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1.
本文利用100m~3系留气艇携带超声风温仪在复杂的盆地地形上空对1000m以下大气进行观测所获得的资料,研究小风稳定条件下大气边界层湍流结构特征。结果表明,在双对数坐标中,纵向速度u谱,垂直速度w谱,温度T谱在惯性区均遵循Kolmogorov的-2/3次律;横向速度V谱有其特殊的情形;协谱uw,wT及近地层的uT协谱在惯性区服从-4/3次律。和平坦、均一、开阔下垫面不同的是谱的峰值频率向高频移动,且没有发现近地层具有的谱峰随高度的明显变化关系。 相似文献
2.
Spectra and Cospectra of Turbulence in an Internal Boundary Layer over a Heterogeneously Irrigated Cotton Field 
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下载免费PDF全文 During the Energy Balance Experiment, patch-to-patch irrigation generated gradients in soil moisture in a north-south oriented cotton field. An internal boundary layer (IBL) developed as a result of strong horizontal advection from relatively dry upstream patches to relatively wet downstream patches associated with the prevailing northerly winds. This generated large eddies of multiple sizes, which had significant influences on the structure of turbulence in the IBL. The power spectra and cospectra of wind speed, temperature, humidity, and energy fluxes measured at two heights within the IBL are presented and used to investigate the influence of the IBL on surface layer turbulence. The spectra and cospectra were greatly enhanced by external disturbances at low frequencies. The peak frequencies of these disturbances did not change with height. The spectra and cospectra typically converged and were parallel to the Kansas spectrum at high frequencies (in the inertial subrange). A clear gap in the spectra of horizontal wind velocity existed at intermediate frequencies when the surface layer was stable. The results indicate that large eddies that originated in the upstream convective boundary layer had considerable impacts on the spectra and cospectra of surface layer turbulence. The influence of these large eddies was greater (1) when the IBL was well-developed in the near surface layer than when the IBL did not exist, (2) at higher levels than at lower levels, and (3) when the atmospheric surface layer (ASL) was unstable than when the ASL was stable. The length scales of these large eddies were consistent with the dominant scales of surface heterogeneity at the experiment site. 相似文献
3.
Spectra and co-spectra of the streamwise (u) and normal or vertical (w) velocity fluctuations have been measured in the inner region of a large Reynolds number laboratory boundary layer over a rough wall. There is reasonable evidence of ak
1
–1
range in theu spectrum (wherek
1 is the streamwise wavenumber). Such a range results from an overlap between a spectral region dominated by largescale, inactive motion, which scales on the boundary-layer thickness, and a region dominated by smaller-scale, active motion which scales on the distance from the wall. Spectra ofw, anduw cospectra, scale in a manner consistent with the dominance by active motion. The present spectral data do not support local isotropy over the inertial subrange. A comparison between measuredw spectra and calculations based on isotropy indicates that the inertial subrange anisotropy is only slightly affected by the magnitude of the non-dimensional mean shear. 相似文献
4.
We present the power spectra of wind velocity and the cospectra of momentum and heat fluxes observed for different wind directions
over flat terrain and a large valley on the Loess Plateau. The power spectra of longitudinal (u) and lateral (v) wind speeds satisfy the −5/3 power law in the inertial subrange, but do not vary as observed in previous studies within
the low frequency range. The u spectrum measured at 32 m height for flow from the valley shows a power deficit at intermediate frequencies, while the v spectrum at 32 m downwind of the valley reaches another peak in the low frequency range at the same frequency as the u spectrum. The corresponding peak wavelength is consistent with the observed length scale of the convective outer layer at
the site. The v spectrum for flat terrain shows a spectral gap at mid frequencies while obeying inner layer scaling in its inertial subrange,
suggesting two sources of turbulence in the surface layer. All the spectra and cospectra from the valley direction show a
height dependency over the three levels. 相似文献
5.
The local effect of intermittency on the inertial subrange energy spectrum of the atmospheric surface layer 总被引：1，自引：0，他引：1
Jozsef Szilagyi Gabriel G. Katul Marc B. Parlange John D. Albertson Anthony T. Cahill 《Boundary-Layer Meteorology》1996,79(1-2):35-50
Orthonormal wavelet expansions are applied to atmospheric surface layer velocity measurements. The effect of intermittent events on the energy spectrum of the inertial subrange is investigated through analysis of wavelet coefficients. The local nature of the orthonormal wavelet transform in physical space makes it possible to identify a relationship between the inertial subrange slope of the local wavelet spectrum and a simple indicator (i.e. the local variance of the signal) of local intermittency buildup. The slope of the local wavelet energy spectrum in the inertial subrange is shown to be sensitive to the presence of intermittent events. During well developed intermittent events (coherent structures), the slope of the energy spectrum is somewhat steeper than -5/3, while in less active regions the slope is found to be flatter than -5/3. When the slopes of local wavelet spectra are ensemble averaged, a slope of -5/3 is recovered for the inertial subrange. 相似文献
6.
7.
Gabriel G. Katul Marc B. Parlange John D. Albertson Chia R. Chu 《Boundary-Layer Meteorology》1995,72(1-2):123-148
Longitudinal velocity and temperature measurements above a uniform dry lakebed were used to investigate sources of eddy-motion anisotropy within the inertial subrange. Rather than simply test the adequacy of locally isotropic relations, we investigated directly the sources of anisotropy. These sources, in a daytime desert-like climate, include: (1) direct interaction between the large-scale and small-scale eddy motion, and (2) thermal effects on the small-scale eddy motion. In order to explore these two anisotropy sources, we developed statistical measures that are sensitive to such interactions. It was found that the large-scale/small-scale interaction was significant in the inertial subrange up to 3 decades below the production scale, thus reducing the validity of the local isotropy assumption. The anisotropy generated by thermal effects was also significant and comparable in magnitude to the former anisotropy source. However, this thermal anisotropy was opposite in sign and tended to counteract the anisotropy generated by the large-scale/smallscale interaction. The thermal anisotropy was attributed to organized ramp-like patterns in the temperature measurements. The impact of this anisotropy cancellation on the dynamics of inertial subrange eddy motion was also considered. For that purpose, the Kolmogorov-Obukhov structure function equation, as derived from the Navier-Stokes equations for locally isotropic turbulence, was employed. The Kolmogorov-Obukhov structure function equation in conjunction with Obukhov's constant skewness closure hypothesis reproduced the measured second- and third-order structure functions. Obukhov's constant skewness closure scheme, which is also based on the local isotropy assumption, was verified and was found to be in good agreement with the measurements. The accepted 0.4 constant skewness value derived from grid turbulence experiments overestimated our measurements. A suggested 0.26 constant skewness value, which we derived from Kolmogorov's constant, was found to be adequate. 相似文献
8.
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
9.
Shuhua Liu Heping Liu M. Xu M. Y. Leclerc Tingyao Zhu Changjie Jin Zhongxiang Hong Jun Li Huizhi Liu 《Boundary-Layer Meteorology》2001,98(1):83-102
Three velocity componentsand temperature were measured usingthree-dimensional sonic anemometers/thermometers attwo levels, above and within a forest canopy, in theChangbai Mountains of northeast China. Turbulencespectral structure, local isotropy anddissipation rates above and within the forest canopywere calculated using the eddy correlation method.Results show that the normalized turbulent spectralcurves have -2/3 slopes in the inertial subrange.While the shapes of the spectra are in good agreementwith the Kansas flat terrain results, the atmosphericturbulence is anisotropic above the forest canopy. Dueto breaking down of large eddies by the foliage,branches and trunks, the spectral peak frequencies forvelocity and temperature are higher withinthan above the forest canopy. Compared withmeasurements from previous studies over flat terrain,the velocity and temperature spectra above andinside the forest canopy appear to shift toward higherfrequencies. The turbulence is approximately isotropicin the inertial subrange within the forest canopy, and isanisotropic above the forest canopy. The turbulentkinetic energy and heat energy dissipation rates aboveand inside the forest canopy are much larger thanthose obtained by Kaimal and Hogstrom over grasslandand grazing land. The distinct features in the resultsof the present experiment may be attributed to thedynamic forcing caused by the rough surface of the forestcanopy. 相似文献
10.
Different flux estimation techniques are compared here in order to evaluate air–sea exchange measurement methods used on moving
platforms. Techniques using power spectra and cospectra to estimate fluxes are presented and applied to measurements of wind
speed and sensible heat, latent heat and CO2 fluxes. Momentum and scalar fluxes are calculated from the dissipation technique utilizing the inertial subrange of the power
spectra and from estimation of the cospectral amplitude, and both flux estimates are compared to covariance derived fluxes.
It is shown how even data having a poor signal-to-noise ratio can be used for flux estimations. 相似文献
11.
Katja Henjes 《Boundary-Layer Meteorology》1999,91(3):367-384
For an extensive turbulent wind speed data set collected on the open ocean, the optimum sampling time is determined to calculate inertial-range spectra. Such spectra are widely used to estimate surface fluxes. The optimum sampling time corresponds to the turbulent memory time, the minimum period after which a given time series can be interpreted as a new independent measurement. In our case, this interval is found to be only about six seconds.Separate spectral levels are calculated from the three measured vector components of the wind. Their ratios are compatible with the assumption of an isotropic inertial subrange, but scatter considerably. Alignment factors are developed based on Kolmogorov's theory, and the aligned spectral levels coincide within a few percent. It is proposed that alignment might be a more reliable test than the ratio of the spectral levels to determine whether observations have taken place in a universal inertial subrange. It is recommended that all three wind components are used to estimate the dissipation rate. 相似文献
12.
B. D. Amiro 《Boundary-Layer Meteorology》1990,52(3):227-246
Atmospheric turbulence was measured within a black spruce forest, a jack pine forest, and a trembling aspen forest, located in southeastern Manitoba, Canada. Drag coefficients (C
d
) varied little with height within the pine and aspen canopies, but showed some height dependence within the dense spruce canopy. A constant C
d
of 0.15, with the measured momentum flux and velocity profiles, gave good estimates of leaf-area-index (LAI) profiles for the pine and aspen canopies, but underestimated LAI for the spruce canopy.Velocity spectra were scaled using the Eulerian integral time scales and showed a substantial inertial subrange above the canopies. In the bottom part of the canopies, the streamwise and cross-stream spectra showed rapid energy loss whereas the vertical spectra showed an apparent energy gain, in the region where the inertial subrange is expected. The temperature spectra showed an inertial subrange with the expected -2/3 slope at all heights. Cospectra of momentum and heat flux had slopes of about -1 in much of the inertial subrange. Possible mechanisms to explain some of the spectral features are discussed. 相似文献
13.
Wavelet and quadrant analyses were applied to turbulent velocity data in order to investigate the transition from the anisotropy of energy-containing eddies to the isotropy of the inertial subrange scales. The quadrant analysis of the wavelet coefficients of longitudinal and vertical velocity components allows the evaluation of the velocity structure functions and the momentum cospectrum as a function of the separation distance and of the quadrants. In an isotropic condition the contribution both of ejections and sweeps (even quadrants), and both of reflections and deflections (odd quadrants), has to be equal. The analysis has shown that in neutrally stratified conditions the transition to isotropy occurs in a frequency range (0.2 < r/z < 3) usually referred to as internal to the inertial subrange (r is separation distance, z is height). In the transition region, as in the isotropic region, the velocity structure functions still agree with the 1941 and 1962 Kolmogorov theories; but on the other hand the structure functions of the even and odd quadrants are fitted by power laws of different slopes in the transition region. The proposed analysis allows the investigation within the transition region of the different dynamical structure in the energy transfer from the energy-containing scales to the isotropic scales. 相似文献
14.
An investigation into high Reynolds number turbulent flow over a ridge top in New Zealand is described based on high-resolution
in-situ measurements, using ultrasonic anemometers for two separate locations on the same ridge with differing upwind terrain
complexity. Twelve 5-h periods during neutrally stratified and weakly stable atmospheric conditions with strong wind speeds
were sampled at 20 Hz. Large (and small) turbulent length scales were recorded for both vertical and longitudinal velocity
components in the range of 7–23 m (0.7–3.3 m) for the vertical direction and 628–1111 m (10.5–14.5 m) for the longitudinal
direction. Large-scale eddy sizes scaled to the WRF (Weather Research and Forecasting) numerical model simulated boundary-layer
thickness for both sites, while small-scale turbulent features were a function of the complexity of the upwind terrain. Evidence
of a multi-scale turbulent structure was obtained at the more complex terrain site, while an assessment of the three-dimensional
isotropy assumption in the inertial subrange of the spectrum showed anisotropic turbulence at the less complex site and evidence
of isotropic turbulence at the more complex site, with a spectral ratio convergence deviating from the 4/3 or unity values
suggested by previous theory and practice. Existing neutral spectral models can represent locations along the ridge top with
simple upwind complexity, especially for the vertical wind spectra, but sites with more orographic complexity and strong vertical
wind speeds are often poorly represented using these models. Measured spectra for the two sites exhibited no significant diurnal
variation and very similar large-scale and small-scale turbulent length scales for each site, but the turbulence energy measured
by the variances revealed a strong diurnal difference. 相似文献
15.
The turbulence in a laboratory convective mixed layer is probed more extensively than in the preliminary study of Willis and Deardorff (1974), and results presented. Turbulence intensities, spectra and probability distributions using mixed-layer scaling compare favorably with similarly scaled field measurements not available or plentiful in 1974. However, the velocity spectra in the convection tank exhibit only a short inertial subrange due to the close proximity of the dissipation subrange to the energy-containing range.The turbulence budget suggests that the convergence of the vertical transport of pressure fluctuations is a rather important term.Results on the entrainment rate are also presented, using both mixed-layer scaling and local interfacial scaling. 相似文献
16.
Spectral characteristics of surface layer turbulence in an urban atmosphere are investigated. The observations used for this purpose represent low wind conditions in the tropics. The normalized power spectral shapes exhibit the usual characteristics in the inertial subrange and obey Monin-Obukhov scaling. However, the low-frequency behaviours do not conform to the previous observed relations. For horizontal components, large energy is contained in the low frequencies in contrast to the vertical component where roll-off to zero frequency is faster.The turbulent kinetic energy dissipation rate estimated from the spectra using Kolmogorov's inertial subrange law is found to be isotropic unlike the velocity variances. The expressions for the dimensionless dissipation rate do not seem to work well in low winds in an urban atmosphere. For the data considered, the dissipation rate exhibits a power law relationship with the mean windspeed and the friction velocity. 相似文献
17.
Data from a research tower in Lake Ontario are used to study the validity of Monin--Obukhov scaling in the marine atmospheric boundary layer under various wave conditions. It is found that over pure wind seas, the velocity spectra and cospectra follow established universal scaling laws. However, in the presence of swells outrunning weak winds, velocity spectra and cospectra no longer satisfy universal spectral shapes. Here, Monin–Obukhov similarity theory, and the classical logarithmic boundary layers, are no longer valid. It is further shown that, in the presence of such swells, the momentum flux can be significantly modified in comparison to pure wind sea values. The implications of these findings for bulk flux estimations and on the inertial dissipation method for calculating fluxes are discussed. 相似文献
18.
Gervasio Degrazia Domenico Anfossi Haroldo Fraga De Campos Velho Enrico Ferrero 《Boundary-Layer Meteorology》1998,86(3):525-534
A new method for deriving the Lagrangian decorrelation time scales for inhomogeneous turbulence is described. The expression for the time scales here derived for the convective boundary layer is compared to those estimated by Hanna during the Phoenix experiment. Then the values of C0, the Lagrangian velocity structure function constant, and of Bi, the Lagrangian velocity spectrum constant, were evaluated from the Eulerian velocity spectra and from the Lagrangian time scales derived, under unstable conditions, from Taylor's statistical diffusion theory. The numerical coefficient of the lateral and vertical Lagrangian spectra in the inertial subrange was found equal to 0.21, in good agreement with previous experimental estimates. 相似文献
19.
A systematic evaluation is conducted of the smoothed spectrum, which is a spectral estimate obtained by averaging over a window of contiguous frequencies. The technique is extended to the ogive, as well as to the cross-spectrum. It is shown that, combined with existing variance estimates for the periodogram, the variance—and therefore the random error—associated with these estimates can be calculated in a straightforward way. The smoothed spectra and ogives are biased estimates; with simple power-law analytical models, correction procedures are devised, as well as a global constraint that enforces Parseval’s identity. Several new results are thus obtained: (1) The analytical variance estimates compare well with the sample variance calculated for the Bartlett spectrum and the variance of the inertial subrange of the cospectrum is shown to be relatively much larger than that of the spectrum. (2) Ogives and spectra estimates with reduced bias are calculated. (3) The bias of the smoothed spectrum and ogive is shown to be negligible at the higher frequencies. (4) The ogives and spectra thus calculated have better frequency resolution than the Bartlett spectrum, with (5) gradually increasing variance and relative error towards the low frequencies. (6) Power-law identification and extraction of the rate of dissipation of turbulence kinetic energy are possible directly from the ogive. (7) The smoothed cross-spectrum is a valid inner product and therefore an acceptable candidate for coherence and spectral correlation coefficient estimation by means of the Cauchy–Schwarz inequality. The quadrature, phase function, coherence function and spectral correlation function obtained from the smoothed spectral estimates compare well with the classical ones derived from the Bartlett spectrum. 相似文献
20.
Some observations of turbulence and turbulent transport within and above plant canopies 总被引：1，自引：0，他引：1
Observations have been made of the structure of turbulence and turbulent exchange within plant canopy layers. A new three-dimensional anemometer was used to measure the eddy fluxes of heat and momentum, and the related cospectra, within and above a corn crop and above a red pine forest. Measured values of momentum and heat fluxes, at each height within the corn canopy, were relatively constant proportions of the flux above the canopy, for the period of a day's observation. Extensive regions obeying a –5/3 power relation were found. Isotropy was found above the forest at high frequencies while above and within the corn crop, the ratios of the lateral and vertical spectral densities to the longitudinal component were less than the expected value in the – 5/3 region. In all situations, the vertical velocity spectra were more peaked than a universal curve, particularly a vertical velocity spectrum from above the forest. It is suggested that the additional variance results from the mixing caused by the individual roughness elements. As expected, the spectra could not be normalized using the height above the soil surface to calculate a non-dimensional frequency, but scaling heights were estimated by matching the frequencies of the peak of each curve with that of the universal curve. Cospectra of uw and wT within the corn canopy were of similar shape and frequency regime, and were basically similar in shape to cospectra above the crop. All of the cospectra were more sharply peaked than universal cospectral curves. 相似文献