ON THE PREDICTION OF TROPICAL CYCLONE LANDFALL AND INFLUENCE ON SOUTHERN CHINA USING MONTHLY OLR ANOMALIES FOR PRIME SUMMER

With the OLR data,the landfall and activity of tropical cyclones(TC) in southern China over a 20-year period(1975～1994) are studied.The result shows that the variation of the monthly anomalous OLR is somewhat teleconnected with the TC activity in southern China.The former is used to predict short-term climate for the latter over months with frequent or no TC influence.To some externt,the relationship between the TC activity in southern China and the monthly mean OLR anomalies is dependent on the climatological location of the subtropical high in northwestern Pacific region.     

THE STRUCTURE OF TROPICAL CYCLONE BY TOVS AND ITS APPLICATION IN NUMERICAL WEATHER PREDICTION

The TOVS data are used to study the structure of a number of tropical cyclones for the year 2000. Differences are found to some extent between what is found and classic conceptual models in that (1) the horizontal structure is asymmetric and variable so that the low-value centers at low levels of the geopotential height field (or the high-value centers at high levels) do not necessarily coincide with the high-value centers of the temperature field; (2) the vertical structure is also variable in the allocation of the anomalies of the geopotential height field between low values at low levels and high values at high levels. It is especially noted that the centers of the anomalies are tilting at both high and low levels or the high level is only at the edge of a high-pressure zone. There is not any significant high-value anomalous center in a corresponding location with the tropical cyclone. The structure of tropical cyclone in the TOVS is also used as reference to modify the structure of typhoon BOGUS in the numerical prediction model system of tropical cyclones. It is found that the modified BOGUS performs better in coordinating with the environment and predicting the track of the tropical cyclone. The demonstration is two-fold — the structure of the typhoon BOGUS is such that it means much in the track prediction and the use of the TOVS-based tropical cyclone structure really helps in improving it. It provides the foundation for modification and evolution of typhoon BOGUS.     

INNER AND OUTER STRUCTURES OF TROPICAL CYCLONE──Ⅰ.BAROTROPIC MODEL

A tropical cyclone is divided into inner and outer regions in which temporal and spacial scales and physical quantities are all different. Making use of the scale analysis and perturbation methods the governing equations of barotropic and baroclinic models are obtained for the two regions, respectively. In the two models the stream and pressure fields are solved analytically and the obtained structrues are approximately consistent with observations. It is shown that there are different governing equations for the inner and outer regions of the tropical cyclone. The inner region is governed by the cyclostrophic wind and an evolution equation, the outer region by the gradient wind and another evolution equation.     

CHARACTERISTICS OF TROPICAL CYCLONES ACTIVITIES VARYING WITH ENVIRONMENTAL FIELDS OF MID- AND LOWER- LATITUDES

1INTRODUCTIONTropicalcyclones(tobedesignatedTChereafter)actwithsignificantlatitudinaldifference[1],someofwhichhavebeenwelldocumented.Forinstance,TCisavortexsystemthatformsandmaintainswiththesupportofsomeextentofCoriolisforce,whichisweakinareasneartheequator(southof4N)andenableslittleTCactivity[2].AsTCismainlysuppliedbylatentheating,higherSSTissuretobeadvantageoustothegenerationanddevelopmentofTC;thesummertimeSSTdecreaseswithincreasinglatitudeinthenorthwesternPacific[3],beingnear26.…     

THE ROLE OF MERIDIONAL WIND STRESS IN THE TROPICAL UNSTABLE AIR-SEA INTERACTION

1INTRODUCTIONAsshowninobservationalfacts,theevolutionofElNi駉displaysastheamplitudeexpansionandmigrationofanomalousdisturbancesinair-seacouplingsystems.Theoreticaladdressofthephenomenonhasbeenattemptedfromtheaspectofcouplingdynamics.Theresultsshowthattheair-seainteractionsystemincludesakindofunstablemode,whichispropagatingindirectionsdeterminedbyfactorsgoverningSSTchanges.Withanair-seacouplingmodel,Lau[1]wasamongtheearliestpeoplewhodiscoveredunstablestationarywavemodesintheair-seaintera…     

AN OPERATIONAL AUTO-MONITORING FOR THE EL NINO EPISODES USING GMS TBB

By making full use of GMS TBB data, diagnosis and analysis of the formation and development of El Nino event in 2002 and 2003 were made. It suggests that the first clue of the El Nino event appeared in December 2001. The event was formed at the end of 2002 after five phases of development, and came into the phase of flourishing in the winter of 2002. From the analysis the dynamics, it is noted that that the position of the ascending branch of Walker cell was moving from the equatorial west Pacific to the equatorial central Pacific in the phase of formation and development of the El Nino event. The process of diagnosis shows that it can provide an important clue for forecasting the genesis and development of the El Nino episodes.     

COMPARISONS BETWEEN DOPPLER AND SIMULATED FEATURES OF A SUPERCELL

Firstly, typical features of a supercell, which occurred in Guangzhou on August 11, 2004, are discussed by using the new generation weather radar data. V-notch, finger-echo, weak echo region, overhang and echo-wall are observed from reflectivity products. A vertical cross section of the radial velocity is made along the direction of the low-level inflow and across the maximum reflectivity core, which displays a part of strong updraft and downdraft. Secondly, a 3-D convective storm model is used to simulate the supercell. The maximum reflectivity and the core thickness of the simulated radar echo are 75 dBz and 14km, respectively. These values are more than the counterparts that are detected by radar. The reason is that attenuation is not calculated in the model. The wind field structure is also given when the storm is the strongest. Divergence, caused by thunderstorm outflow, is in the low level. In the middle and high level, convergence is dominant, but the plume is not simulated at the top. Finally, the evolution of the simulated vertical motion is documented. The interaction between the environmental wind and the updraft, which is formed by the convergence on the ground at the beginning, makes the storm stronger. Then, downdraft occurs and grows. When it becomes dominant, the supercell collapses.     

THE APPLICATION OF TIDAL SIGNAL EXCLUSION SCHEME FROM INITIALIZATION IN A GENERAL CIRCULATION MODEL

In this paper, some corrections was made to the assumption that the forcing is quasi-static, which is the basis of the nonlinear diabatic initialization scheme adopted by a global model T106L19. Thus the tidal signal is expressed and excluded from the i…     

A STUDY ON THE VARIATIONS OF ANNUAL FREQUENCY FOR TROPICAL CYCLONE IN NORTHWEST PACIFIC DURING THE LAST HUNDRED YEARS

In this paper, a study on the variation of annual frequency of tropical cyclone (TC) and its relation with SST, Southern Oscillation index, sunspot relative number and number of days for specific circulation patterns was made by using 1884-1988 data of annual frequency for Northwest Pacific TC occurrence, which had been corrected to tendencies.Preliminary results indicated that in the variation of annual TC frequency there exist obvious p.6riods of 21, 31, 15 and 6 years and sustaining periods lasting 12 years in average.Well-defined processes of inflexion were observed in 1931, 1959 and 1977 over the past hundred years.The results also suggested insignificant statistic tendency of annual TC frequency increasing (decreasing) in winter/spring (summer/autumn )in the El Nino years.When the stratosphere was in the zonally westerly phase, the northern zonal circulation would abnormally develop and solar activity would enhance to favour the generation and development of TC.     

A REGIONAL COUPLED AIR–SEA–WAVE MODEL: SIMULATION OF UPPER-OCEAN RESPONSES TO AN IDEALIZED TROPICAL CYCLONE

In this study a coupled air–sea–wave model system, containing the model components of GRAPES-TCM, ECOM-si and WAVEWATCH III, is established based on an air–sea coupled model. The changes of wave state and the effects of sea spray are both considered. Using the complex air–sea–wave model, a set of idealized simulations was applied to investigate the effects of air–sea–wave interaction in the upper ocean. Results show that air–wave coupling can strengthen tropical cyclones while air–sea coupling can weaken them; and air–sea–wave coupling is comparable to that of air–sea coupling, as the intensity is almost unchanged with the wave model coupled to the air–sea coupled model. The mixing by vertical advection is strengthened if the wave effect is considered, and causes much more obvious sea surface temperature (SST) decreases in the upper ocean in the air–sea coupled model. Air–wave coupling strengthens the air–sea heat exchange, while the thermodynamic coupling between the atmosphere and ocean weakens the air–sea heat exchange: the air–sea–wave coupling is the result of their balance. The wave field distribution characteristic is determined by the wind field. Experiments are also conducted to simulate ocean responses to different mixed layer depths. With increasing depth of the initial mixed layer, the decrease of SST weakens, but the temperature decrease of deeper layers is enhanced and the loss of heat in the upper ocean is increased. The significant wave height is larger when the initial mixed layer depth increases.     

热带气旋路径集合预报方法研究Ⅰ——正压模式结果的初步分析

选择1979～1993年间的热带气旋为试验个例,通过扰动热带气旋初始位置和初始结构,构造集合成员, 用正压原始方程模式,进行路径集合预报试验, 并初步探讨预报成员的集合方法。试验结果表明:热带气旋定位误差影响路径预报,但扰动初始位置的集合平均预报与控制试验的预报水平相接近。扰动热带气旋初始结构的集合预报试验表明,约有60 %～70 %个例的集合路径预报得到改进。此外,试验结果还表明,当环境引导气流较弱时,进行扰动热带气旋初始结构的集合预报,预报结果的改善较明显。     

滞后平均法（LAF）在热带气旋路径集合预报中的应用

本文用-正压模式，采用滞后平均法(LAF)对2000年热带气旋进行路径集合预报试验，并与基于热带气旋初始结构扰动的集合预报方法进行了比较分析，结果表明LAF方法对热带气旋路径预报具有较好的改进作用。但LAF的集合预报效果受模式本身误差的影响，在完美模式的假设下，LAF集合预报相对于控制试验的技巧水平20～40％。     

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.     

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用技术的效果进行了统计,结果表明,数值预报产品统计释用技术的应用改善了热带气旋路径客观预报中预报因子的预报能力,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ＮＷＰ产品并对ＮＷＰ产品进行统计订正。对多种预报模式的预报结果进行综合集成等技术是提高预报技巧和稳定性的有效途径。     

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     

热带气旋路径客观预报的若干问题

对多时刻环境因子与热带气旋路径相关的统计分析表明，初始时刻环境场因子对热带气旋路径的预报能力随预报时效的增长而下降；未来时刻环境因子的预报能力高于初始时刻环境场因子；对于一定预报时效的热带气旋路径，具有较高预报能力环境场因子出现时刻大多不与预报时效同时刻；对于４８￣１２０小时的预报时效，初始时刻后４８－７２小时的环境场因子具有较高的预报能力。对ＮＷＰ产品进行统计释用的热带气旋路径预报模式优于用初如     

APPLICATION OF STATISTICAL INTERPRETATION TECHNIQUES WITH NWP PRODUCTS FOR OBJECTIVE FORECASTING OF TROPICAL CYCLONE MOTION

Statistical study is first performed of the efficiency of the technique of statistical interpretation using the products of NWP. The result shows that the application of the technique has improved the predictabilily of predictors in objective forecasting of tropical cyclone motion, increased the forecasting skill of models and extended the valid period of forecast. Then a discussion is made of some technical problems in the application in the motion forecasting, suggesting: a large sample of data and perfect forecast method be employed in constructing objective forecast models for tropical cyclone motion, predictors be included that are so finely built that they reflect all synoptic features and physical quantity fields and NWP products be used and corrected that are available at multiple times. It is one of the effective ways to improve the skill and stability of the forecast by composite use of outcomes from various forecasting models.     

热带气旋登陆华东的客观预报方案

热带所旋登陆华东属小概率事件。构造适当划分区间的阶梯函数能较好地反映登陆事件条件概率的非线性分布。应用阶梯函数变换的因子对登陆事件概率的预报性能优于线性相关的标准化因子。预报方案应用阶梯函数变换因子，通过非线性相关比筛选和REEP分析构造热带气旋登陆华东的预报模式。应用初始场资料与数值预报产品分别构造了统计－天气学、统计－气候学和统计－动力学的分类预报模式。应用分类预报模式的预报结果进行综合的预报集成提高了预报技巧。预报检验与试验表明本方案对热带气旋登陆华东具有一定的预报能力。     

热带气旋集合预报研究进展

集合预报是减小各种不确定性影响数值预报结果的有效方法,将该方法应用于热带气旋（TC）数值预报的研究开始于1990年代中期,已经取得了很多令人鼓舞的成果。对TC集合预报的研究进展做简要概述,主要包括:（1） TC集合预报技术包括基于单一模式的TC集合预报技术与TC多模式超级集合预报技术,前者包含初值扰动技术和模式扰动技术,后者在大部分情况下预报效果较好。（2） 基于全球中期集合预报系统的TC集合预报,是近年来TC集合预报发展的一个新趋势。（3）将集合预报应用于TC生成与发展的研究是近年来TC集合预报应用的拓展。未来TC集合预报的发展将与数值预报其他技术的发展更紧密地结合,集合预报技术在TC研究中将发挥越来越重要的作用。      

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.