An Investigation into Effect of Randomly Distributed Small Scale Vortices on Vortex Self-Organization

Previous studies concerning the interaction of dual vortices have been made generally in the determin-istic framework. In this paper, by using an advection equation model, eight numerical experiments whose integration times are 30 h are performed in order to analyze the interaction of dual vortices and the vortex self-organization in a coexisting system of deterministic and stochastic components. The stochastic compo-nents are introduced into the model by the way that the Iwayama scheme is used to produce the randomly distributed small-scale vortices which are then added into the initial field. The different intensity of the small-scale vortices is described by parameter K being 0.0, 0.4, 0.6, 0.8, and 1.0, respectively. When there is no small-scale vortex (K=0.0), two initially separated meso-beta vortices rotate counterclockwise mutu-ally, and their quasi-final flow pattern is still two separated vortices; after initially incorporating small-scale vortices (K=0.8, 1.0), the two separated meso-beta vortices of initially same intensity gradually evolve into a major and a secondary vortex in time integration. The major vortex pulls the secondary one, which gradually evolves into the spiral band of the major vortex. The quasi-final flow pattern is a self-organized vortex with typhoon-like circulation, and the relative vorticity at its center increases with increasing in K value, suggesting that small-scale vortices feed the self-organized vortex with vorticity. This may be a pos-sible mechanism responsible for changes in the strength of the self-organized vortex. Results also show that the quasi-final pattern not only relates with the initial intensity of the small-scale vortices, but also with their initial distribution. In addition, three experiments are also performed in the case of various boundary conditions. Firstly, the periodic condition is used on the E-W boundary, but the fixed condition on the S-N boundary; secondly, the fixed condition is set on all the boundaries; and thirdly, the periodic condition is chosen on all the boundaries. Their quasi-final flow patterns in the three experiments are the same with each other, exhibiting a larger scale typhoon-like circulation. Based on these results mentioned above, authors think that the transition of vortex self-organization study from the deterministic system to the coexisting system of deterministic and stochastic components is worth exploring.     

Impacts of Randomly Distributed Small-Scale Vortices on Typhoon Tracks

Impacts of small-scale vortices on typhoon or tropical cyclone(TC) tracks in a system of three components (an idealized subtropical high ridge,a TC,and small-scale vortices) were examined numerically using a barotropic primitive equation model and idealized initial fields.Two small-scale vorticity fields were generated stochastically,where the number of initial small-scale vortices is 100.In the two fields,the number, size,structure as well as the total kinetic energy of the small-scale vortices were all...     

Interaction of typhoon and mesoscale vortex

Under two types of initial tropical cyclone structures that are characterized by high and low vorticity zones, four sets of numerical experiments have been performed to investigate the interaction of a tropical cyclone with an adjacent mesoscale vortex (MSV) and its impact on the tropical cyclone intensity change,using a quasi-geostrophic barotropic vorticity equation model with a horizontal resolution of 0.5 km. The results suggest that the interaction of a tropical cyclone characterized by a high vorticity zonal structure and an MSV would result in an intensification of the cyclone. Its central pressure decreases by more than 14 hPa. In the process of tile interaction, the west and middle segments of the high vorticity zone evolve into two peripheral spiral bands of the tropical cyclone, and the merging of the east segment and the inward propagating MSV forms a new vorticity accumulation area, wherein the maximum vorticity is remarkably greater than that in the center of the initial tropical cyclone circulation. It is this process of merging and strengthening that causes a greater pressure decrease in the center of the tropical cyclone. This process is also more complicated than those that have been studied in the past, which indicated that only the inward transfer of vorticity of the MSV can result in the strengthening of the tropical cyclone.     

Understanding of the Effect of Climate Change on Tropical Cyclone Intensity: A Review

The effect of climate change on tropical cyclone intensity has been an important scientific issue for a few decades.Although theory and modeling suggest the intensification of tropical cyclones in a warming climate,there are uncertainties in the assessed and projected responses of tropical cyclone intensity to climate change.While a few comprehensive reviews have already provided an assessment of the effect of climate change on tropical cyclone activity including tropical cyclone intensity,this review focuses mainly on the understanding of the effect of climate change on basin-wide tropical cyclone intensity,including indices for basin-wide tropical cyclone intensity,historical datasets used for intensity trend detection,environmental control of tropical cyclone intensity,detection and simulation of tropical cyclone intensity change,and some issues on the assessment of the effect of climate change on tropical cyclone intensity.In addition to the uncertainty in the historical datasets,intertwined natural variabilities,the considerable model bias in the projected large-scale environment,and poorly simulated inner-core structures of tropical cyclones,it is suggested that factors controlling the basin-wide intensity can be different from individual tropical cyclones since the assessment of the effect of climate change treats tropical cyclones in a basin as a whole.     

热带气旋莫兰蒂(1010)强度的观测研究和增强条件的诊断分析

热带气旋莫兰蒂(1010)进入台湾海峡后显著加强。本文普查了历史上在台湾海峡与"莫兰蒂"有相似路径的热带气旋,其中几乎没有增强的热带气旋个例;总结了"莫兰蒂"在台湾海峡活动时的强度变化,指出在实时业务中国内外台风预报中心对于"莫兰蒂"强度的判定存在明显偏弱的现象。运用天气学和动力诊断方法,分析了"莫兰蒂"在台湾海峡活动时热带气旋发展的基本条件,结果发现:台湾海峡区域有较高的海表温度、丰富的中低层水汽净流入、强烈的低层辐合和高层辐散、低层涡度净流入,为"莫兰蒂"的发展提供了有利的动力和热力条件,弱的环境风垂直切变又使其强度增长没有受到大的抑制作用。研究结果可为热带气旋强度或强度变化预报提供有意义的参考。     

Growing Threat of Rapidly-Intensifying Tropical Cyclones in East Asia

This study examines the long-term change in the threat of landfalling tropical cyclones(TCs) in East Asia over the period 1975–2020 with a focus on rapidly intensifying(RI) TCs. The increase in the annual number of RI-TCs over the western North Pacific and the northwestward shift of their genesis location lead to an increasing trend in the annual number of landfalling RI-TCs along the coast of East Asia. The annual power dissipation index(PDI), a measure of the destructive potential of RI-TCs at landfall, also shows a significant increasing trend due to increases in the annual frequency and mean landfall intensity of landfalling RI-TCs. The increase in mean landfall intensity is related to a higher lifetime maximum intensity(LMI) and the LMI location of the landfalling RI-TCs being closer to the coast. The increase in the annual PDI of East Asia is mainly associated with landfalling TCs in the southern(the Philippines, South China, and Vietnam) and northern parts(Japan and the Korean Peninsula) of East Asia due to long-term changes in vertical wind shear and TC heat potential. The former leads to a northwestward shift of favorable environments for TC genesis and intensification, resulting in the northwestward shift in the genesis, RI, and LMI locations of RI-TCs. The latter provides more heat energy from the ocean for TC intensification, increasing its chances to undergo RI.     

热带气旋经过台湾岛强度变化特征

用中国气象局整编的1949-2006年共58年的<台风年鉴>或<热带气旋年鉴>资料,将资料线性插值到1小时,挑选出经过台湾岛的热带气旋(TC),用统计分析的方法,揭示TC经过台湾岛时的强度变化特征.结果表明,TC从东侧登陆台湾岛损失的强度为西侧登陆损失强度的2倍以上;TC登陆时的路径方向与台湾中央山脉长轴的交角越接近垂直,其过岛损失的强度越小,在岛逗留的时间越短;TC登陆台湾岛东侧时强度损耗与TC登陆前其自身的强度呈正相关,而登陆台湾岛西侧则没有明显的统计规律;TC从台湾西侧登陆时不但出现强度不变或者增强的几率更大,而且强度增强也更多.     

超强台风 “桑美” (2006) 近海急剧增强过程数值模拟试验

应用PSU/NCAR非静力平衡中尺度模式MM5 (V3.5) 设计试验方案, 对超强台风 “桑美” (2006) 在我国近海的急剧增强和减弱过程进行数值模拟研究, 模式较好地再现了台风的路径和强度变化; 通过地形敏感性试验, 着重研究了地形对近海台风强度变化的影响。结果表明: (1) “桑美” 强度变化与南亚高压、 副热带高压的强度变化呈反相变化关系, 当南亚高压和副热带高压减弱时, 台风急剧增强; 台风中心附近对流层高层辐散的增强导致 “桑美” 急剧增强, 对流层中低层辐散的增强以及中层辐合的增大与 “桑美” 的减弱密切相关; 来自海洋的暖湿气流是 “桑美” 发展的关键条件; 低层气旋性涡旋并入台风环流是 “桑美” 近海急剧增强的重要原因。 (2) 凝结加热过程对 “桑美” 的近海维持和发展增强非常重要, 尤其是对流层中上层凝结潜热的突然增强有利于台风在近海的急剧增强。 (3) 小范围地形对 “桑美” 在近海的强度和路径有一定影响, 但作用相对较小, 而且主要表现在台风登陆前后; 大范围地形导致水平风场的非对称分布和台风中心附近垂直运动的异常, 最终影响到台风的强度变化。     

近海热带气旋强度突变的垂直结构特征分析

应用1949～2003年共55年的《台风年鉴》和《热带气旋年鉴》资料以及NCEP/NCAR再分析资料, 给出热带气旋强度突变标准, 对中国近海突然增强和突然减弱的两组热带气旋进行合成分析和对比分析。结果表明, 近海热带气旋强度变化与南亚高压、 副热带高压的强度变化呈反相变化关系; 环境风垂直切变小于5 m/s是南海近海热带气旋突然增强的必要条件, 热带气旋强度突变对环境风垂直切变变化的响应时间为18～36 h; 热带气旋中心附近存在数值在 -6～6 m/s之间纬向分布的环境风垂直切变密集带, 在热带气旋突然增强时刻, 中心附近环境风垂直切变经向梯度最大; 风垂直切变在热带气旋突然增强过程中逐渐减弱, 而在热带气旋突然减弱过程中逐渐增强; 热带气旋中心附近是高低层相对涡度垂直切变的强负值区, 在热带气旋突然增强过程中相对涡度垂直切变逐渐减小, 在突然增强时刻最小。     

双热带气旋合并过程涡旋强度与吸引效应相关特征数值模拟

利用中尺度模式HWRF(Hurricane Weather Research and Forecast System)模拟双热带气旋"狮子山"(2010)与"南川"(2010)涡旋合并过程,并通过强度敏感性试验揭示两涡旋强度对合并过程的影响。分析表明:在两者的合并过程中,"狮子山"涡旋强度明显大于"南川";"狮子山"涡旋对"南川"涡旋具有更大的"吸引"效应,两者西侧呈相对强的能量、水汽"连体"通道。HWRF能够较好的模拟出双热带气旋"狮子山"与"南川"的强度、移动路径,尤其是两涡旋的合并过程。进一步分析控制试验双热带气旋水平与垂直结构揭示出两涡旋"互旋"过程中,"弱涡旋"并入"强涡旋"相互影响特征。有关"狮子山"与"南川"强度的敏感试验亦表明,两者各自涡旋强度"合并方向"具有关键影响。在敏感性试验中,改变涡旋强度后两者路径亦存在"互旋"现象,但与控制试验两涡旋"合并方向"相反,即敏感性试验热带气旋"狮子山"涡旋削弱,而"南川"涡旋强度相对增强,导致原涡旋西侧水汽、能量输送连体通道明显削弱,同时由于"南川"涡旋的强度强于"狮子山",两者东侧水汽、能量输送通道亦加强,导致"南川"涡旋对"狮子山"的涡旋存在"吸引"效应。"狮子山"涡旋残留云带一部分合并入"南川",一部分则随西南气流进入台风"圆规"。     

Evaluation of Tropical Cyclone Intensity Forecasts from Five Global EnsemblePrediction Systems During 2015-2019

This study presented an evaluation of tropical cyclone (TC) intensity forecasts from five global ensemble prediction systems (EPSs) during 2015-2019 in the western North Pacific region. Notable error features include the underestimation of the TC intensity by ensemble mean forecast and the under-dispersion of the probability forecasts.The root mean square errors (brier scores) of the ensemble mean (probability forecasts) generally decrease consecutively at long lead times during the five years, but fluctuate between certain values at short lead times.Positive forecast skill appeared in the most recent two years (2018-2019) at 120 h or later as compared with the climatology forecasts. However, there is no obvious improvement for the intensity change forecasts during the 5-yearperiod, with abrupt intensity change remaining a big challenge. The probability forecasts show no skill for strongTCs at all the lead times. Among the five EPSs, ECMWF-EPS ranks the best for the intensity forecast, while NCEP-GEFS ranks the best for the intensity change forecast, according to the evaluation for ensemble mean and dispersion. As for the other probability forecast evaluation, ECMWF-EPS ranks the best at lead times shorter than 72 h, while NCEP-GEFS ranks the best later on.     

热带风暴形成过程中的涡旋自组织及其复杂性：一个典型个例的红外云图分析

应用高分辨率的红外卫星云图资料,对台风8807从热带低压发展成热带风暴的过程进行了分析,给出了热带风暴形成过程伴随着复杂涡旋自组织现象的观测证据。结果发现,涡旋自组织可在从数十到十万km2的各种尺度扰动云团之间发生,发生合并的云团除了理想数值试验中的两类前景之外,还存在第三类前景,即较大尺度的云团会发生分裂,部分与其他云团合并。合并形成的新云团可能发展也有可能减弱,这应取决于新云团所处的环境以及是否有其他云团补充并入。用二维Fourier分析可以清楚地看到8807发展成热带风暴的过程可分为两个阶段,一是多涡共存,不同方向、不同尺度系统能量转换频繁阶段,另一是单涡发展阶段,谱密度等值线形态稳定少变。分维计算结果表明,热带风暴形成过程中的相关云团较已有研究分析的云团略显规则,分维略小于已有结果。此外,临界温度取值不同,分维是有差异的,边界温度越低,分维越小。     

登陆华南热带气旋强度变化与大尺度环流的关系

应用UK再分析资料,采用合成分析方法,对比分析了登陆华南的登陆前迅速增强的TC（Rapid Intensifying TC,简称RITC）和迅速减弱的TC（Rapid FillingTC,简称RFTC）登陆前24h的大尺度环流背景特征。结果表明：从外流、入流强度和范围上看,RITC的低空入流和高空外流均明显强于RFTC,两类TC高空外流强度的差异比低空入流明显,RITC的次级环流径向范围大;从外流垂直伸展高度上看,RITC的平均外流主要集中在500hPa以上,而RFFC的平均外流比较分散,向下伸展到850hPa;从高空流场配置看,RITC上空除西北象限外均有较强外流,而RVrC仅在东北象限有较强外流,相应的RITC和RVrC的高空辐散在范围和强度上均有明显的差异,其中RITC的高空辐散明显强于RFTC;强烈的西南季风水汽输送是登陆华南的TC登陆前突然加强的先兆条件,RITC的对流活动明显比RFTc活跃;RITC的纬向风垂直切变比RFTC小,有利于RITC的强度增强。     

环渤海地区下垫面对北上热带气旋强度变化的影响分析

利用统计分析结合数值模拟试验的方法,研究1949—2019年6—9月登陆北上后影响环渤海地区的热带气旋（后统称TC）所经下垫面和强度变化的不同特征,及环渤海地区下垫面对TC强度加强的可能影响。结果表明：71年间共有25例TC影响环渤海地区,按照首次登陆点的不同将其分为山东及山东以北登陆（第一类,11个）,以及山东以南登陆（第二类,14个）两类,第一类TC北上时路径所经下垫面为先海洋后陆地,发生变性的几率较小且北上后无加强,第二类路径所经下垫面为先陆地后海洋,移入环渤海区域后发生变性的几率增大且存在强度加强现象,其中加强的TC共5例;对第二类TC中强度加强的个例“温比亚（2018）”TC进行数值模拟试验表明,增加或降低黄渤海的海温时,TC均表现出加强趋势,将黄渤海修改为草地时,TC不再加强,而海陆分布指数的分析表明无论海温如何变化,TC由陆地移入海洋与强度加强趋势之间关系密切。以上表明TC由陆地移入黄渤海是产生强度增强趋势的主要原因。     

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 aβ-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.     

西北太平洋热带气旋强度突变的分布特征

用42年（1949～1990）资料在西北太平洋区域统计各小区（5°×5°经纬度）内热带气旋强度突变（12 h内热带气旋近中心最大风速变化#A≥|10| m/s）的频数和频率，给出其分布特征。 其中频率迅速变化地带除与地形有关外， 还与黑潮、常年的副热带西风急流和副热带高压的活动位置有密切关系。     

Effect of Horizontal Nonuniformity of Diabatic Heating on Tropical Cyclone Intensity and Structure

1. IntroductionMuch attention has been paid to the role playedby diabatic heating in the genesis and intensificationof tropical cyclone (TC). Based on a two-dimensionalprimitive equation model, Li (1984) proposed that theevolution of TC should be different if the maximumheating appears at different height. Yang et al. (1995)found that abrupt intensification of TC at the mid-latitudes is closely related to the vertical structure ofconvective heating. May and Holland (1998) suggestedthat the…     

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。     

热带气旋预报方法业务预试验的效果分析

通过对参加１９９４年夏季热带气旋预报方法业务预试验的８个方法进行实例分析，初步指出各方法的成功之处与不足，以期得到改进和提高。     

Effect of tropical cyclone intensity and instability on the evolution of spiral bands

The evolution of spiral-band-like structures triggered by asymmetric heating in three tropical-cyclone-like vortices of different intensities is examined using the Three-Dimensional Vortex Perturbation Analyzer and Simulator （3DVPAS） model. To simulate the spiral bands, asymmetric thermal perturbations are imposed on the radius of maximum wind （RMW） of vortices, which can be considered as the location near the eyewall of real tropical cyclones （TCs）. All the three vortices experience a hydrostatic adjustment after the introduction of thermal asymmetries. It takes more time for weaker and stable vortices to finish such a process. The spiral-band-like structures, especially those distant from the vortex centers, form and evolve accompanying this process. In the quasi-balance state, the spiral bands are gradually concentrated to the inner core, the wave behavior of which resembles the features of classic vortex Rossby （VR） waves. The unstable vortices regain nonhydrostatic features after the quasi-balance stage. The spiral bands further from the vortex center, similar to distant spiral bands in real TCs, form and maintain more easily in the moderate basic-state vortex, satisfying the conditions of barotropic instability. The widest radial extent and longest-lived distant bands always exist in weak and stable vortices. This study represents an attempt to determine the role of TC intensity and stability in the formation and evolution of spiral bands via hydrostatic balance adjustment, and provides some valuable insights into the formation of distant spiral rainbands.