共查询到20条相似文献，搜索用时 22 毫秒
1.
结合2014年2月10日和11日拉萨航路的13例飞机颠簸航空器空中报告,检验了世界区域预报系统(WAFS)风场对高空急流的预报能力,并对新增下发的晴空颠簸网格点数据的预报效果和业务化应用进行分析。结果表明:WAFS风场资料具有较高的预报能力,最大晴空颠簸预报比平均晴空颠簸预报具有更高的辨识能力,可选择4为阈值的最大晴空颠簸网格点数据绘制拉萨航路颠簸预报区域图,在业务应用中验证修订使用。 相似文献
2.
We derive a set of governing equations for flow through porous obstacles by employing a two-step averaging processes. The Navier-Stokes equations under the Boussinesq approximation that describe the air space of the porous obstacle are subjected to high-wavenumber a veraging, which leads to a set of high-frequency (wake) turbulence equations. We then use conventional Reynolds-averaging methods to obtain statistically steady mean and turbulence equations that include interactions between wake and shear turbulence. Our method provides a theoretical basis for the cascade of turbulent kinetic energy. We use this approach to analyze the constants and parameters of simpleK-theory and higher-order closure models. We also discuss qualitatively the theory of the turbulence energy generation process and the significance of interactions between different turbulent mechanisms. 相似文献
3.
Paul D. WILLIAMS 《大气科学进展》2017,34(5):576-586
Anthropogenic climate change is expected to strengthen the vertical wind shears at aircraft cruising altitudes within the atmospheric jet streams. Such a strengthening would increase the prevalence of the shear instabilities that generate clear-air turbulence. Climate modelling studies have indicated that the amount of moderate-or-greater clear-air turbulence on transatlantic flight routes in winter will increase significantly in future as the climate changes. However,the individual responses of light,moderate,and severe clear-air turbulence have not previously been studied,despite their importance for aircraft operations. Here,we use climate model simulations to analyse the transatlantic wintertime clear-air turbulence response to climate change in five aviation-relevant turbulence strength categories. We find that the probability distributions for an ensemble of 21 clear-air turbulence diagnostics generally gain probability in their right-hand tails when the atmospheric carbon dioxide concentration is doubled. By converting the diagnostics into eddy dissipation rates,we find that the ensembleaverage airspace volume containing light clear-air turbulence increases by 59%(with an intra-ensemble range of 43%–68%),light-to-moderate by 75%(39%–96%),moderate by 94%(37%–118%),moderate-to-severe by 127%(30%–170%),and severe by 149%(36%–188%). These results suggest that the prevalence of transatlantic wintertime clear-air turbulence will increase significantly in all aviation-relevant strength categories as the climate changes. 相似文献
4.
This paper describes how to measure turbulence in the atmospheric boundary layer (ABL) in order to address certain problems in modern atmospheric physics. These problems mainly relate to the Earth's energy budget (including the hydrological cycle) and biogeochemical cycles. Starting from the main characteristic numbers and the basic equations of atmospheric turbulent flow, we show what turbulence parameters are important to measure. Special attention is given to the various methods used to compute the turbulent fluxes. We analyse the range of scales which has to be measured to properly capture the eddies contributing to the turbulent transfers. This range of scales determines what sensors can be used in the atmospheric surface layer and in the ABL. We describe the most widely used instruments and their performances. The principal platforms used to deploy these instruments are examined. Aircraft are described in more details, because they allow a thorough exploration of the ABL. In the last section, some examples of ABL turbulence signals measured in various conditions are presented. These examples illustrate horizontally homogeneous turbulence as well as inhomogeneous signals for which standard analysis techniques cannot be used. We show how some recent techniques, like wavelet transforms, can help to investigate this kind of signal. At the end, we present what would be interesting to do in the near future for the study of ABL turbulence. 相似文献
5.
We show that traditional Reynolds (block) averaging produces turbulence statistics whose time evolution is incompatible with the Navier–Stokes equation. Specifically, the zero integral scale that block averaging always produces leads to a trivial (zero-equals-zero) solution of the Navier–Stokes equation for autocovariances. We suggest alternative methods for analyzing turbulence time series that do not always generate a zero integral scale and, as a result, yield autocovariances whose time evolutions are compatible with the Navier–Stokes equation. 相似文献
6.
切变湍流的相干结构是湍流研究中的重大发现,它表明湍流在表面上看来不规则运动中具有可检测的有序运动,这种相干结构在切变湍流的脉动生成和发展中起着主宰作用.因此识别和提取相干结构对于认识和研究湍流是非常重要的.用数字滤波法将包含相干结构的大尺度信号提取出来以后,再用子波分析,根据子波能量极大值的判别方法,分别确定出大气湍流三个方向上的速度脉动信号相干结构的频率或时间尺度,然后由确定尺度上的连续子波反演公式,提取出大气湍流三个方向上的速度脉动信号相干结构所对应的波形. 相似文献
7.
T. N. Venkatesh Joseph Mathew Ravi S. Nanjundiah 《Meteorology and Atmospheric Physics》2014,126(3-4):139-160
Many theories and mechanisms have been proposed to explain the phenomenon of clear-air turbulence (CAT), and some of them have been successful in predicting light, moderate and, in some cases, severe turbulence. It is only recently that skill in the forecasting of the severe form of CAT, which could lead to injuries to passengers and damage to aircraft, has improved. Recent observations and simulations suggest that some severe to extreme turbulence could be caused by horizontal vortex tubes resulting from secondary instabilities of regions of high shear in the atmosphere. We have conducted direct numerical simulations to understand the scale relationship between primary structures (larger-scale structures related to one of the causes mentioned above) and secondary structures (smaller-sized, shear structures of the size of aircraft). From shear layer simulations, we find that the ratio of sizes of primary and secondary vortices is of the right order to generate aircraft-scale vortex tubes from typical atmospheric shear layers. We have also conducted simulations with a mesoscale atmospheric model, to understand possible causes of turbulence experienced by a flight off the west coast of India. Our simulations show the occurrence of primary flow structures related to synoptic conditions around the time of the incident. The evidence presented for this mechanism also has implications for possible methods of detection and avoidance of severe CAT. 相似文献
8.
In-Hye Lee Young-Hee Lee Jinkyu Hong 《Asia-Pacific Journal of Atmospheric Sciences》2011,47(3):281-291
Canopy turbulence plays an important role in mass and energy exchanges at the canopy-atmosphere interface. Despite extensive studies on canopy turbulence over a flat terrain, less attention has been given to canopy turbulence in a complex terrain. The purpose of this study is to scrutinize characteristics of canopy turbulence in roughness sublayer over a hilly forest terrain. We investigated basic turbulence statistics, conditionally sampled statistics, and turbulence spectrum in terms of different atmospheric stabilities, wind direction and vertical structures of momentum fluxes. Similarly to canopy turbulence over a homogeneous terrain, turbulence statistics showed coherent structure. Both quadrant and spectrum analysis corroborated the role of intermittent and energetic eddies with length scale of the order of canopy height, regardless of wind direction except for shift of peak in vertical wind spectrum to relatively high frequency in the down-valley wind. However, the magnitude of the momentum correlation coefficient in a neutral condition was smaller than typical value over a flat terrain. Further scrutiny manifested that, in the up-valley flow, temperature skewness was larger and the contribution of ejection to both momentum and heat fluxes was larger compared to the downvalley flow, indicating that thermal instability and weaker wind shear in up-valley flow asymmetrically affect turbulent transport within the canopy. 相似文献
9.
Interaction of a zonal jet and small-amplitude Rossby-wave turbulence is studied within the framework of the barotropic β-plane model. It is demonstrated that turbulent-laminar interaction in this case transfers energy from the wave turbulence to the laminar flow (the effect of negative friction). We derive a conclusion that, as the geophysical turbulence is determined partly by wave turbulence and none of the traditional heuristic models can adequately describe the effect of negative friction associated with wave turbulence, the application of these models to the ‘real’ ocean and atmosphere is unreliable.It is also demonstrated that, as they are affected by the turbulence, all westward jets slowly expand without strengthening. Each jet has a core, within the limits of which the velocity of the fluid is constant. In some cases, the core expands faster than the jet periphery, resulting in jumps on the profile of the flow. All eastward jets are steady irrespective of their profiles. 相似文献
10.
We use large-eddy simulation (LES) to study the turbulent pressure field in atmospheric boundary layers with free convection, forced convection, and stable stratification. We use the Poisson equation for pressure to represent the pressure field as the sum of mean-shear, turbulence–turbulence, subfilter-scale, Coriolis, and buoyancy contributions. We isolate these contributions and study them separately. We find that in the energy-containing range in the free-convection case the turbulence–turbulence pressure dominates over the entire boundary layer. That part dominates also up to midlayer in the forced-convection case; above that the mean-shear pressure dominates. In the stable case the mean-shear pressure dominates over the entire boundary layer.We find evidence of an inertial subrange in the pressure spectrum in the free and forced-convection cases; it is dominated by the turbulence–turbulence pressure and has a three-dimensional spectral constant of about 4.0. This agrees well with quasi-Gaussian predictions but is a factor of 2 less than recent results from direct numerical simulations at moderate Reynolds numbers. Measurements of the inertial subrange pressure spectral constant at high Reynolds numbers, which might now be possible, would be most useful. 相似文献
11.
Summary The principle of the group-kinetic method is elucidated. This method of renormalization serves as the basis for analyzing the spectral structure of turbulence. The spectral distributions include the Kolmogoroff lawk
–5/3 for isotropic turbulence, the power lawk
–1 for shear turbulence, the spectrum for stratified turbulence not in the power law form, the power lawk
–3 for two-dimensional geostrophic turbulence, and the power lawsk
–3,k
–2 andk
–5 for two-dimensional Rossby wave turbulence with uniform and differential rotations. We discuss a spectrum-dependent modeling in reference to the problems of the universal functions and parameters in the similarity theories for the atmospheric surface layer and the planetary boundary layer. A renormalization-based modeling of atmospheric turbulence is proposed. 相似文献
12.
On Reynolds Averaging of Turbulence Time Series 总被引：1，自引：1，他引：0
We show that validity of Reynolds averaging for estimating the (ensemble) mean of a turbulence time series requires that the
series values be both stationary and uncorrelated. In strict statistical terminology, these two conditions are jointly designated as independent identically distributed (i.i.d.). Moreover, we show that when the series values are correlated, knowledge of the correlation between the values is needed
to obtain a reliable estimate of the mean. Last, we contend that a viable averaging algorithm must be Reynolds number (Re) dependent, requiring one version for low Re (Gaussian) turbulence and another for high Re (non-Gaussian) turbulence. Alternatively the median (as opposed to the mean) is recommended as a measure of the central tendency of the turbulence probability density function. 相似文献
13.
A Lagrangian Stochastic Model for Heavy Particle Dispersion in the Atmospheric Marine Boundary Layer
The dispersion of heavy particles and pollutants is often simulated with Lagrangian stochastic (LS) models. Although these
models have been employed successfully over land, the free surface at the air-sea interface complicates the implementation
of traditional LS models. We present an adaptation of traditional LS models to the atmospheric marine boundary layer (MBL),
where the bottom boundary is represented by a realistic wavy surface that moves and deforms. In addition, the correlation
function for the turbulent flow following a particle is extended to the anisotropic, unsteady case. Our new model reproduces
behaviour for Lagrangian turbulence in a stratified air flow that departs only slightly from the expected behaviour in isotropic
turbulence. When solving for the trajectory of a heavy particle in the air flow, the modelled turbulent forcing on the particle
also behaves remarkably well. For example, the spectrum of the turbulence at the particle location follows that of a massless
particle for time scales approximately larger than the Stokes’ particle response time. We anticipate that this model will
prove especially useful in the context of sea-spray dispersion and its associated momentum, sensible and latent heat, and
gas fluxes between spray droplets and the atmosphere. 相似文献
14.
Greene Brian R. Kral Stephan T. Chilson Phillip B. Reuder Joachim 《Boundary-Layer Meteorology》2022,183(3):321-353
Boundary-Layer Meteorology - We explore the potential of a new method for the estimation of profiles of turbulence statistics in the stable boundary layer (SBL). By applying gradient-based scaling... 相似文献
15.
A. Tunick 《Meteorology and Atmospheric Physics》2005,90(3-4):159-164
Summary Due to the increased use of laser and ground-to-satellite communications the need for reliable optical turbulence information
is growing. Optical turbulence information is important because it describes an atmospheric effect that can degrade the performance
of electromagnetic systems and sensors, e.g., free-space optical communications and infrared imaging. However, analysis of
selected past research indicates that there are some areas (i.e., data and models) in which optical turbulence information
is lacking. For example, line-of-sight optical turbulence data coupled with atmospheric models in hilly terrain, coastal areas,
and within cities are few in number or non-existent. In addition, the bulk of existing atmospheric computer models being used
to provide estimates of optical turbulence are basically one-dimensional in nature and assume uniform turbulence conditions
over large areas. As a result, current optical turbulence theory and models may be deficient and in error for inhomogeneous
(nonuniform) turbulence conditions, such as those that occur in urban environments or environments with changing topography
and energy budgets. While it is anticipated that theoretical advances in environmental physics (and like disciplines) will
be a catalyst for much new work this area, in the interim, we suggest that some very practical computational research can
be performed to extend existing low-atmospheric turbulence and micrometeorological calculations beyond current limitations. 相似文献
16.
We report a two-dimensional (alongwind u, vertical w) trajectory-simulation model, consistent with Thomson's (1987) well-mixed criteria, that allows for the non-Gaussian turbulence typical of flow within a plant canopy. The effect of non-Gaussian turbulence was examined by formulating a non-Gaussian u, w joint probability density function (PDF) as the sum of two Gaussian joint-PDFs. The resultant PDF reproduced the desired means, variances, skewnesses, and kurtoses, and the correct covariance. In prediction of the location of maximum concentration downwind of a line source in homogeneous, slightly non-Gaussian turbulence, it proved advantageous to incorporate skewness and kurtosis. However, in the case of inhomogeneous, highly non-Gaussian turbulence, the addition of skewness and kurtosis in the model resulted in substantially worse agreement with measurements than the results of the model using Gaussian PDFs. This may be due to inaccuracy in our PDF formulation. Dispersion predictions from the model with Gaussian PDFs were generally not statistically different from measurements. These results indicate that a two-dimensional Gaussian trajectory-simulation approach is adequate to predict mean concentrations and fluxes resulting from sources within plant canopies. 相似文献
17.
In view of the absence or insufficiency of tropical cyclone(TC) turbulence parameters in current design standards of wind turbines, in this paper, TC turbulence parameter models with roughness length involved are developed based on six landfall TCs observed from meteorological towers located on various underlying surfaces, so as to provide references for the wind turbine design under TC conditions. Firstly, the roughness length values are examined in order to reduce the effect on turbulence parameters of the various underlying surfaces. On this basis, the reference turbulence intensity is normalized by the roughness length. The related turbulence parameters are parameterized, including the turbulence standard deviation and the turbulence spectrum; and the turbulence parameters available under TC conditions for turbulence turbine design are presented finally. Comparisons of the wind parameter models presented in this paper with those used in current turbine design standards suggest that the former can represent TC characteristics more accurately. In order to withstand TCs, we suggest that the turbulence parameter models recommended in this paper be included in future wind turbine design standards under TC conditions. 相似文献
18.
Yu Zhang Heping Liu Thomas Foken Quinton L. Williams Shuhua Liu Matthias Mauder Claudia Liebethal 《Boundary-Layer Meteorology》2010,136(2):235-251
During the Energy Balance EXperiment, the patch-by-patch, flood irrigation in a flat cotton field created an underlying surface
with heterogeneous soil moisture, leading to a dry (warm)-to-wet (cool) transition within the cotton field under northerly
winds. Moreover, the existence of an extremely dry, large bare soil area upstream beyond the cotton field created an even
larger step transition from the bare soil region to the cotton field. We investigated the turbulence spectra and cospectra
in the atmospheric surface layer (ASL) that was disturbed by large eddies generated over regions upstream and also influenced
by horizontal advection. In the morning, the ASL was unstable while in the afternoon a stable internal boundary layer was
observed at the site. Therefore, the turbulence data at 2.7 and 8.7 m are interpreted and compared in terms of interactions
between large eddies and locally generated turbulence under two atmospheric conditions: the unstable ASL beneath the convective
boundary layer (CBL) (hereafter the unstable condition) and the stable ASL beneath the CBL (hereafter the stable condition).
We identified the influences of multiple sizes of large eddies on ASL turbulence under both stratifications; these large eddies
with multiple sizes were produced over the dry patches and dry, large bare soil areas upstream. As a consequence of the disturbance
of large eddies, the broadening, erratic variability, and deviation of spectra and cospectra, relative to those described
by Monin–Obukhov similarity theory, are evident in the low- to mid-frequencies. Transfer of momentum, heat, and water vapour
by large eddies is distinctly observed from the turbulence cospectra and leads to significant run-to-run variations of residuals
of the surface energy balance closure. Our results indicate that these large eddies have greater influences on turbulence
at higher levels compared to lower levels, and in the unstable ASL compared to the stable ASL. 相似文献
19.
纳木错(湖)地区湍流数据质量控制和湍流通量变化特征 总被引：1，自引：0，他引：1
利用中国科学院纳木错多圈层综合观测研究站2009年全年的大气湍流观测资料,应用Foot-print模型分析了青藏高原非均匀下垫面湍流观测数据的数据质量、质量评价及不同下垫面对湍流通量的贡献。结果表明:纳木错(湖)地区因不同土地利用类型的差别,导致地表通量分布不均匀,草地对地表通量的贡献最大;对不同大气层结状态,观测站周围200m范围内的地表通量贡献各不相同,上风向通量贡献源区较大,湍流发展较充分。在不稳定状态和中性状态下,纳木错地区地表通量数据质量较高,即白天观测的通量数据质量较高;在稳定状态下数据质量较低,即夜间的通量数据质量较差;纳木错地区的湍流通量受湖陆风和大气稳定性影响较大。 相似文献
20.
We present some algebraic and numerical simulations of the stable boundary layer. We also discuss the problem of the existence
of a critical Richardson number (Ri), beyond which the turbulence is suppressed. We compare the results of a second-order algebraic model with those of a third-order
numerical model and, to this purpose, numerical simulations of a wind-tunnel flow, which is characterized by various Richardson
numbers, were performed. As far as the second-order model is concerned, solutions, for the Richardson number greater than
any critical value, can be obtained by modifying the time scales of the second-order equation pressure correlation terms in
order to account for a buoyancy damping factor. We show that using a third-order model allows the same results (no critical
Richardson number) to be obtained without modifications to the time scales. It is suggested that the non-locality, accounted
for by the third-order moments, could allow the turbulence to persist also for Ri > 1. 相似文献