山区夜间边界层的数值模拟

本文采用二维数值模式模拟了一个坡地上夜间边界层的发展过程.所得到的结果与1974-1976年在北京北部山区得到的观测资料做了比较.模拟出的夜间辐射逆温层的厚度和形状以及下坡风的廊线都与观测事实大致相符.模式进一步改进后似可做为解决中、小尺度复杂地形上夜间边界层演变的工具.     

夜间边界层的一维数值模拟

本文用一维数值模式,模拟了平坦地形情况下小风、晴空夜间边界层内风、温、湿的演变,计算结果与观测事实有较好的一致性。对有高云或少量中、低云存在时的计算结果分析表明,模式对风速的模拟仍然较好,对温度的模拟比实测值可偏低0.3—1℃,对相对湿度的模拟比实测值可偏高5—10％在符合模式使用范围的情况下,本模式可作为夜间边界层预报的一种方法参考使用。     

高阶矩模式模拟对流边界层的可行性研究

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。     

夜间大气边界层热力因子的数值研究

本文使用了一维非定常热力方程对夜间大气边界层热力结构进行了数值模拟.结果表明:(1)当天气形势变化平稳时,平坦地区夜间边界层热力结构的变化主要受到湍流与辐射传输作用的影响.(2)由于地-气之间热量传输的相互调整作用,使低层湍流变温率与地面温度变率之间表现为有相同周期的变化. 文中通过该模式的计算结果与复杂地形的实验资料的对比,研究了平流作用对温度垂直分布的影响.     

论大气边界层的数值模拟方法

本文采用分层模式和连续模式模拟了一维、稳定的大气边界层中一些主要的气象变量随时间的变化规律,讨论了几种气象条件及下垫面条件下计算结果之间的差异,并且还讨论了常值湍流热通量层存在的条件及其高度随时间的变化,从而给出了两种模式适用的范围.     

夜间城市边界层特征的数值模拟及其应用

用二维非线性的定常模式对城市效应(包括城市热岛之热力作用和城市地面粗糙度增大之动力作用)影响下夜间边界层结构的特征进行了数值模拟,并应用模拟结果计算了城市效应作用下高架源的扩散规律的改变。     

边界层夜间急流的数值试验

为了揭示边界层风温场在日变化过程中的相互联系,展示不同条件下夜间急流形成过程的具体图象,本文应用非定常边界层模式,对四种型式、具有一定代表性的典型初始风场,在不同的温度层结下的日变化过程进行了数值试验,并从边界层动力学角度,剖析了夜间急流形成的物理机制。     

夜间边界层发展的数值研究

本文考虑在水平均匀条件下,利用一维非定常模式研究大气夜间边界层的结构和发展规律。考虑地面的降温率是时间的函数。地转风为常数。 用中性层结条件下的计算值作为时间积分的初值,计算了夜间边界层发展的变化规律。得到了夜间地面冷却条件下逆温层的形成和发展以及低空急流建立的典型图象,最后对几种参数进行了计算、分析和比较。     

A numerical study of second-order turbulent moments in the stably stratified nocturnal boundary layer

The structures and the vertical profiles of turbulent variance and covariance of the stably stratified boundary layer (SBL) are simulated with a second-order closure turbulence model. The results confirm that the vertical profiles of the dimensionless turbulence variance and covariance can be well represented by the form F = A(1 - Z / h)x. Here h is the height of SBL. and both exponent a and coefficient A are the functions of terrain, baroclinicity, radiation cooling and the state of temporal development of SBL. Comparing with Minnesota and Cabauw experiment data, we have analysed the value of a and expounded the main reasons that great difference in a exists among different literatures.     

A model study of the nocturnal boundary layer

In this paper, a second-order model is proposed for the study of the evolution of the nocturnal boundary layer (NBL). The model is tested against the Wangara data on atmospheric boundary layer. The computer results show ihat the model can simulate some important characters observed in the NBL, and that a kind of sudden change may occur in the developing process of NBL.     

夜间城市边界层发展的数值研究

本文使用非定常非线性二维数值模式,研究夜间气流流经城市热岛上空引起的风场、温度场和垂直涡旋扩散参数的调整以及城市热岛环流的发展演变.     

A numerical model study of the structure and similarity scaling of the nocturnal boundary layer (NBL)

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).     

A fine—Mesh numerical model with detailed boundary layer parameterization

A fine-mesh numerical model with thirteen-layer, three-dimensional primitive equation is designed, which has a relatively high vertical resolution in the boundary layer and detailed boundary parameterization. A strong cold frontal process is simulated by the model. Comparison of the simulated results of this process with different models shows that the result of this model is prior to that of others, and that it is necessary to increase the vertical resolution and to take account of the physical processes in the boundary layer.     

A two-dimensional and steady-state numerical model of the planetary boundary layer

In this paper, a two-dimensional and steady-state numerical model of the planetary boundary layer is developed. It includes the horizontal deformation of the eddy exchange coefficients and horizontal turbulence exchange. The difference between the structure of the heat island and cold island is analysed using this model.     

A climatological study of the nocturnal planetary boundary layer

Seventy-five nights of fast-response wind and temperature data taken from a 300 m tower near Augusta, GA, were analyzed to determine the time-height structure of the nocturnal planetary boundary layer. The nights were selected from all four seasons over a wide range of synoptic conditions. Statistical summaries of Pasquill-Gifford stability, boundary-layer depth, nocturnal jet height, directional shear, gravity wave occurrence, and azimuthal meandering were obtained. The diversity of nocturnal conditions for the 75 cases resulted in histograms with broad peaks and slowly-varying distributions.To reduce the overall variance, we grouped the nights into two classes: steady nights and unsteady nights. Nights classified as steady maintained relatively uniform wind conditions. The data base was large enough to permit a further breakdown of the steady nights into three subclasses based on the height and strength of the wind maximum. Unsteady nights were more disturbed, showing time-dependent features in the wind field and were also divided into three subclasses, depending on the predominant features observed: microfrontal passage, trend, or variable conditions. Although the subclasses were based mainly on wind structure, they correlated well with other NPBL properties, such as mixed-layer depth and inversion strength. Thus, the classification procedure tended to group together nights with similar dispersion characteristics.     

Observations in the nocturnal boundary layer

Low-latitude observations of the stably-stratified planetary boundary layer (SBL) above rough terrain are compared to observations of the mid-latitude SBL mainly through the depth h and its dependence upon surface fluxes. This involves the quantity h/L and the similarity prediction h = (u _* L/f)^1/2.Mid-latitude observations are consistent with model calculations for nighttime-averaged quantities and their deviations, as functions of latitude and surface roughness, from the equilibrium values found at large t. The above applies to horizontally-homogeneous terrain.Low-latitude observations of % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGafq4SdCMbae% baaaa!37AB!\[\bar \gamma \] and h/L are significantly smaller than mid-latitude values, apparently the result of katabatic flows at the site and not the differences in latitude. This is consistent with model calculations for non-zero slope terrain.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

Some parameterizations of the nocturnal boundary layer

The evolution and structure of a steady barotropic nocturnal boundary layer are investigated using a higher-order turbulence closure model which includes equations for the mean quantities, turbulence convariances, and the viscous dissipation rate. The results indicate that a quasi-steady nocturnal PBL might be established in 4–10 hours after transition, depending on surface cooling rate. The latter is assumed to be constant in the model. The emphasis is on prediction of eddy viscosity, nocturnal mixing-layer depth, and the stability-dependent universal functions in the geostrophic drag and heat transfer relations. The model predictions are parameterized in the framework of the PBL similarity theory and compared with observations and results of other models.Affiliation with Oak Ridge Associated Universities (ORAU).