非均匀网格的过渡湍流理论及其在大气边界层数值模拟中的应用

本文将Stull提出的均匀网格下的过渡湍流理论推广到非均匀网格情形，推广的非均匀网格的过渡湍流理论满足Stull提出的对过渡矩阵系数的要求并具有清晰的物理意义。然后，将非均匀网格的过渡湍流理论应用于一维大气边界层数值模式中，对Wangara资料进行了模拟，并与均匀网格情形进行了对比。计算表明，非均匀网格的过渡湍流模式能很好地模拟Wangara大气边界层平均量与湍流量的变化；本文非均匀网格的过渡湍流理论的推广是可行的，它可能会在大气边界层数值模拟及其他方面（如：中尺度模式）得到应用。     

A One-Dimensional Finite-Element Boundary-Layer Model with a Vertical Adaptive Grid

A one-dimensional atmospheric boundary-layer model is developed using the finite element method and a 1.5-order e-l turbulence closure scheme. A vertical adaptive strategy is implemented, based upon an heuristic error estimator that depends upon properties of the layer, such as the stratification. The model is used to simulate a moderately stratified stable boundary layer as described in the GABLS (GEWEX Atmospheric Boundary-Layer Study, where GEWEX is the Global Water and Energy Cycle Experiment) First Intercomparison Project, and then a more complicated diurnal cycle, as used in the GABLS Second Intercomparison Project. In the stable boundary-layer experiment, it is shown that including the adaptive strategy can improve the performance of the model such that the error in the model is significantly less (greater than an order of magnitude with an effective resolution of 8 m) than that of the model without adaptivity. The model’s turbulence closure scheme and the adaptivity strategy also successfully simulate the different stability regimes present in the diurnal cycle simulation, and represented all of the expected features.     

深凹地形边界层风场与湍流场结构及扩散规律的数值研究

建立了一个模拟小尺度复杂地形边界层平均流场和湍流场结构分布特征的三维非静力细网格高阶矩湍流闭合模式,并将此模式与一个拉格朗日粒子随机游动大气扩散数值模式相联结,以边界层气象模式的输出作为扩散模式的输入,构成了一个大气扩和模拟系统,成功地模拟了某地实际深凹露天矿区和理想凹坑地形两种情况下的平均流场、雷诺应力和湍流通量场,分析了其分布特征,并模拟了矿坑内污染物的散布规律     

边界层参数化方案对陆气相互作用影响的模拟研究

利用湍流动能闭合方法对区域气候模式RegCM3中的边界层参数化方案进行了改进,然后利用中国东部典型旱、涝年资料进行了改进效果对比试验,并着重分析了边界层参数化方案改进对陆气相互作用的影响,结果表明:采用湍流动能闭合方法可以更合理的描述边界层的高度及其日变化,较为真实地描述边界层的物理过程,使得陆—气间通量及大气各层垂直...     

Eddy exchange coefficients in numerical models of the planetary boundary layer

Specification of the eddy exchange coefficients is perhaps one of the most difficult problems in the numerical modeling of the planetary boundary layer. These coefficients have been computed from finite-difference analogs to analytical expressions associated with surface boundary-layer similarity theory, which is based on observations in an equilibrium surface layer. This procedure leads to erroneous results in the region above the surface layer and in a non-equilibrium surface layer. In addition, differencing problems arise in regions of small vertical wind shear. A new turbulence transport model has been obtained through the closure procedures for the transport equations of the Reynolds stress and the turbulent length scale. The new approach could be used to calculate Reynolds stresses and eddy exchange coefficients throughout a non-neutral planetary boundary layer under non-equilibrium conditions.     

Application of a Large-Eddy Simulation Database to Optimisation of First-Order Closures for Neutral and Stably Stratified Boundary Layers

Large-eddy simulation (LES) is a well-established numerical technique, resolving the most energetic turbulent fluctuations in the planetary boundary layer. By averaging these fluctuations, high-quality profiles of mean quantities and turbulence statistics can be obtained in experiments with well-defined initial and boundary conditions. Hence, LES data can be beneficial for assessment and optimisation of turbulence closure schemes. A database of 80 LES runs (DATABASE64) for neutral and stably stratified planetary boundary layers (PBLs) is applied in this study to optimize first-order turbulence closure (FOC). Approximations for the mixing length scale and stability correction functions have been made to minimise a relative root-mean-square error over the entire database. New stability functions have correct asymptotes describing regimes of strong and weak mixing found in theoretical approaches, atmospheric observations and LES. The correct asymptotes exclude the need for a critical Richardson number in the FOC formulation. Further, we analysed the FOC quality as functions of the integral PBL stability and the vertical model resolution. We show that the FOC is never perfect because the turbulence in the upper half of the PBL is not generated by the local vertical gradients. Accordingly, the parameterised and LES-based fluxes decorrelate in the upper PBL. With this imperfection in mind, we show that there is no systematic quality deterioration of the FOC in the strongly stable PBL provided that the vertical model resolution is better than 10 levels within the PBL. In agreement with previous studies, we found that the quality improves slowly with the vertical resolution refinement, though it is generally wise not to overstretch the mesh in the lowest 500 m of the atmosphere where the observed, simulated and theoretically predicted stably stratified PBL is mostly located. The submission to a special issue of the “Boundary-Layer Meteorology” devoted to the NATO advanced research workshop “Atmospheric Boundary Layers: Modelling and Applications for Environmental Security”.     

南沙海域近海层大气湍流结构及输送特征研究

本文根据南沙群岛渚碧礁的一次大气湍流观测资料，分析研究南沙海域的湍流热通量输送、方差相似性、风速各分量谱、温度谱及各湍流通量协谱等大气湍流结构和输送特征，并与陆地下垫面上的结果作了比较，得到了一些有关南沙海域大气湍流输送及湍流结构的新认识。     

梅雨涡旋与环境场动能的相互作用

在过渡湍流理论基础上建立二维非局地闭合模式，并用所建模式研究沿海地区中尺度海陆风环流和内国界层结构，得到了合理的平均场和湍流场。     

PBL similarity profiles determined from a level-2 turbulence-closure model

A diagnostic model for the determination of similarity profiles of turbulence and mean-wind gradient in the planetary boundary layer is developed. Vertical profiles of a turbulence length scale and the flux Richardson number are formulated through the extension of the relationships for the constant flux layer. These profiles together with a turbulence energy equation and a similarity profile empirically determined for heat or momentum flux are used to compute the turbulence energy. Relationships previously derived from a turbulence closure model are used to compute second moments of turbulence.     

新疆乌鲁木齐地区冬季层积云研究——数值模拟研究

在分析实测结果的基础上,建立了一个边界层与云物理学的数值模式,模拟了云生成的过程。模式包括了边界层内的湍流混合、大气与地表的长波辐射和太阳短波辐射以及云层的辐射平衡等,同时也包括了水的汽、液、固三相物质在大气中的相互转换即云微物理过程。模拟的云及边界层的主要结构特征和演变趋势与实测情况大致吻合。模拟结果还提供了有关云结构及演变过程的一些详细图象。     

THE STUDY ON THE WINTERTIME STRATOCUMULUS CLOUDS OVER ÜRÜMQI,XINJIANG OF CHINA——NUMERICAL MODELING OF STRATOCUMULUS CLOUDS

On the basis of the conceptual model,the development of wintertime stratocumulus cloud has been simulated by using a planetary boundary layer/cloud physics model.The main characteristics of the cloud structure and evolution obtained from the simulation are consistent with those from observations.By analyzing the modeled results,some details of the cloud structures and microphysics processes are discussed.     

层积云覆盖的边界层数值模拟研究(Ⅰ):数值模式的建立

层积云是一种在湍流作用下形成的边界层云,在这种边界层中,层积云顶即边界层顶,云层和非云层耦合在一起,为了加深对这种层积云覆盖的边界层的理解,许多作者已经做了大量的野外观测和数值试验研究,然而在数值模拟研究中存在湍流和云物理模式相互脱节的现象,针对这种缺陷,本文在湍流控制方程组中引入云滴控制方程,发展了一个新的用于研究海区层积云覆盖的边界层的数值模式,所建模式具有如下特点：（1）实现了云物理模式与湍流模式的相互耦合;（2）实现了云滴分档凝结模式和三阶湍流闭合边界层模式相互耦合,利用所建模式对大涡模拟对比试验所采用的个例进行了数值模拟,数值模拟结果表明,该边界层模式能较合理地模拟海区层积云覆盖的边界层微湍流结构和云微物理过程。     

复杂下垫面模拟域大气边界层非局地闭合模拟研究

在非局地闭合大气边界层模拟研究基础上,选取黑河实验研究资料（HEIFE）,利用二维模式对绿洲和沙漠交界地区的内边界层结构进行了模拟研究,模式考虑了两种下垫面条件下动力、热力特性的不同,并加入了湿度及水汽通量的预报。模拟结果表明:二维非局地闭合模式能得到合理的TIBL结构的基本特征,包括平均场、湍流场等,并能模拟给出一些由下垫面特性形成的大气现象,如沙漠地区逆湿现象的生消过程、绿洲的冷岛效应、绿洲与沙漠因热力差异而形成的局部环流形势等细致结构,符合沙漠站白天观测事实的典型特征。     

不同下垫面的大气边界层湍流扩散特征

利用海洋、戈壁、城郊和城市4种不同下垫面上的湍流观测资料,运用多尺度湍流概念和方法计算分析了风速谱和扩散参数等湍流特征量。结果表明:下垫面的粗糙度对大气边界层湍流特征影响很大,随着粗糙度的增大,速度谱的峰值频率向高频方向移动,扩散参数增大。     

Fronts and the boundary layer – some numerical studies

In this paper, we consider boundary-layer effects on atmospheric fronts. For this purpose we developed a dry, hydrostatic, two-dimensional numerical model with turbulence parameterized with the 1/2 -order eddy viscosity closure of Mellor and Yamada. In the surface layer we use Monin–Obukhov similarity and there is an interactive soil model to obtain lower boundary conditions for the atmospheric model. First, effects of turbulence are studied without thermal forcing at the surface and comparisons are made between inviscid and turbulent conditions. Sensitivity studies with respect to surface roughness are also performed. Subsequently we study effects of surface thermal forcing on fronts. The results show that, during summer, fronts display strong diurnal variation. Vertical velocities increase significantly during the day while gradients in temperature and vorticity across the front strengthen in the evening and at night. In winter the diurnal variation is much less pronounced. We attempt to find physical mechanisms responsible for such frontal behaviour and we compare our results with available observations.     

Modelling the mean and turbulent structure of the summertime Arctic cloudy boundary layer

This paper addresses the problem of modelling the summertime Arctic cloudy boundary layer. Specifically we consider the problem of multi-layered clouds in the boundary layer that includes the decoupling of the turbulence between upper and lower clouds. A high-resolution one-dimensional model with second-order turbulence closure and spectral radiative transfer is used to simulate a case study that was obtained during the 1980 Arctic Stratus Experiment. The effects of radiation, large-scale vertical motion and drizzle are investigated in sensitivity studies. Results of this study show that radiative transfer is important to the maintenance of the multiple cloud layers, and suggest that weak rising vertical motion is the most favorable situation to maintain two separate cloud layers.     

The Adaptation of the Atmospheric Boundary Layer to a Change in Surface Roughness

The adaptation of the atmospheric boundary layer to a change in the underlying surface roughness is an interesting problem and hence much research, theoretical, experimental, and numerical, has been undertaken. Within the atmospheric boundary layer an accurate numerical model for the turbulent properties of the atmospheric boundary layer needs to be implemented if physically realistic results are to be obtained. Here, the adaptation of the atmospheric boundary layer to a change in surface roughness is investigated using a first-order turbulence closure model, a one-and-a-half-order turbulence closure model and a second-order turbulence closure model. Perturbations to the geostrophic wind and the pressure gradients are included and it is shown that the second-order turbulence closure model, namely the standard k - model, is inferior to a lower-order closure model if a modification to limit the turbulent eddy size within the atmospheric boundary layer is not included within the model.     

A Study of the Stable Boundary Layer Based on a Single-Column K-Theory Model

We document numerical experiments with a single-column, high-resolution model of the stable boundary layer. The model resolves the logarithmic layer, and does not require inverting the Monin–Obukhov similarity functions in order to calculate the surface fluxes. The turbulence closure is based on the K-theory approach, with a new form of stability functions of the Richardson number, evaluated by using the Surface Heat Budget of the Arctic Ocean (SHEBA) and the Cooperative Atmosphere-Surface Exchange Study (CASES-99) data. A comparison with two, high-resolution large-eddy simulation models shows very good agreement. The reported numerical experiments test the effects of shear, surface cooling, the Coriolis parameter, subsidence, and baroclinicity. The time evolution of the drag coefficient, the heat-transfer coefficient, and the cross-isobar angle is also evaluated.     

夜间近地面稳定边界层湍流间歇与增温

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。     

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).