三类物理过程对台风强度影响的研究

文中设计了一个极坐标系的准地转正压模式 ,一个直角坐标系定常台风环流条件下的准地转正压模式和一个直角坐标系非定常台风环流的准地转正压模式 ,其径向或水平格距均为 2km ,以研究三类物理过程对台风强度的影响 ,即沿方位角方向的线性平流 ,沿径向的线性平流以及非线性平流对中尺度涡旋涡量内传和台风强度变化的影响。结果指出 :沿方位角方向的线性平流可导致螺旋状涡带的形成 ;沿径向的线性平流在一定的参数集合可使涡量内传 ,台风略有增强 ;定常台风环流条件下扰动涡量的非线性平流可使内传涡量明显增加 ,台风明显增强 ;非定常台风环流条件下非线性平流的作用具有两重性 ,一方面可使内传涡量增多 ,有利于台风的增强 ,另一方面 ,在涡量内传过程中 ,原先呈同心圆轴对称的台风基流结构受到破坏 ,形成复杂流型 ,这又使台风趋于减弱。最后讨论了这些结果在台风强度预测方面的可能应用。     

守恒系统中台风强度变化及其可能因子的数值研究

用一个高分辨率的 f平面正压涡度方程模式 ,实施了时间积分为 36h的 2 1组试验 ,研究相邻中尺度涡旋与台风涡旋的相互作用。结果指出 :这种相互作用能否导致台风加强 ,取决于两类因子 :一是台风涡旋最大风速的取值以及圆形基流切变的强弱 ;二是切变基流中的中尺度涡旋的自身条件 ,包括中尺度涡旋的分布、尺度、强度和结构。台风强度与初始中尺度涡旋的尺度、强度之间存在着非线性的联系     

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.     

涡旋Rossby波传播和台风切向风速变化的数值研究

设计了一个高分辨率f平面准地转正压涡度方程半谱模式，用以研究非线性对台风切向风速变化，以及不同初始异常条件下台风环流内涡旋Rossby波传播和台风切向风速变化特征。6类(14组)试验的数值结果表明：非线性使台风切向风速的增强减弱，可能使最大风速半径收缩。初始扰动中心位置对涡旋Rossby波传播和台风切向风速变化的影响明显。扰动中心在最大风速半径附近时，台风最大切向风速增强最多；异常中心在台风外区时，使最大切向风速减小。初始异常尺度(范围)减小对台风最大切向风速变化的影响减弱。双涡分布条件下，台风环流外区的涡旋使内区或近眼壁区对流涡旋对台风最大切向风速的影响减弱。     

涡旋Rossby波传播的不同特征

用一个柱坐标系涡度正压方程的半谱模式，实施了4组试验，研究了不同初始扰动涡旋分布条件下，涡旋Rossby波的传播特征问题。结果指出：正值、负值相间的沿方向角二波分布的初始场，与只有正值涡旋的初始场相比，其后涡旋Rossby波的传播有明显的差别，即前者向内传播的涡量比后者衰减得快，而且前者是单峰传播，后者是双峰传播。     

台风涡旋的结构及其与台风运动的关系

用ＦＳＵ区域模式讨论台风涡旋结构及其与运动的关系，台风涡旋的运动在无基本环流和β平面条件下取决于轴不对称环流。而不对称环流的发展源自于从对称环流动能的转换。其率取决对称环流，不对称环流和地球涡度经向梯度三者的相互作用。由于不对称环流动能产生率随高度不变，故台风作为一个统一体以相同的移速移动。不对称环流的径向结构取决于对称环流的径向结构。     

超强台风SANBA发展演变过程中涡度及环流收支的诊断分析

台风的增强过程与气旋性涡度的急剧发展相伴。使用滑动平均的空间滤波方法对WRF模式的模拟结果进行尺度分离, 进而诊断分析台风SANBA突然增强过程中垂直涡度及环流的发展演变特征。结果表明, 台风突然增强的过程中, 眼壁区上升速度增大, 暖心结构增强, 同时垂直涡度迅速增强。当SANBA从热带风暴发展为强热带风暴时, 对流层低层辐散辐合及垂直速度分布的不均匀对台风涡旋结构的增强强度相当, 在台风内部以增强区域为主同时与减弱区域交错分布; 当SANBA发展增强为强台风时, 对流层低层的散度项与倾斜项在台风中心附近均表现为强的正中心, 台风低层径向入流的增强导致低层辐合加强对台风的增强起到主要作用。台风中心区域平均环流强度随台风的不断增强而不断增大, 且从900 hPa高度不断向高层发展, 其中环流方程中的EED/EET项的发展变化可以表征台风发展初期散度项和倾斜项的主要变化。      

台风内部的中尺度波动与多边形眼墙的形成

用小波变换分析了1948～2003年南海夏季风强度指数序列振荡特征,并研究了Lanczos滤波器滤出的不同时间尺度上南海夏季风强度与SODA资料提供的海洋热力条件的关系。结果表明,南海夏季风强度变化存在准4年的年际变化、约9年周期的十年际变化和38年左右周期的年代际变化。年际变化最强,年代际变化最弱。不同尺度上的南海夏季风强度变化与海洋热力条件的显著相关区有很大的地域差异。南海夏季风强度的年际变化主要与近赤道地区的热带海洋变化有关,相关关系呈准2年变化。若前一年秋冬季节的赤道东印度洋、赤道西太平洋出现海温和温跃层深度正异常和赤道西印度洋、赤道中东太平洋出现海温和温跃层深度负异常时,对应于当年的年际尺度上的南海夏季风加强;反之则减弱。南海夏季风强度与后期海温的对应关系为:南海夏季风加强,秋季时,南海周边海区和澳大利亚东部海区海温显著负相关;冬季时,热带西印度洋、赤道中东太平洋和赤道大西洋海温出现显著的正相关。南海夏季风强度的年代变化受PDO的调制。年代际尺度上南海夏季风强度的变化即与全球变暖有关,也与PDO有关。     

2015年热带气旋“彩虹”的高分辨率数值模拟与风场诊断分析

利用WRF模式,对热带气旋“彩虹”（1522）登陆过程开展了高分辨率数值模拟,模拟验证表明:模式较成功地模拟出了“彩虹”的移动路径、强度变化和降水分布。利用高分辨率模拟资料,分析了“彩虹”登陆期间的大风分布以及热、动力结构特征,结合切向风动量方程开展了模拟诊断,结果表明:切向风动量方程各项在近地面层和边界层顶代表高度上的平面结构诊断分析显示,近地面（0.4 km）层上,VVOR（角动量径向平流项）和VPGF（切向气压梯度项）是切向风变化的最大贡献项;边界层顶（1.3 km）附近,VPGF和VVA（切向动量垂直平流项）对切向风起到正加速作用,而VVOR则根据入流（出流）特征,起到正（负）加速作用。切向风动量方程各项的轴对称平均结构诊断分析显示,“彩虹”登陆前,VVA和VVOR是决定切向风变化的主要贡献项。     

A STUDY ON MESOSCALE VORTICITY PROPAGATION IN A TYPHOON-LIKE VORTEX*

By using an f-plane barotropic quasi geostrophic model in the rectangular coordinates with a grid spacing of 5 km,ten experiments whose integration time is 36 hours are performed in order to study the interaction between a typhoon vortex and a mesoscale vortex whose initial center position is located at 2 r_m northwest to the typhoon center,where r_m is the radius of maximum wind of the typhoon vortex. Results show that the interaction can create a pair of smaller scale vortices or lumps,which extend from the outside region of the typhoon to near its center,resulting in the inward propagation of mesoscale vorticity.In this process,the vorticity concentration of the mesoscale vortex may appear.The coexistence of the propagation and the concentration makes the increase of vorticity in the inside region i.e.a more intensive typhoon.Meanwhile,the intensity of the lump with positive vorticity oscillates with time,with the oscillation period being several hours,the distance from the typhoon center to the lump center also has a similar oscillation period,which reduces the oscillation of typhoon intensity.In the case of stronger circular basic flow,the interaction can make the intensification of typhoon more obviously. In addition,in some parametric conditions,the interaction may break down the continuous vorticity zone,exhibiting a cluster of smaller vorticity lumps.     

Recurvature dynamics of a typhoon

Summary In this paper we present some recent work on typhoon prediction with a high resolution global model. The emphasis of this paper is on typhoon recurvature. Here we include examples of successful typhoon recurvature track forecasts made from a very high resolution global spectral model. The main objective of this study however is to go beyond the forecasts, i.e. to interrogate the history tapes and to diagnose residue-free budgets of the divergence and vorticity. The premise of this paper is that the recurvature of the typhoons depends on both the usual advection of vorticity by the layer mean winds and the advection of divergence in the outflow layers of the storm.The region immediately outside the heavy rain area of the storm experiences large values of divergent outflows which contribute a significant advection of divergence. Through the Dine's compensation this region must, in consort, experience an enhancement of low level convergence and of deep convection, thus contributing to the storm motion. We distinguish two facets of storm motion and recurvature, one based on the conventional steering that invokes the advection of vorticity by a vertical integrated flow, the other is the generation mechanism proposed here. During recurvature the storm appears to move in a direction which is influenced by the rotational and the divergent flow dynamics. Increased vertical resolution in the outflow layer is shown to resolve stronger amplitudes in the outflow layer divergence and thus to contribute to improved forecasts of recurvature. A number of processes seem to simultaneously evolve, these include the strong advection of divergence part of the wind, enhancement of cumulus convection over this region, an enhancement of lower tropospheric convergence, generation of vorticity of the lower troposphere and the attendant recurvature.With 16 Figures     

THE MESOSCALE WAVES AND THE FORMATION OF POLYGONAL EYE WALL IN TYPHOONS

Mesoscale waves in typhoons were diagnosed by using a simulated typhoon data in this paper. Through analyzing the structure of the waves in typhoons, we found that the waves possess the mixed features of gravity inertial waves and vortex Rossby waves. On the one hand, positive geopotential height perturbation is corresponding to negative vorticity perturbation and anticyclonic circulation. At the same time, negative geopotential height perturbation is corresponding to positive vorticity perturbation and cyclonic circulation. The maximum perturbation occurs near the radius of the maximum wind in the typhoon. On the other hand, the mesoscale waves possess the features of strong convergence and divergence and ageostrophic wind. Finally, the authors presented a concept model to explain a linkage mechanism between the mesoscale waves and the formation of polygonal eye wall in the typhoon.     

高层冷涡对台风路径影响的数值模拟和动力分析

通过六层斜压干模式模拟了高层冷涡对台风运动的影响，并用涡度方程各动力项的诊断分析，证实了高层冷涡对台风运动的影响主要是通过改变台风中心周围的环流结构而达到的。分析还指出了总涡度倾向和台风运动的直接联系以及这种联系的持续稳定性。同时也发现总涡度倾向主要来自于涡度水平平流和散度场的贡献。说明台风运动主要由正压性动力因子控制。     

登陆北上山东台风暴雨非对称分布的成因对比分析

应用常规气象观测资料、NCEP 1°×1°再分析资料,选取登陆北上山东地点相近但暴雨落区分别位于台风中心西北侧和东北侧的两个台风,分析暴雨落区相对台风中心非对称分布的成因。结果表明：台风进入中纬度以后,0421号台风“海马”位于高空深槽前,与西风槽相互作用,西风槽携带的冷空气从西北侧侵入台风环流,产生湿斜压锋区强迫抬升、冷暖空气交绥、水汽辐合等因素造成暴雨,暴雨趋于出现在台风中心的西北侧,为高比湿舌前方、较强水汽辐合区与相当位温密集区叠加的区域;而0509号台风“麦莎”与副热带高压相互作用,引起涡度及涡度平流的非对称改变,暴雨区与500 hPa正涡度区或正涡度平流相对应,暴雨趋于出现在台风中心的东北侧,为强正涡度平流区与水汽辐合叠加的区域。     

Study of Effects of Beta Term and Nonlinear Advection on the Structure of Tropical Cyclones

The effects of the Beta term on the typhoon structure are examined within the linear framework in terms of an analytical method of 2-D Fourier representation and numerical experiments by a Beta-plane quasi-geostrophic barotropic model. Results show that the joint effects of the difference of Rossby phase velocities and the dispersion of typhoon energy keep the maximum wind velocity reasonably evolving rather than irrestrictively increasing. On the one hand, the nonlinear advection accelerates typhoon vortex damping, and on the other, the high pressure system formed downstream due to energy dispersion makes it easy to maintain.     

IMPACTS OF UPPER-LEVEL COLD VORTEX ON THE RAPID CHANGE OF INTENSITY AND MOTION OF TYPHOON MERANTI (2010)

Typhoon Meranti originated over the western North Pacific off the south tip of the Taiwan Island in 2010.It moved westward entering the South China Sea,then abruptly turned north into the Taiwan Strait,got intensified on its way northward,and eventually made landfall on Fujian province.In its evolution,there was a northwest-moving cold vortex in upper troposphere to the south of the Subtropical High over the western North Pacific(hereafter referred to as the Subtropical High).In this paper,the possible impacts of this cold vortex on Meranti in terms of its track and intensity variation is investigated using typhoon best track data from China Meteorological Administration,analyses data of 0.5×0.5 degree provided by the global forecasting system of National Centers for Environmental Prediction,GMS satellite imagery and Taiwan radar data.Results show as follows:(1)The upper-level cold vortex was revolving around the typhoon anticlockwise from its east to its north.In the early stage,due to the blocking of the cold vortex,the role of the Subtropical High to steer Meranti was weakened,which results in the looping of the west-moving typhoon.However,when Meranti was coupled with the cold vortex in meridional direction,the northerly wind changed to the southerly at the upper level of the typhoon;at the same time the Subtropical High protruded westward and its southbound steering flow gained strength,and eventually created an environment in which the southerly winds in both upper and lower troposphere suddenly steered Meranti to the north;(2)The change of airflow direction above the typhoon led to a weak vertical wind shear,which in return facilitated the development of Meranti.Meanwhile,to the east of typhoon Meranti,the overlapped southwesterly jets in upper and lower atmosphere accelerated its tangential wind and contributed to its cyclonic development;(3)The cold vortex not only supplied positive vorticity to the typhoon,but also transported cold advection to its outer bands.In conjunction with the warm and moist air masses at the lower levels,the cold vortex increased the vertical instability in the atmosphere,which was favorable for convection development within the typhoon circulation,and its warmer center was enhanced through latent heat release;(4)Vertical vorticity budget averaged over the typhoon area further shows that the intensification of a typhoon vorticity column mainly depends on horizontal advection of its high-level vorticity,low-level convergence,uneven wind field distribution and its convective activities.     

Sensitivity of tropical cyclone intensification to inner-core structure

In this study, the dependence of tropical cyclone (TC) development on the inner-core structure of the parent vortex is examined using a pair of idealized numerical simulations. It is found that the radial profile of inner-core relative vorticity may have a great impact on its subsequent development. For a system with a larger inner-core relative vorticity/inertial stability, the conversion ratio of the diabatic heating to kinetic energy is greater. Furthermore, the behavior of the convective vorticity eddies is likely modulated by the system-scale circulation. For a parent vortex with a relatively higher inner-core vorticity and larger negative radial vorticity gradient, convective eddy formation and radially inward propagation is promoted through vorticity segregation. This provides a greater potential for these small-scale convective cells to self-organize into a mesoscale inner-core structure in the TC. In turn, convectively induced diabatic heating that is close to the center, along with higher inertial stability, efficiently enhances system-scale secondary circulation. This study provides a solid basis for further research into how the initial structure of a TC influences storm dynamics and thermodynamics.     

一次台风变性并入东北冷涡过程的动力诊断分析

台风北移变性并入东北冷涡是造成东北地区夏季大范围暴雨的主要形式之一, 但其中的热动力结构变化特征及其物理机制尚不清晰。本文利用美国国家环境预报中心(NCEP)的再分析资料对一次台风变性并入东北冷涡过程进行动力诊断分析, 分析结果显示:冷涡冷空气的不断侵入以及台风移动形成的相对冷平流使得台风暖心结构消亡, 其低层低压辐合和高层高压辐散结构消失, 变性并入东北冷涡后气旋整层偏冷, 低层出现冷中心。台风变性并入东北冷涡过程中, 冷涡中心附近高空急流南侧的反气旋切变抑制气旋直接往高空发展, 而急流轴左侧的热动力分布特征有利于垂直涡度的发展, 变性后的气旋环流向冷涡的移近有利于急流轴维持倾斜, 从而促进气旋向高空冷涡倾斜发展。同时, 冷空气在气旋低层附近堆积导致等假相当位温线发生倾斜, 造成垂直涡度在气旋中层倾斜发展。台风变性并入东北冷涡后, 高空冷涡槽底的正垂直涡度平流促进气旋由中层直接向高层发展, 而高空冷涡槽底急流促进正垂直涡度平流的维持。气旋高空环流的发展反过来削弱了东北冷涡的高层环流, 导致高空冷涡中心出现北撤。     

台风Matsa(2005)和Wipha(2007)变性过程对比分析

利用日本气象厅热带气旋年鉴资料和JRA-25再分析资料,对0509号台风Matsa和0712号台风Wipha变性过程进行了对比分析。结果表明,台风Matsa和Wipha均是在我国登陆后转向东北方向运动过程中发生变性,但Matsa嵌入中纬度高空锋区,变性为温带气旋后有再加强过程,而Wipha仅外围环流与锋区接触,变性为温带气旋后无再加强过程。通过等熵面位涡分析进一步表明,Matsa变性加强表现为高层正位涡与低层暖平流的耦合,以及高层正位涡下传至中低层;Wipha的变性过程中,高层正位涡并未与低层暖平流耦合,高层正位涡无明显的下传。