资料同化中背景场位势高度误差统计分析的研究

在客观分析中,背景误差协方差对观测信息的传播和平滑、反映不同变量之间的关系有着非常重要的作用.构造合理的背景误差协方差矩阵对于同化系统至关重要,甚至会决定同化分析的好坏.作者主要利用观测余差方法,用T213预报资料和无线电探空观测资料统计我国区域的背景位势高度误差协方差样本,分析背景误差协方差场的结构特征和拟合误差场的空间分布.     

中国气象数值预报系统技术创新研究

项目启动以来,经过课题组成员一年半卓有成效的努力工作,各课题都按照项目专家组批准的年度计划,顺利开展了研究工作.     

925hPa资料对高度场分析和预报的影响

通过连续１５天的平行业务数据预报试验，详细地分析了９２５ｈＰａ资料的应用对高度场分析和预报的影响。结果表明，９２５ｈＰａ资料的加入对印度洋西北部及马来西亚至菲律宾以南热带地区的分析影响较大，对其余地区影响较小。总的来说对形势场分析影响不很大，且对低层的影响大于中高层。同时，可以明显地减小从Ｐ面分析场到模式σ面的垂直插值误差。此外，对２４小时预报场的影响小于对初始场的影响，同时对模式积分的平稳性和预     

斜压大气中飑线的非线性过程与K-dV方程

本文从理论上证明斜压非静力平衡大气中飑线的形成与演变和正压大气中一样可以归结为一类由K-dV方程所描述的大气孤波.讨论了在具有垂直切变的基本气流中这类孤波的结构特征,并与观测事实作了对比.当沿着低空急流出现有限宽度的初始扰动时,这种孤波可以被激发出来.当扰动的强度与宽度达到一定值时,还将形成一种孤波队列.这正是大气中所观测到的飑线或雷雨列队现象.     

热带有限区分裂半隐式斜压初始方程预报模式

本文提出一个采用分裂半隐式时间积分方案的热带有限区多层初始方程数值预报模式。业务预报试验表明模式的计算稳定性较好,预报作业时间较显式方案缩短约三分之二,对热带天气系统有一定预报能力。为了弥补热带大洋上探空资料不足,还试验了插补其他来源的资料,效果也较好。     

Implementation of CMA-GFS 3D-Var System on the Yin-Yang Grid

The global three-dimensional variational (3D-Var) data assimilation is implemented on a new quasi-uniform overset (Yin-Yang) grid on sphere. As a quasi-uniform spherical grid, it covers the sphere by overlapping two perpendicularly oriented grid components which is nothing but low latitude region of the usual latitude-longitude grid. Based on this characteristic of the Yin-Yang grid, it enables us to implement the regional 3D-Var system efficiently and accurately on the Yin or Yang component grid, respectively. The global analysis could update directly from the regional analysis since they have the same configurations like the precondition of eigenvalue decomposition for vertical direction, recursive filtering for horizontal direction, minimization method and observation operator and so on. However, the balance equation and vector wind are needed to be paid more attention on the Yin grid analysis due to its coordinate transformation. How to spread the observation information near the boundary of Yin and Yang grid is a key to the 3D- Var analysis. Extending double the horizontal correlation length distance in the overset boundary of Yin and Yang grid has successfully solved the problem. The results show that the analysis on the Yin-Yang grid is reasonable and similar to the result on the latitude-longitude (LAT-LON) grid. This paper provides a promising strategy for the development of a 3D-Var global system for overset grids.     

ENHANCED REGIONAL NUMERICAL PREDICTION SYSTEM AND ITS PERFORMANCE

During the "8th Five-Year Plan"(1991～1995), a new operational mesoscale numerical predictionsystem is developed, which is called the "Regional Enhanced Numerical Prediction System". The system possesses higher resolution(45 km grid sise in horizontal, 10 layers in vertital), as well as fullphysical processes, and can be run operationally in the Guangzhou Regional Meteorological Centre(GRMC). A plenty of experiments indicate its better performance in predicting various weather systemsaffecting the south of China, especially the typhoon and heavy rain in the "early floods stage"(annuallyspeaking). Verification of the prediction of all typhoon cases affecting the region in 1993～1995 indicatethat rainfall prediction scores of the system are obviously higher than those of the LAFS in the NationalMeteorological Centre, and track prediction error is no larger than those of NWPs in main world centressuch as the National Hurrieane Center of NOAA and the JMA. The aim of the paper is to give a generalized introduction and analysis to the system and its performance.     

JFNK方法概述及其在大气全隐式非静力模式中的应用方案

首先介绍了近年来新发展的非线性方程全隐式数值求解的JFNK方法,及其在地球流体力学方面应用计算实例.可看到,无论在计算精度还是计算效率方面,全隐式数值求解远远超过常规的半隐式计算格式.其次,还讨论了JFNK方法在气象非静力模式中应用方案,并提出了用静力假定和半隐式差分格式来构造预条件处理器,变三维求解为二维求解,简化了方程组求解难度.该方案不仅可用于差分模式,也为用譜方法求解非静力模式提供可能.     

GRAPES全球模式的模式误差估计

现代数值天气模式考虑的物理过程和边界条件越来越复杂, 但是它描述的大气状态和真实的大气流体运动轨迹还有一定的差距, 存在模式误差。在以往的研究中, 模式误差往往被忽略, 在集合卡尔曼滤波同化系统中, 如果忽略模式误差会导致滤波发散现象。本文用不同分辨率的模式预报差异估计了GRAPES全球模式的模式误差, 研究发现模式误差随着分辨率降低而线性增加, 而且模式误差随着预报时效的增加呈现线性增长的趋势。     

数值天气预报中卫星资料同化应用现状和发展

卫星资料已大量应用于数值天气预报,占据了所用观测资料的主体并对数值天气预报效果的改善具有明显的作用。目前卫星资料的同化应用一方面在努力解决受地表辐射、云和降水影响的卫星观测资料的同化问题,以充分利用现有卫星资料并发挥其效能,同时发展适应伴随全球观测系统建立而带来大数量和多种类新类型卫星资料的同化应用。文章介绍了为满足卫星资料在数值天气预报中同化应用现状与发展而建立的两个卫星资料同化研究中心(JCSDA:Joint Center of Satellite Data Assimilation和NWP SAF:Satellite Applications Facility for Numerical Weather Prediction)的基本情况,并简要讨论我国数值天气预报中卫星资料同化应用。