增长模繁殖法在华南暴雨中期集合预报中的应用

采用增长模繁殖法和全球谱模式T106L19对2005年6月发生在华南的暴雨过程进行了中期集合预报试验。结果表明：相对于单一的确定性预报,集合预报能给出更多的预报信息;各成员的降水预报、降水概率预报等丰富的预报产品能够给暴雨预报提供更有价值的信息,减少漏报率,对低压槽线和副高脊线等关键环流系统的预报,集合预报结果更为接近实况。     

Sensitivity of medium-range weather forecasts to the use of reference atmosphere

In this paper, the authors develop the earlier work of Chen Jiabin et al. (1986). In order to reduce spectral truncation errors, the reference atmosphere has been introduced in ECMWF model, and the spectrally-represented variables, temperature, geopotential height and orography, are replaced by their deviations from the reference atmos-phere. Two modified semi- implicit schemes have been proposed to alleviate the computational instability due to the introduction of reference atmosphere. Concerning the deviation of surface geopotential height from reference atmos-phere, an exact computational formulation has been used instead of the approximate one in the earlier work. To re-duce aliasing errors in the computations of the deviation of the surface geopotential height, a spectral fit has been used slightly to modify the original Gaussian grid-point values of orography.A series of experiments has been performed in order to assess the impact of the reference atmosphere on ECMWF medium- range forecasts at the resolution T21, T42 and T63, The results we have obtained reveal that the reference atmosphere introduced in ECMWF spectral model is generally beneficial to the mean statistical scores of 1000-200 hPa height 10-day forecasts over the globe. In the Southern Hemisphere, it is a clear improvement for T21, T42 and T63 throughout the 10-day forecast period, In the Northern Hemisphere, the impact of the reference atmos-phere on anomaly correlation is positive for resolution T21, a very slightly damaging at T42 and almost neutral at T63 in the range of day 1 to day 4. Beyond the day 4 there is a clear improvement at all resolutions.     

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     

Forecasts of hydrological parameters over the Mackenzie River Basin: Sensitivity to initial conditions,horizontal resolution and forecast range

Abstract

As part of the Global Energy and Water Cycle Experiment, Canadian global spectral forecast model predictions of surface water and energy fluxes over the Mackenzie River basin are examined. Two nine‐member ensemble forecasts of one month duration are produced with the operational model, for a spring and a summer case, at a horizontal resolution of about 100 km (T95). The sensitivity to initial conditions is measured by the degree to which the individual forecasts in the ensembles vary one from another. The evolution in time of this estimated error (ensemble standard deviation) is determined for the surface energy and water accumulations, averaged over the basin. For comparison the calculations are repeated for the Mississippi basin and over North America. The greatest sensitivity is found for the net accumulation of precipitation minus evaporation. The spring ensemble is redone at a coarser horizontal resolution (T47), and the results are similar. The forecast uncertainty (ensemble standard deviation) of the area‐averages over the basin appear to be unaffected by this change, although the ensemble mean values are sensitive to the change in resolution. The ensemble standard deviation makes a significant, abrupt increase toward the end of the second week into the forecasts. This investigation suggests a need for an improved model, if the forecasts’ useful range is to extend to one month. Available upgrades to the land‐surface, precipitation and evaporation schemes will be used in subsequent work, and the forecasts reported here will serve as a baseline for comparison.     

Organization of convection and monsoon forecasts

Summary In this paper we address the issue of monsoon forecasts in relation to the organization of convection. Given a physical initialization procedure, within a data assimilation, it is possible to use the detailed distribution of rainfall from mesoconvective precipitating elements to define the initial state of a global model. If that is carried out using a very high resolution model then the initial state can carry within it an organization of convection within the resolvable scales. Then the impact of physical initialization on the maintenance and prediction of tropical weather such as the monsoon can be determined. Lacking such an initialization, one can expect the convectively driven energetics to be biased, and a slow degradation of the forecasts can follow. Several examples of forecasts at different resolutions are discussed here. The main findings of this study are that improved forecast results are obtained when physical initialization is invoked where the observed rain and the model resolution are comparable, i.e. the footprint of the highest resolutions rainfall estimates obtained from satellite based data sets (principally we use the SSM/I instrument over the oceans). At this resolution, we note that the model is able to carry an organization of convection in the initialization and in the forecasts through the medium-range time scale.We have compared our results of monsoon studies at a resolution T255 with those at resolution T62. The transform grid separation at the resolution T255 is approximately 50 km and at the resolution T62, it is approximately 200 km. We find that the model at the higher resolution (T255) performs better and has more realistic energy conversions for the convectively driven synoptic scale monsoon.An organization of convection, at the synoptic scales, is not seen in the forecasts at lower resolutions, T62, where the rainfall patterns are generally much broader and tend to be more zonal. Such organization appears more realistic at the resolution T255. Variances of the energy conversion, calculated in the two-dimensional spectral space, from physically initialized short range forecasts at the higher resolution are seen to be largest on the scales of the monsoon. Similar calculations for the reanalyzed fields at lower resolutions show the spectral distribution of variances to be biased towards local Hadley scale overturnings.With 12 Figures     

淇、卫河流域面雨量预报

根据淇，卫河水系特点，利用LASGREM模式输出的降水预报与T106（T213）降水预报结果，进行加权集成，制作淇，卫河流域分片面雨量预报。     

国家气象中心T213L31数值预报运行监控方案及预报效果评估

T213L31系统是我国新一代中期数值预报业务系统，该文介绍了该系统的实时业务运行流程，着重阐述了实时运行监控方法的设计和实施。通过对整个运行流程的解析、运行相关信息和异常事件的说明以及功能的介绍，使读者可以对T213L31运行监控和维护方法有一个较完整的认识。文章还对T213L31系统准业务和业务运行期间的预报效果进行了较为全面的检验与评估，结果显示:T213系统较国家气象中心的原数值预报业务系统T106L19的预报效果有了明显改进，可用预报时效延长了约1天。但与世界领先的ECMWF的中期数值预报产品相比还存在一定差距，特别是中期时效的预报差距比较明显，还有待于进一步的改进和提高。     

国家气象中心新一代业务中期预报模式T213L31的主要特点

T2 1 3中期数值预报系统于 2 0 0 2年 9月 1日起在国家气象中心正式业务化。作为此系统核心的T2 1 3L31全球模式与原业务模式T1 0 6L1 9相比 ,采用了一些新的数值技术 ,包括半拉格朗日时间积分方案的引入 ,采用规约格点 ,分布内存与共享内存并行相结合 ,从而在目前有限的计算机资源条件下 ,能积分高分辨率的模式。更重要的是 ,模式采用了一些更新、具有更真实物理概念的物理过程参数化方案 ,对于辐射方案、次网格尺度地形参数化、积云对流方案、云方案、陆面过程方案都作了很大改进 ,从而克服了许多T1 0 6L1 9模式中存在的问题 ,明显提高了T2 1 3L31模式的预报技巧。     

Short‐term forecasting with a multi‐level spectral primitive equation model part II ‐ Hemispheric prognoses and verification

The spectral global baroclinic primitive equation model described in Part I of this paper has been extensively tested. The model has been run daily from operational analyses for over a year. From this large sample of forecasts, verification statistics have been collected and compared with similar statistics collected from three competitive grid‐point models. The spectral model is also compared with the grid‐point models in a synoptic case study.

A second case study demonstrates the effect of horizontal resolution and physical effects on spectral model forecasts. The results of these experiments demonstrate that the spectral model is highly competitive with other models, in terms of both accuracy and computational efficiency. On 18 February 1976 the spectral model became the operational Canadian large‐scale forecast model.     

2010年国内外3种数值预报在东北地区的预报检验

对中国国家气象中心T639数值预报、德国降水预报和欧洲中心（ECMWF）数值预报中对中国东北地区的降水、温度和环流模式的预报结果,分别进行检验。结果表明：降水预报中,德国降水预报对中国东北地区的晴雨预报、一般性降水预报效果较好,但T639数值预报的漏报率明显低于德国降水预报,而T639数值预报中24-120 h暴雨预报的TS评分明显高于德国降水预报。温度预报中,T639数值预报对中国东北地区温度预报72 h内基本可用;欧洲中心（ECMWF）数值预报在96 h内效果较好。对于24 h的温度预报准确率,T639数值预报稍高于ECMWF数值预报结果。环流模式方面：48h内T639预报效果好于ECMWF,72 h以后ECMWF预报效果好于T639。     

The impact of observation systems on medium-range weather forecasting in a global forecast system

To investigate the impact of various types of data on medium-range forecasts, observing system experiments are performed using an assimilation algorithm based on the National Centers for Environmental Prediction (NCEP)/Department of Energy (DOE) reanalysis system. Data-denial experiments for radiosonde, satellite, aircraft, and sea surface observations, and selected data experiments for radiosonde and surface data, are conducted for the boreal summer of 1997 and the boreal winter of 1997/1998. The data assimilation system used in this study is remarkably dependent on radiosonde data, which provides information about the three-dimensional structure of the atmosphere. As expected, the impact of radiosonde observations on medium-range forecasts is strongly positive over the Northern Hemisphere and tropics, whereas the satellite system is most beneficial over the Southern Hemisphere. These results are also found in experiments simulating historical changes in observation systems. Over the tropics, assimilation without radiosonde observations generates unbalanced analyses resulting in unrealistic forecasts that must be corrected by the forecast model. Forecasts based on analysis from the observation data before the era of radiosonde observation are found to be less meaningful. In addition, the impacts on forecasts are closely related to the geographical distribution of observation data. The memory of observation data embedded in the analysis tends to persist throughout forecasts. However, cases exist where the effect of forecast error growth is more dominant than that of analysis error, e.g., over East Asia in summer, and where the deficiency in observations is supplemented or the imbalance in analysis is adjusted by the forecast model during the period of forecasts. Forecast error growth may be related to the synoptic correction performed by the data assimilation system. Over data-rich areas, analysis fields are corrected to a greater extent by the data assimilation system than are those over data-poor areas, which can cause the forecast model to produce more forecast errors in medium-range forecasts. It is found that even one month per season is sufficient for forecast skill verification in data impact experiments. Additionally, the use of upper-air observations is found to benefit areas that are downstream of observation data-rich areas.     

有限区分析预报系统及其业务应用

中国国家气象中心在新开发的有限区多元最优插值分析技术及１５层球面网格原始方程模式的基础上建立了一个新的有限区分析预报系统。１９９１年投入业务使用，主要用于２４－４８ｈ降水预报。这个系统是依附于全球同化预报系统的一个分支系统。亦即使用全球谱模式６ｈ预报作为初估值进行有限区细网格分析及使用其１２—６０ｈ预报作为侧边界值进行非同步嵌套预报。作为一个升级模式系统，它的进步表现在：较充分使用了卫星测湿资料及地面资料的细网格多元最优插值分析；同时使用同场及质量场初值，成功地实现了有限区非线性正规模初始化处理；采用位涡拟能守恒差分格式，包含较真实地形的球面坐标原始方程模式；实现了具有不同模式地形的差分模式与谱模式的嵌套及设计了分级降水客观检验系统。     

T63中期数值天气预报谱模式

简要地介绍了国家气象中心中期数值天气预报模式，并且，给出了业务７天预报初步结果，其有效预报达５－６天。     

上海区域数值预报模式集合预报系统的建立与试验

以目前运行的上海区域业务数值预报模式为基础,从预报模式的不确定性出发构造8个预报成员,建立了上海区域数值预报模式集合预报系统的初步模型,并对2004年夏季进行了逐日48 h预报试验。结果表明:集合平均对华东地区城市降水、温度、海平面气压等气象要素的总体预报能力与分辨率高3倍的业务模式相当,其中对雨量较大降水、最低温度、海平面气压(0~24 h)的预报效果好于业务模式;集合预报还能提供客观化、定量化的降水概率预报,对降水的发生、尤其是特大降水的发生有着很好的提示作用。     

THE LIMITED AREA ANALYSIS AND FORECAST SYSTEM AND ITS OPERATIONAL APPLICATION

The limited area analysis and forecast system(LAFS)was developed and has been put intooperational use at National Meteorological Center since January 1991.This system can be regardedas a branch system attached to the global assimilation and medium-range forecast system which isbased on a spectral model T42L9.The main advancements as an upgrade operational system are asfollows:the use of a regional fine mesh optimum interpolation(OI)analysis scheme:the realiza-tion of the nonlinear normal mode initialization for the regional model:the development of a 15L-spherical grid primitive equation model(with real topography and enstrophy conservation)and itsnesting forecast with the spectral model T42L9.     

地表参数对T106模式预报的影响

利用ISLSCP的土壤湿度、植被和NOAA的实时雪盖、海温资料, 通过改变T106模式的地表参数及改进地表通量计算方法, 探讨了地表参数对T106谱模式预报效果的影响.试验表明, 地表参数及地面过程对T106模式的预报结果有较大影响, 试验方案改进了模式的预报效果, 尤其对西太平洋副热带高压的预报, 如对副高特征值588 dagpm线北界和西伸脊点、面积指数和强度指数以及副高整体进退预报都比业务模式更接近实况.     

中期数值模式客观分析质量评估

通过多种方法对不同分辨率中期数值模式客观分析结果进行诊断分析,考查国家气象中心不同版本模式分析同国际优质版本在分析质量上存在的差异。结果表明,国家气象中心中期数值模式客观分析结果同ＥＣＭＷＦ优质版本相比,差异显著地域为：高纬度近极区、我国青藏高原大地形区和太平洋地区。另外,由于模式分辨率的提升,升级版本Ｔ１０６模式比Ｔ６３模式客观分析质量有明显改进。     

Improving Numerical Weather Prediction in Low Latitudes by Optimizing Diffusion Coefficients

The horizontal diffusion coefficients of the operational model (T42L9) in numerical weather prediction are optimized by the steepest descent search of multi-dimensional optimization. In order to improve prediction accuracy in low latitudes, the optimum horizontal diffusion coefficients are chosen, with changing variation of the basic diffusion coefficient with the passage of time, and later forecasts are also made better. In view of the averages of forecast verifications of 9 cases, the forecasts with optimum diffusion coefficients are an improvement on operational forecasts. It means that the forecasts are got much better with optimum values of some important parameters by optimization in numerical weather prediction.     

变网格一体化模式的研究进展

作者介绍了近年来在数值天气预报领域的一个新动向－变网格一体化模式的进展。这种模式可以替代目前业务数值天气预报的有限区模式和全球谱模式，降低业务数值天气预报的计算成本。网格距离的可变性，以及采用半隐式－半拉格朗日式时间差分方案是该模式的主要特点。法国的变网格一体化模式自１９９２年已投入业务使用，其可行性已得到了预报检验的初步证实。     

国家气象中心T63四维资料同化试验

文章简单地介绍了国家气象中心T63四维资料同化系统试验方案及试验的初步结果。试验结果表明，该系统计算稳定，是一个较好的同化方案;T63L16中期数值天气预报谱模式利用它提供的初始条件制作了7天全球预报，预报结果优于T42L9业务系统。