季风涡旋对热带气旋生成影响的理想试验研究

利用新一代非静力平衡中尺度数值模式WRF_ARW（3.3.1版本）模拟季风涡旋中热带气旋生成的过程,从动力和热力作用两方面分析大尺度季风涡旋对热带气旋生成的影响。结果表明:从动力学角度来看,能提供较大环境场涡度的季风涡旋不利于扰动涡旋快速发展成热带气旋。初始阶段,由于季风涡旋尺度大,垂直涡度径向梯度弱。而垂直涡度径向梯度的强弱可以通过“涡度隔离”效应影响对流单体向涡旋中心的聚集合并过程。随着扰动的组织化,径向入流对涡度的平流作用越来越重要。对流单体相对最大风速半径的位置对热带气旋生成作用明显,当其集中在最大风速半径附近时涡旋容易快速发展。此外,环境场相对涡度与热带气旋的尺度存在显著正相关。初始尺度大的涡旋最终具有较大的外围尺度,其涡度的分布范围也更广。从热力学角度来说,较大的环境场相对湿度有利于热带气旋的生成。虽然较大的环境场湿度能够诱发较强的外围对流,但同时也会使最大风速半径以内存在丰富的对流,后者能够提供充分的内区非绝热加热,降低中心气压,促进涡旋发展。      

影响热带气旋结构和运动的两类因子的数值研究

利用一个β平面正压准地转模式，实施了４组时间积分大于５ｄ的试验。结果表明：涡度平流和β效应同样重要，它们对热带气旋的结构和移动均具有明显影响。     

2002年海南一次非热带气旋暴雨成因分析

利用常规地面观测资料和NCEP逐日每6 h水平分辨率为1°×1°的再分析资料,分析海南2002年9月18—21日暴雨天气过程的成因。结果表明:暴雨与南海辐合带活动密切相关,华南沿海的低空急流为暴雨提供有利的水汽条件;对流层中层差动涡度平流破坏海南及邻近地区的准地转平衡,该处的上升运动得到加强;暴雨产生在能量锋附近低层气旋性涡度发展、高层辐散显著的区域;较强的差动假相当位温平流促使大气层结向对流不稳定发展,导致局地暴雨增强。     

双热带气旋相互作用的研究

采用无基本气流的无辐散正压模式模拟了双热带气旋的运动。应用非对称理论研究了双热带气旋的相互作用。双热带气旋中的每个热带气旋主要由通过其中心的非对称气流（即通风气流）作用而移动。这股非对称气流是由其自身的线性和非线性效应产生的非对称涡旋与其配对热带气旋形成的非对称涡旋相叠加而引起的。     

湿斜压性与热带气旋强度突变

应用湿位涡方程和倾斜涡度发展理论 ,研究了热带气旋内部相当位温结构的演变与其强度突变的可能关系 ,并用一套高分辨率的模拟资料对所得结论进行验证。结果表明 ,由于热带气旋眼壁附近等相当位温面陡立 ,湿斜压性变化所激发的倾斜涡度发展是引起该区域垂直涡度突然增大或突然减小的主要原因。当热带气旋中心附近大部分区域的垂直涡度显著增长时 ,热带气旋就会在整体上表现为爆发性或迅速发展。最后还据此对同心双眼结构的出现和消失如何影响热带气旋强度变化进行了探讨。     

热带气旋强度影响其移动的物理机制

应用无基本气流的无辐射正压模式研究热带气旋强度影响其移动的物理机制，结果表明，（１）弱（强）热带气旋的大度尺β涡旋弱（强）通风气流速度小（大），因而其移速慢（快）（２）弱的与强的热带气旋的大尺度β涡旋的方位位相之差，通风气流方向之差都很小，因此其移向的差别也很小；（３）热带气旋移速振荡和移向摆动的周期与小尺度涡旋活动的周期相接近，在热带气旋内部区域；弱（强）热带气旋的切向风速小（大），小尺度涡旋活     

β涡旋的垂直结构及其对热带气旋移动的影响

应用准地转斜压模式数值模拟热带气旋的移动，分析大尺度β涡旋的水平和垂直结构及其对热带气旋移动的。研究结果表明，两β涡旋之间的准均匀流（通风气流）仍然与热带气旋的运动相关。     

热带气旋远距离对西南涡加强作用的个例研究

利用地面观测资料、NCEP再分析资料对2018年7月10～11日一次热带气旋远距离对西南涡加强作用的个例分析。结果表明：南海的热带气旋和西太平洋上的热带气旋对西南涡的发展和维持有远距离的加强作用。热带气旋外围偏南、偏东气流向西伸展与四川盆地东南气流贯通,将南海和西太平洋上的水汽向四川盆地输送。热带气旋通过外围气流远距离改变西南涡周围的风压场分布、暖湿结构、动量特征,从而改变和加强西南涡及其邻域的大气斜压性和非平衡性。     

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.     

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.     

NUMERICAL STUDY ON FUNCTIONS AFFECTING TROPICAL CYCLONE STRUCTURE AND MOTION

By using a beta-plane quasigeostrophic barotropic model,four numerical experiments withintegration time more than five days are performed.Results show that the vorticity advection termand beta term are two basic factors significantly affecting tropical cyclone structure and motion.     

NUMERICAL STUDY ON FUNCTIONS AFFECTING TROPICAL CYCLONE STRUCTURE AND MOTION*

By using a beta-plane quasigeostrophic barotropic model,four numerical experiments with integration time more than five days are performed.Results show that the vorticity advection term and beta term are two basic factors significantly affecting tropical cyclone structure and motion.     

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.     

USE OF A NEW STEERING FLOW METHOD TO PREDICT TROPICAL CYCLONE MOTION

A tropical cyclone is a kind of violent weather system that takes place in warmer tropical oceans and spins rapidly around its center and at the same time moves along surrounding flows. It is generally recognized that the large-scale circulation plays a major role in determining the movement of tropical cyclones and the effects of steering flows are the highest priority in the forecasting of tropical cyclone motion and track. This article adopts a new method to derive the steering flow and select a typical swerving track case (typhoon Dan, coded 9914) to illustrate the validity of the method. The general approach is to modify the vorticity, geostropical vorticity and divergence, investigate the change in the non-divergent stream function, geoptential and velocity potential, respectively, and compute a modified velocity field to determine the steering flow. Unlike other methods in regular use such as weighted average of wind fields or geopoential height, this method has the least adverse effects on the environmental field and could derive a proper steering flow which fits well with storm motion. Combined with other internal and external forcings, this method could have wide application in the prediction of tropical cyclone track.     

关于热带气旋尺度变化机制的初步分析

应用小参数方法和缓变波包理论分析了热带气旋尺度变化的主要原因。分析指出：热带气旋尺度变化主要决定于其内部要 通常的热带气旋内惯性性重力波由中心外传播的情况下，当层结稳定度和惯性稳定度参数随着离中心的距离增加而增加时，热带气旋尺度增加，它可以称为热带气旋“膨胀”；而当层结稳定度和惯性稳定度参数随着离中心的距离增加而减小时，热带气旋尺度减小，它可以称为热带气旋“收缩”。     

A PRELIMINARY ANALYSIS ON MECHANISM OF SIZE CHANGE IN TROPICAL CYLONE

By using the WKB method and slowly-varying wave packet theory the maincause for the sisechange in tropical cyclones is analyzed. It is shown that the size change in tropical cyclones is mainly determined by the inner factors. In general case the angular frequencies of inertio-gravity waves are positive, thus provided that both stratification and inertia are stable, when the parameters of inertial andstatic stabilities increase with the distance from the centre, the sise gets larger; when the parameters of inertial and static stabilities decrease with the distance from the centre, the size gets smaller. The for mer may be called the "expanding" of tropical cyclones and the latter may be called the "shrinking" of tropical cyclones.     

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.