海气耦合系统相似韵律现象的研究

本文首先利用一个相似离差形式的海气耦合模式,探讨了相似韵律现象形成的动力学机制,指出相似韵律现象的产生是由于在月平均环流季节变化的强迫下,海气系统非线性耦合相互作用造成的相似离差扰动的不均匀振荡。文中进一步利用一个全球海气耦合的动力-统计季节长期数值预报模式,对相似韵律现象进行了数值模拟和各种敏感性实验,结果不仅证实了理论分析结果,也为进一步利用该模式进行季节长期数值预报提供了依据。     

An approach to estimating and extrapolating model error based on inverse problem methods:towards accurate numerical weather prediction

Model error is one of the key factors restricting the accuracy of numerical weather prediction(NWP). Considering the continuous evolution of the atmosphere, the observed data(ignoring the measurement error) can be viewed as a series of solutions of an accurate model governing the actual atmosphere. Model error is represented as an unknown term in the accurate model, thus NWP can be considered as an inverse problem to uncover the unknown error term. The inverse problem models can absorb long periods of observed data to generate model error correction procedures. They thus resolve the deficiency and faultiness of the NWP schemes employing only the initial-time data. In this study we construct two inverse problem models to estimate and extrapolate the time-varying and spatial-varying model errors in both the historical and forecast periods by using recent observations and analogue phenomena of the atmosphere. Numerical experiment on Burgers’ equation has illustrated the substantial forecast improvement using inverse problem algorithms. The proposed inverse problem methods of suppressing NWP errors will be useful in future high accuracy applications of NWP.     

缓变地形下Rossby波振幅演变满足的带有强迫项的KdV方程

运用非线性方法与摄动法,讨论了当地形随时间缓变时Rossby波振幅的演变问题.从均值流体准地转涡度方程推导,得到Rossby波振幅演变满足带有强迫项的KdV方程的结论,而地形随时间的缓慢变化诱导了该方程的强迫项. 关键词： 非线性Rossby波 带有强迫项的KdV方程 摄动法 缓变地形     

大尺度大气运动方程组解的一些性质——定常外源强迫下的非线性适应

本文从大尺度大气运动方程组出发,讨论了定常外源强迫下大气系统的长期行为。建立了基本的泛函空间和算子方程,证明了解的存在唯一性定理,在此基础上讨论了整体吸收集以及其中的不变点集的存在性。揭示了系统向外源的非线性适应过程。     

混沌系统中可预报性的研究

针对简化的气候模式、Rossler吸引子和超混沌系统,进一步阐明了不确定原理,在数值求解时由于计算机固有精度而引起的舍入误差,造成对解的不确定性,存在最优步长和最大有效计算时间.运用自忆性原理,导出了各混沌系统的自忆性方程,取最优步长时,其预报性能有明显的改善 关键词： 自忆性 不确定原理 最优步长     

Analogue correction method of errors and its application to numerical weather prediction

In this paper, an analogue correction method of errors (ACE) based on a complicated atmospheric model is further developed and applied to numerical weather prediction (NWP). The analysis shows that the ACE can effectively reduce model errors by combining the statistical analogue method with the dynamical model together in order that the information of plenty of historical data is utilized in the current complicated NWP model. Furthermore, in the ACE, the differences of the similarities between different historical analogues and the current initial state are considered as the weights for estimating model errors. The results of daily, decad and monthly prediction experiments on a complicated T63 atmospheric model show that the performance of the ACE by correcting model errors based on the estimation of the errors of 4 historical analogue predictions is not only better than that of the scheme of only introducing the correction of the errors of every single analogue prediction, but is also better than that of the T63 model.     

自忆模式中差分格式的稳定性研究

基于大气运动是一种不可逆过程的观点，引进了忆及过去时次资料的记忆函数，导出热传导的自忆性方程，研究了方程分别取Richardson和DuFort-Frankel格式，回溯阶p取1时的稳定性.探讨了多时刻模式中数值积分有时发散的问题，揭示了由过去时次资料动态求取记忆函数，改变了原定设计的差分格式，且它是一个时间平滑因子的本质. 关键词： 回溯阶差分格式 多时次 稳定性 记忆性     

基于延伸期可预报性的集合预报方法和数值试验

集合预报是考虑初始条件和模式不确定性的有效途径. 结合延伸期可预报性特征,对具有不同特性的可预报分量和随机分量采用不同的集合预报方案和策略,发展了一种基于延伸期可预报性的集合预报新方法(PBEP).该方法以延伸期数值预报模式为平台,对可预报分量采用多个模式误差订正方案,从考虑模式不确定性的角度进行集合;而对随机分量则利用历史资料从气候概率的角度给出集合概率分布,避免模式误差对随机分量概率分布的影响.试验结果表明,相比于国家气候中心的业务动力延伸集合预报系统,该集合预报方法对全球各区域环流预报技巧均有提高,对不同空间尺度的波也有不同程度的改进,显示出潜在的业务应用前景.     

受下垫面强迫的一类强对流系统特征及预报

本文根据具有强迫耗散非线性动力系统理论,提出了至少有些类型的中尺度对流系统可以是以大尺度场为控制变量的中尺度动力系统的吸引子,它的发生是大尺度场演变到一定的临界点使原来的状态失稳而迅速进入到吸引子的过程。这样预报它的发生就成了吸引子的计算而不严格依赖中尺度初始状态。用一个十层原始方程有限区域谱模式对发生在华东中尺度试验期间的实际个例进行了计算,结果证实了理论分析。     

A NEW APPROACH TO IMPROVE THE NUMERICAL WEATHER PREDICTION

For certain particular initial values, the results of numerical weather prediction are extremely sensitive to the errors in some parameters of the models, which probably is one of the reasons to bring about serious failures to the forecast. In this paper, this speculation is shown by an example of numerical experiments, and it is suggested that the parameters in the models be modified with the information provided by observational data of the recent atmospheric evolution to avoid failures of the forecast. The numerical simulation tests with a simple quasi-geostrophic barotropic model have obtained satisfying results.