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1.
An atmospheric surface-layer (ASL) experiment conducted at a meteorological site in the Oostelijk-Flevoland polder of the Netherlands is described. Turbulent fluctuations of wind velocity, air temperature and static pressure were measured, using three 10 m towers.Simultaneous turbulent signals at several heights on the towers were used to investigate the properties of the turbulent structures which contribute most significantly to the turbulent vertical transports in the unstable ASL. These turbulent structures produce between 30 and 50% of the mean turbulent vertical transport of horizontal alongwind momentum and they contribute to between 40 and 50% of the mean turbulent vertical heat transport; in both cases this occurs during 15 to 20% of the total observation time.The translation speed of the turbulent structures equals the wind speed averaged over the depth of the ASL, which scales on the surface friction velocity. The inclination angle of the temperature interface at the upstream edge of the turbulent structures to the surface is significantly smaller than that of the internal shear layer, which is associated with the temperature interface. The turbulent structures in the unstable ASL are determined by a large-scale temperature field: Convective motions, which encompass the whole depth of the planetary boundary layer (PBL), penetrate into the ASL. The curvature of the vertical profile of mean horizontal alongwind velocity forces the alignment of the convective cells in the flow direction (Kuettner, 1971), which have an average length of several hundreds of metres and an average width of a few tens of metres. This mechanism leads to the formation of turbulent structures, which extend throughout the depth of the ASL. 相似文献
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The Characteristics of Turbulence Structure and Transfer over the Middle Area of the Tibetan Plateau 
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下载免费PDF全文 In this paper, turbulent data obtained from the Damxung site during the Secondary Tibetan Plateau Science Experiment (TIPEX) in 1998 are used to study the characteristics of the turbulent spectra, turbulence transport, and the dissipation rates of turbulent kinetic energy, temperature variance, and humidity variance in the middle area of the Tibetan Plateau. The turbulent spectra of wind velocity, potential temperature, and humidity satisfy the-2/3 power law in the high frequency range. Horizontal transportation of heat and water vapor is negligible compared with vertical transportation under strong unstable conditions, and as the stability parameter z/L increases (where z is the observational height, and L is the Monin Obukhov length), horizontal transportation becomes dominant under near-neutral, neutral, and stable conditions. The non-dimensional temperature and humidity variances are 20% less than the temperature and humidity gradient variances. These deficits appear to increase as the absolute stability parameter increases. Moreover, the effects of turbulence transportation and pressure variance exist throughout the entire stability region. 相似文献
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本文基于海陆风环流的形成机制,在研究分析海陆风环流形成的物理模型基础上,建立了海陆风环流的数学模型。根据此基础,以大连地区海陆风环流为计算实例,模拟了海陆风形成的压力场、速度场、温度场和湍流动能场的日变化及太阳辐射日变化的过程地面的能量变化及导致的湍流动能的变化,预测出海陆风环流的水平湍流扩散系数和动量、温度和湍流动能的垂直湍流扩散系数,为求解海陆风中的污染物扩散浓度以进行环境污染损失评价提供参考。应用此模型,对大连地区的海陆风环流进行了数值模拟,定性与定量地给出了海陆风场中的速度、压力、温度及湍流动能分布情况和主要参数值。结果表明,海陆风环流的大气压力场局地日变化较小,温度场变化较明显。在中午前后,动量、温度和湍流动能的垂直扩散系数达到了最大值。模拟结果与其他文献模拟结果的对比表明,本文建立的模型模拟与实验的结果相符,但预测精度仍需要进一步检验。 相似文献
5.
Ultrasonic wind measurements, sonic temperature and air temperature data at two heights in the advection experiment MORE II
were used to establish a complete budget of sensible heat including vertical advection, horizontal advection and horizontal
turbulent flux divergence. MORE II took place at the long-term Carbo-Europe IP site in Tharandt, Germany. During the growing
period of 2003 three additional towers were established to measure all relevant parameters for an estimation of advective
fluxes, primarily of CO2. Additionally, in relation to other advection experiments, a calculation of the horizontal turbulent flux divergence is proposed
and the relation of this flux to atmospheric stability and friction velocity is discussed. In order to obtain a complete budget,
different scaling heights for horizontal advection and horizontal turbulent flux divergence are tested. It is shown that neglecting
advective fluxes may lead to incorrect results. If advective fluxes are taken into account, the sensible heat budget based
upon vertical turbulent flux and storage change only, is reduced by approximately 30%. Additional consideration of horizontal
turbulent flux divergence would in turn add 5–10% to this sum (i.e., the sum of vertical turbulent flux plus storage change
plus horizontal and vertical advection). In comparison with available energy horizontal advection is important at night whilst
horizontal turbulent flux divergence is rather insignificant. Obviously, advective fluxes typically improve poor nighttime
energy budget closure and might change ecosystem respiration fluxes considerably. 相似文献
6.
While the importance of baroclinicity in determining the structure of the planetary boundary layer (PBL) is well recognized, the actual effect of baroclinicity on the structure is not well understood. Results based on simulations obtained using the turbulent kinetic energy-dissipation rate of turbulent kinetic energy closure model of the turbulent flow in a neutral baroclinic PBL provide additional insight into the role of baroclinicity. The baroclinic PBL is characterized by significant shear production of turbulent kinetic energy throughout the complete boundary-layer depth. The turbulent mixing length is bounded by the presence of a stable temperature inversion layer indicating that the depth of the baroclinic PBL is determined by the inversion height. Significant turbulent shear stresses exist throughout the baroclinic PBL and the air is relatively well-mixed except in the surface layer. 相似文献
7.
Boundedness of Turbulent Temperature Probability Distributions,and their Relation to the Vertical Profile in the Convective Boundary Layer 总被引：3，自引：3，他引：0
Alexander Graf Dirk Schüttemeyer Heiner Geiß Axel Knaps Michael Möllmann-Coers Jan H. Schween Stefan Kollet Bruno Neininger Michael Herbst Harry Vereecken 《Boundary-Layer Meteorology》2010,134(3):459-486
Higher-order moments, minima and maxima of turbulent temperature and water vapour mixing ratio probability density functions
measured with an eddy-covariance system near the ground were related to each other and to vertical boundary-layer profiles
of the same scalars obtained through airborne soundings. The dependence of kurtosis on squared skewness showed a kurtosis
intercept below the Gaussian expectation, suggesting a compression of the probability density function by the presence of
natural boundaries. This hypothesis was corroborated by comparing actual minima and maxima of turbulent fluctuations to estimates
obtained from the first four sample moments by fitting a four-parameter beta distribution. The most sharply defined boundaries
were found for the minima of temperature datasets during the day, indicating that negative temperature fluctuations at the
sensor are limited by the availability of lower temperatures in the boundary layer. By comparison to vertical profiles, it
could be verified that the turbulent minimum of temperature near the ground is close to the minimum of potential temperature
in the boundary layer. The turbulent minimum of water vapour mixing ratio was found to be equal to the mixing ratio at a height
above the minimum of the temperature profile. This height roughly agrees with the top of the non-local unstable domain according
to bulk Richardson number profiles. We conclude that turbulence statistics measured near the surface cannot be solely explained
by local effects, but contain information about the whole boundary layer including the entrainment zone. 相似文献
8.
2010年春季北京地区强沙尘暴过程的微气象学特征 总被引：3，自引：1，他引：2
利用北京大学校园地区PM10质量浓度观测资料、中国科学院大气物理研究所325m气象塔气象要素梯度和湍流观测资料,分析了北京地区2010年3月20～22日两次强沙尘暴过程微气象学要素和沙尘参量的时空演变以及湍流输送特征,为理解北京地区强沙尘暴天气沙尘输送规律和微气象学特征提供参考。结果表明:3月20～22日强沙尘暴过程前后不同高度温度先升后降,气压和相对湿度则相反。强沙尘暴来临时,高层风速先迅速增大,低层风速增加略有滞后,风切变明显加强,PM10浓度最大值和风速极大值出现时间较吻合。强沙尘暴过境时,不同高度向下的湍流动量输送、向上的湍流热量输送和湍流动能明显加强。与3月21日非沙尘暴日相比,强沙尘暴过程湍流动量通量增加,有利于沙尘粒子的水平和垂直输送过程;由于冷锋过境,水平热通量增大;垂直热通量因白天温度垂直梯度减小而减小,夜间因逆温层被破坏而增加;水平湍流动能对湍流动能占主要贡献,垂直湍流动能仅占水平湍流动能的10%～25%。 相似文献
9.
Lech Łobocki 《Boundary-Layer Meteorology》2017,164(3):353-365
Analysis of second-moment budget equations in a slope-oriented coordinate frame exhibits the pathways of exchange between the potential energy of mean flow and the total turbulent mechanical energy. It is shown that this process is controlled by the inclination of the potential temperature gradient. Hence, this parameter should be considered in studies of turbulence in slope flows as well as the slope inclination. The concept of turbulent potential energy is generalized to include baroclinicity, and is used to explain the role of along-slope turbulent heat flux in energy conversions. A generalization of static stability criteria for baroclinic conditions is also proposed. In addition, the presence of feedback between the turbulent heat flux and the temperature variance in stably-stratified flows is identified, which implies the existence of oscillatory modes characterized by the Brunt–Väisäla frequency. 相似文献
10.
If no correction is performed, the inertia of the sensors for temperature and humidity in research aircraft leads to an error in the calculation of turbulent fluxes. Simple considerations give an estimation of the order of magnitude of these errors. A simple method for the in-situ estimation of temperature sensor inertia is given. 相似文献
11.
Turbulence data from the planetary boundary layer (PBL) indicate the presence of deterministic turbulent structures. These structures often show up as asymmetric ramp patterns in measurements of the turbulent fluctuations of a scalar quantity in the atmospheric surface layer (ASL). The sign of the slope of the sharp upstream edge of such a triangular pattern depends on the thermal stability conditions of the ASL.The turbulent structures in the ASL have been tracked by a detection method which searches for rapid and strong fluctuations in a signal — the VITA (variable interval time averaging) technique. This detection method has previously been employed in laboratory boundary layers. The VITA detection method performs well in the ASL and reveals the presence of vertically coherent turbulent structures, which look similar to those in laboratory shear flows. At the moment that a sharp temperature interface appears, the horizontal alongwind velocity shows a sharp increase, along with a sudden decrease of vertical velocity, independent of the thermal stability conditions of the ASL. The fluctuating static pressure reveals a maximum at that moment. The vertical turbulent transports show a twin-peak character around the time that the sharp jumps in the temperature and the velocity signals appear. 相似文献
12.
An analysis is made of the effect of spatial separation of a pair of parallel temperature sensors on the variance and spectrum of spatial temperature derivatives in a turbulent flow. The results of the analysis are compared with experimental results obtained when the separation between the sensors is in a direction either perpendicular or parallel to that of the main stream. 相似文献
13.
Stanton numbers, mean temperature profiles, and turbulent heat flux profiles are presented for thermal boundary layers which develop over a uniformly rough surface downstream of steps in wall temperature. Artificially thickened hydrodynamic layers were employed in order to create large unheated starting lengths compared to boundary-layer thickness, where the unheated starting length is the distance between the temperature step and hydrodynamic boundary-layer origin. Kernel functions for Stanton number distributions with downstream distance are presented which agree with measurements even when the hydrodynamic layers are significantly thicker than thermal layers. Other effects of unheated starting lengths on rough-wall thermal boundary-layer behavior are described, including significant alterations in profiles of mean temperature and turbulent heat flux. Both change shape as the magnitude of the unheated starting length increases, even though logarithmic regions of temperature profiles in wall coordinates and turbulent Prandtl number distributions are largely unaffected by unheated starting-length effects. 相似文献
14.
本文利用1986年夏季青藏高原试验（TIPMEX-86）期间获取的资料，计算分析了该年6月和7月拉萨和那曲近地层摩擦速度u*、特征温度θ*、Monin-Obukhov长度L及理查逊数Ri在不同大气层结及不同高度的分布特征。分析结果表明:不同大气层结下，湍流运动形式是不同的，湍流热力场的变化远远大于湍流动力场。就空间变化而言，θ*随高度变化较大，而u*的变化较小。对大气层结而言，在稳定条件下，u*、θ*随高度变化较大；在不稳定条件下，θ*、u*随高度变化较小。在不稳定层结相近的状况下，高原开阔草地上的各种湍流参数，接近或大于北京城郊非均匀地形的数值，而在很稳定的层结下，则高原的参数值小于北京。 相似文献
15.
Interaction between sensible heat and water vapor diffusion in the lower atmosphere leads to the necessity of solving two simultaneous turbulent diffusion equations. This solution is obtained by the construction of Green's function which when incorporated in the boundary conditions produces two integral equations. These are solved by transformation into two algebraic equations by means of the Laplace Transformation. The results show how for a simple steady-state case, sensible heat and water vapor transfer and also the water surface temperature depend on the meteorological conditions and the rate of change of energy content of the water body. Due to advection, the water surface temperature and the turbulent fluxes vary in the downwind direction. However, for practical calculations of the mean evaporation or heat transfer, the error introduced by the use of an average temperature is usually quite small and negligible. 相似文献
16.
建立了一个农林复合带地区一维非静力大气边界层能量闭合模式，对1000m以下的大气边界层内的风、温、湿作了24h的预报，并对下垫面3种不同参数化方案(农作物、森林、无植被)的输出结果与实测值进行了分析和比较；同时通过敏感性试验，突出比较了农作物和森林下垫面对大气边界层垂直流场，湍流垂直交换和湍能的影响。结果表明，本模式能改善边界层风速、位温和湿度预报的模拟效果，下垫面植被对边界层气象要素大小和分布有显著的作用，对湍能垂直分布有一定影响。 相似文献
17.
Miao Manqian 《Boundary-Layer Meteorology》1987,41(1-4):41-56
A two-dimensional primitive equation model has been used to describe the changes of the fields of horizontal wind, temperature and vertical eddy exchange coefficient and the development and evolution of urban heat island circulation for the thermal and dynamical effects of urbanlization, while the air flows over a city in the nighttime. Because the turbulence and average fluid are in a condition of unbalance to each other, the turbulent energy varies with time. So the equations are closed by introducing the equation of the variable rate of turbulent energy in the model. We are able to obtain the distribution and change of the turbulent energy over the urban area in this way. Finally we examine the effect of urbanization by using the differences of the actual ground pollutant concentration and the vertical distribution of concentration emitted by an elevated pollutant source.In order to verify this model, the profiles of horizontal velocity and temperature that are predicted by this model are compared with observed data for Changzhou city. 相似文献
18.
沙尘暴垂直输运的两相流理论Ⅱ：气柱挟卷模式 总被引：1，自引：1，他引：0
为了改进气块法对沙尘沉降问题的研究,文中利用气柱法,考虑沙尘气体与环境的交换作用以及气柱内湍流交换作用.计算结果表明,均匀场中有利于沉降的条件为较大的初始沙尘浓度扰动与较小的初始温度扰动,而且温度扩散系数越大越有利于沙尘沉降,沙尘浓度扩散系数越大越不利于沙尘沉降,湍流过程在均匀场中对沙尘沉降影响不大.考虑剑更真实的环境场,得出在环境的垂直沙尘浓度梯度与温度梯度的参数域中,初始沙尘扰动越大越有利于沙尘沉降,初始温度扰动越大,越小利于沙尘沉降.同时给出4种不利于沙尘沉降的过程:(1)上升浓度变化过程;(2)下沉浓度变化过程;(3)上升温度变化过程;(4)下沉温度变化过程.根据这些过程分析参数对沙尘沉降的影响得到:温度扩散系数越大越有利沙尘沉降;沙尘浓度扩散系数越大不利十沙尘沉降;垂直温度湍流交换系数越大有利于缓降区甚至是非沉降区的上升;垂直沙尘浓度湍流交换系数越大越有利于沙尘沉降. 相似文献
19.
WRF模式中QNSE方案的湍流长度尺度系数的调整试验研究 总被引：2，自引：0，他引：2
边界层参数化方案中湍流混合对数值模拟起着重要的作用,湍流混合作用的恰当描述对于温度、湿度、风场以及降水的准确模拟至关重要。我国长江中下游流域人口密集,暴雨灾害频发,很有必要寻找一种适合该地区降水模拟的边界层参数化方案。本文运用WRF（Weather Research and Forecasting）中尺度数值模式,以QNSE（Quasi-Normal Scale Elimination）边界层参数化方案为基础,将其中湍流混合长度尺度系数调整为可变参数。本文将Noh et al.（2003） 提出的Prandtl公式与Janji?提出的修正湍流长度尺度系数的方法相结合,通过考虑非局地项的强迫、地表稳定度与边界层高度对湍流长度尺度系数的影响,强调大气的动力结构特征与热力结构特征对湍流混合的共同影响,从而提高QNSE边界层参数化方案在不同地理环境下的模拟能力。文章通过进行长江中下游地区的典型暴雨试验,将调整参数后的QNSE方案与原方案进行比较,重点分析调整参数后的方案与原方案对关键基本气象要素场、边界层结构特征以及降水的模拟能力,并将模拟结果与观测结果进行对比,结果表明:调整参数后的方案一定程度上改进了地表温度、边界层结构以及降水的模拟效果。进一步研究表明,调整参数后的方案主要通过改变边界层混合缓解水汽混合比、位温模拟方面的误差。 相似文献
20.
沙漠地区沙尘天气近地层湍流输送特征分析 总被引：12，自引：3，他引：12
利用1996－04－20－50－10在内蒙古自治区吉兰泰气象站以及1997－04－05－27在内蒙古自治区阿拉善右旗气象站观测到的风，温，湿廓线资料，应用空气动力学方法，计算了每天各观测时次的流动量通量，湍流感热通量和湍流潜热通量，并且比较分析了荒漠下垫面不同沙尘天气状况下的湍流动量通量，感热通量和潜热通量的日变化。结果表明，在沙漠地区春季无降水天气状况下，晴空条件下，白天热力湍流基于动力湍流，在近地层最重要的物质交换是湍流感热交换，浮尘天气条件下，近地层湍流输送较晴空天气条件下弱；扬沙天气条件下，近地层湍流感热交换和湍流动力量流感热通量的峰值大于交换，并且湍流动量通量的峰值较晴空峰值大将近一个量级，湍流感热通量的峰值大于浮尘天气峰值，但小于晴空条件下峰值，沙尘暴天气条件下，湍流动量通量和感热通量一样都是最重要的湍流交换，湍流交换强于扬沙天气，强的感热对沙漠地局地性沙尘暴的产生和加强起着重要作用。 相似文献