共查询到20条相似文献，搜索用时 171 毫秒
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对流边界层中粒子随机扩散模式和高斯模式的比较 总被引：1，自引：1，他引：1
用粒子随机扩散模式和高斯模式模拟的对应３种源高的横风向各分浓度的结果与水槽试验的结果进行比较,发现粒子随机扩散模式能较好地模拟出水槽试验结果,说明该模式能用来模拟对流边界层的扩散,而高斯模式不能完全反映对流边界层的扩散。比较两种模式的模拟结果,发现粒子随机扩散模式由于考虑了对流边界中由卷流和热泡引起的垂直方向上湍流的非均一性,比高斯模式能较好的模拟出污染物在垂直方向上充分混合较快、水平方向上扩散范 相似文献
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对流边界层大涡模式的改进及对夹卷速度的研究 总被引：9，自引：0，他引：9
对已建的对流边界层(CBL)大涡模式进行了改进，将次网格闭合方案改为次网格能量闭合，并考虑了水汽的源汇项和水汽相变潜热的作用。通过对均匀下垫面上由热扰动发展的对流边界层的模拟及与实验结果的比较表明，模式较好地模拟了对流边界层的主要物理结构，较好地反映了各物理量之间的对应关系。本文在一定的对流理查森数(Ri*)范围内给出了一些算例，对无量纲夹卷速度(We/W*)进行了研究。结果表明，无量纲夹卷速度随地表热通量(Qs)的增大而增大，随对流边界层上部温度递减率（γ)的增大而减小。当9.06≤Ri*≤45.29时，无量纲夹卷速度We/W*可以拟合成A(Ri*)-1的形式，其中A=0.226。并且与我们的对流槽实验结果，Sullivan等人的大涡模拟结果以及Deardorff等人的对流槽实验结果作了比较，四者吻合较好。 相似文献
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本文建立了二阶矩闭合的大气边界层数值模式,并模拟了Wangara资料第33天09:00—18:00时对流边界层的发展过程。计算结果与实测资料比较吻合,同时利用该模式研究了高阶矩模式模拟对流边界层的可行性,结果指出:二阶矩方程中的湍流扩散项对模拟对流边界层内的挟卷和反梯度现象起主要作用。而局地时间变化项仅影响对流边界层内的边界湍流扩散项。因此,假如处理好二阶矩方程中的湍流扩散项,高阶矩模式和大涡模式一样可以很好地模拟对流边界层的发生、发展。 相似文献
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边界层对流对示踪物抬升和传输影响的大涡模拟研究 总被引：3，自引：1，他引：2
利用"西北干旱区陆气相互作用野外观测实验"加密观测期间敦煌站的实测资料以及大涡模式, 通过一系列改变地表热通量和风切变的敏感性数值试验, 分析了地表热通量和风切变对边界层对流的强度、形式, 以及对对流边界层结构和发展的影响。模拟结果显示风切变一定, 增大地表热通量时, 由于近地层湍流运动增强, 向上输送的热量也较多, 使对流边界层变暖增厚, 而且边界层对流的强度明显增强, 对流泡发展的高度也较高。当地表热通量一定, 增大风切变时, 由于风切变使夹卷作用增强, 将逆温层中的暖空气向下卷入混合层中, 使对流边界层增暖增厚, 但是对流泡容易破碎, 对流的强度也较弱。另外通过在模式近地层释放绝对浓度为100的被动示踪物方法, 用最小二乘法定量地分析了地表热通量和风切变分别与示踪物抬升效率和传输高度的关系。分析结果表明, 风切变小于10.5×10-3 s-1时, 增大地表热通量加强了上层动量的下传, 使示踪物的抬升效率也线性增大;地表热通量小于462.5 W m-2时, 增大风切变减弱了边界层对流的强度, 从而使示踪物的抬升效率减弱。当风切变一定时, 示踪物的平均传输高度随地表热通量增加而增大, 而地表热通量一定, 只有风切变大于临界值时, 示踪物平均传输高度才随风切变的增加而增大, 而临界风速的大小由地表热通量决定。 相似文献
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用大涡模式研究对流边界层湍流 总被引：1，自引：0，他引：1
利用三维对流边界层的大涡模拟模式研究对流边界层湍流统计特征量,模拟结果与前人的同类模拟工作及实验观测结果相比较,得到了一致的结论.
相似文献
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大涡模式水平分辨率对边界层夹卷过程及示踪物垂直传输的影响 总被引：1，自引：0，他引：1
利用敦煌干旱区野外加密观测资料,结合大涡模式模拟研究模式水平分辨率对边界层对流、夹卷过程及示踪物垂直传输的影响。结果表明:模式水平分辨率越高,模拟的边界层对流泡个数越多,尺度越小,且对流强度越强;提高模式水平分辨率,夹卷层位温方差增大,水平速度方差减小,垂直速度方差增大,且上升冷气流对夹卷层热通量的贡献最大。模式水平分辨率越高,垂直速度、位温及示踪物绝对质量浓度概率密度函数分布变化范围相对越广,且模拟的细微变化特征越清晰。另外,提高模式水平分辨率,模拟的示踪物空间分布特征更加细致,示踪物传输高度也较高。综合考虑到分辨率越高在模拟过程中产生的噪音越大且计算时间越久等问题,认为采用200 m水平分辨率时,模式既能较好地模拟出边界层对流的平均结构,又能模拟出边界层湍流的较细微分布特征,是较为理想的选择。 相似文献
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本文建立了一个大气对流边界层模式,构造此模式时,假设对流边界层中水平动量和热量在垂直方向上的湍流输送、扩散是由大涡与小涡组成的系统完成的。文中,用此模式作了一实例模拟,计算结果表明:模拟的结果与实测的结果相当一致。 相似文献
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In this paper, taking its turbulent exchange coefficient as a function of the Lagrangian timescale and standard variance of the turbulence in atmosphere, the atmospheric dispersion PDFmodels are obtained on the basis of atmospheric diffusion K-theory. In the model the statistics ofwind speed are directly used as its parameters instead of classic dispersion parameters. The bi-Gaussian PDF is derived in convective boundary layer (CBL), from the statistics of verticalvelocity in both of the downdraft and updraft regions that are investigated theoretically in the otherpart of this paper. Giving the driven parameters of the CBL (including the convective velocity scalew* and the mixing depth h_i) and the time-averaged wind speed at release level, the PDF model isable to simulate the distribution of concentration released at any levels in the CBL. The PDF'ssimulations are fairly consistent with the measurements in CONDORS experiment or the resultsbrought out by some numerical simulations. 相似文献
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实验速度场测量技术及对流边界层特征研究 总被引：3，自引：0，他引：3
在对流槽中对对流边界层(CBL)温度场实验研究的基础上,进一步尝试通过实验技术测量速度场并分析研究CBL中的速度场特征。在应用PIV测量技术时选用铝粉作示踪粒子。实验证明了在混合层中速度分布明显具有对流边界层热泡特性;混合层顶部的速度分布很好地反应出夹卷层的结构特征;湍流速度特征量的垂直分布合理,与野外实测结果和类似的对流槽实验结果接近;误差分析表明示踪粒子的跟随性良好,粒子速度的测量结果能真实地反应流体的运动特征,从而得证了分析结果的可靠性。 相似文献
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Frank Beyrich 《Boundary-Layer Meteorology》1995,74(1-2):1-18
Sodar has been used for about 20 years to determine mixing height. However, estimation of the height of a convective boundary layer (CBL) that exceeds the sodar-probing range is still an unsolved question. As one possible way, it is suggested that one adapt a simple mixed-layer model to sodar observations during the morning growth period of the CBL, when its top can be clearly detected. Results are compared with other methods for CBL-height estimation from sodar data that have been proposed in the literature. Finally, some prognostic aspects are discussed. 相似文献
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Parameterization of Entrainment in a Sheared Convective Boundary Layer Using a First-order Jump Model 总被引：1，自引：0，他引：1
Si-Wan Kim Soon-Ung Park David Pino Jordi Vilà-Guerau de Arellano 《Boundary-Layer Meteorology》2006,120(3):455-475
Basic entrainment equations applicable to the sheared convective boundary layer (CBL) are derived by assuming an inversion layer with a finite depth, i.e., the first-order jump model. Large-eddy simulation data are used to determine the constants involved in the parameterizations of the entrainment equations. Based on the integrated turbulent kinetic energy budget from surface to the top of the CBL, the resulting entrainment heat flux normalized by surface heat flux is a function of the inversion layer depth, the velocity jumps across the inversion layer, the friction velocity, and the convection velocity. The developed first-order jump model is tested against large-eddy simulation data of two independent cases with different inversion strengths. In both cases, the model reproduces quite reasonably the evolution of the CBL height, virtual potential temperature, and velocity components in the mixed layer and in the inversion layer.The part of this work was done when the first author visited at NCAR. 相似文献
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A laboratory study of the turbulent velocity characteristics in the convective boundary layer 总被引：4，自引：0，他引：4
Based on the measurement of the velocity field in the convective boundary layer （CBL） in a convection water tank with the particle image velocimetry （PIV） technique, this paper studies the characteristics of the CBL turbulent velocity in a modified convection tank. The experiment results show that the velocity distribution in the mixed layer clearly possesses the characteristics of the CBL thermals, and the turbulent eddies can be seen obviously. The comparison of the vertical distribution of the turbulent velocity variables indicates that the modeling in the new tank is better than in the old one. The experiment data show that the thermal＇s motion in the entrainment zone sometimes fluctuates obviously due to the intermittence of turbulence. Analyses show that this fluctuation can influence the agreement of the measurement data with the parameterization scheme, in which the convective Richardson number is used to characterize the entrainment zone depth. The normalized square velocity wi^2/w＊^2. at the top of the mixed layer seems to be time-dependent, and has a decreasing trend during the experiments. This implies that the vertical turbulent velocity at the top of the mixed layer may not be proportional to the convective velocity （w＊）. 相似文献
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Development of the Convective Boundary Layer Capping with a Thick Neutral Layer in Badanjilin: Observations and Simulations 总被引：1，自引：0，他引：1
In this study,the development of a convective boundary layer (CBL) in the Badanjilin region was investigated by comparing the observation data of two cases.A deep neutral layer capped a CBL that occurred on 30 August 2009.This case was divided into five sublayers from the surface to higher atmospheric elevations:surface layer,mixed layer,inversion layer,neutral layer,and sub-inversion layer.The development process of the CBL was divided into three stages:S1,S2,and S3.This case was quite different from the development of the three-layer CBL observed on 31 August 2009 because the mixed layer of the five-layer CBL (CBL5) eroded the neutral layer during S2.The specific initial structure of the CBL5 was correlated to the synoptic background of atmosphere during nighttime.The three-stage development process of the CBL5 was confirmed by six simulations using National Center for Atmospheric Research (USA) large-eddy simulation (NCAR-LES),and some of its characteristics are presented in detail. 相似文献
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We present a Lagrangian stochastic model of vertical dispersion in the convective boundary layer (CBL). This model is based on a generalized Langevin equation that uses the simplifying assumption that the skewed vertical velocity probability distribution is spatially homogeneous. This approach has been shown to account for two key properties of CBL turbulence associated with large-scale coherent turbulent structures: skewed vertical velocity distributions and long velocity correlation time. A 'linear-skewed' form of the generalized Langevin equation is used, which has a linear (in velocity) deterministic acceleration and a skewed random acceleration. 'Reflection' boundary conditions for selecting a new velocity for a particle that encounters a boundary were investigated, including alternatives to the standard assumption that the magnitudes of the particle incident and reflected velocities are positively correlated. Model simulations were tested using cases for which exact, analytic statistical properties of particle velocity and position are known, i.e., well-mixed spatial and velocity distributions. Simulations of laboratory experiments of CBL dispersion show that (1) the homogeneous linear-skewed Langevin equation model (as well as an alternative 'nonlinear-Gaussian' Langevin equation model) can simulate the important aspects of dispersion in the CBL, and (2) a negatively-correlated-speed reflection boundary condition simulates the observed dispersion of material near the surface in the CBL significantly better than alternative reflection boundary conditions. The homogeneous linear-skewed Langevin equation model has the advantage that it is computationally more efficient than the homogeneous nonlinear-Gaussian Langevin equation model, and considerably more efficient than inhomogeneous Langevin equation models. 相似文献
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大气对流边界层中的涡漩结构 总被引：4，自引：1，他引：4
大气边界层中存在尺度从几百米到几十公里的大涡漩运动。它们在边界层中动量、热量、水汽等垂直输送中起重要作用。作者从边界层中对流和上部稳定层中波动相互作用的观点，发展得出大涡结构的对流波动理论。根据此理论，大涡的波谱构成主要由上、下层大气中风向、风速、层结以及两层之间的温度跃变等因素决定。本文根据卫星云图和天气资料分析了一次冷空气爆发流经暖洋面上形成云街、对流单体以及它们之间的相互演化的过程，并用对流波动理论，依据各阶段的大气条件计算出它们的波数构成，并得出了垂直速度、辐合带、界面扰动的分布，解释了云街、对流单体的形成、结构及相互转化的原因 相似文献
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Large vortices with scales ranging from hundreds meters to tens of kilometers are generallyfound in the atmospheric convective boundary layer(CBL).These vortices play important roles in the vertical transport of momentum,heat,water vaporand other tracers in the boundary layer.On the basis of the view of interaction between theconvection in CBL and the gravity waves in the upper stable layer the authors developed aconvection-wave theory on the formation of large vortices.According to the theory thewavenumber spectrum of the large vortices mainly depends on the atmospheric conditions in bothof the upper and lower layers,such as wind speed,wind direction shear,stratification as well astemperature jump.In the present paper satellite image and weather data in a case of cold air outbreak over warmocean are analyzed to study every stage of the convective processes,such as cloud street,convective cell as well as their transformation.According to the theory the wavenumbercompositions for cloud street and convective cell are calculated,respectively,on the basis of theatmospheric conditions at every stage.The distributions of vertical motions,convergent band anddisturbed interface are obtained and compared with the cloud patterns in the convective processes.Thus the study seems to offer a likely explanation for the origin of large vortices in CBL. 相似文献