共查询到20条相似文献，搜索用时 546 毫秒
1.
David P. Chock 《Boundary-Layer Meteorology》1978,14(3):397-402
Lumley's model is extended to predict the effect of convection velocity fluctuations on eddy convection velocity for the high-frequency region of the longitudinal, transverse and scalar phase spectra in the atmospheric boundary layer. The resulting model predicts that the eddy convection velocity will be higher than the mean wind speed. The increase over the mean wind speed is largest for the longitudinal spectrum. 相似文献
2.
M. L. Wesely 《Boundary-Layer Meteorology》1988,44(1-2):13-31
The variances of fluctuations of scalar quantities can be measured and interpreted to yield indirect estimates of their vertical fluxes in the atmospheric surface layer. Strong correlations among scalar fluctuations indicate a similarity of transfer mechanisms, which is utilized in some of the variance techniques. The ratios of the standard deviations of two scalar quantities, for example, can be used to estimate the flux of one if the flux of the other is measured, without knowledge of atmospheric stability. This is akin to a modified Bowen ratio approach. Other methods such as the normalized standard-deviation technique and the correlation-coefficient technique can be utilized effectively if atmospheric stability is evaluated and certain semi-empirical functions are known. In these cases, iterative calculations involving measured variances of fluctuations of temperature and vertical wind velocity can be used in place of direct flux measurements. For a chemical sensor whose output is contaminated by non-atmospheric noise, covariances with fluctuations of scalar quantities measured with a very good signal-to-noise ratio can be used to extract the needed standard deviation. Field measurements have shown that many of these approaches are successful for gases such as ozone and sulfur dioxide, as well as for temperature and water vapor, and could be extended to other trace substances. In humid areas, it appears that water vapor fluctuations often have a higher degree of correlation to fluctuations of other trace gases than do temperature fluctuations; this makes water vapor a more reliable companion or reference scalar. These techniques provide some reliable research approaches but, for routine or operational measurement, they are limited by the need for fast-response sensors. Also, all variance approaches require some independent means to estimate the direction of the flux.This research has been funded as part of the National Acid Precipitation Assessment Program by the U.S. Environmental Protection Agency through IAGDW89930069-01 to the U.S. Department of Energy. 相似文献
3.
超声波测风仪与气象业务用风向标测风仪相比具有诸多优势,可为气象业务中风向风速观测急需解决的较多问题提供解决方案。为促成超声波风速仪尽早在气象部门业务应用,同时解决资料同化等问题,研究和选择适用于超声波测风仪的风速平均(平滑)算法显得极为重要。为此,从超声波测风仪测量原理出发,介绍了超声波测风仪获取数据的特点;利用台站获取的超声波测风仪风速的秒数据,采用不同时段、不同平均(平滑)方法,计算风速多种形式的平均值,通过统计、分析和比较,获得了标量和矢量不同算法下风速平均值的特性差异及其之间的误差,进一步验证了标量平均大于矢量平均的结论。通过对超声波测风仪的风速算法研究及其误差分析,对减小因算法带来的风速测量误差提供方法,同时探讨了超声波测风仪在气象业务使用的可能和方向。 相似文献
4.
Nocturnal Boundary-Layer Regimes 总被引：17，自引：6，他引：11
L. Mahrt 《Boundary-Layer Meteorology》1998,88(2):255-278
This study analyzes turbulence data collected over a grassland site in the nocturnal boundary layer. Examination of the dependence of the nocturnal boundary layer on stability suggests three regimes: a) the weakly stable case, b) a transition stability regime where many of the variables change rapidly with increasing stability and c) the very stable case. The value of z/L where the downward heat flux is a maximum defines the stability boundary between the weakly stable and transition regimes, where L is the Obukhov length. In the present analysis, the downward heat flux reaches a maximum at z/L approximately equal to 0.05 for 10 m, although comparison with other data indicates that this is not a universal value. For weaker stability, the heat flux decreases with decreasing z/L due to weaker temperature fluctuations. In the transition stability regime, the heat flux decreases rapidly with increasing stability due to restriction of vertical velocity fluctuations by the increasing stratification.For weakly stable conditions, the variances scale according to Monin-Obukhov similarity theory. For very stable conditions, the variances are contaminated by non-turbulent horizontal motions and do not follow the scaling laws. An alternative length scale based on variances is developed which explains more of the variance of the transfer coefficients compared to the Obukhov length. 相似文献
5.
M. W. Rotach 《Boundary-Layer Meteorology》1993,66(1-2):75-92
6.
Dispersion of a Point-Source Release of a Passive Scalar Through an Urban-Like Array for Different Wind Directions 总被引：1，自引：1，他引：0
The dispersion of a point-source release of a passive scalar in a regular array of cubical, urban-like, obstacles is investigated
by means of direct numerical simulations. The simulations are conducted under conditions of neutral stability and fully rough
turbulent flow, at a roughness Reynolds number of Re
τ
= 500. The Navier–Stokes and scalar equations are integrated assuming a constant rate release from a point source close to
the ground within the array. We focus on short-range dispersion, when most of the material is still within the building canopy.
Mean and fluctuating concentrations are computed for three different pressure gradient directions (0°, 30°, 45°). The results
agree well with available experimental data measured in a water channel for a flow angle of 0°. Profiles of mean concentration
and the three-dimensional structure of the dispersion pattern are compared for the different forcing angles. A number of processes
affecting the plume structure are identified and discussed, including: (i) advection or channelling of scalar down ‘streets’,
(ii) lateral dispersion by turbulent fluctuations and topological dispersion induced by dividing streamlines around buildings,
(iii) skewing of the plume due to flow turning with height, (iv) detrainment by turbulent dispersion or mean recirculation,
(v) entrainment and release of scalar in building wakes, giving rise to ‘secondary sources’, (vi) plume meandering due to
unsteady turbulent fluctuations. Finally, results on relative concentration fluctuations are presented and compared with the
literature for point source dispersion over flat terrain and urban arrays. 相似文献
7.
The longitudinal (i.e., in the direction of the mean wind) spectra and cospectra of wind components and temperature fluctuations in the atmospheric surface layer during neutral conditions were carefully investigated by Kader (1984, 1987) for a broad range of wave numbers which included wavelengths far beyond the large-scale limit of the inertial subrange. At the same time, some direct measurements of spatial correlation functions of the longitudinal wind component and temperature were performed by Zubkovskii and Fedorov (1986) and Zubkovskii and Sushko (1987). Section 2 of the present paper gives a review of the available results on longitudinal spectra and cospectra of wind velocity and temperature fluctuations in neutral stratification and examines the consequences of these results related to the longitudinal autocorrelation and symmetrized cross-correlation functions of surface-layer turbulence. In Section 3 it is shown that the correlation equations of Section 2 agree satisfactorily with some recent measurements of the longitudinal correlation functions in the range of distances from 3 m to 100 m. Some measurements of the lateral correlation functions of atmospheric turbulence are also presented in Section 3. It is shown that these measurements lead to some predictions concerning the never-measured lateral space spectra of surface-layer turbulence. 相似文献
8.
The effect of averaging time on velocity variances 总被引：1，自引：0，他引：1
Prof. Dr. H. A. Panofsky 《Meteorology and Atmospheric Physics》1988,38(1-2):64-69
Summary Based on recent spectral models, relations have been proposed between the variances of vertical and lateral velocities and averaging time. A few observations agree reasonably well with the models. The popular 0.2 power law for standard deviations is valid only for the lateral velocity under unstable conditions, particularly for short periods. For periods exceedings five minutes or so, the variation becomes slower unless the winds are very light and the boundary layer is thick. For neutral and slightly stable conditions the variation of standard deviation, with averaging time from five minutes to sixteen minutes, is so slow that it can be neglected for practical applications. The same is generally true for vertical velocity fluctuations.With 3 FiguresWe just received word that our collegue and good friend died on February 28, 1988. 相似文献
9.
The Characteristics of Turbulence Structure and Transfer over the Middle Area of the Tibetan Plateau 
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下载免费PDF全文 In this paper, turbulent data obtained from the Damxung site during the Secondary Tibetan Plateau Science Experiment (TIPEX) in 1998 are used to study the characteristics of the turbulent spectra, turbulence transport, and the dissipation rates of turbulent kinetic energy, temperature variance, and humidity variance in the middle area of the Tibetan Plateau. The turbulent spectra of wind velocity, potential temperature, and humidity satisfy the-2/3 power law in the high frequency range. Horizontal transportation of heat and water vapor is negligible compared with vertical transportation under strong unstable conditions, and as the stability parameter z/L increases (where z is the observational height, and L is the Monin Obukhov length), horizontal transportation becomes dominant under near-neutral, neutral, and stable conditions. The non-dimensional temperature and humidity variances are 20% less than the temperature and humidity gradient variances. These deficits appear to increase as the absolute stability parameter increases. Moreover, the effects of turbulence transportation and pressure variance exist throughout the entire stability region. 相似文献
10.
Arnold F. Moene Berenice I. Michels Albert A. M. Holtslag 《Boundary-Layer Meteorology》2006,120(2):257-274
For the presentation and analysis of atmospheric boundary-layer (ABL) data, scales are used to non-dimensionalise the observed quantities and independent variables. Usually, the ABL height, surface sensible heat flux and surface scalar flux are used. This works well, so long as the absolute values of the entrainment ratio for both the scalar and temperature are similar. The entrainment ratio for temperature naturally ranges from −0.4 to −0.1. However, the entrainment ratio for passive scalars can vary widely in magnitude and sign. Then the entrainment flux becomes relevant as well. The only customary scalar scale that takes into account both the surface flux and the entrainment flux is the bulk scalar scale, but this scale is not well-behaved for large negative entrainment ratios and for an entrainment ratio equal to −1. We derive a new scalar scale, using previously published large-eddy simulation results for the convective ABL. The scale is derived under the constraint that scaled scalar variance profiles are similar at those heights where the variance producing mechanisms are identical (i.e., either near the entrainment layer or near the surface). The new scale takes into account that scalar variance in the ABL is not only related to the surface flux of that scalar, but to the scalar entrainment flux as well. Furthermore, it takes into account that the production of variance by the entrainment flux is an order of magnitude larger than the production of variance by the surface flux (per unit flux). Other desirable features of the new scale are that it is always positive (which is relevant when scaling standard deviations) and that the scaled variances are always of order 1–10. 相似文献
11.
Characteristics of Submeso Winds in the Stable Boundary Layer 总被引：2，自引：2，他引：0
Larry Mahrt 《Boundary-Layer Meteorology》2009,130(1):1-14
The characteristics of submeso motions in the stable boundary layer are examined using observations from networks of sonic
anemometers with network sizes ranging from a few hundred metres to 100 km. This study examines variations on time scales
between 1 min and 1 h. The analysis focuses on the behaviour of the spectra of the horizontal kinetic energy, the ratios of
the three velocity variances, their kurtosis, the dependence of horizontal variability on time scale, and the inter-relationship
between vertical vorticity, horizontal divergence and deformation. Motions on larger time and space scales in the stable boundary
layer are found to be nearly two-dimensional horizontal modes although the ratio of the vorticity to the divergence is generally
on the order of one and independent of scale. One exception is a small network where stronger horizontal divergence is forced
by a decrease in surface roughness. The horizontal variability, averaged over 1 h, appears to be strongly influenced by surface
heterogeneity and increases with wind speed. In contrast, the time dependence of the horizontal structure on time scales less
than one hour tends to be independent of wind speed for the present datasets. The spectra of the horizontal kinetic energy
and the ratio of the crosswind velocity variance to the along-wind variance vary substantially between networks. This study
was unable to isolate the cause of such differences. As a result, the basic behaviour of the submeso motions in the stable
boundary layer cannot be generalized into a universal theory, at least not from existing data. 相似文献
12.
The frequency response of different types of sonic anemometers due to spatialaveraging of turbulent fluctuations along the sonic path is investigated byapplying modeling procedures and by sonic measurements. The data wereobtained simultaneously at up to 4 heights over extreme smooth andhomogeneous terrain during stationary situations, varying fromslightly stable to unstable. It is shown thatcorrections for the variance of the vertical wind component areneeded for measurements close to the ground. A correction procedure, based ona response function for the vertical wind and on parameters derived frompower spectra, is applied to the measurements. At a height of about onemetre, the variance of the vertical wind component is typicallyunderestimated by about 10%. The error decreases with increasing height. It isalso shown that in the height range down to one metre other turbulencequantities, as for example the variances of the horizontal wind components andthe turbulent fluxes of momentum and sensible heat, are not markedly affectedby the sonic spatial response. Experimental data support these findings. 相似文献
13.
Summary We present a multivariate statistical interpolation method for optimal averaging of incomplete climatological data. This
objective analysis is based on a linear regression of the data under the constraints of unbiasedness and minimized analysis
error variance. One of the important features of the presented interpolation is the efficient exchange of common information
between the analysed variables. This exchange is controlled by the covariances and leads to a remarkable reduction of the
analysis error variance compared with theunivariate optimal interpolation. The second moment statistics are estimated exclusively
on the basis of the given data using empirical orthogonal functions (EOFs).
Another important feature of the analysis is the partition of the entire analysis area into subregions. The estimation of
the covariances and the calculation of the EOFs are carried out in each of these subregions separately. This results in a
robust covariance estimation, and the regional dynamical characteristics are taken into account as well. The analysis is applied
to the monthly horizontal wind data of the Comprehensive Ocean-Atmosphere Data Set (COADS). Uni-, bi-, and trivariate analyses
of the vector wind and the scalar wind velocity are performed for the Januaries 1951–1993 restricted to the Atlantic Ocean.
The results show a remarkable decrease of the analysis error when the number of simultaneously analysed variables is increased.
Received May 28, 1999 Revised October 10, 1999 相似文献
14.
A novel dynamic mixing length (DML) subgrid-scale (SGS) model is proposed to improve the large-eddy simulations of the wind
field and contaminant dispersion around a group of buildings. Wind field and contaminant dispersion in two kinds of building
array geometries are simulated using the model, with wind-tunnel experimental data used to validate the model. The relative
errors in the lateral profiles of the streamwise mean velocities behind the sixth row of the buildings of the staggered obstacle
array and the aligned obstacle array at the half height of the building are 15 and 9%, respectively. The DML velocity fluctuations
in the staggered and aligned obstacle arrays are in agreement with those of the experiment. The results indicate that the
DML model can make a more accurate prediction of the mean velocity and velocity fluctuations. The DML model is highly suitable
for the simulation of multi-scale turbulent flow in urban canyons, of high Reynolds number turbulent flow and of complex turbulent
flow. 相似文献
15.
The probability density functions (pdf’s) of the wind increments are measured under different weather conditions in the atmospheric
boundary layer, including the extreme weather of a typhoon and sand storm. It is found that in each case the measured pdf’s
with respect to different time lags coincide by suitable scaling transformation. This property is similar to that of the stable
distributions. However, fitting results show that the tails of the stable distributions are generally heavier than that of
the measured ones. Beside, the stable distributions (except for the Gaussian distribution) have infinite variance, which implies
infinite average kinetic energy. In fact, it can be proved that if the tails of the pdf’s are heavy enough, the variance will
be infinite. Therefore, the tail-truncated stable distributions with finite variances are introduced to fit the data and the
fitting results are excellent. 相似文献
16.
17.
利用长白山森林生态系统定位研究站观测资料,及2003年8月和9月涡旋相关资料,分析和比较了该地区近地层包括风速、风向、大气稳定度在内的平均场特征,以及湍流强度、无量纲化风脉动方差相似性和地表通量变化特征。结果表明:(1)8月和9月稳定度都基本集中在0附近;(2)风速2 m·s-1的环境中,湍流发展最为旺盛,随着风速的增大湍流强度先迅速减小,当风速增大到3 m·s-1后,湍流强度偏离0值变大了一些,再继续增大到一定风速大小以后,湍流强度基本不随风速变化;(3)无量纲化三维风脉动方差符合Monin-Obukhov相似理论的"1/3"定律,其最佳通用相似函数在稳定和不稳定条件下都可以拟合得到;(4)地表通量均表现出明显的日变化特征,8月以潜热为主,感热较小;9月仍以潜热为主,但是相比8月明显偏小,感热变化不大。 相似文献
18.
Vladimír Fuka Zheng-Tong Xie Ian P. Castro Paul Hayden Matteo Carpentieri Alan G. Robins 《Boundary-Layer Meteorology》2018,167(1):53-76
Scalar dispersion from ground-level sources in arrays of buildings is investigated using wind-tunnel measurements and large-eddy simulation (LES). An array of uniform-height buildings of equal dimensions and an array with an additional single tall building (wind tunnel) or a periodically repeated tall building (LES) are considered. The buildings in the array are aligned and form long streets. The sensitivity of the dispersion pattern to small changes in wind direction is demonstrated. Vertical scalar fluxes are decomposed into the advective and turbulent parts and the influences of wind direction and of the presence of the tall building on the scalar flux components are evaluated. In the uniform-height array turbulent scalar fluxes are dominant, whereas the tall building produces an increase of the magnitude of advective scalar fluxes that yields the largest component. The presence of the tall building causes either an increase or a decrease to the total vertical scalar flux depending on the position of the source with respect to the tall building. The results of the simulations can be used to develop parametrizations for street-canyon dispersion models and enhance their capabilities in areas with tall buildings. 相似文献
19.
Patricia Jones Boyle Kenneth L. Davidson Donald E. Spiel 《Dynamics of Atmospheres and Oceans》1987,10(4)
Surface stress values obtained from the NOAA Ship OCEANOGRAPHER during STREX indicate that wind speed and stability dependent bulk derived stress values are two to three times too low in surface pre-frontal, pre-trough and pre-ridge regions of transiting synoptic systems. The measured stress values were based on calculations of turbulent kinetic energy dissipation rates using hot film measured velocity variances. Bulk stress values obtained with wind speed (neutral drag coefficient) and stability dependencies in the Large and Pond derivation agreed very well with the measured values in other regions of the synoptic systems. In situ wave information was not adequate to relate differences to coupled vector wind and wave fields. However, analyses and interpretation of wind and stability effects suggest that wind wave interaction was the reason for the observed sub-synoptic (mesoscale) stress enhancements. 相似文献
20.
A Simple Method of Estimating Scalar Fluxes Over Forests 总被引：1，自引：0，他引：1
Nelson Luis Dias Jinkyu Hong Monique Y. Leclerc T. Andrew Black Z. Nesic P. Krishnan 《Boundary-Layer Meteorology》2009,132(3):401-414
A simple aerodynamic-variance method is proposed to fill gaps in continuous CO2 flux measurements in rainy conditions, when open-path analysers do not function. The method requires turbulent conditions
(friction velocity greater than 0.1 ms–1), and uses measurements of mean wind speed, and standard deviations of temperature and CO2 concentration fluctuations to complement, and at times replace, eddy-covariance measurements of friction velocity, sensible
heat flux and CO2 flux. Friction velocity is estimated from the mean wind speed with a flux-gradient relationship modified for the roughness
sublayer. Since normalised standard deviations do not follow Monin-Obukhov similarity theory in the roughness sublayer, a
simple classification scheme according to the scalar turbulence scale was used. This scheme is shown to produce sensible heat
and CO2 flux estimates that are well correlated with the measured values. 相似文献