环境地转基本气流的计算及热带气旋运动与其偏差的统计分析

利用国家气象中心T63L16的1.875×1.875经纬网格点资料和中央气象台编号的热带气旋实时中心位置资料,计算了1996年全年25个热带气旋,共126个时次的环境地转基本气流,分析了环境地转基本气流的垂直分布特征,并对热带气旋的实际运动与环境地转引导气流的偏差(后文将称其为引导偏差,即热带气旋的实际中心位置与按引导气流推算出的位置之间的偏差)进行了分析,发现引导气流的计算区域不同,其引导偏差是不一样的。得到了引导气流的最佳计算区域,并且发现热带气旋运动与环境地转基本气流的垂直切变结构的关系以及引导偏差与引导气流的速度、气旋本身的初始纬度位置和强度等有关。结果还表明,200～1000 hPa的深层加权平均的基本气流的引导效果最佳,可作为最佳引导气流使用。了解这些规律和特征,对热带气旋运动预报具有一定的参考意义。     

SOME ASPECTS OF OBJECTIVE FORECASTING OF TROPICAL CYCLONE MOTION

As shown in a statistical analysis of the relationship between environmental fields at varied timeand tropical cyclone motion, the forecasting ability of the initisl environmental field predictors for tropical cyclone motion decreases with the increase of valid time period of forecast;it is higher with these predictors at a fUture time than at an initial time. The work also indicates that for the tropical cyclone motion over a given period of valid forecast, better predictors appear at times mostly differing from thevalid periods; for periods at 48-120 h the environmental predictors at 48-72 h are more capable of forecasting. With statistical interpretation of NWP products, a predictive model for tropical cyclone motionis superior in performance over a statistical forecasting model that employes predictors of the initial field in the basic framework. The concluding remarks can be used as reference in the construction of an objective prediction model for tropical cyclone motion.     

K-MEANS CLUSTERING FOR CLASSIFICATION OF THE NORTHWESTERN PACIFIC TROPICAL CYCLONE TRACKS

Based on the Joint Typhoon Warning Center (JTWC) best-track dataset between 1965 and 2009 and the characteristic parameters including tropical cyclone (TC) position, intensity, path length and direction, a method for objective classification of the Northwestern Pacific tropical cyclone tracks is established by using K-means Clustering. The TC lifespan, energy, active season and landfall probability of seven clusters of tropical cyclone tracks are comparatively analyzed. The characteristics of these parameters are quite different among different tropical cyclone track clusters. From the trend of the past two decades, the frequency of the western recurving cluster (accounting for 21.3% of the total) increased, and the lifespan elongated slightly, which differs from the other clusters. The annual variation of the Power Dissipation Index (PDI) of most clusters mainly depended on the TC intensity and frequency. However, the annual variation of the PDI in the northwestern moving then recurving cluster and the pelagic west-northwest moving cluster mainly depended on the frequency.     

STOCHASTIC SIMULATION OF TROPICAL CYCLONE TRACKS IN THE NORTHWEST PACIFIC REGION WITH CLASSIFICATION MODEL

Accurate simulation of tropical cyclone tracks is a prerequisite for tropical cyclone risk assessment. Against the spatial characteristics of tropical cyclone tracks in the Northwest Pacific region, stochastic simulation method based on classification model is used to simulate tropical cyclone tracks in this region. Such simulation includes the classification method, the genesis model, the traveling model, and the lysis model. Tropical cyclone tracks in the Northwest Pacific region are classified into five categories on the basis of its movement characteristics and steering positions. In the genesis model, Gaussian kernel probability density functions with the biased cross validation method are used to simulate the annual occurrence number and genesis positions. The traveling model is established on the basis of the mean and mean square error of the historical 6 h latitude and longitude displacements. The termination probability is used as the discrimination standard in the lysis model. Then, this stochastic simulation method of tropical cyclone tracks is applied and qualitatively evaluated with different diagnostics. Results show that the tropical cyclone tracks in Northwest Pacific can be satisfactorily simulated with this classification model.     

数值预报产品统计释用技术在热带气旋路径客观预报中的应用

首先对应用数值预报产品统计释脾技术的效果进行了统计。结果表明,数值预报产品和技术的应用改善了热带气旋路径客观预报中预测因子的预报能力,提高了模式的预报技巧并拓展了有效预报时效。继而对热带气旋路径客观预报中若干统计释用技术问题进行了讨论,并指出：在应用数值预报产品构造热带气旋路径客观预报模式时,采用大样本资料和完全预报方法,细心构造反映各种天气系统特征和物理量场的预报因子,应用多时刻产品并对ＮＷＰ产     

热带气旋定量降水预报的动力相似方案

该文提出一个热带气旋定量降水预报(QPF) 的动力相似方案。方案应用热带气旋初始参数、历史过程的天气形势场和物理量场及数值预报产品, 构造预报区域内当前时刻至未来时刻环境要素场的多元客观相似判据。通过定义非线性的相似指数综合评估历史热带气旋样本与预报热带气旋在多元判据下的连续动态相似程度, 以此找到相似样本。应用相似样本的历史降水量记录进行相似指数的权重综合, 得到热带气旋未来6~48 h降水量的定点、定量预报值。预报试验表明该方案具有一定的预报技巧。     

综合评估环境场影响的热带气旋路径客观相似预报模式

提出一个综合评估环境场影响的热带气旋路径客观相似预报模式。模式应用热带气旋参数、初始和未来环境场，构造客观的相似判据。通过定义非线性的相似指数综合评估历史热带气旋样本在多元判据下的相似程度，从而找到相似样本。应用相似样本的历史路径进行坐标变换和相似指数的权重综合，得到预报路径。模式检验和预报试验表明该模式具有预报技巧。     

影响热带气旋路径的敏感性试验与研究

针对热带气旋观测中的敏感区域问题,用数值模拟的方法,以GRAPES-TCM为试验模式,对登陆中国的2个热带气旋“派比安”与“圣帕”进行了敏感性试验,并通过模拟其他4个热带气旋路径对试验结果进行了验证.结果显示,初始场的不确定性导致了热带气旋路径的不确定性,但初始场中涡旋场的变化对路径几乎没有影响,环境场中位于涡旋外、距...     

Seasonal forecasting of tropical cyclones in the North Indian Ocean region: the role of El Niño-Southern Oscillation

In this study, we have investigated the contribution of El Niño-Southern Oscillation (ENSO) to the North Indian Ocean (NIO) tropical cyclone (TC) activity and seasonal predictability. A statistical seasonal prediction model was developed for the NIO region tropical cyclone genesis, trajectories and landfalls using the Southern Oscillation index (SOI: as a metric of ENSO) as a predictor. The forecast model utilised kernel density estimation (KDE), a generalised additive model (GAM), Euler integration, and a country mask. TCs from the Joint Typhoon Warning Centre were analysed over the 35-year period from 1979 to 2013. KDE was used to model the distribution of cyclone genesis points and the cyclone tracks were estimated using the GAM, with velocities fit as smooth functions of location according to ENSO phase and TC season. The best predictor lead time scales for TC forecast potential were assessed from 1 to 6 months. We found that the SOI (as a proxy for ENSO) is a good predictor of TC behaviour 2-months in advance (70% skill). Two hindcast validation methods were applied to assess the reliability of the model. The model was found to be skillful in hindcasting NIO region TC activity for the pre and post monsoon season. The distribution of TC genesis, movement and landfall probabilities over the study period, as well as the hindcast probabilities of TC landfall during ENSO events, matched well against observations over most of the study domain. Overall, we found that the phase of ENSO has the potential to improve NIO region TC seasonal forecast skill by about 15% over climatological persistence.     

数值预报产品检验和评估

通过国家级数值预报T213模式、EC模式下发产品对影响海南的热带气旋主观性检验结果表明,T213模式不管是对稳定路径还是转折路径的热带气旋在生成、移动路径以及登陆点都与实况相差很大;而EC模式对不管是转折还是稳定路径的热带气旋,都能够对移动路径、登陆点以及转折点都能够做出准确的预报;而在客观性检验的结果中也可看出T213模式和EC模式的预报能力的优劣性。因此,总体来说,在热带气旋的数值预报产品中,EC模式的预报能力明显比T213模式强,具有很高的参考意义。另外在温度场的预报中,T213模式相对于MM5模式,其预报能力具有一定的可信度,在日常预报中具有参考价值。     

主分量分析在热带气旋强度客观预报中的试用

为了解主分量因子分析在热带气旋强度客观预报中的应用效能,在NCEP再分析资料、T106L19模式产品和热带气旋历史观测资料基础上,采用主分量因子分析技术,结合多元线性回归和BP型人工神经网络,开展了西北太平洋热带气旋的强度客观预报技术研究试验。试验包含完全预报法原理下的预报因子有无主分量分析、线性与非线性预报方法建模等方面的比较。结果表明,预报因子的主分量分析通过降低线性回归和BP人工神经网络模型的维数,提高因子间独立性,可减小模型强度预报平均绝对误差,提高模型实际预报能力。     

Improved tropical cyclone track predictions using error recycling

Summary Errors produced by a nonlinear predictive scheme contain information about both the observations and the prediction system. Therefore, its error history would be expected to contribute to increasing the skill of the predictions if it is included in the forecast. In this study an error recycling procedure is developed for tropical cyclone track prediction. Errors are defined here as differences between the model forecast and the best track position. Error histories are incorporated into a nonlinear analogue, or simplex, forecast scheme and applied to tropical cyclone track prediction, using the archives of observed position data associated with the forecast errors. Various forecast experiments of the cyclone tracks are performed: standard simplex predictions using observed positions only; simplex predictions improved by error forecasts based on libraries of both observations and the recycled forecast errors; and, finally, predictions that include NWP-model forecasts and their errors as predictors. The resulting gains in skill of predictions out to 72 hours ahead are found to be substantial. Received August 12, 1999 Revised November 5, 1999     

热带气旋路径强度预报——SAPC法

SAPC——逐段相似气候持续性热带气旋路径、强度预报方法，既考虑了热带气旋的气候持续性规律，又考虑了与现时热带气旋状态特别相似的历史热带气旋路径、强度变化规律，用不同的相似条件和权重，把气候路径、相似路径和持续性路径作了有机的统一。该方法克服了预报路径的大曲率变化，考虑了随时间、地点变化的热带气旋的气候规律，根据热带气旋的现时状态，即可随时制作路径、强度预报。历史资料和实际应用表明该方法有实用价值。     

Ensemble Forecasts of Tropical Cyclone Track with Orthogonal Conditional Nonlinear Optimal Perturbations

This paper preliminarily investigates the application of the orthogonal conditional nonlinear optimal perturbations(CNOPs)–based ensemble forecast technique in MM5(Fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model). The results show that the ensemble forecast members generated by the orthogonal CNOPs present large spreads but tend to be located on the two sides of real tropical cyclone(TC) tracks and have good agreements between ensemble spreads and ensemble-mean forecast errors for TC tracks. Subsequently, these members reflect more reasonable forecast uncertainties and enhance the orthogonal CNOPs–based ensemble-mean forecasts to obtain higher skill for TC tracks than the orthogonal SVs(singular vectors)–, BVs(bred vectors)– and RPs(random perturbations)–based ones. The results indicate that orthogonal CNOPs of smaller magnitudes should be adopted to construct the initial ensemble perturbations for short lead–time forecasts, but those of larger magnitudes should be used for longer lead–time forecasts due to the effects of nonlinearities. The performance of the orthogonal CNOPs–based ensemble-mean forecasts is case-dependent,which encourages evaluating statistically the forecast skill with more TC cases. Finally, the results show that the ensemble forecasts with only initial perturbations in this work do not increase the forecast skill of TC intensity, which may be related with both the coarse model horizontal resolution and the model error.     

热带气旋强度变化研究进展

自20世纪90年代后期以来,热带气旋强度变化研究越来越受到人们的重视,随着研究的不断深入,热带气旋强度变化研究取得了可喜的进展,文中总结近年来热带气旋强度变化的主要研究成果,主要包括(1)热带气旋的发生、发展和最大可能强度的研究;(2)行星涡度梯度、环境均匀流、环境流场垂直切变以及热带气旋外流与环境流的相互作用对热带气旋强度的影响及物理机制;(3)热带气旋结构与强度的变化关系,着重总结环境流场导致的非对称结构变化而引起的热带气旋强度变化以及对涡旋倾斜发展理论验证,分析了涡旋Rossby波的最新研究;(4)海洋热状况变化以及海洋飞沫对热带气旋强度的影响研究成果。分析指出,今后进一步开展用现代化卫星探测资料研究热带气旋强度变化外,还应加强热带气旋外流与环境流场的相互作用,海-气交界面的参数化问题,热带气旋结构变化与TC强度变化关系以及这种关系的物理本质的研究,通过深入研究,认识热带气旋强度变化的物理机制,提高热带气旋强度变化的预报能力。     

热带气旋相似和最大概率集成预报方法及其预报业务试用

利用建立在计算机系统的热带气旋历史资料，经反复试验提出了一套集热带气旋发生的日期相似、地理位置相似、路径相似和强度相似等相结合的挑选“最相似”热带气旋的方案；并利用所挑选的路径和强度“最相似”历史样本，分别对各预报时效的移动方向、移动速度和强度进行分级概率值统计，根据最大概率值选取相应的移向、移速和强度作为热带气旋路径和强度的预报。本方法已在计算机系统成功开发并投入业务试用，检验结果表明：本方法具有一定的预报能力，其输出的未来24、48、72小时的路径和强度预报对预报员有一定参考价值。     

NUMERICAL EXPERIMENT OF THE EFFECT OF ENVIRONMENTAL FLOWS ON TROPICAL CYCLONE MOTION

A barotropic prirnitive equation model is used to simulate the tropical cyclone motion.Tropical cyclonemovements under different environmental flow backgrounds were examined and sensitivity of tropical cyclonetracks were discussed.Conclusions of practical significance have been obtained in this paper.     

热带气旋路径趋势数值预报的试验研究

给出了一个嵌套于欧洲中期天气预报中心全球谱模式中的套网格模式，用于预报热带气旋路径趋势，提出了一种以欧洲中期天气预报中心提供的时距为24小时的预报场为基础的“接力预报”方法；设计了五种不同的“接力预报”方案；并对8507号和8509号两个热带气旋就各种不同预报方案进行了数值预报试验。结果表明，本模式对热带气旋路径趋势具有较强的预报能力，对疑难路径也具有一定的预报能力，为开展热带气旋的路径趋势预报提供了一个新的途径。文中还对影响热带气旋路径趋势的一些主要因子结合各预报结果进行了分析，为模式尽早投入业务提供了一定的依据。     

THE ENSEMBLE FORECASTING OF TROPICAL CYCLONE MOTION I：USING A PRIMITIVE EQUATION BAROTROPIC MODEL

1INTRODUCTIONErrorsofnumericalforecastingcomprisethoseintheinitialvalue,modelandcomputationandthefirstkindoferrorbecomesmoreandmoreoutstandingwiththeon-goingdevelopmentofcomputersandnumericalmodels.Subjecttoavailableobservationmeans,therealatmosphereisanythingbutapproximatelymeasured.Meanwhile,oneshouldpayattentiontothepossibility,assuggestedbyLorenz[1],thatanyslightdifferencesduringtheinitialstatemayleadtoresultsthatturnouttobetotallydissimilarfromwhatwouldbeexpectedotherwise,asfarasdefi…     

我国热带气旋研究十年进展

90年代初,国内外开展了几次大规模的热带气旋现场试验,取得了许多宝贵的加 密观测资料。利用这些资料,对热带气旋尤其是异常热带气旋开展了一系列的研究。我国科学家在国家科技攻关85-906项目中的“台风科学、业务试验和天气动力学理论的研究”等与热带气旋有关的课题和国际热带气旋研究合作项目“SPECTRUM(SpecialExperimentConcerningTyphoonRecurvatureandUnusualMovement)”中对台风的突变现象和预报技术进行了重点研究。从而在过去10年中,在台风运动突变、结构和强度突变、台风暴雨的突然增幅、热带气旋路径预报方法研究等方面都取得了新的进展。作者将对这些进展作简要综述。