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本文用一个准二维的原始方程组进行了套网格模式的数值试验。文中介绍了单向套网格和双向套网格的试验结果。试验表明在粗细网格边界上采用松弛法有较好的效果。 相似文献
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桂冰 《南京气象学院学报》2006,29(3):422-428
在交错网格的情况下，构造了一类不需解Riemann问题的求解三维双曲守恒律的二阶显式差分格式，证明了该格式在CFL（Courant-Friedrichs-Lewy）条件限制下为MmB（Maximum and minimum Bounds）格式，进行了并行计算数值试验，得到的试验结果令人满意。在交错网格的情况下构造的这类差分格式，不需要求解Riemann问题，不需要进行特征分解，可用于求解弱双曲方程组，计算快、编程简便。 相似文献
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传统的高阶精度有限差分格式通常是在均匀网格的基础上推导得到的,在非均匀网格的情况下它会出现精度退化的问题。基于泰勒展开方法构造了一种适用于非均匀网格的2阶、4阶和6阶精度中央有限差分方案,利用Burgers方程和一维平流方程对新方案的性能进行测试,着重分析新方案对其误差大小及分布形态的改进效果。数值模拟结果表明:在非均匀网格下,提高差分方案的精度可明显减小数值解误差(降低了70%~88%),特别是当差分精度从2阶提高到4阶的时候。同时,高阶精度方案在梯度变化较大或者网格距较粗区域的模拟结果更有优势,4阶和6阶精度方案在以上区域的误差远小于2阶精度方案。方案可用于提高数值天气预报模式中非均匀分层模式的垂直差分计算精度。 相似文献
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陆维松 《南京气象学院学报》1983,(1)
本文用“单向”(one—way)方法进行正压原始方程套网格试验。粗、细网格均采用空间分解准拉格朗日格式和由廖洞贤等提出的与此差分格式一致的内边界条件(即方案二)。试验结果表明,用方案二作出的24小时细网格预报,与按半动量格式和粗网格直接给细网格提供内边界条件(即方案一)所得的结果相比,去除了在流出处出现的不稳定,系统的流入、流出也较好。这两种方案再加上Davies“松弛区域”的方法(分别为方案四,方案三),其结果与上述类似,且方案四比方案二还要好些。 相似文献
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本文用“单向”(one—way)方法进行正压原始方程套网格试验。粗、细网格均采用空间分解准拉格朗日格式和由廖洞贤等提出的与此差分格式一致的内边界条件(即方案二)。试验结果表明,用方案二作出的24小时细网格预报,与按半动量格式和粗网格直接给细网格提供内边界条件(即方案一)所得的结果相比,去除了在流出处出现的不稳定,系统的流入、流出也较好。这两种方案再加上Davies“松弛区域”的方法(分别为方案四,方案三),其结果与上述类似,且方案四比方案二还要好些。 相似文献
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非跳点网格在模式动力—物理过程的耦合方面具有独特的优势,但是由于二阶精度差分方案下非跳点网格频散误差较大而很少被使用于数值天气预报模式。随着近年来数值模式计算精度的不断提高,非跳点网格在频散关系方面的计算误差是否会发生变化还有待研究。本文在高阶精度差分格式下通过浅水波方程对跳点网格和非跳点网格的频散关系进行理论分析和数值试验,主要得到以下结论:（1）在低波数区跳点网格的频散关系基本不随计算精度的提高而变化,但是非跳点网格下的频散关系则随着计算精度的提高而更加接近真实解。在四阶精度下,非跳点网格的频散关系已经非常接近跳点网格。（2）差分精度提高以后,在高波数区非跳点网格仍然存在频率极大值,而且极值中心随着计算精度的提高而逐渐向更高波数区移动。跳点网格在计算精度提高以后高波数区的频率仍然随波数单调增加,且更接近真实解。（3）在高阶精度非跳点网格模拟试验的基础上,结合高阶扩散项对高频短波进行滤除,可以得到与二阶精度跳点网格相接近的模拟结果。总之,在高阶精度有限差分方案下利用非跳点网格构造模式动力框架是一种比较可行的做法。 相似文献
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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。 相似文献
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研究证明,在一定条件下,有限多维Taylor展式算符可以化为几个一维算符的积。利用这个结果,可以使二维插值分解为两个一维插值,从而,显著节省计算量。还给出了多维的,任意精度的,空间分解的平流方程的差分格式,并对格式的计算稳定性,物理性质进行了讨论。结果指出,在一维或二维的情况,这种格式的计算稳定性判据是对于二维,它比一般判据对时间的要求宽。还指出,在三维的情况,对一定的d,当Δt=d/max|V|时,ΔR必须满足才能保证计算稳定。在一般所给数据情况下,须Δp大于30mb。 相似文献
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本文建立了一个用于研究“雅安天漏”的有限区域数值预报模式，并用该模式对１０个“雅安天漏”个例进行了数值预报试验，取得了较满意的结果。该模式动力框架的主要特点是：（１）模式的基本方程组便于构造出完全能量守恒的差分格式；（２）采用了静力扣除；（３）模式的垂直坐标选用了η坐标；（４）选用Ｅ网格作为变量的水平分布形式；（５）位势高度与其他预报量在垂直方向交错分布；（６）对Ｅ网格的波解分离问题采取了特殊的处理技巧；（７）首次采用“半格距”差分解决了矩形Ｅ网格及球坐标Ｅ网格沿对角线的差分计算；（８）采用显示分解的时间积分方案；（９）尽量保留初始场信息。模式的物理过程主要包括：（１）大尺度凝结降水；（２）对流调整及对流降水；（３）水平扩散和垂直通量输送；（４）地面辐射收支和边界层参数化。试报降水的主要降水中心及降水范围与观测分析比较相似。大于１０ｍｍ和２５ｍｎ降水的ＴＳ平均评分分别为０．４１和０．３２。 相似文献
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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 相似文献
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Peter P. Sullivan James C. McWilliams Chin-Hoh Moeng 《Boundary-Layer Meteorology》1996,80(1-2):167-202
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. 相似文献
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国家气象中心台风数值模式的改进及其应用试验 总被引：13，自引：4，他引：9
在国家气象中心台风数值模式中进行了扩大预报区域,两次嵌入人造台风模型和模式网格初始移动3个方案试验。试验结果表明:3个方案对台风路径预报效果都有所改进。该文还介绍了应用国家气象中心台风数值模式进行台风中心强度预报的进展。 相似文献
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《Dynamics of Atmospheres and Oceans》1999,29(2-4):397-413
A coastal shallow water model generally involves at least one coastal boundary which is curvilinear in nature. Representation of this curvilinear boundary needs special attention when a finite difference scheme is used. To incorporate the curvilinear coastal boundary and off-shore islands properly in the numerical scheme, we need fine resolution which may not be necessary away from the coast. In order to tackle this problem, a nested numerical scheme may be used where fine resolution for the coastal boundary region is nested into a course resolution scheme covering the whole analysis area. But this involves comparatively more memory and CPU time in the solution process. The present study aims at developing a storm surge model that may subsequently be modified for operational forecasting purpose for the coast of Bangladesh. A vertically integrated model is developed in a cylindrical polar coordinate system capable of incorporating bending of the coastline and off-shore islands with considerable accuracy without using any nesting. A comparison of CPU time and memory in the numerical computations between two types of modelling is described and it is found that the cylindrical polar coordinates model is economic. The model is applied for estimating the water levels at different coastal and island stations associated with a few storms that hit the coast of Bangladesh. It is found that the computed and observed water levels are in good agreement. Considering the computing time and other factors, it is found that the Polar Coordinates model is more suitable for operational forecasting purpose along the coast of Bangladesh. 相似文献
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在复杂地形条件下嵌套细网格模式的基础上，建立了与球圈模式相嵌套的区域模式系统，对几种不同条件下的嵌套误差进行了比较分析，研究了区域模式嵌套误差的特征分布及时空演变特征。初步分析表明:区域模式嵌套造成的误差在不同区域的分布不同，且不同的物理量在时空的分布也不同；动能场的误差主要在边界区上层的流入区，感热场的误差在边界区上层，水汽的误差在边界区上层的流入区；侧边界输入时间间隔对模式嵌套误差有一定的影响。有限区细网格模式在上层长波误差大于粗网格环圈模式上层误差，在下层短波模拟的误差比粗网格环圈模式的下层误差要小。相速误差对侧边界嵌套误差的影响在下层很严重，嵌套误差的大小与大小模式的网格距之比有关；在大小模式物理参数化过程一致的条件下，无日变化的区域模式其嵌套误差远大于有日变化的区域模式嵌套误差。 相似文献
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1.IntroductionAlthoughGCMsprovedsuccessfulinreproducingthebasicfeaturesoflarge--scaleatmosphericcirculations(Gates,1992),theyaretoocoarsetodescribethedetailsofregionalclimatepatterns(Grotch,etal.,1991).Intheregionswheretheatmosphericdynamicalandphysicalforcingsvaryonascaleoflessthanafewhundredkilometers,suchasinthepresenceofcomplexterrain,afactorof10orgreaterincreaseinmodelhorizontalresolutionmayberequiredtosimulatetherealisticregionalresponsestothefutureclimatechanges.Duetothelimitationsinb… 相似文献