云迹风资料在热带气旋移向预报中的应用

利用云迹风并结合实测风,从涡度方程出发,对１９９８年南海和西太平洋的几个热带气候进行诊断计算。结果反映,涡度局地变率ｅ↓ζ／ｅｔ对热带气旋移动有指示意义,它既可批示热带气旋正常路径,在引导气流不明显的情况下,也能对气旋的转折路径有较明显的反映,气旋常朝涡度局地变率最在的方向移动。当热带气旋周围有数个ｅ↓ζ／ｅｔ中心时写和提交 矢量合成法确定了气旋的最大可能移动方向。此外,玷如引导气流一样,热带气旋     

Impact of vortex-removal from environmental flow in cyclone track prediction using Lagrangian advection model

In the present study, a new approach is discussed to find out the residual steering flow from the high-resolution global Numerical Weather Prediction (NWP) model-forecasted wind fields, which have been used in the Lagrangian advection model to determine the track of tropical cyclones formed in the Indian Ocean. The Lagrangian advection model is newly developed model and conceptually closer to the dynamical models, which utilizes environmental steering flow and the effect due to earth’s rotation (the beta-effect) to determine the motion of cyclone. In this approach, the effect of environmental flow on the cyclone track is examined by removing the existing cyclone vortex from the steering flow which is determined by potential vorticity approach. A new approach based on vortex pattern matching has been used to identify the cyclone vortex and to remove it from the steering flow. The tracks of five tropical cyclones (viz., Nargis, Khai_Muk, Nisha, Aila and Phyan) which were formed in the North Indian basin during the period 2008–2009 have been generated by the Lagrangian advection model using the proposed scheme. The position errors were computed with respect to the Joint Typhoon Warning Center (JTWC) best track analysis positions and compared with that of without-vortex-removal scheme. The results show that the mean track errors for five cyclones are reduced by 6–35?% for 12–72?h forecast in case of vortex-removal scheme as compared to the without-vortex-removal scheme.     

华东沿海地形对登陆热带气旋运动影响的理想数值研究

利用中尺度数值模式设计一组高分辨率理想试验,采用位涡趋势方法定量诊断分析热带气旋在登陆我国华东沿海地形时,其运动发生的精细化变化以及不同因子的贡献。结果表明,平地的存在使得登陆热带气旋移速相对更快,当华东沿海地形存在时,热带气旋移速显著增大,这种增速现象主要是由于平地和地形所引起的非对称气流以及相应的引导气流变化所致,这很可能是导致预报路径误差的一个重要原因。平地试验中,陆地在热带气旋低层激发出中小尺度的非对称气流,与之不同的是,实际地形的加入激发出更大尺度并且更强的非对称偏南气流。位涡趋势方法的诊断结果表明,非引导效应总体而言对热带气旋运动贡献较小,这是因为这些因子相互抵消,但在不同的垂直层次上,不同的非引导因子贡献存在明显的差异。     

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。     

热带气旋运动的动力学研究进展

热带气旋运动是由各种形式的外部强迫、内部过程及其相互作用所决定的。特别是环境气流与气旋环流以及β效应之间的相互作用可以产生次级的非对称气流,使热带气旋偏离大尺度环境气流的引导。这种偏差,被称为广义的β漂移。本文讨论了控制β漂移的物理因子和物理过程,尤其是涡旋结构与环境气流切变对它的影响,以及β漂移在热带气旋路径预报上的应用。另外,还总结了双台风相互作用、热带气旋摆动和与下垫面强迫有关的物理过程的影响。     

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。     

EFFECT OF THE NONLINEAR TERM ON MOVEMENT AND DEVELOPMENT OF TROPICAL CYCLONE

The dynamics of tropical cyclone is investigated in a nondivergent barotropic model with nobasic flow. The effect of nonlinear term on the movement and development of tropical cyclone isemphatically demonstrated. The advection of asymmetric vorticity by the symmetric flow (AAVS)produces the small-scale gyres (SSGs). The SSGs counterclockwise rotate around the tropicalcyclone center. The interaction of SSGs with the large-scale beta gyres (LSBGs) leads to theoscillation in translation speed and vacillation in translation direction for tropical cyclone. Theadvection of symmetric vorticity by the asymmetric flow (ASVA) steers the symmetric circulationof tropical cyclone. The ventilation flow vector determined by the asymmetric flow is closecorrelated with the motion vector of tropical cyclone. The nonlinear advection of relative vorticityis an order of magnitude greater than the linear advection of planetary vorticity, However, theasymmetric circulation created by the planetary vorticity advection provides a background conditionfor anomalous motions of the tropical cyclone. The combination of the linear and nonlinear effectsresults in accelerated, decelerated, changing direction and/or counterclockwise looping motions ofthe tropical cyclone.     

EFFECT OF THE NONLINEAR TERM ON MOVEMENT AND DEVELOPMENT OF TROPICAL CYCLONE*

The dynamics of tropical cyclone is investigated in a nondivergent barotropic model with no basic flow. The effect of nonlinear term on the movement and development of tropical cyclone is emphatically demonstrated. The advection of asymmetric vorticity by the symmetric flow(AAVS) produces the small-scale gyres(SSGs). The SSGs counterclockwise rotate around the tropical cyclone center. The interaction of SSGs with the large-scale beta gyres(LSBGs) leads to the oscillation in translation speed and vacillation in translation direction for tropical cyclone. The advection of symmetric vorticity by the asymmetric flow(ASVA) steers the symmetric circulation of tropical cyclone. The ventilation flow vector determined by the asymmetric flow is close correlated with the motion vector of tropical cyclone. The nonlinear advection of relative vorticity is an order of magnitude greater than the linear advection of planetary vorticity, However, the asymmetric circulation created by the planetary vorticity advection provides a background condition for anomalous motions of the tropical cyclone. The combination of the linear and nonlinear effects results in accelerated, decelerated, changing direction and/or counterclockwise looping motions of the tropical cyclone.     

Simulated sensitivity of tropical cyclone track to the moisture in an idealized monsoon gyre

In this study, the sensitivity of tropical cyclone (TC) track to the moisture condition in a nearby monsoon gyre (MG) is investigated. Numerical simulations reveal that TC track is highly sensitive to the spatial distribution of relative humidity (RH). In an experiment conducted with higher (lower) RH in the eastern (western) semicircle of an MG, the TC experiences a sharp northward turning. In contrast, when the RH pattern is reversed, the simulated TC does not show a sharp northward turning. The RH distribution modulates the intensity and structure of both the TC and MG, so that when the TC is initially embedded in a moister environment, convection is enhanced in the outer core, which favors an expansion of the outer core size. A TC with a larger outer size has greater beta-effect propagation, favoring a faster westward translational speed. Meanwhile, higher RH enhances the vorticity gradient within the MG and promotes a quicker attraction between the TC and MG centers through vorticity segregation process. These cumulative effects cause the TC to collocate with the MG center. Once the coalescence process takes place, the energy dispersion associated with the TC and MG is enhanced, which rapidly strengthens southwesterly flows on the eastern flanks. The resulting steering flow leads the TC to take a sharp northward track.     

台湾岛地形诱生次级环流系统对热带气旋异常运动的影响机制

对经过中国台湾岛和海南岛、吕宋岛、日本诸岛以及朝鲜半岛的热带气旋在过岛前后的运动、结构和强度的时空变化进行了统计诊断分析。研究结果表明,台湾岛附近热带气旋运动左偏（定义为偏于以前路径的左侧）机率最大,且台湾岛周围是产生诱生低压的高频区。采用理想东、西风环境场作为数值模拟背景场,数值研究了岛屿地形强迫与台湾附近的环境流场的相互作用及其对热带气旋运动偏转的影响,提出了岛屿地形强迫、背景场和热带气旋涡旋三者相互作用对热带气旋路径突然转折影响的观点,即台湾地形有利于环境场中诱生出一对偏差偶极涡,这对诱生偏差偶极涡将导致逼近岛屿的热带气旋产生运动方向的突然偏折,且在不同基本气流条件下,岛屿地形对热带气旋运动可能产生显著不同的影响。     

CALCULATION OF BASIC ENVIRONMENTAL GEOSTROPHIC FLOW AND STATISTICAL STUDY ON TC TRACK AND ITS DEVIATION

Using the T63L16 analysis data with the resolution of 1.875╳1.875 degree of latitude and longitude obtained from National Meteorological Center (NMC) and the real central position information of tropical cyclone (referred to as TC hereafter) numbered by NMC, the basic environmental geostrophic flow at 126 time levels of 25 TCs in 1996 are calculated. The vertical distribution features of the flows are analyzed. Besides, the deviation of real TC tracks from the flows (referred as steering deviation hereafter, namely, the deviation between the real central position of TC and the position calculated according to the steering flow) is also investigated. The result shows that the steering deviation would be different if the domain used to calculate the steering flow is different. The present paper obtains the optimum domain size to calculate the steering flow. It is found that the steering deviation is related to the velocity of steering flow and the initial latitude and intensity of TC itself, and that TC motion has relationship with the vertical shear structure of environmental geostrophic flow. The result also shows that the optimum steering flow is the deep-layer averaged basic flow from 1000 hPa to 200 hPa. Having the knowledge of these principle and features would help make accurate forecast of TC motion.     

Feedback between convective heating and dynamics and movements of tropical cyclones

Summary It is shown that there exists a mechanism that can cause north-northwest movement of tropical cyclones in addition to already recognised mechanisms such as steering current and beta drift. This mechanism depends on the interaction between organised convection and dynamics. In the initial stages of formation of a cyclone, it is assumed that the hydrodynamic instabilities result in an incipient disturbance that organises some convection giving rise to a heat source. The atmospheric response to a localized heat source located off the equator in the northern hemisphere produces a low level vorticity field with a maximum in the northwest sector of the original heat source. If the Ekman-CISK which depends on the low level vorticity, was the dominating mechanism for moisture convergence, the location of the heat source would move to the new location of vorticity maximum. A repetition of this process would result in a northwest movement of the heat source and hence that of the cyclone. The movement of a tropical vortex under the influence of this mechanism which depends on asymmetries created by linear dispersion of Rossby waves is first illustrated using a linear model. It is then demonstrated that this process also enhances the motion of a tropical vortex in a nonlinear model. Importance of this feedback and the resulting movements of a tropical vortex in determining the actual track of a cyclone and in bogusing an initial vortex for prediction models are illustrated.With 6 Figures     

DEVELOPMENT OF A TROPICAL CYCLONE IN BAROTROPIC ENVIRONMENTAL FLOWS

Development of a tropical cyclone in barotropic environmental flows is investigated with a shallow water model. It is found that the tropical cyclone develops only when it is embedded in an environmental now with a southward relative vorticity gradient. The related physical mechanism is explained by analyzing the kinetic energy conversion between the environmental flow and tropical cyclone circulation.     

Simulations of the motion of tropical cyclone-like vortices in the presence of synoptic and mesoscale circulations

Initial mesoscale vortex effects on the tropical cyclone(TC) motion in a system where three components coexist(i.e.,an environmental vortex(EV),a TC,and mesoscale vortices) were examined using a barotropic vorticity equation model with initial fields where mesoscale vortices were generated stochastically.Results of these simulations indicate that the deflection of the TC track derived from the initial mesoscale vortices was clearly smaller than that from the beta effect in 60% of the cases.However,they may have a more significant impact on the TC track under the following circumstances.First,the interaction between an adjacent mesoscale vortex and the TC causes the emergence of a complicated structure with two centers in the TC inner region.This configuration may last for 8 h,and the two centers undergo a cyclonic rotation to make the change in direction of the TC motion.Second,two mesoscale vortices located in the EV circulation may merge,and the merged vortex shifts into the EV inner region,intensifying both the EV and steering flow for the TC,increasing speed of the TC.     

VENTILATION FLOW IN A BAROCLINIC VORTEX RELATED TO TROPICAL CYCLONE MOTION*

The tropical cyclone motion is numerically simulated with a quasi-geostrophic baroclinic model.The flow field of a tropical cyclone is decomposed into its axisymmetric and asymmetric components.The relation between the ventilation flow vector and the motion vector of the tropical cyclone is investigated.The results of numerical experiments indicate:(1) There are both large-scale beta gyres and small-scale gyres in the asyrnmetric flow field.(2) The interaction between small-scale gyres and large-scale beta gyres leads to the oscillation of translation speed and translation direction for the tropical cyclone.(3) There are the large deviations between the ventilation flow vector calculated by means of Fiorino and Elsberry's method and the motion vector of tropical cyclone.(4) The ventilation flow vector computed using the improved method closely correlates with the motion vector of the tropical cyclone.     

斜压涡旋中的通风气流与热带气旋移动的关系

应用准地转斜压模式数值模拟了热带气旋的移动。将热带气旋的流场分解为轴对称分量和非对称分量，研究非对称流场中的通风气流矢量与热带气旋移动矢量的关系。数值试验结果表明：（１）在热带气旋的非对称流场中，不但有大尺度β涡旋，而且还有小尺度涡旋。（２）小尺度涡旋与大尺度β涡旋之间的相互作用导致热带气旋移向的摆动和移速的振荡。（３）应用Ｆｉｏｒｉｎｏ和Ｅｌｓｂｅｒｒｙ的方法计算的通风气流矢量与热带气旋移动矢量有很大偏差。（４）应用改进的方法计算的通风气流矢量与热带气旋移动矢量相关密切。     

热带气旋内部非对称积云对流对其移动的影响

在一个简单的两层板对称CISK模式中，我们考虑了热带气旋内部非对称积云对流的作用，并由此推导出热带气旋移动的动力学速度公式。利用SPECTRUM-90这套热带气旋试验资料，本文着重分析了热带气旋内部非对称积云对流对其运动的影响，以探索热带气旋移动与引导气流偏差的可能机理。计算结果表明，考虑积云对流非对称作用产生的动力学速度确能明显改善热带气旋的路径预报效果，尤其对于一些疑难路径，这种改善作用更突出。因此，CISK理论不仅是热带气旋发展和维持的重要机制，而且对热带气旋移动的影响也不可忽视。     

热带气旋低层水平流场的平面动力系统分析

利用中国气象局上海台风研究所整理的热带气旋最佳路径资料,热带气旋云图、气象雷达回波图资料,ECMWF ERA-Interim再分析风场资料;并用大气运动方程和天气学原理分析得到热带气旋低层水平流场结构,根据流场建立平面非线性自治动力系统。结果表明,TC在成熟阶段或发展很强时期,由两组二维驻定微分方程组解确定水平流场,TC眼区以内气流沿顺时针方向流动,TC眼区以外气流沿逆时针方向流动。TC眼区内外相反方向风场之间为风向切变圆环,圆环上不断有气旋形成,并存在低空急流,是狂风暴雨出现区域。结论与合成雷达回波观测结果一致。      

1965-2010年7-9月影响中国的热带气旋降水变化趋势分析

利用中国气象局逐日台站降水和上海台风研究所最佳台风路径等资料,对1965—2010年夏季(7—9月)影响中国热带气旋降水的变化趋势及影响机制进行了分析。热带气旋降水主要影响中国东部和南部,夏季平均的热带气旋降水由沿海向内陆,由东南向西北递减。自1965年以来,夏季影响中国的热带气旋降水呈现华东及东南沿海增多,华南沿海、海南岛以及西南地区减少的变化趋势。分析发现,一方面夏季西北太平洋副热带高压加强西伸,导致同期中国东部地区上空水汽辐合增强;另一方面热带气旋的引导气流发生变化,使夏季热带气旋盛行路径由南海向东亚沿岸偏移,这两个因子的共同作用致使影响中国的热带气旋降水发生变化。     

VENTILATION FLOW IN A BAROCLINIC VORTEX RELATED TO TROPICAL CYCLONE MOTION

The tropical cyclone motion is numerically simulated with a quasi-geostrophic baroclinic model.The flow field of a tropical cyclone is decomposed into its axisymmetric and asymmetric components.The relation between the ventilation flow vector and the motion vector of the tropical cyclone is inves-tigated.The results of numerical experiments indicate:(1) There are both large-scale beta gyres andsmall-scale gyres in the asyrnmetric flow field.(2) The interaction between small-scale gyres andlarge-scale beta gyres leads to the oscillation of translation speed and translation direction for the tropi-cal cyclone.(3) There are the large deviations between the ventilation flow vector calculated bymeans of Fiorino and Elsberry's method and the motion vector of tropical cyclone.(4) The ventila-tion flow vector computed using the improved method closely correlates with the motion vector of thetropical cyclone.