双重套网格数值模式对一次暴雨系统模拟的比较试验

本文以自嵌套方式，将一个有限区域暴雨数值模式编制成单向和双向的套网格模式，同时又将这两个套网格模式分别与Ｔ４２Ｌ９模式进行了单向嵌套。形成了单向，双向两个双重套网格模式。运用这两个模式对１９９１年７月江淮流域的一次特大暴雨过程进行了数值试验。     

A comparison of 3D model results with observations for an isolated CCOPE thunderstorm

Summary This paper is concerned with the simulation of deep convection for the CCOPE 19 July 1981 case study. Clark's three-dimensional (3D) cloud model modified to use the bulk water parameterization scheme of Lin et al. has been used in the simulation of the CCOPE 19 July 1981 case in coarse mesh, fine mesh, and interactive grid nested schemes, respectively. Comparisons with observations show this 3D grid nested cloud model is capable of both capturing both the dynamic and microphysical properties of the cloud.In the nested grid fine mesh model simulation, the timing and mode of cloud growth, the diameter of liquid cloud, the cloud top rate of rise, the maximum cloud water content, and the altitude of first radar echo are consistent with observations. The simulated thunderstorm begins to dissipate, after precipitation reaches the ground as indicated by the decreasing values of maximum updraft and maximum liquid cloud water content, and ends as a precipitating anvil as was observed in the actual thunderstorm. The model precipitation developed through ice phase processes consistent with the analysis of observations from the actual thunderstorm.Qualitative comparisons of the actual radar RHIs with simulated reflectively patterns from the 3D model show remarkable similarity, especially after the mature stage is reached. Features of the actual RHI patterns, such as the weak echo region, upshear anvil bulge, strong upwind reflectivity gradients, and the upwind outflow region near the surface are reproduced in the simulation. Comparison of the actual radar PPIs with horizontal cross sections of radar reflectivity simulated by the 3D model, however, show modest differences in the storm size with the 3D simulated thunderstorm being 1–2 km longer in the west-east direction than the actual thunderstorm. The model-predicted maximum updraft speed is smaller than the 2D model-predicted maximum updraft speed, but still greater than what was observed.Comparisons among the nested grid fine mesh model (MB), nested grid coarse mesh model (MA), fine mesh model (FM), coarse mesh model (CM), and 2D model results previously published show that the nested grid fine mesh model (MB) gives the best simulation result. The various 3D model simulation results are generally similar to each other except for the difference in the domain maximum values. The domain maximum values in the fine mesh models (MB and FM) are generally higher than the coarse mesh models as a result of averaging over a smaller area.With 7 Figures     

一种渐变网格方案及其与嵌套网格方案的比较

本文给出了一种渐变网格及其相应的数值积分方案，并利用线性平流方程，分别采用该渐变网格、不等距网格和3种嵌套网格共5种方案进行数值试验。结果表明，在套网格方案中，采用精度较高且截断误差相近的不同格式进行嵌套计算误差较小；而变网格(包括渐变网格和不等距网格)方案既能简化积分过程，又能避免反射波，从而明显地提高了计算精度。     

Present climate simulation over Korea with a regional climate model using a one-way double-nested system

Summary This study investigates the capability of the regional climate model RegCM3 to simulate surface air temperature and precipitation over the Korean Peninsula. The model is run in one-way double nested mode, with a 60 km grid point spacing “mother” domain encompassing the eastern regions of Asia and a 20 km grid point spacing nested domain covering the Korean Peninsula. The simulation spans the three-year period of 1 October 2000 through 30 September 2003 and the boundary conditions needed to run the mother domain experiment are provided from the NCEP reanalysis of observations. The model results are compared with a high density station observation dataset to examine the fine scale structure of the surface climate signal. The model shows a good performance in capturing both the sign and magnitude of the seasonal and inter-annual variations of the surface variables both over East Asia as a whole and over the Korean Peninsula in the nested system. Some persistent biases are however present. Surface temperature is systematically underestimated, especially over mountainous regions in the warm season. This feature may be due to the relatively coarse representation of the Korean topography. The simulated precipitation over the mother domain successfully reproduces the broad spatial pattern of observed precipitation over East Asia along with its seasonal evolution. On the other hand, fine scale details from the nested results show a varying level of quality for the different individual years. Because of the better resolved topographic forcing, the increased resolution of the nested model improves the spatial agreement with the fine scale observation fields for temperature and cold season precipitation. For summer monsoon precipitation the simulation of individual monsoon convective events and tropical storms is however more important than the topographic forcing, and therefore the performance of the nested system is more case-dependent.     

Regional Nested Model Simulations of Present Day and 2 × CO2 Climate over the Central Plains of the U.S.

A nested regional climate model is used to generate a scenario of climate change over the MINK region (Missouri, Iowa, Nebraska, Kansas) due to doubling of carbon dioxide concentration (2 × CO₂) for use in agricultural impact assessment studies. Five-year long present day (control) and 2 × CO₂ simulations are completed at a horizontal grid point spacing of 50 km. Monthly and seasonal precipitation and surface air temperature over the MINK region are reproduced well by the model in the control run, except for an underestimation of both variables during the spring months. The performance of the nested model in the control run is greatly improved compared to a similar experiment performed with a previous version of the nested modeling system by Giorgi et al. (1994). The nested model generally improves the simulation of spatial precipitation patterns compared to the driving general circulation model (GCM), especially during the summer. Seasonal surface warming of 4 to 6 K and seasonal precipitation increases of 6 to 24% are simulated in 2 × CO₂ conditions. The control run temperature biases are smaller than the simulated changes in all seasons, while the precipitation biases are of the same order of magnitude as the simulated changes. Although the large scale patterns of change in the driving GCM and nested RegCM model are similar, significant differences between the models, and substantial spatial variability, occur within the MINK region.     

Modeling heavy precipitation in complex terrain

Summary A numerical prediction model is described which uses the full set of prognostic equations on a domain roughly the size of the United States with a 96 km horizontal grid resolution and six sigma-coordinate levels. Within this grid resides a nested domain of approximately 1000×1000 km with 24 km horizontal resolution. In this nested grid only modifications to the wind field by the better resolved terrain are considered on the lowest two sigma levels. The terrain effects necessitate adjustments in the location of these two sigma levels. Adjusted wind fields cause modifications in the mass and moisture divergence fields, hence in precipitation. These modifications are averaged into the appropriate meteorological fields on the larger grid.The algorithms used by our model allow continuous interaction between both grids with high computational efficiency.The relative importance of synoptic forcing and terrain is demonstrated for the cases of the Big Thompson, Colorado, flood of 1976 and the Cheyenne, Wyoming, flood of 1985.With 15 Figures     

次网格对流参数化效果对水平分辨率的敏感生试验

使用单向嵌套的五层有限域模式进行了次网格对流参数化效果对水平分辨率的敏感性试验.使最细网格覆盖主要降水区,并依次嵌套.设计了四种水平分辨率不同的网格,其水平格距分别为381,190.5,95.25及47.625km.对同一降水个例使用上述各种网格分别作了24小时累计降水量预报(积分48小时)试验.结果表明:(1)总降水量(降水最大值及等面积平均最大值)随网格距的减小而增大.当水平格距减小为50km左右时,便可以很好地预报出一般天气尺度降水的落区及雨量分布;(2)随水平分辨率的提高,次网格对流凝结对总降水的     

辽东半岛一次大暴雨的中尺度模拟及物理结构分析

2005年7月25日辽东半岛南部及海峡地区发生了大暴雨天气。利用中尺度模式MM5的双向二重嵌套网格对其进行模拟, 表明该模式对这次暴雨过程有较好的模拟能力。模拟的地面气压场及流场基本与客观分析场一致。模拟结果较好地再现了辽东半岛大暴雨的大尺度和中尺度天气系统的发展和演变, 揭示了造成此次暴雨的中尺度系统结构为高空强辐散, 低空强辐合及对应的强上升运动和气旋性涡柱是造成此次暴雨的动力机制, 低空西南气流对这次暴雨的产生和发展起着重要的作用。     

WRF模式物理参数化方案对一次局地大暴雨预报的影响研究

基于WRF(Weather Research and Forecasting)模式及其3Dvar(3-Dimentional Variational)资料同化系统,采用36、12、4 km嵌套网格进行快速更新循环同化和不同的微物理及积云对流参数化方案对比试验,对2011年5月8日鲁中一次局地大暴雨过程进行了研究。结果表明,快速更新循环同化地面观测资料是影响模式降水落区预报准确性的关键因素,不同的微物理和积云对流参数化方案主要影响降水强度预报。采用不同的微物理参数化方案和积云对流参数化方案进行降水预报对比试验表明,LIN方案和WSM6(WRF Single-Moment 6-class)微物理参数化方案对降水预报均较好,LIN方案降水预报较WSM6方案略强。4 km网格预报使用K-F (Kain-Fritsch)积云对流参数化方案或不使用积云对流参数化方案,预报的降水均较好。4 km网格使用旧的K-F积云对流参数化方案,预报的近地层大气风场偏弱,导致大气动力抬升作用偏弱,从而造成模式降水预报偏弱。     

一个三重嵌套的中尺度模式及暴雨模拟试验

该文介绍了新近发展的一个高分辨率有限区模式(HLAM)。它是通过三重嵌套在现有计算机(CYBER-992)条件下实现的，其范围、地理位置及侧边界宽度均设计为灵活可变，尤其水平分辨率可按任意倍数提高。利用水平分辨率为50km左右的模式版本进行了实际资料的降水个例实验。结果是令人鼓舞的:(1)与嵌套的低分辨率(格距增大4倍)模式预报比较，不论低压中心位置、强降水落区、雨带走向及降水中心位置的预报都更接近实况;(2)高分辨率模式积分区域虽然缩小，但并未影响预报效果，其48小时预报仍有较高精度。初步试验表明，进一步完善和改进后的HLAM完全可以发展为一个用于中尺度研究及业务使用的高分辨率区域模式。     

A grid nesting method for large-eddy simulation of planetary boundary-layer flows

A method for performing nested grid calculations with a large-eddy simulation code is described. A common numerical method is used for all meshes, and the grid architecture consists of a single outer or coarse grid, and nested or fine grids, which overlap in some common region. Inter-grid communication matches the velocity, pressure and potential temperature fields in the overlap region. Resolved and sub-grid scale (SGS) turbulent fluxes and kinetic energy on the fine grid are averaged to the coarse grid using a conservation rule equivalent to Germano's identity used to develop dynamic SGS models.Simulations of a slightly convective, strong shear planetary boundary layer were carried out with varying surface-layer resolutions. Grid refinements in the (x, y, z) directions of up to (5, 5, 2) times were employed. Two-way interaction solutions on the coarse and fine meshes are successfully matched in the overlap region on an instantaneous basis, and the turbulent motions on the fine grid blend smoothly into the coarse grid across the grid interface. With surface-layer grid nesting, significant increases in resolved eddy fluxes and variances are found. The energy-scale content of the vertical velocity, and hence vertical turbulent fluxes, appear to be most influenced by increased grid resolution. Vertical velocity spectra show that the dominant scale shifts towards higher wavenumbers (smaller scales) and the magnitude of the peak energy is increased by more than a factor of 3 with finer resolution. Outside of the nested region the average heat and momentum fluxes and spectra are slightly influenced by the fine resolution in the surface layer. From these results we conclude that fine resolution is required to resolve the details of the turbulent motions in the surface layer. At the same time, however, increased resolution in the surface layer does not appreciably alter the ensemble statistics of the resolved and SGS motions outside of the nested region.     

Heavy rainfall in complex terrian: insights from a numerical model

Summary A numerical model is employed to study heavy rainfall events in complex terrain. The model uses a limited-fine-mesh grid and a nested grid, but does not utilize the same set of equations on both grids. Two similar, heavy rainfall cases are contrasted with each other and with a moderate precipitation case. Sensitivity experiments illustrate the effects of topography, synoptic forcing and diabatic heating on these episodes. Model results indicate that heavy rainfall in complex terrain requires a suitable superposition of mass, momentum and moisture fields in relation to the topography. It is the mass and momentum fields, however, which primarily control the location of heaviest precipitation. Synoptically similar events may be different in their underlying causes. The diabatic heating distribution may in some cases be essential to creating such episodes heavy rain.With 22 Figures     

一次大暴雨过程中急流次级环流的激发及作用

使用双向嵌套数值模式MM4对1992年7月23日发生在副高北侧京津冀 地区的一次大暴雨过程进行了成功的数值模拟。利用模拟得到的高时空分辨率资料，对 伴随高、低空急流的次级环流进行了诊断，结果表明:激发次级环流的主要因子和台风、 夏季江淮气旋有明显不同；总的次级环流在降水前，有利于天气区不稳定能量的积累， 而在降水过程中提供了持续稳定的上升运动条件；急流和暴雨之间通过次级环流存在着 正反馈相互作用。     

Comparison of Measured and Numerically Simulated Turbulence Statistics in a Convective Boundary Layer Over Complex Terrain

The Weather Research and Forecasting (WRF) model can be used to simulate atmospheric processes ranging from quasi-global to tens of m in scale. Here we employ large-eddy simulation (LES) using the WRF model, with the LES-domain nested within a mesoscale WRF model domain with grid spacing decreasing from 12.15 km (mesoscale) to 0.03 km (LES). We simulate real-world conditions in the convective planetary boundary layer over an area of complex terrain. The WRF-LES model results are evaluated against observations collected during the US Department of Energy-supported Columbia Basin Wind Energy Study. Comparison of the first- and second-order moments, turbulence spectrum, and probability density function of wind speed shows good agreement between the simulations and observations. One key result is to demonstrate that a systematic methodology needs to be applied to select the grid spacing and refinement ratio used between domains, to avoid having a grid resolution that falls in the grey zone and to minimize artefacts in the WRF-LES model solutions. Furthermore, the WRF-LES model variables show large variability in space and time caused by the complex topography in the LES domain. Analyses of WRF-LES model results show that the flow structures, such as roll vortices and convective cells, vary depending on both the location and time of day as well as the distance from the inflow boundaries.     

1997年7月19日影响北京地区的暴雨个例分析

针对在实际业务预报中经常遇到的北京地区降水的两种特殊性(明显天气系统移来时，北京地区降水明显比周围偏多或偏少)，选取一个实例利用中尺度非静力模式(MM5)对降水比周围偏多情况进行了高分辨率数值模拟和敏感性试验。结果表明，该模式比较成功地模拟了此次天气过程及其相关的中尺度系统的发生发展，凝结潜热对天气过程的发生发展有重要作用，而地形在天气过程中也起着主要作用，低层潜在不稳定能量的储备和输送是暴雨发生不可缺少的条件。     

珠三角关键大气挥发性有机物的模拟精度评估

大气挥发性有机物（VOCs）是导致臭氧污染的关键前体物,是城市空气质量建模不可或缺的重要组成部分,但由于其非常复杂的构成和来源以及监测数据缺乏,目前对其模拟精度的了解仍非常有限。本文利用嵌套网格空气质量模式预报系统（NAQPMS）对珠江三角洲（简称珠三角）地区2017年9月21日至11月20日的VOCs开展了模拟试验,并利用光化学监测网8个地面站点的VOCs浓度监测数据,对模式模拟的关键VOCs组分进行了精度评估。结果发现,模式对强活性的甲苯、乙烯和二甲苯具有较高的模拟精度,模拟浓度偏差百分比为0.4%～26.6%,模拟能较好再现其日均浓度变化趋势和日变化的双峰特征。但是模式对化学反应活性强且与植物排放密切相关的异戊二烯具有很大的模拟偏差,偏差比近100%,无法再现其白天浓度高、夜间浓度低的观测日变化特征。通过分析发现,现有模拟系统主要考虑人为污染物排放而未考虑生物源排放,可能是导致这一模拟偏差的关键原因。同时,评估结果也表明模式在VOCs空间分布模拟上仍面临很大的不确定性。本文结果揭示了珠三角VOCs模拟面临的关键不确定性,表明融合VOCs观测数据来揭示并减小VOCs模拟的不确定性具有非常迫切的需求。     

Nesting Turbulence in an Offshore Convective Boundary Layer Using Large-Eddy Simulations

The applicability of the one-way nesting technique for numerical simulations of the heterogeneous atmospheric boundary layer using the large-eddy simulation (LES) framework of the Weather Research and Forecasting model is investigated. The focus of this study is on LES of offshore convective boundary layers. Simulations were carried out using two subgrid-scale models (linear and non-linear) with two different closures [diagnostic and prognostic subgrid-scale turbulent kinetic energy (TKE) equations]. We found that the non-linear backscatter and anisotropy model with a prognostic subgrid-scale TKE equation is capable of providing similar results when performing one-way nested LES to a stand-alone domain having the same grid resolution but using periodic lateral boundary conditions. A good agreement is obtained in terms of velocity shear and turbulent fluxes, while velocity variances are overestimated. A streamwise fetch of 14 km is needed following each domain transition in order for the solution to reach quasi-stationary results and for the velocity spectra to generate proper energy content at high wavelengths, however, a pile-up of energy is observed at the low-wavelength portion of the spectrum on the first nested domain. The inclusion of a second nest with higher resolution allows the solution to reach effective grid spacing well within the Kolmogorov inertial subrange of turbulence and develop an appropriate energy cascade that eliminates most of the pile-up of energy at low wavelengths. Consequently, the overestimation of velocity variances is substantially reduced and a considerably better agreement with respect to the stand-alone domain results is achieved.     

Modelling of concentration fluctuations in canopy turbulence

The knowledge of the concentration probability density function (pdf) is of importance in a number of practical applications, and a Lagrangian stochastic (LS) pdf model has been developed to predict statistics and concentration pdf generated by continuous releases of non-reactive and reactive substances in canopy generated turbulence. Turbulent dispersion is modelled using a LS model including the effects of wind shear and along-wind turbulence. The dissipation of concentration fluctuations associated with turbulence and molecular diffusivity is simulated by an Interaction by Exchange with the Conditional Mean (IECM) micromixing model. A general procedure to obtain the micromixing time scale needed in the IECM model useful in non-homogeneous conditions and for single and multiple scalar sources has been developed. An efficient algorithm based on a nested grid approach with particle splitting, merging techniques and time averaging has been used, thus allowing the calculation for cases of practical interest. The model has been tested against wind-tunnel experiments of single line and multiple line releases in a canopy layer. The approach accounted for chemical reactions in a straightforward manner with no closure assumptions, but here the validation is limited to non-reacting scalars.     

用业务有限区模式预报台风路径的初步试验

利用国家气象中心新的有限区业务分析预报系统（ＬＡＦＳ）￣［１］，根据实例台风资料的一些参数和客观分析场，形成包含理想台风模型的模式初值，并将一个和业务有限区预报模式基本相同的、水平分辨率更高的预报模式和有限区预报模式单向嵌套，进行台风路径预报的初步试验。      

颗粒物干沉降对AERMOD模型预测大气污染的影响

AERMOD模型是《环境影响评价技术导则—大气环境》中的推荐模式。为了更好地验证颗粒物干沉降作用对该模型预测结果的影响,选取福州市的煤堆场作为面源污染源,对预测范围内所有网格点PM10、TSP最大地面浓度进行预测。结果表明：所有网格点TSP地面浓度考虑干沉降时,约为不考虑干沉降时的0.13;PM10地面浓度考虑干沉降时,约为不考虑干沉降时的0.70,干沉降对TSP的影响大于PM10。同一粒径分布下,密度对颗粒物干沉降的影响较大,密度增加对可吸入颗粒物干沉降的影响大于总悬浮颗粒物,当密度大于3 g.cm-3时,所有网格点PM10与TSP地面浓度比值的平均值接近于0.98,认为粒径大于10μm的颗粒物基本完全沉降。此后,随着密度增加网格点处地面浓度的减小主要由PM10的沉降引起。AERMOD考虑干沉降时,距离污染源中心500 m外的网格点处地面浓度,PM10/TSP〉0.98,大于10μm的粗颗粒几乎完全沉降。