NUMERICAL EXPERIMENTS OF THE INFLUENCE OF DIABATIC HEATING ON TROPICAL CYCLONE ASYMMETRIC STRUCTURE

Using the barotropic volticity equation that contains forcing from diabatic heating with appropriate parameterization. a number of numerical experiments are conducted for the tropical cyclone that is initially symmetric The result shows that the diabatic heating has important effects on the asymmetric structure in addition to the roll of the β term and nonlinear advection term in its formation. It again confirms the conclusion that the diabatic heating is a possible mechanism responsible for such structures in the tropical cyclone.

ASYMMETRICAL STRUCTURES OF THE TEMPERATURE AND HUMIDITY OF TROPICAL CYCLONES

Based on NCEP/CFSR 0.5° reanalysis data and the best track data from the Japan Tokyo Typhoon Center,composite and comparative analyses demonstrate the asymmetrical structures of the temperature and humidity in tropical cyclones over the Western North Pacific and the South China Sea from 1979 to 2010.The results are shown as follows.(1) With intensifying tropical cyclones,the flow field tends to become gradually more axisymmetric;however,the asymmetry of the specific humidity in the outer regions is more obvious.(2) In general,tropical cyclones have a non-uniform,vertical, "double warm-core" structure.The "warm-cores" in the lower level of weak tropical cyclones and in the higher level of strong tropical cyclones are the stronger of the two.(3) The distribution area of a "warm-core" is enhanced with cyclone intensification and tends to become more axisymmetric.At 200 hPa,the "warm-core" of a weak cyclone has a weak anticyclone in the center,whereas that of a strong cyclone has a weak cyclone in the center.(4)The "wet-core" of a tropical cyclone is primarily located in the lower level(700-850 hPa).With the cyclone's intensification,the intensity of the "wet-core" increases and the scope of the 0.8 g kg^(-1) specific humidity anomaly tends to expand to higher levels.(5) With the cyclone's deepening,the pseudo-equivalent potential temperature at different levels in different regions increases.In addition,the largest warming rates at each intensity level in the different regions occur in the core area,followed in turn by the envelope and outer areas.

The Role of β-effect and a Uniform Current on Tropical Cyclone Intensity

A limited-area primitive equation model is used to study the role of the β-effect and a uniform current on tropical cyclone (TC) intensity. It is found that TC intensity is reduced in a non-quiescent environment compared with the case of no uniform current. On an f-plane, the rate of intensification of a tropical cyclone is larger than that of the uniform flow. A TC on a β-plane intensifies slower than one on an f-plane. The main physical characteristic that distinguishes the experiments is the asymmetric thermodynamic (including convective) and dynamic structures present when either a uniform flow or β-effect is introduced. But a fairly symmetric TC structure is simulated on an f-plane. The magnitude of the warm core and the associated subsidence are found to be responsible for such simulated intensity changes. On an f-plane, the convection tends to be symmetric, which results in strong upper-level convergence near the center and hence strong forced subsidence and a very warm core. On the other hand, horizontal advection of temperature cancels part of the adiabatic heating and results in less warming of the core, and hence the TC is not as intense. This advective process is due to the tilt of the vortex as a result of the β-effect. A similar situation occurs in the presence of a uniform flow. Thus, the asymmetric horizontal advection of temperature plays an important role in the temperature distribution. Dynamically, the asymmetric angular momentum (AM) flux is very small on an f-plane throughout the troposphere. However, the total AM exports at the upper levels for a TC either on a β-plane or with a uniform flow environment are larger because of an increase of the asymmetric as well as symmetric AM export on the plane at radii >450 km, and hence there is a lesser intensification.

OUTER VORTEX WIND STRUCTURE CHANGES DURING AND FOLLOWING TROPICAL CYCLONE SECONDARY EYEWALL FORMATION

Some recent studies have utilized flight-level(700 mb) winds to document the maximum wind speeds(Vmax)and radius of Vmax(Rmax) of the original and secondary eyewalls during 24 Atlantic hurricane eyewall replacement cycles(ERC).In this study,Hurricane Wind(H*Wind) analyses of Atlantic hurricanes during 2003-2005 are utilized to document changes in the outer vortex surface wind profile beyond the secondary eyewall,with a focus on the radii of gale-force winds(R34) that are often defined operationally as size changes.In Mode 1,complete and partial ERCs in which the pre-,during-,and post-ERC outer wind profiles have approximately the same shape,the outward displacements of Rmax leads to size(R34) increases as much as 100 km.Mode 2 ERCs are characterized by sharpened wind profiles outside the secondary eyewall that offset the larger Rmax radii to produce only small R34 increases.While statistically significant results are not obtained,the differences in size changes for Mode 1 and Mode 2 SEF cases suggest practical significance for forecasts and warnings.

The Effect of Asymmetric Wind Structures of Tropical Cyclones on Their Tracks

A model is proposed relating a variety of factors of tropical cyclones (TCs)to their tracks, and attentions are paid to the influence of the asymmetric wind structures of TCs.Ideal numerical calculation shows that the asymmetric wind structures of TCs have conspicuousinfluence on their motion tracks. When moving due westward initially, an axisymmetric TC willdeflect right, and the overall trend is eastward. When it is asymmetric but the asymmetry is notsharp, wherever the area of maximum wind is, the TC deflects northwest first, and then, to variousareas depending on the positions of the areas of maximum wind, i.e. for the area of maximum wind inQuadrant Ⅰ, to the southeast; for in Quadrant Ⅱ, to the northeast; for in Quadrant Ⅲ, to thenorthwest; for in Quadrant IV, to the southwest. And in the above four cases, the TC tracks are allaccompanied by clockwise looping motions. With the asymmetry of the TC intensifiying, the track ofthe TC motion will be stretched further. For the area of maximum wind in Quadrants Ⅰ and Ⅱ, the TCtracks are still accompanied by clockwise looping motions; for the area of maximum wind inQuadrants Ⅲand Ⅳ, the TC tracks become oscillatory, without clockwise looping motions.

Mean Structure of Tropical Cyclones Making Landfall in China's Mainland

The mean kinematic and thermodynamic structures of tropical cyclones （TCs） making landfall in main-land China are examined by using sounding data from 1998 to 2009. It is found that TC landfall is usually accompanied with a decrease in low-level wind speed, an expansion of the radius of strong wind, weakening of the upper-level warm core, and drying of the mid-tropospheric air. On average, the warm core of the TCs dissipates 24 h after landfall. The height of the maximum low-level wind and the base of the stable layer both increase with the increased distance to the TC center;however, the former is always higher than the latter. In particular, an asymmetric structure of the TC after landfall is found. The kinematic and thermodynamic structures across various areas of TC circulation diff er, especially over the left-front and right-rear quadrants （relative to the direction of TC motion）. In the left-front quadrant, strong winds locate at a smaller radius, the upper-level temperature is warmer with the warm core extending into a deep layer, while the wet air occupies a shallow layer. In the right-rear quadrant, strong wind and wet air dwell in an area that is broader and deeper, and the warmest air is situated farther away from the TC center.

Characteristics of the Asymmetric Flow of Tropical Cyclone Shanshan(2006) During Its Turning and Intensification Period

In this paper,characteristics of the asymmetric flow of Tropical Cyclone（TC） Shanshan（2006） during its turning and intensification period over the oceanic area east of Taiwan are investigated,based on the simulation results from the nonhydrostatic mesoscale model WRF（Weather Research and Forecasting）.It is found that the symmetric flow strengthened as the TC intensified,whereas the amplitude of the asymmetric flow of wavenumber 2 increased more significantly,which was strong enough to be comparable with or even exceed that of wavenumber 1,becoming the main part of the asymmetric flow sometimes.The asymmetric waves rotated around the TC center mainly counterclockwise.The closer to the center,the faster the asymmetric waves rotated.Moreover,the asymmetric flow rotated rapidly（slowly） during the slow（rapid） intensification of the TC,and the radial wavenumber showed an increase during the TC intensification.Furthermore,because of the superposition of intensified symmetric flow with the positive perturbation of the asymmetric flow,the maximum wind speed of TC Shanshan became larger.During the merger of the double eyewalls of Shanshan,the symmetric flow showed less increase in strength and the intensification of maximum wind speed was mainly related to the energy accumulation caused by the phase change of the asymmetric waves.The energy accumulation was realized when the asymmetric waves altered the strength and distribution of the inner and outer maximum wind cores,leading to the combination of the inner and outer eyewalls and eventually resulting in the intensification of the TC.

Mechanism for initial brows-like meso-scale vortex effects on tropical cyclone track

We used a two-dimensional quasi-geostrophic barotropic model simulation to study effects of an initial brows-like meso-scale vortex on tropical cyclone (TC) track. Our results show that the impact of each of the three foundational factors (the environ- mental current, the asymmetric structure and the asymmetric convection system) on TC track varies with time and the im- portance of each of the factors is different for the different TC motion time period. They show two kinds of the effects. One is a direct way. The asymmetric outer wind structure and the positive longitudinal wind speed averaged in radial-band (100-300) km in the period of (0-11) h are caused by the introduction of the initial brows-like meso-scale vortex, which results in TC track to turn to the north from the northwest directly. The other is an indirect influence. First, initial TC axisymmetric circula- tion becomes a non-axisyrnmetric circulation after the addition of the meso-scale vortex. The initial non-axisymmetric circula- tion experiences an axisymmetrizational process in the period of (0-11) h. Second, axisymmetrizationed TC horizontal size is enlarged after t=-12 h. Third, both the TC asymmetric structure and the TC energy dispersion induced-anticyclone are intensi- fied, which quickens the TC motion and results in the track to turn to the north indirectly. The TC motion is characterized by the unusual track under the direct and the indirect effect. The formation of the unusual track should be attributed to the com- mon effects of three factors, including the environmental flow, the TC asymmetric structure and the asymmetric convection system.

台风异常运动及其外区热力不稳定非对称结构的影响效应

本文数值模拟研究揭示了台风外区热力不稳定非对称结构对其异常路径的影响问题，提出了台风运动非对称结构的影响，不仅表现在台风涡旋动力结构特征上，而且反映在台风外区三维非对称热力结构特点方面，即包括温、湿不稳定层结分布特征及其强弱程度因素。台风外区不同热力非对称分布特征将导致台风移动轨迹的显著差异，且构成各类“旋转”、“打转”、“转向”

热带西南季风对0214号热带气旋“黄蜂”的影响

采用中国数值预报创新基地最新开发的三维变分同化系统 (Grapes 3DVAR)的分析场为模式初值场 ,利用广州热带海洋气象研究所开发的南海热带气旋业务预报模式 ,在模拟试验 (控制试验 )的基础上 ,对强、弱热带西南季风作对比试验 (异常试验 )研究。试验结果表明 :除环境引导气流外 ,“黄蜂”偏心结构变化引起的偏心运动变化对热带气旋移向、移速的变化起了一定的作用 ;西南季风对热带气旋“黄蜂”的动力结构、热力结构和移动路径都有一定的影响 ;热带西南季风通过改变热带气旋的不对称结构和削弱副热带高压西侧这两个途径 ,造成热带气旋路径右偏。

热带气旋眼墙非对称结构的研究综述

热带气旋的眼墙非对称结构与其发展过程密切相关。在热带气旋移动过程中,非对称风场伴随着边界层内非对称摩擦而引起的辐合,影响着热带气旋眼墙内的对流分布。此外,风垂直切变作为影响热带气旋强度的重要因子,将上层暖心吹离表层环流,引起眼墙垂直运动的非对称,导致云、降水在方位角方向的非均匀分布。当存在平均涡度的径向梯度时,罗斯贝类型的波动可以存在于涡旋内核区域,影响眼墙非对称结构。海洋为热带气旋提供潜热和感热形式的能量,是热带气旋发展的重要能量来源,关于海洋如何影响热带气旋眼墙非对称结构的相关研究较少。文中着重回顾了热带气旋与海洋相互作用的研究成果,并提出海洋影响热带气旋眼墙非对称结构的机制。海洋对热带气旋最显著的响应特征是冷尾效应,该效应通过降低海表温度,减少海洋向大气输送的潜热和感热,从而影响热带气旋眼墙非对称结构。此外,海浪改变海表粗糙度,通过边界层影响移动热带气旋的眼墙结构。

热带气旋海面最大风速半径的计算

利用含有摩擦的平面极坐标水平运动方程组 ,引入藤田气压模式 ,在热带气旋域内最大风速为已知的条件下 ,经过合理的简化和推导 ,得到了呈稳定状态的海面移动非对称热带气旋的最大风速半径的计算方案。分析结果表明 ,当最大风速越小、中心气压越低、环境温度和气压越高、纬度越低或摩擦系数越小时 ,热带气旋的最大风速半径就越大 ;反之 ,最大风速半径就越小。最大风速和它半径上的最小风向内偏角出现在热带气旋移向的右后侧。对91 0 9号和 91 1 5号热带气旋的计算表明 ,最大风速半径在发展初期增加 ,在发展后期减小 。

热带气旋风场模型构造及特征参数估算

探讨了利用热带气旋风场分布的经验模型估算热带气旋尺度 (8级大风圈半径 )的方法 .用美国联合台风警报中心整编的 2 0 0 1年西北太平洋热带气旋的“最佳尺度”资料 ,确定了各模型的经验常数 ,并计算了各模型的估算精度 .结果表明 ,“VBogus”模型能获得热带气旋 (TropicalCyclone ,简称TC)尺度的较好估算 .基于“VBogus”模型 ,通过拟合热带气旋尺度的非对称分布 ,构造了能描述热带气旋非对称风场的“修正VBogus”模型 ,并估算了该模型中各参数在不同季节和不同地理区域的取值 ,为热带气旋尺度变化和非对称结构机制等问题的研究和应用提供新依据 .

热带风暴Bilis(2006)登陆期间一波非对称降水分布成因的探讨

利用中尺度数值模式WRF-ARW对Bilis(2006)进行数值模拟,并进行地形和下垫面因素2个敏感性试验,诊断分析Bilis(2006)登陆期间一波非对称降水结构形成的动力因子。综合分析3个试验,结果表明环境垂直风切变对Bilis(2006)一波非对称降水结构形成的影响显著大于地形、登陆过程下垫面属性的改变和风暴移动速度的影响,冷空气的侵入对降水形成也有重要贡献。垂直切变的作用使顺切变左侧形成强降水,冷空气的作用与垂直切变的作用相互配合可能是顺切变方向和顺切变方向右侧强降水的主要成因。

9414号热带气旋(DOUG)非对称结构和对降水影响的分析

ＤＯＵＧ热带气旋在靠近华东沿海大陆北上过程中，气旋西侧的降水强度显著减弱，主要是ＤＯＵＧ气旋的完全非对称结构造成的。本文从大尺度天气系统配置、卫星云图和中尺度数值模式计算结果分析了ＤＯＵＧ气旋内区和外区非对称结构的成因和演变。外区的非对称结构主要由环境场的大尺度天气系统的东高西低气压场配置造成的。气旋近中心中－β尺度的辐散下沉系统的发展是造成内区非对称结构的主要原因。二者的形成是相互独立的。但内区非对称结构的发展会促使外区非对称结构的加强。

热带气旋“蒲公英”两次登陆过程的灾害与结构特征

2004年7月1～3日，热带气旋“蒲公英”自生成到影响浙江沿海地区期间，不仅持续时间长、强度大，移动路径长、变化较复杂，而且创下了近3年来台湾风灾损失的最高纪录，同时也给浙江等沿海地区造成了一定的经济损失。作者主要利用卫星云图资料、NCEP再分析资料，从宏观上对热带气旋“蒲公英”两次登陆过程中的强度及其引发的风雨灾害进行了分析。结果表明，“蒲公英”登陆台湾期间，东亚环流形势呈典型的鞍形场分布，有利于处于两高之间热带气旋“蒲公英”的维持和北上转向。而在其登陆浙江沿海地区后，浙江沿海地区处于较强的偏东气流中，“蒲公英”中心处于高空槽后，气流下沉以及缺少水汽和能量充沛供应使得其减弱为热带风暴。无论是其登陆台湾还是浙江沿海地区，台风垂直方向始终呈深厚气旋性涡柱结构，但中心附近低层辐散，中层辐合，不利于中心附近的对流发展。相反，台风外围螺旋云带内不仅中低层辐合，高层辐散，辐合层较深厚，且存在高湿和强上升运动，因而有利于对流云团的发展。对流云团发展强度的不同使得“蒲公英”两次登陆期间引发的风雨灾害明显不同。

非对称的非绝热加热对热带气旋移动影响的数值研究

采用中尺度数值模式（ＭＭ４），以９４１４号台风为个例，应用卫星资料，引入非对称的非绝热加热，讨论其对９４１４号台风移动的影响．计算结果表明，引入与实况吻合的非对称非绝热加热分布后，该台风的路径预报和降水预报有明显改进，若同时考虑台风范围初始水汽场的非对称分布，这种改进作用尤为明显．从业务应用考虑，还构造了几种典型的螺旋状结构的非绝热加热计算方案引入模式的热力过程中，结果表明：不同螺旋状结构的加热分布对台风的移动有不同的影响，当选择与实况云系分布相近的螺旋状结构时，也可提高台风路径预报正确率。

非绝热加热对热带气旋非对称结构影响的数值试验

利用含非绝热加热强迫的正压涡度方程。将非绝热加热作适当的参数化处理，对初始对称结构的热带气旋作了一系列数值试验，结果表明：不仅β项、平流项在热带气旋非对称结构的形成中有重要作用，而且非绝热加热对热带气旋的非对称结构亦有重要影响，从而验证了非绝热加热是热带气旋非对称结构形成的一种可能机制的结论。

边缘区域扰动演变对台风结构的影响

在台风环流边缘区域给出不稳定模态的扰动四波分布作为初始场，用准地转正压模式实施四组数值积分，研究了边缘区域扰动演变及其对台风非对称结构及外区流型的影响。结果表明：线性平流对于外缘区域扰动的发展起主要作用。尸项导致一个气旋一反气旋涡旋对和非对称结构的形成。非线性平流则使外缘区域较小尺度的涡旋破碎，形成更小尺度的涡旋。在线性平流、β项和非线性平流的共同作用下，台风结构与外区形成象螺旋云系的分布。外缘区域扰动引起的结构变化，进而能影响到台风的移动路径。

1005号热带气旋“乌鲁伊”移动路径分析

利用欧洲格点资料,应用天气学方法,从环流场演变、β效应、不对称结构等方面对1005号热带气旋"乌鲁伊"活动过程进行了分析,探讨了"乌鲁伊"不同阶段路径变化的原因.结果表明,澳大利亚大陆高压维持稳定以及热带气旋"托马斯"与"乌鲁伊"之间的相互作用是"乌鲁伊"西行北抬的根本原因.在"乌鲁伊"台风西行过程中,中高纬度环流场进行强烈调整是引起"乌鲁伊"移动路径南翘西折的关键,大陆高压在低纬向"乌鲁伊"北侧嵌入、以及地面气压场上从北指向南的气压梯度力突然增强,对热带气旋"乌鲁伊"移动路径南翘有直接影响.对西风指数的分析表明,"乌鲁伊"的南翘过程与西风指数从最低值484.4 m2/s2向644.3 m2/s2升高过程相对应,"乌鲁伊"移动路径西折与西风指数维持在644.3 m2/s2以上有关.500 hPa位势高度梯度场分析表明,热带气旋"乌鲁伊"从东向西、向南、向西南稳定移动过程中,东南侧和西北侧等梯度线中心数值的差值几乎为0,呈现出对称分布的特点;在热带气旋"乌鲁伊"南翘、西折时,东南侧与西北侧等梯度线数值发生显著变化,南翘时差值为-16.6 m/s2,西折时差值则为12.0 m/s2.500 hPa位势高度梯度场的变化对"乌鲁伊"南翘西折路径具有很好的预示作用.