NUMERICAL SIMULATION OF MESOSCALE STRUCTURES OF TYPHOON AND OROGRAPHIC EFFECTS USING MM5*

The track,landfall,dynamic and thermodynamic and cloud-rain physical mesoscale structures and their evolution of typhoon HERB 1996 in 36 h from 0000 UTC 31 July to 1200 UTC 1 August 1996 were simulated by using the non-hydrostatic mesoscale model MM5.This period covered the process of typhoon HERB landfall at Taiwan and Fujian Provinces.Results show that the model successfully simulated the landfall process of typhoon HERB,revealed the most important characteristics of the mesoscale dynamic and thermodynamic and cloud-rain physical structure during its landfall.The simulated typhoon track was close to the observation.The center of cyclonic circulation simulated at 0000 UTC on 1 August 1996 (24 h integration) was located in shore near Fuqing,Fujian Province at which the typhoon was reported to landfall two hours later.It shows that strong upward motion formed by low level convergence existed in the eye-wall and subsidence at the eye.The wind field shows clear asymmetrical structure near the typhoon center.The cloud and rainband was screw-typed distributed around typhoon center,and consisted of meso-β scale rain cores.During the period of typhoon HERB staying near and passing over Taiwan,the lower cloud was developed in the eye region so that the previous clear typhoon eye on the satellite pictures became fuzzy.Observation shows that the typhoon center was "warm",but the model simulations with higher space resolution show that in the mid-troposphere the region of eye-wall with stronger upward motion and more cloud-and rain-water was warmer than the eye.During the period of typhoon passing over Taiwan and its following landfall at Fujian,the track of model typhoon deviated about 30 km northward (i.e.,rightward) because of the orographic effects of Taiwan Island,but the strength of the typhoon was not affected remarkably.The amount of rainfall on Taiwan in the 36 h simulations was enhanced more than six times by the orographic lifting of Taiwan Mountain.     

EFFECTS OF THREE KINDS OF PHYSICAL PROCESSES ON TYPHOON INTENSITY*

This paper designs three quasi-geostrophic barotropic models with a radial/horizontal grid length being 2 kin,one in the polar coordinates,one on a stationary typhoon circulation condition and another on a non-stationary typhoon circulation condition in the Cartesian coordinates,to investigate the effects of azimuthal and radial linear advections,and nonlinear advection on the inward propagation of mesoscale vorticity and the changes of typhoon intensity.Results show that the azimuthal linear advection may result in the formation of spiral vorticity bands;the radial linear advection in a certain parameter set is able to transfer vorticity inwards,leading to a slight enhancement of typhoon;the nonlinear advection of perturbation vorticity on a stationary typhoon circulation condition may transfer more vorticities inwards,thus resulting in a distinct enhancement of typhoon;and the nonlinear advection on a non-stationary typhoon circulation condition possesses duality,i.e.on the one hand,the advection increases the vorticity of inward propagation,thus favorable to the intensification of typhoon,and on the other hand,in the inward propagation process of vorticity the originally concentric and axisymmetric structure of typhoon basic flow is damaged,and a complex flow pattern forms,which in turn tends to weaken the circulation of typhoon.At last the paper discusses the possible applications of those results in typhoon intensity prediction.     

STUDY OF THE RANDOMNESS INHERENT IN THE TYPHOON MOVEMENT*

A difference scheme is adopted to perform numerical integrations of a deterministic barotropic vorticity equation for four designed experiments,and the 1-D and 2-D sequences are obtained for the velocity of the typhoon center with the aid of model output,together with the correlation dimension and K entropy investigated.Results show that there exists randomness inherent in the center movement in the model atmosphere.Eventually the influence of localized heat sources and basic flow upon the stochasticity and predictability of the track of typhoon is discussed.     

非地转湿Q矢量在台风“云娜”暴雨过程中的分析应用

应用非地转湿Q矢量理论,对2004年8月12-15日台风“云娜”登陆后造成的大范围持续暴雨过程进行诊断分析。结果表明,非地转湿Q矢量能比较清楚地揭示台风暴雨的演变过程,非地转湿Q矢量的散度负值区和流场辐合区与未来12小时的强降水落区有较好的对应关系；非地转湿Q矢量的散度的垂直分布能够反映台风外围对流发展的深度,对判断台风在陆地上的维持有一定的意义。     

THE IMPACT OF MID-LATITUDE CIRCULATION OVER THE TIBETAN PLATEAU ON THE TRACK OF TYPHOON OVER THE NORTHWEST PACIFIC*

There is a close relationship between variation of middle latitude synoptic system over the Tibetan Plateau and movement of typhoon over the Northwest Pacific.This paper tries to discuss the mechanism of it through the numerical simulation and dynamic diagnosis.25-year statistical results during the period from 1970 to 1995 indicate that the relationship between middle latitude circulation over the Plateau and the track of typhoon over the Northwest Pacific are as follows.When longwave trough in 500 hPa isobaric surface over the Plateau.it is favourable to typhoon's westward movement:on the contrary,large scale anticyclone over the Plateau is favourable to typhoon's recurvature.We simulated the typhoon under these two flow patterns with MM5 model.Numerical simulation results showed that:(a)Longwave trough on 500 hPa surface over the Plateau makes subtropical high extended westward so as to typhoon south to high moves westward in easterly steering flow.(b)Anticyclone over the Plateau will bring about the longwave trough developing along the east coast of Asia,it'will usually cause typhoon recurring in front of the developed trough.In addition,the results of dynamic diagnosis show the physical mechanism on impact of synoptic system over the Plateau on the downstream synoptic system,that is,the transport of disturbance kinetic energy over the upstream Plateau makes the downstream trough developed.And then it affects the steering flow of typhoon.Because of existence of the high ridge over the Plateau.the energy transport channel moves to north.On the contrary,the trough exists over the Plateau,the energy transport channel moves to south.The southerly in front of trough over the Plateau and the southerly in the east part of typhoon transport low potential vorticity of low latitude into subtropical high.That is beneficial to development of subtropical high and affects typhoon's movement.These results fully reflect the impact of interaction between mid-latitude and low latitude on synoptic system.     

台风Dan(9914)的水汽输送特征

利用ECMWF 2.5°×2.5°的再分析资料,用大尺度水汽通量流函数和速度势以及水汽收支对台风Dan(9914)在形成、加强和减弱过程中的水汽输送和收支进行了诊断分析。结果表明:台风Dan西行期的水汽主要从西边界和东边界流入台风,水汽主要是来自于副热带高压南侧偏东气流对水汽的输送;转向北移后则以西边界流入的水汽占主导作用,水汽主要是来自南海。台风Dan的水汽输送主要集中在对流层中低层,一般在925 hPa有最大的水汽总收支。在Dan发生发展的不同时期,由大尺度水汽通量流函数和速度势表示的水汽通量输送和辐合也有明显的变化,表明水汽输送和辐合在Dan的发生发展及消亡过程中有一定作用。     

TRAJECTORY ANALYSES OF THE DUSTSTORMS OVER EAST ASIA*

The transports of dust are calculated using 3-dimensional(3-D) trajectory method for three cases of duststorms in the terrain-following coordinate system,and the synoptic processes are also discussed for each case.The case of 17-20 April 1980,a severe duststorm was associated with the rapid development of a cyclone over the Mongolia Plateau.The dust moved from west to east across several deserts,formed a typical dust path in spring.The other two were weaker and the dust was triggered by the strong wind behind the cold front from northwest or north.Because the vertical velocity is considered in 3-D trajectory analysis,trajectories calculated should better reveal the transport rule of the dust particles and the results seem to be more consistent with the synoptic processes.The trajectory analysis on the 2-D isobaric surfaces is simpler but can be used only in the conditions with weak vertical wind shear and weak vertical velocity.The difference of trajectories at lower levels between two methods may be caused by the different treatment of orography.     

一次台风暴雨过程的数值模拟和中尺度分析

利用改进的有限区域数值预报模式（AREM）,对“艾利”台风在福建省登陆所造成的特大暴雨过程进行了数值模拟;采用空间带通滤波技术,对模拟结果进行尺度分离,揭示出对此次暴雨天气过程有直接影响的中尺度系统,即中尺度低压和中尺度辐合线;对这些中尺度系统的物理量场特征和它们与强降水的关系进行了分析研究。结果表明：强降水与中尺度系统的散度场有较好的对应关系,中尺度系统与地形相互作用形成很强的辐合抬升作用是造成中尺度暴雨的直接原因。     

NUMERICAL SIMULATION AND MESOSCALE ANALYSIS OF A TORRENTIAL RAIN CAUSED BY TYPHOON

A heavy storm rainfall caused by Typhoon Acre (No.0418) when landing at Fujian has been successfully simulated by using AREM model. The simulation result is scale-separated by spatial band-pass filtering, which reveals the mesoscale low pressure and convergence line that has direct impact on this rainfall process. The physical characteristics of the two mesoscale systems and their relation with rainfall are also analyzed. Study shows that there exists a well corresponding relationship between the storm rainfall and mesoscale divergence and strong updraft arising from the convergence, which is caused by the interactions between the mesoscate systems and topographic features, and is directly responsible for the rainfall.     

多时刻台风Bogus资料同化对台风"天鹅"的影响

基于GRAPES(Global/Regional Assimilation and Predition System)三维变分同化系统,设计在6小时内分别应用三小时一次和逐小时的台风定位和定强信息对台风进行多次BDA(Bogus Data Assimilation)同化,在多次BDA中只同化近似程度高的涡旋风分量而近似...     

HEAVY PRECIPITATION IN HONG KONG, 1951-2000*

Daily precipitation amounts greater than 50 mm from 1951 to 2000 in Hong Kong were analyzed to determine their seasonal and annual frequencies.A total of 627 extreme rainfall days happened and 334 (53.27%) days occurred in summer.Non significant increasing trends for annual precipitation and number of heavy rain days were detected.Daily surface weather maps were used to identify the synoptic weather types producing the heavy rainfall.It was discovered that tropical cyclone and low pressure induced most of the heavy precipitation.Seven out of twelve years with counts of heavy rain days over fifteen coincided with E1 Nino events.     

SOME RELATIONS BETWEEN ASYMMETRIC STRUCTURE AND MOTION OF TYPHOONS*

The analysis of the SPECTRUM(Special Experiment Concerning Typhoon Recurvature and Unusual Movement) data indicates that the structure of recurving target typhoons 9015(Abe),9019(Flo) and 9020(Gene) at different stages of moving processes showed different motion features.On different time scales,temporal variations of typhoon structure and motion speed displayed different features.     

ANALYSIS OF TYPHOON MATSA （NO.0509） AFFECTING SHANDONG PROVINCE

The characteristics of the moving course of Typhoon Matsa (No.0509), associated heavy rain and physical quantities fields have been analyzed, with the focus on the reason of the typhoon’s abrupt northeastward turn in Anhui Province and heavy rain concentrating in the northeast of typhoon center instead of near it. Meaningful conclusions are as follows. The reasons for typhoon abrupt turning are that the subtropical high pressure was moving southward and divergence fields of 200 hPa were to the right of the typhoon center; there was no obvious cold air invading Shandong after the typhoon entered the westerly belt; the southeasterly jet of typhoon and shear brought heavy rainfall to the Shandong peninsula before the typhoon entered Shandong. But after the typhoon’s movement into Shandong, the typhoon’s inverted trough brought the rainfall to the northern and central Shandong.     

0509号台风"麦莎"影响山东分析

分析了0509号台风的移动路径、强降水分布及物理量场分布,重点分析台风在安徽突然转向东北和强降水不在中心附近而是偏于中心东北侧的原因。结果表明:副高突然南落及200hPa辐散偏向台风中心右侧是台风在安徽转向进入江苏的原因;台风进入西风带以后没有明显的冷空气侵入;台风进入山东前,半岛大暴雨是由台风右侧东南急流和切变线引起,而台风进入山东境内时,鲁北、鲁中强降水由台风倒槽引起。     

0509号台风麦莎影响山东分析

分析了0509号台风的移动路径、强降水分布及物理量场分布,重点分析台风在安徽突然转向东北和强降水不在中心附近而是偏于中心东北侧的原因。结果表明：副高突然南落及200hPa辐散偏向台风中心右侧是台风在安徽转向进入江苏的原因;台风进入西风带以后没有明显的冷空气侵入;台风进入山东前,半岛大暴雨是由台风右侧东南急流和切变线引起,而台风进入山东境内时,鲁北、鲁中强降水由台风倒槽引起。     

台风Lekima(1909)登陆前后动热力结构变化对浙江极端降水的影响

利用NCEPFNL 1°×1°的全球再分析资料、FY-2F卫星相当黑体亮温TBB资料、中国自动站与CMORPH降水产品融合的逐时降水资料和多普勒天气雷达资料,重点分析了台风Lekima(2019)发展演变过程中的动热力结构变化和水汽分布特征与浙江极端强降水之间的关系.台风Lekima(2019)近海急剧加强为具有特殊双...     

“麦莎”台风暴雨落区非对称分布的诊断分析

利用FY-2C气象卫星资料、常规资料和NCEP再分析资料，对2005年第9号台风“麦莎”登陆后暴雨落区非对称分布的成因进行诊断分析，并讨论其动力学和热力学特征。结果表明：（1）FY-2C红外-通道辐射亮温（TBB）场能够清晰地揭示台风暴雨落区的分布以及造成这种非对称分布的云系结构特征；（2）水汽图像展示了此次降水过程中，对流层中上层主要的水汽型，来自南海和东海强盛的热带水汽羽直抵台风中心东部，中纬度地区的极锋水汽羽东移，其尾端并入台风北部，受二者共同作用，台风降水呈非对称分布；（3）台风中心附近的垂直流场、涡度、假相当位温和整层积分的水汽通量散度等物理量的非常规分布以及低层冷空气的契入，共同解释了台风云系的非对称结构及强雨区非对称分布的形成原因。     

A CLOUD-RESOLVING MODELING STUDY OF SURFACE RAINFALL PROCESSES ASSOCIATED WITH LANDFALLING TYPHOON KAEMI(2006)

The detailed surface rainfall processes associated with landfalling typhoon Kaemi(2006) are investigated based on hourly data from a two-dimensional cloud-resolving model simulation. The model is integrated for 6 days with imposed large-scale vertical velocity, zonal wind, horizontal temperature and vapor advection from National Center for Environmental Prediction (NCEP) / Global Data Assimilation System (GDAS) data. The simulation data are validated with observations in terms of surface rain rate. The Root-Mean-Squared (RMS) difference in surface rain rate between the simulation and the gauge observations is 0.660 mm h^-1, which is smaller than the standard deviations of both the simulated rain rate (0.753 mm h^-1) and the observed rain rate (0.833 mm h^-1). The simulation data are then used to study the physical causes associated with the detailed surface rainfall processes during the landfall. The results show that time averaged and model domain-mean P_s mainly comes from large-scale convergence (Q_WVF) and local vapor loss (positive Q_WVT). Large underestimation (about 15%) of P_s will occur if Q_WVT and Q_CM (cloud source/sink) are not considered as contributors to P_s. Q_WVF accounts for the variation of P_s during most of the integration time, while it is not always a contributor to P_s. Sometimes surface rainfall could occur when divergence is dominant with local vapor loss to be a contributor to P_s. Surface rainfall is a result of multi-timescale interactions. Q_WVE possesses the longest time scale and the lowest frequency of variation with time and may exert impact on P_s in longer time scales. Q_WVF possesses the second longest time scale and lowest frequency and can explain most of the variation of P_s. Q_WVT and Q_CM possess shorter time scales and higher frequencies, which can explain more detailed variations in P_s. Partitioning analysis shows that stratiform rainfall is dominant from the morning of 26 July till the late night of 27 July. After that, convective rainfall dominates till about 1000 LST 28 July. Before 28 July, the variations of in rainfall-free regions contribute less to that of the domain-mean Q_WVT while after that they contribute much, which is consistent to the corresponding variations in their fractional coverage. The variations of Q_WVF in rainfall regions are the main contributors to that of the domain-mean Q_WVF, then the main contributors to the surface rain rate before the afternoon of 28 July.     

THE INSTABILITY OF TRAJECTORY AND ERROR GROWTH*

The purpose of this paper is to study the dynamical mechanism of error growth in the numerical weather prediction.The error is defined in the sense of generalized energy,simply called energy error.From the spectral form of the primitive equations,we have derived the evolution equations of error in detail.The analyses of these equations have shown that the error growth rate is determined by the tangent linear equations.The nonlinear advection caused by the error perturbation itself contributes nothing to the error growth rate,and only redistributes the error.Furthermore,an approach to calculation of the error growth rate has been developed,which can also be used to study the local instability of time-independent basic state as well as time-dependence basic state.This approach is applied to well-known Lorenz's system,and the results are indicative of the correctness and significance of the theoretical analyses.     

9806号台风非对称结构形成及其高纬西折路径分析

对9806号台风在弱环境场中的向北移动，至强环境场中折向西行的物理机制进行了分析，得出在弱环境场中台风可形成不对称结构，其物理量如高度的变化在台风进入强环境场后与环境场叠加，从而改变台风移向，强弱环境场的更替，可能是9806号台风移向突变的重要原因。