共查询到19条相似文献，搜索用时 219 毫秒
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蛙跳(leapfrog)时间差分格式采用Asselin-Robert时间滤波方案去除计算解能够降低原始方程组的时间差分格式的计算精度,采用二阶Adams-Bashforth格式构造的欧拉前差方案可弥补蛙跳格式的不足,即:在不存在计算解的条件下去除滤波的影响,更大程度的保持方程组的计算准确性。本文基于NCAR CAM3.0(Community Atmosphere Model 3.0)完善的软件平台,将原模式的三时间层蛙跳时间差分方案修改为两时间层二阶Adams-Bashforth时间差分格式,对与重力波有关项使用中央差隐式处理,以此构建半隐式大气环流谱模式。利用动力检验的方法探讨模式对垂直分辨率的敏感性,从而寻找模式在较小计算代价下提高计算效果的可能。通过斜压波实验发现,提高垂直分辨率使模式具有更强的斜压波模拟能力,其模拟效果甚至已经与提高水平分辨率的效果相当,可以作为一种弥补模式运算效率不足的可行方案。 相似文献
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用低分辨率的初始方程二层模式在给定下垫面温度下模拟了一月及七月全球海平面气压场,其中加热项主要是感热垂直输送。计算采用守恒的Lilly空间差分格式及Matsuno的时间差分格式。海平面气压的初值给成常数值,高空的风速及气温的初值给成纬向平均的气侯值。在数值模拟中,下垫面温度用一月及七月的气候实际值。计算的冬半球海平面气压与观测值相当一致,而夏半球的结果稍差些。本模式所求得的全球海平面气压场能与实况相比,结果并不差于高分辨率的复杂模式。 相似文献
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一类计算性系统误差消除与斜压原始方程天气气候模式改进 总被引：1，自引：0，他引：1
斜压原始方程半隐式全能量守恒格式的构造问题长期没有解决。本研究在成功地构造实现其全能量完全守恒的半隐式方案基础上，进行了此守恒方案与欧洲中期天气预报中心（ECMWF）的σ－坐标原始方程全球谱模式半隐式方案间的实际资料对比实验。实验表明，850hPa平均预报高度场RMS误差在积分一周以后得到明显改进，到第30天其预报误差降低达到了50％，进一步的对比实验表明，对流层中部和下部的月预报平均高度场RMS误差也显降低，而且一些明显的系统性误差也得到大幅度改进。更加详细的分析显示，这些收益的很大一部分是从超长波成分的改进中得到的。这说明，通过构造守恒性时间差分方案消除了响应的计算性系统误差源汇，进而能够使模式气候漂移得到显改进，而这种误差源汇存在于传统的，现仍被普遍采用的斜压原始方程天气气候模式中。 相似文献
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显式自由表面模型时间分裂格式的一个积分方案 总被引：5，自引：0，他引：5
Zhou Weidong 《大气科学进展》2002,19(2):255-265
讨论了有关显式自由表面模型的时间分裂格式中的分裂误差。在传统的积分方案中，由于采用蛙跳格式，斜压动量方程具有三层的时间离散结构，但是，正压动量方程在相应的时间层上只有二层的离散结构。因此，正压方程与斜压方程的时间离散结构是不相容的。分析结果表明，这是导致分裂误差的原因。本提出一种能保持时间离散结构相容的正压和斜压方程的时间积分方案。该积分方案的分裂误差很小因此特别适合于需要长期积分的气候研究。该方案在北太平洋的一个自由表面模型中得到了应用。 相似文献
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物理守恒律保真格式构造与数值预报斜压原始方程传统谱模式改进研究 总被引：8，自引：1，他引：8
文中构造并证明了一般二次和三次物理守恒律时间差分保真格式两个构造定理，以往一些主要时间离散守恒格式构造方案可作为两个定理特例给出。它们不仅可为解决更加广泛类别的时间离散保真格式构造基本问题提供适用数学基础，而且也为结合已有瞬时空间离散守恒格式，解决更加广泛类别的时－空离散意义下保真格式构造基本问题提供适用的数学基础。此外，文中两个定理还可解决两大类问题的线性和非线性计算不稳定性问题。斜压原始方程传统半隐式全球谱－垂直有限差分模式目前是世界上许多国家的业务预报和大气环流模式。本工作利用文中新构定理，构造并且实现了斜压原始方程全球谱－垂直有限差分模式半隐式高阶全能量守恒方案。以往该项基本问题无论在理论还是实践上长期以来一直都未能得到解决。该项全能量守恒半隐式全球谱模式方案适用于实测资料的长时间数值预报积分。使用ＦＧＧＥ夏季资料进行的１３个个例３０ｄ数值积分实验表明：新型全能量半隐式保真方案可以有效地改进传统预报方案中关于能量质量守恒性质的系统性偏差。值得注意的是，实验统计分析还显示：在本文实验条件下，传统方案中由于时间离散过程中原物理守恒律性质破坏导致的系统误差（简称Ｚ类误差），对于实验总体均方根系统误差的贡献 相似文献
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关于半拉格朗日半隐式大气模式的时步问题 总被引：1，自引：0，他引：1
讨论半拉格朗日半隐式大气模式中时步的限制,展示时步过大时用一般的首尾两点平均方案计算非线性源汇项的严重误差,提出精确的源汇项计算格式并作了特例计算和比较,讨论了被模拟的大气过程和波动的特征对时步的要求,指出柯朗数NC=C·△t/△X是大气模式时空步长匹配的重要参数.指出云降水和大气化学过程特征时间对相应的正定变量的计算时步的限制. 相似文献
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基于浅水波方程组建立一维溃坝流模型,并给出数值模拟结果.其中,空间离散采用HWENO(Hermit Weighted Essentially Non-Oscillatory) 格式,时间离散采用四步TVD(Total Variation Diminishing)Runge-Kutta模拟堤坝溃决时洪水演进过程。模拟结果表明：较采用WENO格式所得数值解更精确-同时,相比WENO格式的相应算法,该算法解决一维溃坝流问题能更有效地减弱振荡,对间断具有更高的分辨率 相似文献
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设计了适用于四维变分同化系统的扰动预报模式GRAPES_PF。根据GRAPES的地形追随坐标非静力原始方程组,采用小扰动分离方法推导微分形式的线性扰动预报方程组,并利用与GRAPES非线性模式相似的数值求解方案求解线性扰动微分方程组。在设计扰动预报模式时采用了两个时间层半隐式半拉格朗日方案对动量方程、热力学方程、水汽方程和连续方程进行时间差分,空间差分方案的变量分布水平方向采用Arakawa C跳点网格,垂直方向采用Charney/Phillips跳层。利用代数消元法进一步推导得到只包含未来时刻扰动Exner气压的亥姆霍兹方程,进而通过广义共轭余差法（GCR）求解,在此基础上得到未来时刻扰动量的预报值。基于所开发的扰动模式开展了数值试验。首先在非线性模式中施加一个中尺度初始扰动高压,得到初始扰动在非线性模式中的后续演变,然后将相同的初始扰动作为扰动模式的初值进行时间积分,将扰动模式预报的结果与非线性模式的结果做了对比。结果表明,所开发的扰动模式GRAPES_PF较好地模拟了惯性重力内波的传播过程:初始高压扰动激发了一个迅速向外传播的惯性重力内波,在气压场向风场适应的过程中,水平风场、垂直运动、位温和湿度等变量均出现了扰动增量,与非线性模式得到的结果相当接近。GRAPES_PF作为GRAPES非线性模式的合理线性模式为建立基于线性扰动预报的区域四维变分同化系统奠定了科学基础。 相似文献
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The Dynamical and Climate Tests of an Atmospheric General Circulation Model Using the Second-Order
Adams-Bashforth Method 
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下载免费PDF全文 The Asselin-Robert time filter used in the leapfrog scheme can degrade the accuracy of calculations. The second-order Adams-Bashforth method with the same accuracy as the leapfrog scheme is not subject to time splitting instability. A new semi-implicit atmospheric general circulation spectral model is developed on the basis of NCAR (National Center for Atmospheric Research) CAM3.0 (Community Atmosphere Model3.0). In this new model, the second-order Adams-Bashforth method is used as an alternative to the leapfrog scheme, and a Crank-Nicholson scheme is incorporated for the treatment of fast gravity modes. In this paper, the new model is tested by the Held-Suarez test and an idealized baroclinic wave test. Results of the Held-Suarez test show that the second-order Adams-Bashforth model has similar climate states to those of many other global models and it converges with resolutions. Based on the idealized baroclinic wave test, the capability of di?erent time di?erencing methods for keeping the initial steady-state are compared.This convinces a better ability of the second-order Adams-Bashforth method in maintaining the stability of the initial state. Furthermore, after the baroclinic wave is triggered through overlaying the steady-state initial conditions with the zonal perturbation, the second-order Adams-Bashforth method has an excellent property of convergence, and can represent the process of the baroclinic wave development much better than
the original scheme in CAM3.0. A long-term integration of the new model during the period of 1980-1999 is also carried out and compared with that of CAM3.0. It is found that due to the reduction of simulation errors of prognostic variables, the second-order Adams-Bashforth method also has a better simulation ability for the diagnostic variables, such as precipitation. 相似文献
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Comparison of different order Adams-Bashforth methods in an atmospheric general circulation model 下载免费PDF全文
下载免费PDF全文 The Asselin-Robert time filter used in the leapfrog scheme does degrade the accuracy of calculations. As an attractive alternative
to leapfrog time differencing, the second-order Adams-Bashforth method is not subject to time splitting instability and keeps
excellent calculation accuracy. A second-order Adams-Bashforth model has been developed, which represents better stability,
excellent convergence and improved simulation of prognostic variables. Based on these results, the higher-order Adams-Bashforth
methods are developed on the basis of NCAR (National Center for Atmospheric Research) CAM 3.1 (Community Atmosphere Model
3.1) and the characteristics of dynamical cores are analyzed in this paper. By using Lorenz nonlinear convective equations,
the filtered leapfrog scheme shows an excellent pattern for eliminating 2Δt wave solutions after 20 steps but represents less computational solution accuracy. The fourth-order Adams-Bashforth method
is closely converged to the exact solution and provides a reference against which other methods may be compared. Thus, the
Adams-Bashforth methods produce more accurate and convergent solution with differencing order increasing. The Held-Suarez
idealized test is carried out to demonstrate that all methods have similar climate states to the results of many other global
models for long-term integration. Besides, higher-order methods perform better in mass conservation and exhibit improvement
in simulating tropospheric westerly jets, which is likely equivalent to the advantages of increasing horizontal resolutions.
Based on the idealized baroclinic wave test, a better capability of the higher-order method in maintaining simulation stability
is convinced. Furthermore, after the baroclinic wave is triggered through overlaying the steady-state initial conditions with
the zonal perturbation, the higher-order method has a better ability in the simulation of baroclinic wave perturbation. 相似文献
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This paper introduces a new consistent dissipation operator. It is based on the explicit square conservation scheme and the theory of consistent dissipation. The operator makes full use of the advantages of the Leap-frog scheme, i.e., its second order time precision and its explicit solution manner. Meanwhile, it overcomes the fatal disad-vantage, the absolute instability in computations, of the scheme. When it is applied to the explicit square conservation scheme, the time precision of the scheme reaches to third order. Especially, the computational stability of this scheme is as good as the third order explicit Runge-Kutta scheme. The CPU time required in computations by the scheme is less than that required by the explicit square conservation scheme with the consistent dissipation operator constructed from the Runge-Kutta method. Therefore, the new operator is an economical one. The application of the operator to the improvement of the dynamical model of the L2IAP AGCM shows its time-saving property and its good effects 相似文献
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Three-Step Difference Scheme for Solving Nonlinear Time-Evolution Partial Differential Equations 下载免费PDF全文
下载免费PDF全文 In this paper, a special three-step difference scheme is applied to the solution of nonlinear time-evolution equations, whose coefficients are determined according to accuracy constraints, necessary conditions of square conservation, and historical observation information under the linear supposition. As in the linear case, the schemes also have obvious superiority in overall performance in the nonlinear case compared with traditional finite difference schemes, e.g., the leapfrog（LF） scheme and the complete square conservation difference（CSCD） scheme that do not use historical observations in determining their coefficients, and the retrospective time integration（RTI） scheme that does not consider compatibility and square conservation. Ideal numerical experiments using the one-dimensional nonlinear advection equation with an exact solution show that this three-step scheme minimizes its root mean square error（RMSE） during the first 2500 integration steps when no shock waves occur in the exact solution, while the RTI scheme outperforms the LF scheme and CSCD scheme only in the first 1000 steps and then becomes the worst in terms of RMSE up to the 2500th step. It is concluded that reasonable consideration of accuracy, square conservation, and historical observations is also critical for good performance of a finite difference scheme for solving nonlinear equations. 相似文献
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天气雷达测定区域降水量方法的改进与比较 总被引：9，自引：1，他引：9
讨论变分校准法用于雷达－雨量计系统联合探测降水。由雷达反射率因子Ｚ和地面降水强度Ｉ实时地获得最优Ｚ－Ｉ关系，在求解欧拉方程时采用多重网格法，不仅可提高计算结果的精度，还可大大提高计算速度。 相似文献
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