共查询到20条相似文献，搜索用时 31 毫秒
1.
Local similarity theory, an analogy to the Monin-Obukhov similarity theory, is successfully applied to airborne observations in a coastal area of South Australia. The boundary layer over this highly non-uniform surface is characterized by extensive variations in its thermal stratification and turbulence characteristics. However, the behaviour of some statistical parameters of second- and higher moments seems to be determined mainly by local forcing, while horizontal advection plays a less important role. For these parameters, local scaling is effective. It is shown that the dimensionless variances of vertical velocity and potential temperature are functions of z/ only, where is the local Monin-Obukhov length and z is the height above ground. The dimensionless variance of horizontal velocity components is found to depend on h/, where h is the height of the oundary layer. Similarity relationships for some triple correlations are also discussed. The empirically determined local similarity relationships are found to agree with those obtained from surface-layer similarity. Finally, to illustrate the complexity of the local forcing, distributions of vertical energy and momentum fluxes, from which the local scaling parameters are derived, are shown. 相似文献
2.
C. R. Wood A. Lacser J. F. Barlow A. Padhra S. E. Belcher E. Nemitz C. Helfter D. Famulari C. S. B. Grimmond 《Boundary-Layer Meteorology》2010,137(1):77-96
Flow and turbulence above urban terrain is more complex than above rural terrain, due to the different momentum and heat transfer
characteristics that are affected by the presence of buildings (e.g. pressure variations around buildings). The applicability
of similarity theory (as developed over rural terrain) is tested using observations of flow from a sonic anemometer located
at 190.3 m height in London, U.K. using about 6500 h of data. Turbulence statistics—dimensionless wind speed and temperature,
standard deviations and correlation coefficients for momentum and heat transfer—were analysed in three ways. First, turbulence
statistics were plotted as a function only of a local stability parameter z/Λ (where Λ is the local Obukhov length and z is the height above ground); the σ
i
/u
* values (i = u, v, w) for neutral conditions are 2.3, 1.85 and 1.35 respectively, similar to canonical values. Second, analysis of urban mixed-layer
formulations during daytime convective conditions over London was undertaken, showing that atmospheric turbulence at high
altitude over large cities might not behave dissimilarly from that over rural terrain. Third, correlation coefficients for
heat and momentum were analyzed with respect to local stability. The results give confidence in using the framework of local
similarity for turbulence measured over London, and perhaps other cities. However, the following caveats for our data are
worth noting: (i) the terrain is reasonably flat, (ii) building heights vary little over a large area, and (iii) the sensor
height is above the mean roughness sublayer depth. 相似文献
3.
A one-dimensional numerical model based on the equations of mean motion and turbulent kinetic energy (TKE), with Delage's (1974) mixing-length parameterization has been used to simulate the mean and turbulent structure of the evolving stably stratified nocturnal boundary layer (NBL). The model also includes a predictive equation for the surface temperature and longwave radiational cooling effects.In the absence of advective and gravity wave effects, it is found that the model-simulated structure, after a few hours of evolution, could be ordered fairly well by a similarity scaling (u
*0, *0, L
0, and h) based on surface fluxes and the NBL height. Simple expressions are suggested to describe the normalized profiles of momentum and heat fluxes, TKE, eddy-viscosity and energy dissipation. A good ordering of the same variables is also achieved by a local scaling (u
*0, * and L) based on the height-dependent local fluxes. The normalized TKE, eddy viscosity and energy dissipation are unique functions of z/L and approach constant values as z/L , where L is the local Monin-Obukhov length. These constants are close to the values predicted for the surface layer as z/L , thus suggesting that the Monin-Obukhov similarity theory can be extended to the whole NBL, by using the local (height-dependent) scales in place of surface-layer scales. The observed NBL structure has been shown to follow local similarity (Nieuwstadt, 1984). 相似文献
4.
Long-Term Mean Wind Profiles Based on Similarity Theory 总被引：1，自引：1，他引：0
We provide general forms for long-term mean wind profiles from similarity-based wind profiles, beginning with a probabilistic
adaptation of Monin–Obukhov similarity theory. We develop an analytical formulation for the stability distributions prevailing
in the atmospheric surface layer, which in turn facilitates the derivation of a long-term mean wind profile based on Monin–Obukhov
similarity theory. The modelled stability distributions exhibit good agreement with measurements from sites having different
local conditions. The long-term wind profile formulation is further extended to include the influence of the depth of the
atmospheric boundary layer (h), which becomes relevant for heights above h/3, and the resultant long-term ‘tall’ profile form also matches observations. 相似文献
5.
利用长白山脉哈尔巴岭气象塔高频率湍流梯度观测数据,分析了2007—2009年间2月和7月2 m、30 m和100 m 3个观测高度湍流统计特征,对复杂下垫面局地相似理论适用性进行了检验,求出了无量纲风速标准差、无量纲温度和湿度标准差与稳定度关系的经验公式,发现了该地域湍流统计特征的新现象。结果表明:(1)冬季和夏季对流条件下2 m、30 m和100 m高度上无量纲风速标准差与稳定度Z/L之间能较好的满足1/3幂律,但夏季能更好地满足1/3幂律,且变化趋势明显,而冬季变化趋势平缓,接近直线。通过和其他学者的研究结果进行比较,发现了一些差异。(2)冬季无量纲温度、湿度标准差观测值随稳定度分布十分离散,但总体变化趋势基本满足-1/3幂律,而夏季观测值分布集中,变化趋势较好地满足-1/3幂律,反映出该地域无量纲温度、湿度标准差与稳定度关系随季节变化十分明显,且夏季对流强于冬季。(3)在30 m和100 m高度上,摩擦速度具有明显的日变化,但2 m高度上摩擦速度的变化比较特异,出现了夜间高于日间的情况,通过研究三维风速的脉动资料,发现夜间的风速脉动资料明显偏大,是导致夜间摩擦速度u*取值较大的直接原因,这种现象的发生可能是由该地域地形效应和下垫面特征引起的。 相似文献
6.
Nine profiles of the temperature structure parameter C
T
2
and the standard deviation of vertical velocity fluctuations (
w) in the convective boundary layer (CBL) were obtained with a monostatic Doppler sodar during the second intensive field campaign of the First ISLSCP Field Experiment in 1987. The results were analyzed by using local similarity theory. Local similarity curves depend on four parameters: the height of the mixed layer (z
i
), the depth of the interfacial layer (), and the temperature fluxes at the top of the mixed layer (Q
i
) and the surface (Q
o). Values of these parameters were inferred from sodar data by using the similarity curve for C
T
2
and observations at three points in its profile. The effects of entrainment processes on the profiles of C
T
2
and
wnear the top of the CBL appeared to be described well by local similarity theory. Inferred estimates of surface temperature flux, however, were underestimated in comparison to fluxes measured by eddy correlation. The measured values of
wappeared to be slightly smaller than estimates based on available parmeterizations. These discrepancies might have been caused by experimental error or, more likely, by the distortion of turbulence structure above the site by flow over the nonuniform terrain at the observation site. 相似文献
7.
Measurements of the fluctuations of wind, temperature and humidity were made with an instrumented aircraft at altitudes from 30 to 300m above Lake Ontario. The variations of the standard deviations of these fluctuations are examined. By applying Monin-Obukhov similarity theory based on local fluxes, it is shown that the vertical velocity, temperature and humidity fluctuations scale with the local Monin-Obukhov length. In the limit of free convection, 1/3 and –1/3 power laws are approached with constants of 1.2, 1.2, and 0.8 for vertical velocity, temperature and humidity, respectively. The von Karman scale lengths increase with height but were much larger than those found by Taylor et al. (1970). 相似文献
8.
9.
Zbigniew Sorbjan 《Boundary-Layer Meteorology》2012,142(1):21-31
Empirical similarity functions of the Richardson number, obtained from bin-averaged data in the lower part of the stable boundary
layer, show an undesired dependence on height at which the observations are collected. A correction of this flaw is proposed
and tested by employing the neutral mixing length l
o
as a similarity scale for height. The function of height describing l
o
is assumed to be linear in the surface layer, and approaching a specified value with increasing height. The modification
does not alter the dependence of similarity functions on the Richardson number, and is shown to be supported by the Cooperative
Atmospheric-Surface Exchange Study-1999 (CASES-99) data. 相似文献
10.
Correlation Coefficients in Urban Turbulence 总被引：3，自引：2，他引：1
Monim H. Al-Jiboori 《Boundary-Layer Meteorology》2008,126(2):311-323
Based on fluctuational observations of three-component wind velocity (u′, v′, w′) and temperature, T′, from a meteorological tower of 325 m located in Beijing, China, a number of turbulent linear correlation coefficients are
calculated using a local scaling approach for turbulence statistics. The further applicability of this scaling is investigated
by the formulation of similarity relationships for correlation coefficients of momentum transfer e.g., |r
uw
|, |r
vw
| and |r
uv
|, heat transfer e.g., |r
uT
|, |r
vT
| and |r
wT
|, and the ratios |r
wT
/r
uw
| and |r
vT
/r
vw
|. Under various stratifications, empirical similarity relationships for most of these correlation coefficients are derived
to be function of a single local stability parameter and found to be in good agreement with experimental results. 相似文献
11.
局地相似性在近地面层大气中的一个应用 总被引：7，自引：1，他引：7
利用Ｕ．Ｈｏｇｓｔｒｏｍ教授提供的瑞典Ｕｐｐｓａｌａ大学气象系于１９８６年夏季在Ｕｐｐｓａｌａ市郊农田中观察到的近地面层大气资料，对近地面层大气的局地相似性进行了论证，并给出了一套相似性函数的经验常数。结果表明，局地相似性比Ｍｏｎｉｎ－Ｏｂｕｋｈｏｖ相似性更适合于描述复杂下垫面近地面层大气。 相似文献
12.
A. R. Brown 《Boundary-Layer Meteorology》1996,81(2):167-200
A large-eddy model has been used to simulate the dry atmospheric boundary layer across the range of stabilities between free convection and neutral shear flow. Results for the similarity coefficients, A
i
, B
i
and C
i
are presented. The results are also used to evaluate the performance of a local mixing length model, and of two modified exchange coefficient models which attempt to incorporate some non-local effects. 相似文献
13.
R. A. Brown 《Boundary-Layer Meteorology》1978,14(3):381-396
A two-layer, first-order closure model for the Planetary Boundary Layer (PBL) is developed with the objective of parameterizing the surface stress with respect to the synoptic scale. The model includes stability effects by considering stratification-dependent secondary flow in the outer layer and empirical corrections to the surface layer flow. It shows the compatibility of simple eddy viscosity closure solutions with similarity theory by producing the now well-known Rossby similarity equations. It allows further insight into the Rossby similarity parameters by relating them to a single similarity parameter which is the ratio of the characteristic scales of the PBL and the surface layer.The measured and derived values of the similarity parameters A and B are compared with AIDJEX data and other published values. The variation in these values in stably stratified conditions is predicted and two alternate similarity parameters are calculated, one a constant and the other with a small variation and decreasing influence on the drag coefficient in stable stratification. The result is an empirical resistance law for a geostrophic drag coefficient variation which parameterizes an observed order-of-magnitude change in surface stress with changes in roughness or PBL stratification. This variation is related to similarity parameters characteristic of the region and to measurable changes in the geostrophic departure angle. 相似文献
14.
Observations obtained over a glacier surface in a predominantlykatabatic flow and with a distinctwind maximum below 13-m height are presented. The data werecollected using a 13-m high profilemast and two sonic anemometers (at about 2.5-m and 10-m heights).The spectra at frequencies belowthat of the turbulence range appear to deviate considerably fromthe curves obtained by Kaimal andco-workers during the 1968 Kansas experiment. The characteristicsof these deviations are compared tothe observations of others in surface-layers disturbed by anykind of large-scale outer-layer (orinactive) turbulence. In our case the disturbances arelikely to be induced by the highmountain ridges that surround the glacier. Moreover, the deviationsobserved in the cospectra seemto result from an, as yet, unspecified interaction between theinactive outer-layer turbulenceand the local surface-layer turbulence. Near the distinctwind maximum turbulence production ceasedwhile turbulence itself did not, probably the result ofturbulence transport from other levels. Consequently, we studied thelocal similarity relations using w instead of u* as an alternative velocity scale. Wellbelow the wind maximum, and for relatively low stability(0< Rig <0.2), the flow behaves accordingto well established local-scaling similarity relationshipsin the stable boundary layer. For higherstability (Rig > 0.2), and near or above the wind maximum, the boundary-layer structure conforms tothat of z-less stratification suggesting that the eddy sizeis restricted by the local stability ofthe flow. In line with this we observed that the sensibleheat fluxes relate remarkably well to thelocal flow parameters. 相似文献
15.
The relaxed eddy accumulation (REA) method allows the measurement of trace gas fluxes when no fast sensors are available for eddy covariance measurements. The flux parameterisation used in REA is based on the assumption of scalar similarity, i.e., similarity of the turbulent exchange of two scalar quantities. In this study changes in scalar similarity between carbon dioxide, sonic temperature and water vapour were assessed using scalar correlation coefficients and spectral analysis. The influence on REA measurements was assessed by simulation. The evaluation is based on observations over grassland, irrigated cotton plantation and spruce forest.Scalar similarity between carbon dioxide, sonic temperature and water vapour showed a distinct diurnal pattern and change within the day. Poor scalar similarity was found to be linked to dissimilarities in the energy contained in the low frequency part of the turbulent spectra ( < 0.01 Hz).The simulations of REA showed significant change in b-factors throughout the diurnal course. The b-factor is part of the REA parameterisation scheme and describes a relation between the concentration difference and the vertical flux of a trace gas. The diurnal course of b-factors for carbon dioxide, sonic temperature and water vapour matched well. Relative flux errors induced in REA by varying scalar similarity were generally below ± 10%. Systematic underestimation of the flux of up to − 40% was found for the use of REA applying a hyperbolic deadband (HREA). This underestimation was related to poor scalar similarity between the scalar of interest and the scalar used as proxy for the deadband definition. 相似文献
16.
L. Cvitan 《Meteorology and Atmospheric Physics》2006,93(3-4):235-246
Summary The stability parameter μ is suggested as the one which is determinable with satisfying accuracy for routine application by
means of commonly accessible meteorological data at the Molve location (Croatia). The similarity functions applied for vertical
wind speed simulation in the planetary boundary layer (PBL) at Molve were useful for the determination of local stability
classes. Universal similarity functions were applied for unstable and neutral stability, whereas local similarity functions
were established for stable stratification. Wind speed simulations were performed using two types of wind models. The Monin-Obukhov
similarity theory was included in both types. However, it turned out that for the operative determination of the stability
of the 35 m deep lowest layer, the stability parameter μ was locally a better stability parameter than the Monin-Obukhov parameter
z/L. That was possibly because 35 m deep lowest layer sometimes (depending upon stability) includes a large proportion of
the Ekman layer and parameter μ is originally designed for the deeper part of PBL than z/L that is originally designed for
the surface layer. At Molve, the input data for local wind models as well as for the stability parameter μ were wind speed
at 35 m and temperature at 2 and 35 m above the ground. 相似文献
17.
D. Cava G. G. Katul A. M. Sempreviva U. Giostra A. Scrimieri 《Boundary-Layer Meteorology》2008,128(1):33-57
Within the canopy sub-layer (CSL), variability in scalar sources and sinks are known to affect flux–variance (FV) similarity
relationships for water vapour (q) and carbon dioxide (C) concentrations, yet large-scale processes may continue to play a significant role. High frequency time series data for temperature
(T), q and C, collected within the CSL of an uneven-aged mixed coniferous forest in Lavarone, Italy, are used to investigate these processes
within the context of FV similarity. This dataset suggests that MOST scaling describes the FV similarity function of T even though the observations are collected in the CSL, consistent with other studies. However, the measured FV similarity
functions for q and C appear to have higher values than their temperature counterpart. Two hypotheses are proposed to explain the measured anomalous
behaviour in the FV similarity functions for q and C when referenced to T. Respired CO2 from the forest floor leads to large positive excursions in the C time series at the canopy top thereby contributing significantly to both C variance increase and C vertical flux decrease—both leading to an anomalous increase in the FV similarity function. For q, transport of dry air from the outer-layer significantly increases both the variance and the water vapour flux. However,
the expected flux increase is much smaller than the variance increase so that the net effect remains an increase in the measured
FV similarity function for water vapour above its T counterpart. The hypothesis here is that identifying these events in the temporal and/or in the frequency domain and filtering
them from the C and q time series partially recovers a scalar flow field that appears to follow FV similarity theory scaling. Methods for identifying
both types of events in the time and frequency domains and their subsequent effects on the FV similarity functions and corollary
flow variables, such as the relative transport efficiencies, are also explored. 相似文献
18.
Local Imbalance of Turbulent Kinetic Energy in the Surface Layer 总被引：1，自引：1，他引：0
We utilize experimental data collected in 2002 over an open field in Hanford, Washington, USA, to investigate the turbulent
kinetic energy (TKE) budget in the atmospheric surface layer. The von Kármán constant was determined from the near-neutral
wind profiles to be 0.36 ± 0.02 rather than the classical value of 0.4. The TKE budget was normalized and all terms were parameterized
as functions of a stability parameter z/L, where z is the distance from the ground and L is the Obukhov length. The shear production followed the Businger–Dyer relation for −2 < z/L < 1. Contrary to the traditional Monin–Obukhov similarity theory (MOST), the shear, buoyancy and dissipation terms were found
to be imbalanced due to a non-zero vertical transport over all stabilities. Motivated by this local imbalance, modified parameterizations
of the dissipation and the turbulent transport were attempted and generated good agreement with the experimental data. Assuming
stationarity and horizontal homogeneity, the pressure transport was estimated from the residual of the TKE budget. 相似文献
19.
C. Huntingford 《Boundary-Layer Meteorology》1996,79(3):307-312
The Penman-Monteith Big Leaf Model is expressed in terms of eight similarity variables. A simple relationship is derived relating these nondimensional variables to the inverse of the Monin-Obukhov length, L, multiplied by height. Placing this surface energy balance model within such a framework may be of use when coupling to atmospheric models where similarity variables have already been defined. 相似文献
20.
Spectral similarity between scalars at very low frequencies in the unstable atmospheric surface layer over the Tibetan plateau 总被引：1，自引：7，他引：1
Jun Asanuma Ichiro Tamagawa Hirohiko Ishikawa Yaoming Ma Taiichi Hayashi Yongqiang Qi Jiemin Wang 《Boundary-Layer Meteorology》2007,122(1):85-103
Similarity between temperature and water vapour was investigated in the Fourier domain by using their coherency spectra, defined
as the correlation coefficient between their Fourier modes, and the relative efficiency of their vertical transport. The class-averaged
values of these indices were computed from the turbulence measurements over sparse grasslands on the Tibetan plateau during
the intensive observations of GEWEX (Global Energy and Water Experiment) Asian Monsoon Experiment (GAME). It was found that
the energy-containing eddies at scales up to 100z (z being height) are characterised by well-maintained similarity between these scalars. The scalars are highly correlated with
each other, and their transport efficiencies are almost equal within this scale range. In contrast, similarity was not always
maintained at scales larger than 1000z. Detailed analyses showed that this breakdown of similarity occurs occasionally or sporadically, suggesting that it is caused
by events whose average return period is not much smaller than the current averaging time, i.e. 30 min. We speculate that
entrainment of drier and warmer air at the top of the atmospheric boundary layer caused the scalar dissimilarity at this scale
range. 相似文献