Quadratic discrimination through orthogonal transformation and its application to long-range forecasting of drought and excessive rainfall

The method of quadratic discrimination through orthogonal transformation is introduced to optimize quadratic discriminant function, which has been proved more effective than the method of stepwise multiple discrimination. It is noteworthy that, in the case of a large number of predictors, it is better to make a preliminary choice by using stepwise multiple discrimination or stepwise regression so that the calculation can be made more stable and the effectiveness of discrimination can be improved.     

持续性强降水的区域模式动力中期预报研究

持续性强降水及其次生灾害给人民的生产和生活造成严重影响, 延伸其模式动力预报能力对防灾、减灾具有重要意义。随着对持续性强降水过程形成机理及模式动力中期预报认识的不断提高, 以减小模式初始条件误差、边界条件误差以及内场预报误差为目标提出了一系列动力中期预报技术方法, 主要包括:针对边界条件提出低通滤波技术方案, 改进了5 d以上的环流及降水预报; 针对模式预报内场进行谱逼近技术试验, 对提前3—7 d的小雨以上量级的降水预报改进明显; 针对初始条件进行多尺度混合更新初值技术预报试验, 融合全球预报的大尺度场及区域模式预报的中小尺度场进行15 d预报, 明显提高了50及100 mm以上的持续性累积降水预报时效。      

A numerical study on forecasting the Henan extraordinarily heavy rainfall event in August 1975

This study is essentially an experiment on the control experiment in the August 1975 catastrophe which was the heaviest rainfall in mainland China with a maximum 24-h rainfall of 1060.3 mm, and it significantly demonstrates that the limited area model can still skillfully give reasonable results even only the conventional data are available. For such a heavy rainfall event, a grid length of 90 km is too large while 45 km seems acceptable. Under these two grid sizes, the cumulus parameterization scheme is evidently superior to the explicit scheme since it restricts instabili-ties such as CISK to limited extent, The high resolution scheme for the boundary treatment does not improve fore-casts significantly.The experiments also revealed some interesting phenomena such as the forecast rainfall being too small while af-fecting synoptic system so deep as compared with observations. Another example is the severe deformation of synoptic systems both in initial conditions and forecast fields in the presence of complicated topography. Besides, the fixed boundary condition utilized in the experiments along with current domain coverage set some limitations to the model performances.     

Neuroid BP-type Model Applied to the Study of Monthly Rainfall Forecasting

A neuroid BP-type three-layer mapping model is used for monthly rainfall forecasting in terms of 1946-1985 Nanjing monthly precipitation records as basic sequences and the model has the form i × j ＝ 8 × 3, K = 1; by steadily modifying the weighing coefficient, long-range monthly forecasts for January to December, 1986 are constructed and 1986 month-to-month predictions are made based on, say, the January measurement for February rainfall and so on, with mean absolute error reaching 6,07 and 5,73 mm, respectively. Also, with a different monthly initial value for June through September, 1994, neuroid forecasting is done, indicating the same result of the drought in Nanjing dur-ing the summer, an outcome that is in sharp agreement with the observation.     

WRF模式对江苏一次强降水过程的模拟分析

利用NCEP最终分析资料,使用WRF模式模拟了2008年7月22—23日出现在江苏的一次强降水天气过程。结果表明：WRF模式能较好地模拟出这次降水的区域,对这种中尺度天气系统具有良好的预报能力。在这次降水过程中,低空风场切变线和冷空气以及与高空急流的合理配置加强了强降水区垂直环流的发展,使降水区对流发展;而高空辐散、低空辐合的流场特征也促进了强降水的产生;这次过程的水汽输送在850hPa上最强,850hPa的强水汽输送是产生强降水必需的水汽条件;从能量方面看,江苏全境都处于K指数高值区,特别是江苏中北部有相当高的能量聚集,为强降水提供了不稳定条件。暴雨区上空螺旋度呈低层正中心、高层负值区的分布,螺旋度的高低层耦合是触发并维持低压暴雨的动力机制。     

降水落区多模式超级集合预报系统

利用多个数值模式的雨量预报集合为站点雨量预报初值,遵循预报员对降水预报分析的思路,将其以系统、能量、水汽、地形等因子对降水所作的定性预报分析结论转换为因子信度,利用因子信度对站点雨量预报初值作增减的强迫运算,并将地面站点上的相关要素转换为强迫系数,再次对站点雨量预报值作增减的强迫运算,由此得出包含多模式集合预报值、人对诸多定性因子分析信息、站点地面要素差异等综合因素的站点雨量定时定量预报值,从而实现降水客观、定点、定量预报.     

降水落区多模式超级集合预报系统

利用多个数值模式的雨量预报集合为站点雨量预报初值，遵循预报员对降水预报分析的思路，将其以系统、能量、水汽、地形等因子对降水所作的定性预报分析结论转换为因子信度，利用因子信度对站点雨量预报初值作增减的强迫运算，并将地面站点上的相关要素转换为强迫系数，再次对站点雨量预报值作增减的强迫运算，由此得出包含多模式集合预报值、人对诸多定性因子分析信息、站点地面要素差异等综合因素的站点雨量定时定量预报值，从而实现降水客观、定点、定量预报。     

面雨量分析和预报技术改进

松花江是我国重点防汛的七大江河之一,流域面积广阔,洪涝基本取决于流域内降水的多少。1998年超历史记录的特大洪水,就是由于流域内区域性的暴雨、特大暴雨造成的。利用流域内各气象站点逐日降水量计算出流域内各区域的面雨量值,并结合水位资料分析了嫩江、松花江流域水位变化与面雨量的关系。在此基础上,利用逐步回归、相似技术建立了流域内各区域面雨量的预报方法。经检验、试报,有较好的预报参考价值。在MICAPS业务平台上开发的面雨量预报业务系统可以投入业务运行。     

降水资料同化在梅雨锋特大暴雨个例模拟中的应用研究

利用暴雨数值预报模式AREM,以2009年6月29日发生在长江中下游地区的一次梅雨锋特大暴雨过程为例,以NCEP预报场为背景场,首先开展了不同化任何资料(无同化试验)以及分别利用GRAPES-3DVAR同化系统和局地分析预报系统(LAPS)同化地面、探空资料的3组数值试验,然后进一步开展了降水资料一维变分同化方法在GRAPES-3DVAR同化系统及LAPS系统中二次同化的效果研究,结果表明:(1)采用GRAPES-3DVAR系统同化地面、探空资料的数值试验,其降水预报效果不如无同化试验结果;而采用LAPS资料同化系统同化地面、探空资料的数值试验,其降水预报效果优于无同化试验结果,即就本个例而言,GRAPES-3DVAR同化系统对背景场的修正为负效果,LAPS同化系统对背景场的修正为正效果。(2)降水资料1DVAR方法在GRAPES-3DVAR同化系统中的应用,对物理量场有重要影响,使雨带上空变得更暖更湿,天气系统的配置更利于降水发生,中尺度系统的演变更有利于模拟出与实况更加接近的雨带位置、强度、中尺度结构特征,因而极大地改善了降水模拟效果,其模拟的1、6、24h累积降水量位置、强度、中尺度结构特征都有较明显改善。(3)降水资料1DVAR方法在LAPS系统中的应用同样改善了降水预报效果,使雨带落区位置更加接近实况。     

Combination of Meteosat- and synoptic data to determine rainfall: A case study

Summary A pilot study was carried out to determine the capability of satellite data for mapping rainfall and to prove possibilities for combination with synoptic parameters. The investigations were based on digital infrared Meteosat data of the central and southern European region during two periods in 1979. The effective infrared emission temperatures were combined with parameters derived from synoptic maps. The rainfall distribution was extracted from synoptic surface data. The vorticity and its advection with the thermal wind were derived from the 850 hPa and 500 hPa topographies. For the investigated periods appreciable agreement was observed between the rainfall areas and the areas with positive advection of vorticity. Another requirement for the occurrence of precipitation is a relative minimum of cloud top temperature and vorticity. As supplement to synoptic charts satellite data are able to provide information on rainfall areas with high areal and temporal resolution.With 6 Figures     

Validation of satellite rainfall products for operational flood forecasting: the case of the Evros catchment

An extensive validation of two of the most popular and recently upgraded satellite rainfall products, 3B42 and 3B42RT, was performed over the Evros catchment in southeastern Europe using data recorded from January 2000 to April 2009. For conducting this validation study, the Climate Prediction Center's (CPC) ground data were used. The satellite data products were aggregated to daily time series, remapped to spatial resolution of 0.5°, validated against CPC, and intercompared using a variety of statistical indices and coefficients. After the validation process, all three data sets (CPC, 3B42, and 3B42RT) were separately fed in a statistical rainfall?Crunoff model, in order to predict the five major recorded flood events which occurred in the Evros catchment during the last decade. It has been found that post-calibration with ground data, which is present only in 3B42 product, is a necessity for operational flood forecasting and similar studies conducted in areas at mid-latitudes. Knowledge of rainfall events with small intensities is crucial for estimating the total rainfall height and drastically improves the skill of the satellite product.     

我国地面降水的分级回归统计降尺度预报研究

利用TIGGE资料中欧洲中期天气预报中心(ECMWF,the European Centre for Medium-Range Weather Forecasts)、日本气象厅(JMA,the Japan Meteorological Agency)、美国国家环境预报中心(NCEP,the National Centers for Environmental Prediction)以及英国气象局(UKMO,the UK Met Office)4个中心1~7 d预报的日降水量集合预报资料,并以中国降水融合产品作为"观测值",对我国地面降水量预报进行统计降尺度处理。采用空间滑动窗口增加中雨和大雨雨量样本,建立分级雨量的回归方程,并与未分级雨量的统计降尺度预报进行对比。结果表明,对于不同模式、不同预报时效以及不同降水量级,统计降尺度的预报技巧改进程度不尽相同。统计降尺度的预报技巧依赖于模式本身的预报效果。相比雨量未分级回归,雨量分级回归的统计降尺度预报与观测值的距平相关系数更高,均方根误差更小,不同量级降水的ETS评分明显提高。对雨量分级回归统计降尺度预报结果进行二次订正,可大大减少小雨的空报。     

WRF模式对弱强迫系统中雷暴预报个例研究

用WRF2．2版本,针对2006年7月13日洛阳市区,发生在副高边缘偏东南暖湿气流中的雷暴进行了模拟预报,结果表明WRF模式能描述弱强迫天气尺度系统中的中小尺度对流系统,能捕捉到常规天气图上难以分辨出来的雷暴单体。模式输出的中尺度要素场可以确定雷暴发生的地点;模式探空的对流有效位能、抬升指数、沙瓦特指数、K指数随时间演变曲线的拐点,能指示雷暴发生的时间。个例分析表明WRF模式在预报弱强迫天气系统雷暴时具有较好的性能,用WRF模式来作雷暴的分析预报早一条可行的徐径。     

江淮流域一种中间尺度暴雨系统的研究

通过一次江淮流域暴雨天气过程的分析,发现在对流层低层存在一种中间尺度扰动。它形成于对流层低层的冷锋锋区上,其流场的气旋性环流特征和结构在600—900米高度上最明显。它是产生江淮流域暴雨的主要天气系统之一。6小时雨量可达15—35毫米,一次扰动过程的总降水量约100—120毫米,水汽辐合主要集中在900米—700毫巴层。扰动的时间尺度为1—2天,计算结果表明,这类扰动的发生、发展与对流层低层锋区斜压性的位能释放有较好的关系。     

长江上游流域面雨量预报系统

以T213数值预报产品降水格点为基础，采用权重方法和逐次订正法计算，然后根据统计、经验、模式等方法订正来预报单站降水，采用泰森多边形法计算长江上游流域面雨量的“四川省气象台长江上游流域面雨量预报系统”。     

长江上游流域面雨量预报系统

以T213数值预报产品降水格点为基础,采用权重方法和逐次订正法计算,然后根据统计、经验、模式等方法订正来预报单站降水,采用泰森多边形法计算长江上游流域面雨量的"四川省气象台长江上游流域面雨量预报系统".     

A case analysis of heavy rainfall causing flash floods

Summary The whole area of Mount Medvednica and the surrounding lowland including the Zagreb city area experienced extensive rainfall on 3 to 4 July 1989 causing flash floods. Daily precipitation amounts measured at 0600 UTC on 4 July were in proportion to the mean monthly totals of July for this region. The maximum rainfall amounts for periods of 2 to 12 hours recorded during this storm, had a return period greater than one hundred years in this region. They were produced by intensive development of a mesoscale convective system along the slowly moving frontal zone lying over north-western Croatia. The interaction between mesoscale processes and the synoptic scale development led to the intensive transformation of the initial air masses at the frontal line into those with a much stronger convective potential.With 5 Figures     

The operational seasonal forecasting of the summer rainfall in China

The paper presents a review of the success and failure of the practical results from summer drought and flood forecasts and seasonal precipitation forecasts in the period from 1976 to 1985. An analysis is made on the anomaly of the general circulation winch gives rise to summer precipitation and drought-flood occurrences in the country. It is proposed that the subtropical high over the West Pacific, the South Asia high and middle-latitude westerlies are the major synoptical regimes producing summer weather in China. The analysis focuses on the features of low-frequency oscillation and abnormality of the West Pacific sub-tropical high in the monthly 500 hPa mean charts, and on their interactions with the sea temperature of the North Pacific and the Equatorial Pacific. The result shows that there exist quasi-cycles of 3－4 years, 11 years and 19 years or so in the subtropical high with the feature of strong persistence and seasonal changes. There is a rather good correlation between the behaviour of the subtropical high and changes in the cold current area in the East Pacific, and especially during the El Nino period, there is an ob-vious coupling with abnormal changes of the intensity of the subtropical high. Analysis is also made on the effect of the thermal condition of the Tibetan Plateau, the Northern Hemisphere westerly circulation and the astronomical factors on the West Pacific subtropical high, the South Asia high and precipitation in the rainy season in China.