共查询到19条相似文献,搜索用时 140 毫秒
1.
湍流频散对边界层风廓线的影响 总被引:2,自引:0,他引:2
应用包括湍流粘性和频散的新的Reynolds平均动量方程,分析了边界层的垂直风速廓线,发现包含湍流频散的地面层的风速廓线对经典的风廓线指数规律有一个对数规律的修改;而且在不稳定层结下比在稳定层结下,湍流的频散效应更为显;在中性条件下,指数规律退化为对数规律并且Karman常数被另外一个常数所代替,而这个新常数也可以通过相似理论来获得。 相似文献
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湍流的粘性和频散效应 总被引:7,自引:0,他引:7
本文应用Prandtl混合长理论导得了既包含湍流粘性又包含湍流频散的新的Reynolds平均运动方程组.分析指出:(1)湍流不仅存在粘性效应,而且存在频散效应;(2)正是湍流的频散效应可能导致能量逆转(即常说的负粘性现象,实质为一定条件下的负频散现象),并给出了能量逆转的必要条件和充分条件;(3)给出了湍流的KdV-Burgers方程模型. 相似文献
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临近绿洲的沙漠上空近地面层内水汽输送特征 总被引:20,自引:22,他引:20
1991年7月在HEIFE实验区沙漠站进行了一次水汽输送观测实验。观测发现近地面层内比湿廓线常常出现极小值,该极小值高度为零水汽通量面的高度。这个高度以上水汽向下输送,廓线呈逆湿特征,这个高度以下水汽向上输送,廓线呈蒸发特征。沙漠上空近地面层内水汽不是常通量,在一个固定高度上观测到的水汽通量和“潜热通量”不能代表地面的蒸发量和潜热通量。 相似文献
6.
我国沙尘天气微气象学和湍流输送特征研究进展 总被引:2,自引:0,他引:2
基于风蚀起沙的物理机制,从微气象学角度回顾了国内沙尘天气的研究进展,介绍了沙尘天气过程近地面层微气象学特征,以及湍流通量演变规律和湍流作用对沙尘暴过程参数化的影响。同时,结合国外的相关研究,探讨了国内在沙尘天气研究方面存在的不足和今后的研究方向,如:开展沙尘暴过程数值模式湍流参数化方案的分析及与卫星和实验观测结果的比对研究;获取沙尘天气过程近地面层气象要素垂直廓线的精细分布,加深理解不同沙尘天气演变规律及特征;加强不同沙尘源区土壤湿度对起沙阈值影响的研究;开展不同粒径土壤的起沙率以及沙尘通量廓线演变规律的研究等。 相似文献
7.
青藏高原近地面层微气象学特征 总被引:12,自引:3,他引:12
Liu Huizhi Zhang Hongsheng Bian Lin'gen Chen Jiayi Zhou Mingyu Xu Xiangde Li Shiming Zhao Yijun 《大气科学进展》2002,19(1):73-88
利用1998年5月-7月在改则、当雄和昌都三测站获得的近地面层气象要素变化的观测资料,分析了青藏高原近地面层风速、温度和湿度日变化特征及廓线规律,发现高原近地面层微气象学特征具有自己的特点;同时还讨论了高原近地面层白天出现的逆湿现象。 相似文献
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夜间近地面稳定边界层湍流间歇与增温 总被引:1,自引:1,他引:1
在夜间晴空条件下,近地面大气湍流表现出很强的间歇性,这种间歇现象导致夜间气温短时的急剧下降,随后大幅度增温。近地面大幅度增温表明此时存在着很大的湍流热通量散度,常通量层的概念这时不存在。从各高度层温度和风速变化的曲线上分析,我们发现湍流大多在距离地面较高一点的高度上发生发展,然后向下层传递,尽管上层的湍流可能是由于下层的某一触发机制向上传递而引起的。湍流偶尔也出现自下向上传递的过程,但这一过程较少发生。湍流的这种上下传递说明稳定边界层大气经常处于非平衡状态,在运用相似理论研究稳定边界层大气结构时要特别注意这一情形。 相似文献
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Effects of turbulent dispersion of atmospheric balance motions of planetary boundary layer 总被引:1,自引:0,他引:1
New Reynolds' mean momentum equations including both turbulent viscosity and dispersion are used to analyze atmospheric balance motions of the planetary boundary layer. It is pointed out that turbulent dispersion with r 0 will increase depth of Ekman layer, reduce wind velocity in Ekman layer and produce a more satisfactory Ekman spiral lines fit the observed wind hodograph. The wind profile in the surface layer including tur-bulent dispersion is still logarithmic but the von Karman constant k is replaced by k1 = 1 -2/k, the wind increasesa little more rapidly with height. 相似文献
12.
Rainer Roth 《Boundary-Layer Meteorology》1970,1(2):131-136
A model is described, in which the mean vertical wind profile and turbulence spectra at different heights are calculated for a turbulent boundary layer without thermal stratification. The model makes use of Heisenberg's formula for the transfer of turbulent energy and is based on the assumption of a constant shearing stress in that boundary layer. As a result, a logarithmic wind profile follows with 0.39 as the value of von Kármán's constant, which is — in this model — strongly related to the inertial subrange of the turbulent energy spectra and therefore to the Kolmogoroff constant.This paper is based on studies done by the author during a one-year visit to CSIRO Division of Meteorological Physics, Aspendale, Australia, and was presented at the AGARD Specialists Meeting on The Aerodynamics of Atmospheric Shear Flows sponsored by the Fluid Dynamics Panel at Munich, Germany, during 15–17 Sept. 1969. 相似文献
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Results from large-eddy simulations and field measurements have previously shown that the velocity field is influenced by
the boundary layer height, z
i
, during close to neutral, slightly unstable, atmospheric stratification. During such conditions the non-dimensional wind
profile, φ
m
, has been found to be a function of both z/L and z
i
/L. At constant z/L, φ
m
decreases with decreasing boundary layer height. Since φ
m
is directly related to the parameterizations of the air–sea surface fluxes, these results will have an influence when calculating
the surface fluxes in weather and climate models. The global impact of this was estimated using re-analysis data from 1979
to 2001 and bulk parameterizations. The results show that the sum of the global latent and sensible mean heat fluxes increase
by 0.77 W m−2 or about 1% and the mean surface stress increase by 1.4 mN m−2 or 1.8% when including the effects of the boundary layer height in the parameterizations. However, some regions show a larger
response. The greatest impact is found over the tropical oceans between 30°S and 30°N. In this region the boundary layer height
influences the non-dimensional wind profile during extended periods of time. In the mid Indian Ocean this results in an increase
of the mean annual heat fluxes by 2.0 W m−2 and an increase of the mean annual surface stress by 2.6 mN m−2. 相似文献
14.
In the first part of this study, results of a computational fluid dynamics simulation over an array of cubes have been validated
against a set of wind-tunnel measurements. In Part II, such numerical results are used to investigate spatially-averaged properties
of the flow and passive tracer dispersion that are of interest for high resolution urban mesoscale modelling (e.g. non resolved
obstacle approaches). The results show that vertical profiles of mean horizontal wind are linear within the canopy and logarithmic
above. The drag coefficient, derived from the numerical results using the classical formula for the drag force, is height
dependent (it decreases with height). However, a modification of the formula is proposed (accounting for subgrid velocity
scales) that makes the drag coefficient constant with height. Results also show that the dispersive fluxes are similar in
magnitude to the turbulent fluxes, and that they play a very important role within the canopy. Vertical profiles of turbulent
length scales (to be used in k–l closure schemes, where k is the turbulent kinetic energy and l a turbulent length scale) are also derived. Finally the distribution of the values around the mean over the reference volumes
are analysed for wind and tracer concentrations. 相似文献
15.
In this paper we study the effect of atmospheric stability on the growth of surface gravity waves. To that end we numerically solved the Taylor-Goldstein equation for wind profiles which deviate from a logarithmic form because stratification affects the turbulent momentum transport. Using Charnock's relation for the roughness height z
0 of the wind profile, it is argued that the growth rate of the wave depends on the dimensionless phase velocity c/u
* (where u
* is the friction velocity) and a measure of the effect of atmospheric stability, namely the dimensionless Obukhov length gL/u
*
2, whereas it only depends weakly on gz
t
/u
*
2 (where z
t
is the roughness height of the temperature profile). Remarkably for a given value of u
*
/c, the growth rate is larger for a stable stratification (L > 0) than for an unstable one (L < 0). We explain why this is the case. If, on the other hand, one considers the growth rate as a function of c/U
10 (where U
10 is the windspeed at 10 m), the situation reverses for c/U
10 < 1. For practical application in wave prediction models, we propose a new parameterization of the growth rate of the waves which is an improvement of the Snyder et al. (1981) proposal because the effect of stability is taken into account. 相似文献
16.
Turbulence Structure of the Unstable Atmospheric Surface Layer and Transition to the Outer Layer 总被引:4,自引:4,他引:0
K.G. McNaughton 《Boundary-Layer Meteorology》2004,112(2):199-221
We present a new model of the structure of turbulence in the unstable atmospheric surface layer, and of the structural transition between this and the outer layer. The archetypal element of wall-bounded shear turbulence is the Theodorsen ejection amplifier (TEA) structure, in which an initial ejection of air from near the ground into an ideal laminar and logarithmic flow induces vortical motion about a hairpin-shaped core, which then creates a second ejection that is similar to, but larger than, the first. A series of TEA structures form a TEA cascade. In real turbulent flows TEA structures occur in distorted forms as TEA-like (TEAL) structures. Distortion terminates many TEAL cascades and only the best-formed TEAL structures initiate new cycles. In an extended log layer the resulting shear turbulence is a complex, self-organizing, dissipative system exhibiting self-similar behaviour under inner scaling. Spectral results show that this structure is insensitive to instability. This is contrary to the fundamental hypothesis of Monin--Obukhov similarity theory. All TEAL cascades terminate at the top of the surface layer where they encounter, and are severely distorted by, powerful eddies of similar size from the outer layer. These eddies are products of the breakdown of the large eddies produced by buoyancy in the outer layer. When the outer layer is much deeper than the surface layer the interacting eddies are from the inertial subrange of the outer Richardson cascade. The scale height of the surface layer, z
s, is then found by matching the powers delivered to the creation of emerging TEAL structures to the power passing down the Richardson cascade in the outer layer. It is z
s = u
*
3
/ks, where u
* is friction velocity, k is the von Kármán constant and s is the rate of dissipation of turbulence kinetic energy in the outer layer immediately above the surface layer. This height is comparable to the Obukhov length in the fully convective boundary layer. Aircraft and tower observations confirm a strong qualitative change in the structure of the turbulence at about that height. The tallest eddies within the surface layer have height z
s, so z
s is a new basis parameter for similarity models of the surface layer. 相似文献
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18.
Miles' inviscid theory of surface wave generation by wind is (a) modified by replacing the logarithmic shear velocity profile with one which applies right down to the wave surface and which exhibits an explicit dependence on the roughness of the surface, and (b) extended to include the effects of the interaction of wave with air flow turbulence by considering the wave-modified mean flow as the mean of the actual turbulent air flow over water waves and using this in a mixing-length model.The surface pressure is shown to depend significantly on the flow conditions being aerodynamically smooth or rough. Its component in phase with the surface elevation is practically unaffected by the wave-turbulence interaction. However, such interaction tends to increase the rate of energy input ß from wind to waves travelling in the same direction, e.g., the increase is 2gk
2 for aerodynamically rough flow, where gk is the Von Karman constant. It also provides damping of waves in an adverse wind which can be about 10% of the growth rate in a favourable wind. 相似文献
19.
S. S. Zilitinkevich 《Boundary-Layer Meteorology》1989,46(4):367-387
The logarithmic + polynomial approximation is suggested for vertical profiles of velocity components in a planetary boundary layer (PBL) at neutral and stable stratification. The resistance law functions A and B are determined on the basis of this approximation, using integral relations derived from the momentum equations, the Monin-Obukhov asymptotic formula for the wind profile in a stably stratified near-surface layer and the known expressions for the PBL depth. This result gives a realistic and convenient method for calculating the surface friction velocity and direction and the total dissipation rate of mean flow kinetic energy in terms of geostrophic velocity, buoyancy flux at the surface, the roughness parameter and the Coriolis parameter. In the course of these derivations a review is given of current views on the main problems of the neutral and stable PBL. 相似文献