谱模式T63L9正规模初值化方案及试验

推导了全球谱模式T63L9的正规模,对求得的垂直和水平正规模做了分析,与其他文献进行了比较.在此基础上,为其资料四维同化系统研制了一套合适的绝热非线性正规模初值化方案,并进行了一系列试验.分析表明:方案的研制是成功的,它有效地消除了模式早期积分中虚假的高频振荡,明显改进了短期预报的效果;初值化不仅对随后的一次预报有明显的改进,而且通过同化循环,提高了整个资料同化和预报的质量.     

中期数值天气预报业务系统讲座 第二讲 四维资料同化业务系统

该文简单地叙述了国家气象中心四维资料同化业务系统中的各子系统,即资料处理、客观分析、初值化和模式预报子系统。该系统能较好地为预报模式提供初始条件。并对四维资料同化业务系统中的分析质量进行了评述。     

第二讲 四维资料同化业务系统

该文简单地叙述了国家气象中心四维资料同化业务系统中的各子系统,即资料处理、客观分析、初值化和模式预报子系统。该系统能较好地为预报模式提供初始条件。并对四维资料同化业务系统中的分析质量进行了评述。     

四维资料同化的试验研究

四维资料同化是近年来气象科学上的一个新课题,为了探讨一些基本问题,本文用正压原始方程模式进行了高度观测资料的更新和同化的初步试验研究。 试验结果表明,将测站的实测资料内插到网格点上,再用这种资料作更新或四维资料同化可以减小观测误差的影响,避免所谓排斥现象;四维资料同化方案中需要有气压场和风场间的调整。本文提出了一种简便的四维资料同化方案,用这种方案对观测资料进行同化,得到某一时刻的分析场,再用这种分析场作初值与直接用该时刻的观测场作初值分别作数值预报,其预报结果是前者比后者明显地好,进一步说明了四维同化工作有其重要意义,不但使用非定时的气象观测资料需要四维资料同化,而且在四维同化基础上可以改进数值预报。     

变分同化方法在Lorenz系统中的简单应用研究

利用Lorenz模式作变分同化数值试验，通过对一个简单系统的讨论，介绍四维变分同化方法。对初值敏感性和观测点的个数及观测值作了对比试验，发现随着模式对初值敏感性的增加，同化效果会越来越差；观测点越少，观测值误差越大，这些都会影响同化效果，甚至导致同化失败。     

基于扰动模式的四维变分资料同化系统框架的设计完善和数值试验

为了建立一个应用于区域数值预报的四维变分资料同化（4DVar）系统,在近期开发的扰动预报模式GRAPES_PF基础上,开发完善增量四维变分同化系统框架。该框架中暂不包含物理过程（长短波辐射、边界层过程、对流参数化和云微物理等）。对比业务使用的GRAPES 3DVar系统,增加了温度控制变量。将无量纲Exner气压与流函数的线性风压平衡方程直接在地形追随垂直坐标面上求解,且通过广义共轭余差法（GCR）求解扰动亥姆霍兹（Helmholtz）伴随方程。利用人造“探空”资料对2015年10月台风“彩虹”进行了理想数值试验。试验结果表明,所开发的扰动四维变分同化框架得到了预期的结果,即同化更多资料并反复受到模式约束的四维变分同化系统能有效改善初值质量,进而改善区域数值预报。建立的区域四维变分同化框架合理可行,为进一步发展包含完整物理过程的区域四维变分同化系统奠定了研究基础。      

一种四维同化方法的试验研究

文章利用一个有限区模式对一种资料四维同化过程作了试验研究，以考察四维资料同化对模式的预报过程的作用。试验结果表明:四维资料同化可以为模式提供一组四维动力协调的积分初值。对由于资料或模式原因造成的积分开始时的高频振荡有很好的抑制作用，使模式的积分稳定性增强。      

区域资料四维同化试验

根据国家气象中心有限区分析预报系统的基本方案，设计一个以6小时为周期的间歇区域资料四维同化方案，对我国的两次暴雨过程进行两种不同粗细水平分辨率的资料四维同化和短期模式预报的试验。结果表明，由同化方案初值获得的短期预报明显好于LAFS方案的预报结果，高分辨率同化方案对预报的改进更明显。     

改进的台风初值化方案及四维变分同化的个例试验

由于洋面上常规观测资料严重不足,使得客观分析的结果难以准确地描写初始台风的热力结构和环流特征,这是造成台风数值预报误差较大的重要原因.传统的Bogus方案虽然对台风预报有很大改进,但是仍有许多不足.文中在前人研究工作的基础上,对Bogus方案进行了改进,提高了对台风强度的描述能力,并结合四维变分资料同化的方法,利用模式动力学约束,自动生成具有非对称环流结构的台风初值,最后进行了四维变分同化试验和数值模拟试验.数值结果表明:这种结合Bogus方法和四维变分同化方法的台风初值化方案对于台风的路径模拟和强度模拟均有较好的改进.     

一种新的资料同化方法

为寻求一种快速有效的四维变分资料同化(英文缩写4DVar)作了有意义的尝试,提出了映射观测的新概念和反向四维变分资料同化的新思路,并以此为基础建立了三维变分映射资料同化(英文缩写为3DVM:3-DimensionalVariational data assimilation of Mapped observation)。该方法与传统的四维变分资料同化一样,不仅考虑了模式的动力和物理约束,使得同化后的初值与模式协调,而且通过模式方程对同化窗口中不同时刻的观测资料作了最佳拟合。与传统四维变分同化方法不同的是,由3DVM得到的初值不在同化窗口的始端,而在窗口的末端。正是所求初值时刻的改变,使得该方法的计算代价大大减少,几乎与三维变分资料同化(英文缩写3DVar)相当,这实际上是用3DVar的代价实现了4DVar的功能。同时,由于3DVM不再需要切线性和伴随近似来计算代价函数的梯度也提高了同化的精度。对具体的台风个例(Dan)用AMSU-A反演的温度场进行变分同化模拟试验,发现3DVM能比传统4DVar产生更好的初值,而且所花计算时间只需4DVar的1/7。     

Improving Precipitation Forecasts over the Global Tropical Belt

Summary  This study explores the nowcasting and short-range forecasting (up to 3 days) skills of rainfall over the tropics using a high resolution global model. Since the model-predicted rainfall is very sensitive to model parameters, four key model parameters were first selected. They are the Asselin filter coefficient, the fourth order horizontal diffusion coefficient, the surface moisture flux coefficient, and the vertical diffusion coefficient. The optimal values were defined as those which contributed to the best one day rainfall forecasts in the present study. In order to demonstrate and improve the precipitation forecast skill, several numerical experiments were designed using the 14-level Florida State University Global Spectral Model (FSUGSM) at a resolution of T106. Comparisons were also made of the short-range forecasts obtained from a control experiment subjected to normal mode initialization (NMI) versus experiments based on physical initialization (PI). The latter experiments were integrated using the original FSUGSM and a modified version. This modified FSUGSM was developed here by applying a reverse cumulus parameterization alorithm to the regular forecast model, which restructures the vertical humidity distribution and constrains the large-scale model’s moisture error growth during the model integration. An improved short-range rainfall prediction skill was achieved from the modified FSUGSM in this study. The results showed a better agreement between model-based and observed rainfall intensity and pattern. Received January 18, 1999     

非线性正规模初值化原则在有限区模式的实现

本文在普遍情况下导出了与非线性正规模初值化方法等价的、用模式变量表达的初值化准则与运算迭代公式.由于模式的正规模态在初值化计算中不明显地出现,故本文的结果对于正规模态难以求得的有限区模式的初值化有重要意义_试验实例表明,按本文的方案作初值处理,对于消除初值中的不平衡是十分有效的.     

The application of non‐linear normal mode initialization to an operational forecast model

Abstract

The non‐linear normal mode initialization technique used in shallow water equation models by Baer (1977) and Machenhauer (1977) is now applied to a full baroclinic primitive equations forecast model. The initialization procedure is shown to be capable of completely removing high frequency oscillations from model integrations, even in the presence of topography. The procedure also produces a consistent and physically realistic initial vertical motion field.     

On Normal Mode Aided Modelling: Application to Asian Monsoon

Summary A new concept of utilizing generalized normal mode initialization (NMI) for modelling is investigated. This NMI-balancing adapts real data to model solutions. For eigenmodes of typical (climatological) structure and a simple 1- or more-layer shallow water model, anomalous flow of special episodes or events can be identified with mode groups giving distinctive signals. If these signals are part of the model solution or of the complement of the data to the model solution and how this is changed by introducing additional physical mechanisms to the model, gives hints for improvement. In applying this to multi-scale interactions of Asian monsoon, in particular a seventeen-years background knowledge and the anomalous flow of years 1991, 1977, 1978 we have a challenging test frame. Particular topics are: (1) Mei Yu rains in China, the representation of particular aspects of them by certain mode groups, the degree of independence of the corresponding signals on other modes, and the role of dissipation; (2) detection of El Ni?o-Southern Oscillation (ENSO) in atmospheric (reanalysis) data minus the NMI-balanced model solution; (3) Madden-Julian Oscillations (MJO) and the introduction of diabatic processes, and finally (4) aspects of dynamic stability. From among the results which are new or we simply have become aware of we pull out that atmospheric processes generally can be represented by modes or mode groups neither straight forward nor uniquely. Introduction of some dissipation schemes to the model was not helpful but rather destroyed the realistic structure of atmospheric dynamics. A parameterization of diabatic processes passes signals present in the data but not in the NMI-balanced model solution through to such being part of the latter, in case of MJO but not yet in case of ENSO. Ocean dynamics proves to be indispensable. Nevertheless there are imprints of essential atmospheric processes hidden on certain (e.g., most unstable) modes and partially recovered by NMI-balancing. Received July 19, 1999 Revised December 29, 1999     

Fengyun-4 Geostationary Satellite-Based Solar Energy Nowcasting System and Its Application in North China

Surface solar irradiance (SSI) nowcasting (0–3 h) is an effective way to overcome the intermittency of solar energy and to ensure the safe operation of grid-connected solar power plants. In this study, an SSI estimate and nowcasting system was established using the near-infrared channel of Fengyun-4A (FY-4A) geostationary satellite. The system is composed of two key components: The first is a hybrid SSI estimation method combining a physical clear-sky model and an empirical cloudy-sky model. The second component is the SSI nowcasting model, the core of which is the derivation of the cloud motion vector (CMV) using the block-matching method. The goal of simultaneous estimation and nowcasting of global horizontal irradiance (GHI) and direct normal irradiance (DNI) is fulfilled. The system was evaluated under different sky conditions using SSI measurements at Xianghe, a radiation station in the North China Plain. The results show that the accuracy of GHI estimation is higher than that of DNI estimation, with a normalized root-mean-square error (nRMSE) of 22.4% relative to 45.4%. The nRMSE of forecasting GHI and DNI at 30–180 min ahead varied within 25.1%–30.8% and 48.1%–53.4%, respectively. The discrepancy of SSI estimation depends on cloud occurrence frequency and shows a seasonal pattern, being lower in spring–summer and higher in autumn–winter. The FY-4A has great potential in supporting SSI nowcasting, which promotes the development of photovoltaic energy and the reduction of carbon emissions in China. The system can be improved further if calibration of the empirical method is improved.     

Normal mode initialization for simple models

Summary The normal mode initialization procedures of Phillips (1960) and Temperton (1988) are re-examined and applied to one-dimensional linear and non-linear primitive equations models. The linear method is obtained by setting the first and second substantial time derivatives of the divergence to zero. The resulting state is free of gravity waves. In the non-linear procedure, the substantial time derivatives calculated from the model equations of the gravitational modes are set to zero by implicitly adjusting these modes only. Five-day numerical integrations are performed using both models. The results clearly show the importance of proper initialization. Analytical solutions support the numerical results.With 2 Figures     

THE IMPACT OF INITIAL FORCED WIND ON THE PREDICTABILITY OF THE ZEBIAK-CANE COUPLED OCEAN-ATMOSPHERE MODEL

With simultaneous observed sea surface temperature anomaly (SSTA), the difference between NCEP/NCAR 925hPa reanalysis wind stress anomaly (NCEPWSA) and FSU wind stress anomaly (FSUWSA) is analyzed, and the prediction abilities of Zebiak-Cane coupled ocean-atmosphere model (ZC coupled model) with NCEPWSA and FSUWSA serving respectively as initialization wind are compared. The results are as follows. The distribution feature of NCEPWSA matches better with that of the observed SSTA than counterpart of FSUWSA both in 1980s and in 1990s; The ZC ocean model has a better skill under the forcing of NCEPWSA than that of FSUWSA, especially in 1990s. Meanwhile, the forecast abilities of the ZC coupled model in 1990s as well as in 1980s have been improved employing NCEPWSA as initialization wind instead of FSUWSA. Particularly, it succeeded in predicting 1997/1998 El Ni?o 6 to 8 months ahead; further analysis shows that on the antecedent and onset stages of the 1997/1998 El Ni?o event, the horizontal cold and warm distribution characteristics of the simulated SSTA from ZC ocean model, with NCEPWSA forcing compared to FSUWSA forcing, match better with counterparts of the corresponding observed SSTA, whereby providing better predication initialization conditions for ZC coupled model, which, in turn, is favorable to improve the forecast ability of the coupled model.     

非线性正规模初值化及其对资料同化和预报的影响

文章介绍了国家气象中心中期数值预报谱模式（T42L9）的非线性正规模初值化方案（NNMI）。讨论了该方案对资料同化和预报的影响。试验表明，应用前5个垂直模，经2次迭代能够得到一个对分析资料修正较小的平衡初始场。它成功地消除了预报中虚假的高频重力波振荡，对改进资料同化和模式预报起了重要作用。