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Forming proper ensemble forecast initial members with four-dimensional variational data assimilation method

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Chinese Science Bulletin 1999年第16期44卷 1527-1531页

作者： Jiandong Gong Weijing Li jifan chou Natl Climate Ctr Beijing 100081 Peoples R China Lanzhou Univ Dept Atmospher Sci Lanzhou 730000 Peoples R China

A method has been presented to improve ensemble forecast by utilizing these initial members generated by four-dimensional variational data assimilation (4-D VDA), to conquer limitation of those initial members generated by Monte Carlo forecast (MCF) or lagged average forecast (LAF). This method possesses significant statistical characteristic of MCF, and by virtue of LAF that contains multi-time information and its initial members are harmonic with

关键词： ensemble forecast initial member generating four-dimensional variational data assimilation method numeri-cal forecast experiments.

Theory of three-pattern decomposition of global atmospheric circulation

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Science China Earth Sciences 2020年第9期63卷 1248-1267页

作者： Shujuan HU Bingqian ZHOU Chenbin GAO Zhihang XU Qingwan WANG jifan chou Key Laboratory for Semi-Arid Climate Change of the Ministry of Education College of Atmospheric SciencesLanzhou UniversityLanzhou 730000China

This paper reviews the three-pattern decomposition of global atmospheric circulation(3P-DGAC)developed in recent years,including the decomposition model and the dynamical equations of global horizontal,meridional,and zonal circulations.Compared with the traditional two-dimensional(2D)circulation decomposition method,the 3P-DGAC can effectively decompose the actual vertical vorticity into two components that are caused by the horizontal circulation and convergent/divergent movement(associated with the meridional and zonal circulations).It also decomposes the vertical velocity into the components of the meridional vertical circulation and the zonal vertical circulation,thus providing a new method to study the dynamical influences of convergent/divergent motions on the evolution of actual vertical vorticity and an accurate description of local vertical circulations.The 3P-DGAC is a three-dimensional(3D)circulation decomposition method based on the main characteristics of the actual atmospheric movements.The horizontal,meridional,and zonal circulations after the 3P-DGAC are the global generalization of Rossby waves in the middle-high latitudes and Hadley and Walker circulations in low latitudes.Therefore,the three-pattern decomposition model and its dynamical equations provide novel theoretical tools for studying complex interactions between middle-high and low latitude circulations as well as the physical mechanisms of the abnormal evolution of large-scale atmospheric circulations under the background of global warming.

关键词： Horizontal circulation Meridional circulation Zonal circulation Three-pattern decomposition of global atmospheric circulation(3P-DGAC) Dynamical equations

An Online Model Correction Method Based on an Inverse Problem:Part I—Model Error Estimation by Iteration

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Advances in Atmospheric Sciences 2015年第10期32卷 1329-1340页

作者： XUE Haile SHEN Xueshun chou jifan State Key Laboratory of Severe Weather Chinese Academy of Meteorological Sciences School of Atmospheric Sciences Lanzhou University Center for Numerical Prediction China Meteorological Administration

Errors inevitably exist in numerical weather prediction （NWP） due to imperfect numeric and physical parameterizations. To eliminate these errors, by considering NWP as an inverse problem, an unknown term in the prediction equations can be estimated inversely by using the past data, which are presumed to represent the imperfection of the NWP model （model error, denoted as ME）. In this first paper of a two-part series, an iteration method for obtaining the MEs in past intervals is presented, and the results from testing its convergence in idealized experiments are reported. Moreover, two batches of iteration tests were applied in the global forecast system of the Global and Regional Assimilation and Prediction System （GRAPES-GFS） for July-August 2009 and January-February 2010. The datasets associated with the initial conditions and sea surface temperature （SST） were both based on NCEP （National Centers for Environmental Prediction） FNL （final） data. The results showed that 6th h forecast errors were reduced to 10% of their original value after a 20-step iteration. Then, off-line forecast error corrections were estimated linearly based on the 2-month mean MEs and compared with forecast errors. The estimated error corrections agreed well with the forecast errors, but the linear growth rate of the estimation was steeper than the forecast error. The advantage of this iteration method is that the MEs can provide the foundation for online correction. A larger proportion of the forecast errors can be expected to be canceled out by properly introducing the model error correction into GRAPES-GFS.

关键词： model error past data inverse problem error estimation model correction GRAPES-GFS

An Online Model Correction Method Based on an Inverse Problem:PartⅡ——Systematic Model Error Correction

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Advances in Atmospheric Sciences 2015年第11期32卷 1493-1503页

An online systematic error correction is presented and examined as a technique to improve the accuracy of real-time numerical weather prediction, based on the dataset of model errors （MEs） in past intervals. Given the analyses, the ME in each interval （6 h） between two analyses can be iteratively obtained by introducing an unknown tendency term into the prediction equation, shown in Part I of this two-paper series. In this part, after analyzing the 5-year （2001-2005） GRAPES- GFS （Global Forecast System of the Global and Regional Assimilation and Prediction System） error patterns and evolution, a systematic model error correction is given based on the least-squares approach by firstly using the past MEs. To test the correction, we applied the approach in GRAPES-GFS for July 2009 and January 2010. The datasets associated with the initial condition and SST used in this study were based on NCEP （National Centers for Environmental Prediction） FNL （final） data. The results indicated that the Northern Hemispheric systematically underestimated equator-to-pole geopotential gradient and westerly wind of GRAPES-GFS were largely enhanced, and the biases of temperature and wind in the tropics were strongly reduced. Therefore, the correction results in a more skillful forecast with lower mean bias and root-mean-square error and higher anomaly correlation coefficient.

关键词： model error past data inverse problem error estimation model correction GRAPES-GFS

Dynamic-statistics combined forecast scheme based on the abrupt decadal change component of summer precipitation in East Asia

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Science China Earth Sciences 2015年第3期58卷 404-419页

作者： GONG ZhiQiang ZHAO JunHu FENG GuoLin chou jifan Laboratory for Climate Studies National Climate Research Center CMA College of Atmospheric Science Lanzhou University

基于 19832011 CMAP 数据，在东亚的降水异例和它的附近的海区域(此后叫的东亚为短) 在 1999 前表明 ++ 模式并且 + 模式以后；这个十的变化在相应 EOF3 部件主要被包含。然而， NCC_CGCM 预报结果是相当不同的，它在 1999 前揭示 ++ ... 详细信息

基于 19832011 CMAP 数据，在东亚的降水异例和它的附近的海区域(此后叫的东亚为短) 在 1999 前表明 ++ 模式并且 + 模式以后；这个十的变化在相应 EOF3 部件主要被包含。然而， NCC_CGCM 预报结果是相当不同的，它在 1999 前揭示 ++ 模式并且 ++ 模式以后。同时，基于这些关键 SST 区域改进 NCC_CGCMs 预报精确性的概率被讨论，并且动态统计的联合预报计划为增加在东亚在夏天降水包含的十的变化的信息被构造。独立样品预报结果显示这个预报计划罐头有效地修改十的变化信息在东亚在夏天降水包含了的 NCC_CGCMs (特别在 30 敢琠敨攠癮的区域吗？？

关键词：年代际变化东亚地区预测计划夏季降水动态统计组件系统误差修正预测准确率

Forecast scheme and strategy for extended-range predictable components

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Science China Earth Sciences 2013年第5期56卷 878-889页

作者： ZHENG ZhiHai HUANG JianPing FENG GuoLin chou jifan National Climate Center China Meteorological Administration College of Atmospheric Sciences Lanzhou University

Although extended-range forecasting has exceeded the limit of daily predictability of weather,there are still partially predictable characteristics of meteorological fields in such forecasts.A targeted forecast scheme and strategy for extended-range predictable components is proposed.Based on chaotic characteristics of the atmosphere,predictable components and unpredictable random components are separated by using the standpoint of error growth in a numerical model.The predictable components are defined as those with slow error growth at a given range,which are not sensitive to small errors in initial conditions. A numerical model for predictable components(NMPC)is established,by filtering random components with poor predictability.The aim is to maintain predictable components and avoid the influence of rapidly growing forecast errors on small scales. Meanwhile,the analogue-dynamical approach(ADA)is used to correct forecast errors of predictable components,to decrease model error and statistically take into account the influence of random components.The scheme is applied to operational dynamical extended-range forecast(DERF)model of the National Climate Center of China Meteorological Administration (NCC/CMA).Prediction results show that the scheme can improve forecast skill of predictable components to some extent, especially in high predictability regions.Forecast skill at zonal wave zero is improved more than for ultra-long waves and synoptic-scale waves.Results show good agreement with predictability of spatial scale.As a result,the scheme can reduce forecast errors and improve forecast skill,which favors operational use.

关键词：预测计划组件模型误差预测误差成分分析数值模型预报技巧可预见性

Large-scale low-frequency rainfall regimes and their transition modes in summertime over China

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Chinese Science Bulletin 2006年第11期51卷 1355-1367页

作者： REN Hongli ZHANG Peiqun chou jifan LI Weijing GAO Li College of Atmospheric Sciences Lanzhou University Lanzhou 730000 China Laboratory for Climate Studies National Climate Centre China Meteorological Administration Beijing 100081 China LASG Institute of Atmospheric Physics Chinese Academy of Sciences Beijing 100029 China

Seven large-scale low-frequency rainfall regimes (LFRRs) in summertime are identified for China in a 10-dimensional phase space by using a 40-year daily precipitation dataset. Corresponding to the local extrema of observed probability density in phase space, the LFRRs are characterized by the persistence and transitions that reflect the spread and jump features of low-frequency rainfall centers. The LFRRs are generally consistent with summer monsoon rainbelts on the intraseasonal timescale, and there exist the preferred transition relationships between the LFRRs. Four LFRRs’ transition modes (LFRRTMs), which are the dominant components of the interannual and intraseasonal variability of sum- mer rainfall in China, are further induced. Analyses of atmospheric circulation system show that the anomalies of the subtropical high over the western Pacific (SHWP) and blockings in mid-high latitudes, the low-latitude circulation anomalies, and the wavetrains over the East Asia-Pacific region (EAPWs), play crucial roles in the occurrence and transitions of the LFRRs. Moreover, the evolution of the SHWP and blockings, the distribution and movement of the EAPWs, and the intraseasonal variability of the East Asian-Pacific jet stream may be principal factors of the formations of the LFRRTMs.

关键词：夏季降雨相空间低频降雨体系大尺度预报

数值天气预报的创新之路——从初值问题到反问题

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气象学报 2007年第5期65卷 673-682页

作者：丑纪范兰州大学大气科学学院兰州730000

基于大气并非是一个确定论的系统,从信息论的视角考察了数值天气预报问题。认为表征初值和边值的数据可以视为输入信息(信息源),而数值模式则不过是一个信息变换机构,它把输入信息变换成预报结论而输出来,输出的预报结论则是未来天气状... 详细信息

基于大气并非是一个确定论的系统,从信息论的视角考察了数值天气预报问题。认为表征初值和边值的数据可以视为输入信息(信息源),而数值模式则不过是一个信息变换机构,它把输入信息变换成预报结论而输出来,输出的预报结论则是未来天气状况的信息。于是预报的准确性受制于:一是输入信息所包含的输出信息的信息量,另一是信息在变换过程中丢失的信息量。从初值的形成过程揭示出了当前观测系统在一个时刻提供的数据没有包含初值所要求的全部信息,而缺失的部分或多或少的隐藏在过去的观测数据中。提为初值问题意味着只依据一个时刻的状态导致输入的信息量缺失,应考虑过去的历史数据以增加输入数据中所包含的预报量的信息。文中指出由于输出信息比输入还多的数值模式是不存在的,这样的改进带有根本性。进一步论证了数值模式的误差信息,也或多或少的隐藏在过去的历史数据中,为了充分使用过去的观测数据,本文建议改变问题的提法,不提成初值问题,提成反问题。资料同化本质上是反问题,其欠定性不应人为夸大。提成反问题的数值天气预报能充分应用过去的历史资料,将天气方法、统计方法、动力方法有机地结合在一起。对于这个反问题如何具体求解方面,在分析了业务和研究的区别,模式的普适性和针对性的统一的基础上,给出了反问题的具体解决途径。强调无需构建新模式(这是非常困难的工作),只需运行现成的模式,借助所关心的预报对象的历史数据来改造现成模式,因而是完全可行的。

关键词：数值天气预报反问题信息论

Advancement and prospect of short-term numerical climate prediction

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Chinese Science Bulletin 2001年第18期46卷 1497-1502页

作者： chou jifan & XU Ming1. Department of Atmospheric Sciences, Lanzhou University, Lanzhou 730000, China 2. Training Center of Chinese Meteorological Administration, Beijing 100081, China Department of Atmospheric Sciences Lanzhou University Lanzhou China Training Center of Chinese Meteorological Administration Beijing China

The defects of present methods of short-term numerical climate prediction are discussed in this paper, and four challenging problems are put forward. Considering our under developed computer conditions, we should innovate in the approcuch of numerical climate prediction on the basis of our own achievements and experiences in the field of short-term numerical climate prediction. It is possibly an effective way to settle the present defects of short-term numerical climate prediction.

关键词： short-term climate numerical prediction defects innovation.