smith 《Boundary-Layer Meteorology》2008,129(3):371-393
Dispersion estimates with a Gaussian plume model are often incorrect because of particle settling (β), deposition (γ) or the vertical gradient in diffusivity (K
v
(z) = K
0 + μz). These “non-Gaussian” effects, and the interaction between them, can be evaluated with a new Hankel/Fourier method. Due
to the deepening of the plume downwind and reduced vertical concentration gradients, these effects become more important at
greater distance from the source. They dominate when distance from the source exceeds L
β
= K
0
U/β
2, L
γ
= K
0
U/γ
2 and L
μ
= K
0
U/μ
2 respectively. In this case, the ratio β/μ plays a central role and when β/μ = 1/2 the effects of settling and K gradient exactly cancel. A general computational method and several specific closed form
solutions are given, including a new dispersion relation for the case when all three non-Gaussian effects are strong. A more
general result is that surface concentration scales as C(x) ~ γ
−2 whenever deposition is strong. Categorization of dispersion problems using β/μ, L
γ
and L
μ
is proposed. 相似文献
15.
Dispersion of Heavy Particles Emitted from Area Sources in the Unstable Atmospheric Boundary Layer 总被引：2，自引：2，他引：0
Reliable predictions of the daytime dispersal of heavy particles in the unstable atmospheric boundary layer are important in a variety of disciplines. For many applications, particles disperse from area sources near the ground, and corresponding theoretical solutions are desired to reveal insight into the physical processes. Here, theoretical solutions recently developed for neutral conditions are modified to include the effects of atmospheric instability. The Obukhov length L O and convection velocity w ? are introduced to characterize the patterns of particle dispersion, in additional to friction velocity u ? and settling velocity w s used in the neutral case. The major effects of atmospheric instability are accounted for by modifying the vertical velocity variance profile and considering the ratio of velocity scales w ?/u ?. Theoretical predictions including the mean concentration profile, plume height, and horizontal transport above the source, and ground deposition flux downwind from the source agree well with large-eddy simulation results while the particle plume is within the atmospheric surface layer. The deposition curve is characterized by a power-law decay whose exponent depends on u ?, w s, and w ?. A second steeper power-law develops once the plume extends into the mixed layer. This effect is enhanced with increasing atmospheric instability, implying that particles disperse farther from the source. 相似文献
16.
Peter Bange 《Boundary-Layer Meteorology》1993,62(1-4):303-311
An expression for concentration fluctuations in a smoke plume is derived from airborne measurements ofNO
X. A linear relation between the standard deviation of the fluctuations around a Gaussian concentration profile and the average gradient in the concentrations is assumed. With this relation the probability density function of expectedNO
2 concentrations at 3 km from a source ofNO
X is modelled under the assumption of photostatic equilibrium, and is compared with measurements. A parametrisation for the concentration fluctuations of std(C)= 26(+/–7)*dc/dr is proposed (r in metres). CalculatedNO
2 distributions are in reasonable agreement with the measurements and the averageNO
2 concentration appeared not to be affected by the concentration fluctuations in theNO
X concentration. The spatial resolution of all measurements was 40 m. 相似文献
17.
J. Wieringa 《Boundary-Layer Meteorology》1972,2(4):406-426
For 390 ten-minute samples of turbulent flux, made with a trivane above a lake, the vertical alignment is determined within 0.1 ° through azimuth-dependent averaging. One degree of instrumental misalignment is found to produce an average tilt error of 9 ± 4% for momentum flux, and 4 ± 2% for heat flux. The tilt error in the vertical momentum flux depends mainly ons
u/u*, and cannot be much diminished with impunity by high-pass pre-filtering of the turbulence signals. The effects of rain on trivane measurements of vertical velocity are shown to be negligible at high wind speeds, and adaptable to correction in any case.The normalized vertical velocity variance,s
w/u*, appears to be proportional to the square root ofz/L for unstable stratification. For a wind speed range of 2 to 15 m s–1, the eddy correlation stresses measured at 4- and 8-m heights can be reasonably well estimated by using a constant drag coefficientC
d=1.3 X 10-3, while cup anemometer profile measurements give an overestimate of eddy stress at high wind speeds. A good stress estimate is also obtained from the elevation variance; it is suggested that trivane measurement of this variance might be made from a mobile platform, e.g., a moderately stabilized spar buoy. 相似文献
18.
R. Singh P. C. Joshi C. M. Kishtawal P. K. Pal 《Meteorology and Atmospheric Physics》2006,94(1-4):1-10
Summary A new methodology for deriving daily averages of near surface specific humidity (Q
a
) is developed. Remotely sensed parameters, total water vapor (W), boundary-layer water vapor (W
b
), and sea-surface temperature (SST) are used to derive Q
a
. Genetic algorithm (GA) is used to find the empirical function relating the input (W, W
b
, and SST) and output (Q
a
) parameters. The input data consist of 2 years (1999–2000) of daily W, W
b
, from SSM/I (Special Sensor Microwave Imager), and SST data from AVHRR (Advanced Very High Resolution Radiometer). COADS
(Comprehensive Ocean Atmospheric Data Set) observations of Q
a
are used to develop and evaluate the new methodology.
The performance of the algorithm is measured with COADS observations, which are not used in the development phase. The global
mean rms error for daily averages Q
a
is 1.5 ± 0.40 g/kg. Slightly higher discrepancies between Q
a
derived from the new method and COADS observations are found over the Northwestern Pacific, North Atlantic oceans and Arabian
Sea. This method improves upon the humidity retrieval of Liu (1986), Schulz et al (1993), and Chou et al (1997). 相似文献
19.
采用水量平衡模型和Penman公式分别计算了珠江流域七个子流域1961—2000年实际蒸散发(I_(ETa))和潜在蒸散发(I_(ETp)),并对供水条件变化下I_(ETa)与I_(ETp)的关系进行了定量化分析,对各子流域I_(ETa)和I_(ETp)关系的理论从属性进行判定,主要结论如下:1)珠江流域年实际蒸散发量远低于潜在蒸散发量,多数子流域I_(ETa)值不到I_(ETp)值的1/2。7个流域面积加权平均I_(ETa)为681.4 mm/a,I_(ETp)为1 560.8 mm/a。从蒸散发的变异性来看,则实际蒸散发I_(ETa)的变异性明显要高于潜在蒸散发I_(ETp)。2)东江、西江、北江、柳江和盘江等5个流域实际蒸散发I_(ETa)都与降水量呈现正相关关系,韩江、郁江两个流域I_(ETa)随降水变化的变化趋势不明显。各子流域的潜在蒸散发I_(ETp)与降水量呈现显著负相关关系。7个子流域平均情况下,随着降水量的增加,I_(ETa)呈现明显的增加趋势,而I_(ETp)呈现明显的下降趋势。3)通过对降水量P与实际蒸散发I_(ETa)及潜在蒸散发I_(ETp)的联合回归方程P-IET回归系数的T检验,判定韩江、柳江和盘江等三个子流域以及七流域面积加权平均I_(ETa)与P和I_(ETp)与P的关系满足理论意义上的严格互补相关;东江、西江、北江等三个流域I_(ETa)与P和I_(ETp)与P的关系满足"非对称"互补相关。4)基于极端干旱和极端湿润的边界条件,推导出非对称条件下的实际蒸散发互补相关理论模型。 相似文献
20.
A wind-tunnel study was conducted to investigate ventilation of scalars from urban-like geometries at neighbourhood scale
by exploring two different geometries a uniform height roughness and a non-uniform height roughness, both with an equal plan
and frontal density of λ
p
= λ
f
= 25%. In both configurations a sub-unit of the idealized urban surface was coated with a thin layer of naphthalene to represent
area sources. The naphthalene sublimation method was used to measure directly total area-averaged transport of scalars out
of the complex geometries. At the same time, naphthalene vapour concentrations controlled by the turbulent fluxes were detected
using a fast Flame Ionisation Detection (FID) technique. This paper describes the novel use of a naphthalene coated surface
as an area source in dispersion studies. Particular emphasis was also given to testing whether the concentration measurements
were independent of Reynolds number. For low wind speeds, transfer from the naphthalene surface is determined by a combination
of forced and natural convection. Compared with a propane point source release, a 25% higher free stream velocity was needed
for the naphthalene area source to yield Reynolds-number-independent concentration fields. Ventilation transfer coefficients
w
T
/U derived from the naphthalene sublimation method showed that, whilst there was enhanced vertical momentum exchange due to
obstacle height variability, advection was reduced and dispersion from the source area was not enhanced. Thus, the height
variability of a canopy is an important parameter when generalising urban dispersion. Fine resolution concentration measurements
in the canopy showed the effect of height variability on dispersion at street scale. Rapid vertical transport in the wake
of individual high-rise obstacles was found to generate elevated point-like sources. A Gaussian plume model was used to analyse
differences in the downstream plumes. Intensified lateral and vertical plume spread and plume dilution with height was found
for the non-uniform height roughness. 相似文献