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1.
组合法确定近地面层湍流通量和通用函数 总被引：17，自引：3，他引：17
本文发展了确定近地面层湍流通量的组合法,得到了它们的一般表达式。并用这种方法确定近地面层MO相似性函数。利用ITCE的观测资料作为实例计算,结果表明这种方法是可行的。 相似文献
2.
Eeva Mäkiranta Timo Vihma Anna Sjöblom Esa-Matti Tastula 《Boundary-Layer Meteorology》2011,140(1):105-123
Sonic anemometer and profile mast measurements made in Wahlenbergfjorden, Svalbard Arctic archipelago, in May 2006 and April
2007 were employed to study the atmospheric boundary layer over sea-ice. The turbulent surface fluxes of momentum and sensible
heat were calculated using eddy correlation and gradient methods. The results showed that the literature-based universal functions
underestimated turbulent mixing in strongly stable conditions. The validity of the Monin-Obukhov similarity theory was questionable
for cross-fjord flow directions and in the presence of mesoscale variability or topographic effects. The aerodynamic roughness
length showed a dependence on the wind direction. The mean roughness length for along-fjord wind directions was (2.4 ± 2.6)
× 10−4 m, whereas that for cross-fjord directions was (5.4 ± 2.8) × 10−3 m. The thermal stratification and turbulent fluxes were affected by the synoptic situation with large differences between
the 2 years. Channelling effects and drainage flows occurred especially during a weak large-scale flow. The study periods
were simulated applying the Weather Research and Forecasting (WRF) model with 1-km horizontal resolution in the finest domain.
The results for the 2-m air temperature and friction velocity were good, but the model failed to reproduce the spatial variability
in wind direction between measurement sites 3 km apart. The model suggested that wind shear above the stable boundary layer
provided a non-local source for the turbulence observed. 相似文献
3.
A new surface-flux parameterization is presented and its impact on climate simulations with the Canadian Centre for Climate Modelling and Analysis (CCCMA) general circulation model (GCM) is discussed. The parameterization is based on the Monin-Obukhov similarity theory using well established flux-profile relationships for the unstable conditions. However, recently proposed new relationships are used in stable conditions. The new formulation allows different roughness lengths for heat and momentum, and gives transfer coefficients that are in agreement with Monin-Obukhov similarity theory. It also includes a parameterization for the free-convective boundary layer, which often occurs over warm surfaces within light winds. In circumstances where the surface layer is not neutrally stratified the proposed flux parameterization yields surface transfer coefficients that are different from those resulting from the standard surface flux formulation used in the GCM. The most marked effects of implementing the new formulation in the GCM are found over land and adjacent oceanic regions in winter where significant differences are found in the surface heat and moisture fluxes and surface temperatures. 相似文献
4.
Inhomogeneity of the Land Surface and Problems in theParameterization of Surface Fluxes in Natural Conditions 总被引：1，自引：0，他引：1
Summary Eddy correlation techniques to determine the turbulent fluxes of heat, moisture and momentum in the near-surface atmospheric
layer rely on the Monin-Obukhov similarity theory, which requires stationarity and horizontal homogeneity. Experiments at
specially selected sites over land and particularly over sea are used to develop this concept. Recent experiments, deliberately
conducted in non-ideal conditions, show an underestimation of turbulent fluxes. Results from the field experiments FIFE, KUREX,
TARTEX and SADE, point to a relationship between the underestimation of turbulent fluxes and terrain inhomogeneity. In order
to systematically correct for this effect a scheme is suggested which uses fetch lengths of different types of surface in
the sites surrounding the environment. In addition, horizontal differences in atmospheric stability above different surfaces
are included in the correction scheme. This scheme might be useful for the design of validation experiments in non-homogeneous
terrain.
Received April 9, 1997 Revised July 16, 1997 相似文献
5.
Turbulent characteristics and bulk transfer coefficients over the desert in the HEIFE area 总被引：1，自引：0，他引：1
Ichiro Tamagawa 《Boundary-Layer Meteorology》1996,77(1):1-20
Observations of surface-layer turbulence and turbulent fluxes were made over a desert in northwestern China as a part of HEIFE (HEIhe river Field Experiment). These show that the normalized variations of the vertical wind component and of the air temperature obey Monin-Obukhov similarity well, especially in free convective conditions. However, the variations of specific humidity do not obey Monin-Obukhov similarity.Mean bulk transfer coefficients of sensible heat and momentum flux are obtained as functions of stability over a wide stability range from the observed data of turbulent fluxes and mast profiles. However, the bulk transfer coefficient for water vapor could not be obtained because of the large scatter of the data. In free convective conditions, the sensible heat flux was found to be approximately proportional to the 1.4 power of temperature difference between the surface and 20m. The bulk transfer coefficient of sensible heat is also obtained as a function of the bulk Richardson number for practical convenience. 相似文献
6.
The measurement of turbulent surface-layer fluxes by use of bichromatic scintillation 总被引：4，自引：2，他引：4
Scintillation measurements with a HeNe and a CO2 laser were used to derive turbulent fluxes of heat and momentum in the surface layer. This was achieved by the structure constant or dissipation technique, i.e., by relating the measured structure constants and inner scales of refractive index fluctuations to structure constants of temperature fluctuations and dissipation rates of turbulent kinetic energy, respectively, and then assuming Monin-Obukhov similarity.The resulting heat fluxes agree well with measurements using the eddy correlation technique but for averaging periods of 10 min, the optical data show a much smoother and physically more plausible behaviour. The optically derived friction velocities are in good agreement with estimates derived from wind velocity and surface roughness. It was also observed that for stationary conditions, 1-min averaged optical measurements already provide good estimates for longer averaged heat and momentum fluxes.Even though some uncertainty remains about the empirical constants and Monin-Obukhov similarity expressions used, the method clearly proves to be of great value for monitoring surface-layer turbulence. 相似文献
7.
Two surface layer parameterization schemes along with five planetary boundary layer (PBL) schemes in the Weather Research and Forecasting model (WRF) are analyzed in order to evaluate the performance of the WRF model in simulating the surface variables and turbulent fluxes over an Indian sub-continent region. These surface layer schemes are based on the fifth-generation Pennsylvania State University—National Center for Atmospheric Research Mesoscale Model (MM5) parameterization; (a) Old MM5 scheme having Businger-Dyer similarity functions and (b) revised MM5 scheme utilizing the functions that are valid for full ranges of atmospheric stabilities. The study suggests that each PBL scheme can reproduce the diurnal variation of 2 m temperature, momentum flux and sensible heat flux irrespective of the surface layer scheme used for the simulations. However, a comparison of model-simulated values of surface variables and turbulent fluxes with observed values suggests that each PBL scheme is found to systematically over-estimate the nocturnal 2 m temperature and 10 m wind speed with both the revised and old schemes during stable conditions. 相似文献
8.
Similarity of scalars under stable conditions 总被引：5，自引：5，他引：0
The question whether two different scalars have the same behaviour in the surface layer under stable conditions is investigated. Similarity of two scalars is defined in terms of the equality of their corresponding dimensionless Monin-Obukhov similarity functions. Previous theoretical and experimental results concerning the issue are briefly reviewed: they are found to be contradictory. An analytical derivation of the square of the correlation coefficient between two scalars is obtained based on the correlation structure of the turbulent dissipation functions for stable conditions, when it can be assumed that the divergence of the vertical transport of scalar variance/covariance is negligible. The resulting expression elucidates some earlier conflicting results, and helps to establish the equality of the similarity functions for all scalars in the stable surface layer. A statistical analysis in the time domain is also performed using temperature and humidity turbulence data measured in nocturnal stable conditions during FIFE-89. Our results, both from the analytical derivation and the statistical analysis of turbulence data, confirm that under validity of the Monin-Obukhov similarity theory assumptions, the corresponding similarity functions for temperature and humidity are equal to within the statistical uncertainty of the measurements. An important consequence is that the eddy diffusivities of temperature and humidity are also equal.Now at SIMEPAR — Sistema Meteorológico do Paraná and UFPR — Universidade Federal do Paraná, Caixa Postal 318 CEP 80001-970, Curitiba PR Brazil. 相似文献
9.
Monin–Obukhov similarity functions for the structure parameters of temperature and humidity are needed to derive surface heat and water vapour fluxes from scintillometer measurements and it is often assumed that the two functions are identical in the atmospheric surface layer. Nevertheless, this assumption has not yet been verified experimentally. This study investigates the dissimilarity between the turbulent transport of sensible heat and water vapour, with a specific focus on the difference between the Monin–Obukhov similarity functions for the structure parameters. Using two datasets collected over homogeneous surfaces where the surface sources of sensible heat and water vapour are well correlated, we observe that under stable and very unstable conditions, the two functions are similar. This similarity however breaks down under weakly unstable conditions; in that regime, the absolute values of the correlations between temperature and humidity are also observed to be low, most likely due to large-scale eddies that transport unsteadiness, advection or entrainment effects from the outer layer. We analyze and demonstrate how this reduction in the correlation leads to dissimilarity between the turbulent transport of these two scalars and the corresponding Monin–Obukhov similarity functions for their structure parameters. A model to derive sensible and latent heat fluxes from structure parameters without measuring the friction velocity is tested and found to work very well under moderately to strongly unstable conditions (−z/L > 0.5). Finally, we discuss the modelling of the cross-structure parameter over wet surfaces, which is crucial for correcting water vapour effects on optical scintillometer measurements and also for obtaining surface sensible and latent heat fluxes from the two-wavelength scintillometry. 相似文献
10.
局地相似性关系在城市边界层中的适用性验证 总被引：1，自引：0，他引：1
利用中国科学院大气物理研究所325 m铁塔在2003年8月期间47和120 m高度上的湍流观测资料,对局地相似性关系在城市边界层的适用性进行了检验。结果表明：47 m高度仍属于城市冠层之上的近地面常通量层,莫宁－奥布霍夫相似性关系基本适用。但120 m高度则基本属于近地面层与自由对流层之间的过渡高度,在该处,相似性关系部分适用。同时,给出了不同的层结稳定度条件下47和120 m高度上的无量纲速度和温度标准差与稳定度之间的局地相关表达式。 相似文献
11.
本文从湍流产生和发展的本质出发,以湍流动能和湍流混合长为湍流输送的决定因子,用因次分析的方法得到了一套可包括局地自由对流在内的不稳定大气近地层Monin－Obukhov相似性函数。这套相似性函数不仅有较充分的理论依据,而且还有较明确的物理含意。它能在极端情况下自动蜕化出局地自由对流相似性预测形式。 相似文献
12.
13.
Surface energy balance,parameterizations of boundary-layer heights and the application of resistance laws near an Antarctic Ice Shelf front 总被引：2，自引：0，他引：2
A study of the surface energy balance with turbulent fluxes obtained by the Monin-Obukhov similarity theory and a comparison with results for resistance laws are presented for the strong baroclinic conditions in the vicinity of the Filchner/Ronne Ice Shelf front. The data are taken from a field experiment in the Antarctic summer season 1983/84. For the first time in the coastal Antarctic region, this data set comprises synchronous energy balance measurements over the polynya and the ice shelf together with soundings of the boundary layer, yielding vertical profiles of the wind velocity and temperature over the ice shelf, at the ice shelf front and over the polynya.Over the ice shelf, the radiation balance is the largest component of the energy fluxes and is mainly compensated by the subsurface energy flux and the turbulent heat flux in the daily mean. Over the polynya, turbulent fluxes of sensible and latent heat lead to large energy losses of the water surface in the night-time and in situations of very low air temperatures.Different parameterizations for boundary-layer height are compared using tethered sonde and energy balance measurements. With the height of the inversion base over the polynya and the height of the critical bulk Richardson number over the ice shelf, external parameters for the application of resistance laws were determined. The comparison of turbulent surface fluxes obtained by the energy balance measurements and by the resistance laws shows good agreement for the convective conditions over the polynya. For the stably stratified boundary layer over the ice shelf with small amounts of the turbulent heat flux, the deviation is large for the case of a cold air outflow with a superposed inertial oscillation. 相似文献
14.
A long-standing problem in large-eddy simulations (LES) of the planetary boundary layer (PBL) is that the mean wind and temperature profiles differ from the Monin-Obukhov similarity forms in the surface layer. This shortcoming of LES has been attributed to poor grid resolution and inadequate sub-grid-scale (SGS) modeling. We study this deficiency in PBL LES solutions calculated over a range of shear and buoyancy forcing conditions. The discrepancy from similarity forms becomes larger with increasing shear and smaller buoyancy forcing, and persists even with substantial horizontal grid refinement. With strong buoyancy forcing, however, the error is negligible.In order to achieve better agreement between LES and similarity forms in the surface layer, a two-part SGS eddy-viscosity model is proposed. The model preserves the usual SGS turbulent kinetic energy formulation for the SGS eddy viscosity, but it explicitly includes a contribution from the mean flow and a reduction of the contributions from the turbulent fluctuations near the surface. Solutions with the new model yield increased fluctuation amplitudes near the surface and better correspondence with similarity forms out to a distance of 0.1–0.2 times the PBL depth, i.e., a typical surface-layer depth. These results are also found to be independent of grid anisotropy. The new model is simple to implement and computationally inexpensive.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
15.
PARAMETERISING SUB-GRID SCALE VERTICAL TRANSPORT IN ATMOSPHERIC MODELS UNDER STATICALLY STABLE CONDITIONS 总被引：3，自引：4，他引：3
YVES DELAGE 《Boundary-Layer Meteorology》1997,82(1):23-48
Five different formulations of the stability functions used forvertical turbulent transfer in atmospheric models are compared in a 1-Dmodel of the nocturnal boundary layer. One of them has a critical valueof the Richardson number around 0.2 and leads to the traditional log-linear profile, while other more empirical formulations maintain sometransfer at values of Ri around 1.0. Although no new observationalevidence is presented, it is suggested that the latter formulations aremore appropriate for use in atmospheric models because the unresolvedvariability inside a model grid box induces some turbulent transfer evenat super-critical values of the mean Ri. The study shows that themagnitude of the stability functions is principally important in theeffective range of Ri values found in the stable boundary layer and thattheir slopes near the origin are less important. This permits the use inatmospheric models of a simple explicit function of Ri containing asingle parameter, with results similar to those obtained with earlier morecomplex formulations. The results of the simulation with the 1-D model are used toexamine the errors introduced by the relatively thick surface layers of most atmospheric models, in which, for the stable case, the traditionalassumption of constancy of the fluxes with height is often clearlyviolated. When a height variation of the fluxes is introduced in surface-layer formulations, the error in the magnitude of the surface fluxes isdecreased with some of the formulations but not all of them. This lackof sensitivity is explained by a compensation mechanism in which theassumed decrease of the fluxes with height implies a correspondingdecrease of the Obukhov length which acts in the oppositedirection, reducing, and sometimes eliminating, the adverse effect of theunrealistic specification of the fluxes. It may be argued that thiscompensation mechanism also explains the wide range of validity of theMoini-Obukhov similarity theory. 相似文献
16.
边界层局地相似理论在草原下垫面的适用性检验 总被引：3，自引：0，他引：3
利用锡林浩特草原平坦下垫面塔层湍流资料,对常值通量层的高度进行了估计,检验了局地相似理论在均匀草原下垫面的适用性,对Monin-Obukhov相似理论和局地相似理论在常值通量层以上的大气边界层的适用性进行了比较。结果表明:(1)对于锡林浩特草原来说,常值通量层厚度在50m左右;(2)通过分析无量纲风速和温度梯度、无量纲风速方差、无量纲标量(温度T、水汽q、CO2浓度C)方差与稳定度z/L之间的关系,验证了局地相似理论在均匀草原下垫面70m以下大气边界层的适用性;(3)感热通量尺度与浮力长度尺度之间存在线性关系;(4)从经典Monin-Obukhov长度、局地Monin-Obukhov尺度和浮力长度尺度的对比分析来看,局地尺度更适用于50m以上的大气边界层,而浮力长度尺度不适用于50m以上的大气边界层。 相似文献
17.
荒漠戈壁下垫面表面动量和感热湍流通量参数化研究 总被引：9，自引：0，他引：9
用合理筛选以后的野外观测资料，研究了荒漠戈壁地表湍流通量参数化的问题。首先，分析了Monin-obukhov相似函数的特征，并拟台出了其经验公式。结果表明，风速和温度相似性函数随稳定度参数的变化曲线与典型经验曲线差异较小，并且在经验曲线分布范围以内，但中性时的值有所不同。同时，还用该资料给出了动量和标量粗糙度(感热粗糙度)长度的平均值及其标量粗糙度随摩擦速度的变化关系。发现标量粗糙度的平均值大约比动量粗糙度的小一个量级，并且随摩擦速度的增大而减小，但明显比其理论预测值要大。 相似文献
18.
Helmut Kraus 《Boundary-Layer Meteorology》1993,66(3):219-235
The Prandtl-layer concept, assuming constant turbulent fluxes in the lowest meters or decameters of the atmosphere under horizontal homogeneous and steady-state conditions, is widely used; and it is also one of the fundamentals of Monin-Obukhov similarity theory. Thus, surface-layer condensation processes-essentially formation of shallow fog layers-implying convergence and divergence of turbulent fluxes of water vapour, liquid water content and sensible heat, cannot be treated within this concept. This paper tries to overcome this restriction by a modified Monin-Obukhov theory, which deals with constant fluxes of total water content and moist static energy (instead of water vapour and sensible heat). It shows that surface-layer fog situations (under steady-state and horizontally homogeneous conditions and neglecting radiational effects) can be treated by this modified theory, which yields turbulent vertical fluxes of sensible heat, water vapour and liquid water content and their divergences.The paper also derives a simple formula for the divergence of the turbulent flux of water vapour (E/z) under saturation conditions, which elucidates convergence ofE very close to the ground and divergence ofE higher up independent of whether the stratification is stable or unstable, i.e., whether there is fog over cold or warm ground. Model computations with the modified Monin-Obukhov theory are in full accordance with this formula. Thus a steam-fog case can be given as a demonstration of vertical profiles of turbulent fluxes of sensible heat, water vapour and liquid water content and their divergences. 相似文献
19.
Stratified Atmospheric Boundary Layers 总被引：32，自引：24，他引：8
L. Mahrt 《Boundary-Layer Meteorology》1999,90(3):375-396
Various features of different stability regimes of the stable boundary layer are discussed. Traditional layering is examined in terms of the roughness sublayer, surface layer, local similarity, z-less stratification and the region near the boundary-layer top. In the very stable case, the strongest turbulence may be detached from the surface and generated by shear associated with a low level jet, gravity waves or meandering motions. In this case, similarity theory and the traditional concept of a boundary-layer break down. The elevated turbulence may intermittently recouple to the surface. Inability to adequately measure turbulent fluxes in very stable conditions limits our knowledge of this regime. 相似文献
20.
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