热带气旋的温带变性过程对下游影响的研究进展

热带气旋(TC)在向高纬度地区移动过程中往往会转变为温带气旋,称之为温带变性(ET)过程。ET过程涉及到热带系统与中纬度环流的复杂相互作用,并对局地系统直至大范围环流均产生影响,这种影响甚至向下游延伸到半球的尺度。由于ET过程及其下游影响给中纬度地区带来严重灾害性天气,而对其的预报一直是一个难题,因而关于此问题的科学研究和业务预报是近年来国际上的一个热点,国内的有关工作也已开展。从TC在ET过程中与中纬度环流的相互作用、ET过程对中纬度下游环流的影响和ET过程及其下游影响的数值预报三个方面总结和分析了近年来国内外的有关研究进展,为国内学术界进一步开展相关研究提供参考。主要进展包括:(1) TC高层出流输出低位涡(PV)空气改变温带上层结构以及TC环流直接作用于中纬度流是TC-中纬度流相互作用的主要方式;TC相对于上游槽的位置对ET过程及其下游影响很关键;各种物理过程在相互作用中起到不同的作用;(2) TC所激发的Rossby波在与急流相联系的上层PV梯度上向下游频散是下游发展的主要方式;下游发展具有显著的边界俘获和上下层耦合发展的特征;(3) 目标观测、集合预报和变分同化等技术的发展提高了ET及其下游影响的数值预报水平。      

变性再发展热带气旋Yaji(2006)的数值模拟研究

利用中尺度模式WRF对2006年14号热带气旋Yaji的变性过程进行了双重嵌套模拟。结果表明,采用高分辨率的TRMM/TMI卫星反演SST资料,在第一重区域(网格距为15km)采用WSM3微物理方案和Betts-Miller对流参数化方案,在第二重移动嵌套区域(网格距为5km)采用Lin微物理方案,不采用对流参数化方案,模式能较好地模拟Yaji的路径和变性前后的强度演变,其中模拟的路径平均误差为64km,强度平均误差为2.5hPa,模拟的风场分布与Quickscat卫星反演的风场分布也较为吻合。利用模拟资料还研究了Yaji变性过程中的非对称流特征。     

Chaba (0417) 台风变性前后热力结构特征

运用美国NOAA-15极轨气象卫星高分辨率的AMSU探测资料, 结合NCEP/NCAR再分析资料和GMS-5气象卫星红外云顶亮温(TBB)资料, 对2004年Chaba(0417)台风(TC)变性前后的热力结构特征进行分析。发现变性前TC暖核结构呈对称分布, 在高空存在一强暖心; 变性后原TC对称暖心结构消失, 存在于温带气旋上空的相对暖区呈现出倾斜的非对称分布, 在高、低层各形成一弱的暖区中心, 锋面的斜压特性显著。通过热力结构对比, 进一步揭示出TC在向高纬度方向移动时, 与中纬度系统相互作用发生变性, 实质上是两个相继过程, 即热带气旋的消亡和温带气旋的生成发展。TC西侧高空干冷空气的入侵下沉, 破坏了其发展所需的水汽条件, 造成TC对称暖核结构的削弱和损毁。与此同时, 在TC残留区域, 由于空气较暖且存在气旋式环流, 暖空气在东侧呈气旋式上升, 与西侧高空入侵下沉的干冷空气形成偶极, TC暖气团与冷空气相交发展形成斜压的结果, 则为温带气旋的生成和发展创造了有利条件。     

爆发性气旋的锋生位涡反演诊断

本文采用基于埃特尔位涡反演诊断和锋生函数诊断的锋生位涡反演诊断方法,对一次发生在西太平洋地区的爆发性气旋过程进行了诊断分析和机制研究。本文主要从锋生演变的角度,定量诊断了与对流层顶折迭现象相联系的高层位涡扰动,由凝结潜热释放造成的中层位涡扰动,与低层锋区扰动相联系的低层位涡扰动以及以低层水平辐合辐散为主要成份的非平衡风场在气旋发生发展的不同阶段所起的作用和影响,并对以上各物理过程相互作用,造成气旋爆发性发展的机制进行了分析讨论。     

热带气旋变性过程客观判别方法在“海马”变性过程中的应用

介绍了一种判别热带气旋变性过程的客观方法.此客观方法使用三个判别参数: 对流层低层热力非对称参数B、高低层的热成风、对变性过程进行诊断判别.此方法使用格点的数值预报产品,计算简单、使用方便,便于业务化.同时针对2004年影响我国的0421号热带风暴"海马",使用NCEP再分析资料对其变性过程进行了分析验证,结果表明:此客观方法所定义的三个判别参数B、、在"海马"的变性过程中有很好的指示作用.     

ANALYSIS OF STRUCTURE EVOLUTION AND ENVIRONMENTAL CONDITIONS OF TROPICAL CYCLONES OVER THE WESTERN NORTH PACIFIC DURING EXTRATROPICAL TRANSITION

Fifty-eight extratropical transition (ET) cases in the years 2000-2008, including 2,021 observations (at 6-hour intervals), over the western North Pacific are analyzed using the cyclone phase space (CPS) method, in an effort to get the characteristics of the structure evolution and environmental conditions of tropical cyclones (TCs) during ET over this area. Cluster analysis of the CPS dataset shows that strong TCs are more likely to undergo ET. ET begins with the increment of thermal asymmetry in TCs, along with the generation and intensification of an upper-level cold core, and ends with the occurrence of a lower-level cold core. ET lasts an average duration of about 28 hours. Dynamic composite analysis of the environmental field of different clusters shows that, in general, when TCs move northward, they are gradually embedded in the westerlies and gradually transform into extratropical cyclones under the influence of the mid- and higher-latitude baroclinic systems. As for those TCs which complete ET, there is always much greater potential vorticity gradient in the northwest of them and obvious water vapor transport channels in the environment.     

A Study of the Extratropical Transformation of Typhoon Winnie （1997）

The complicated evolutive process of how a tropical cyclone transforms into an extratropical cyclone is still an unresolved issue to date, especially one which arises in a weakly baroclinic environment. Typhoon Winnie （1997） is studied during its extratropical transformation stage of extratropical transition （ET） with observational data and numerical simulations. Results show that Winnie experienced its extratropical transformation to the south of the subtropical high without intrusion of the mid-latitude baroclinic zone. This is significantly different from previous studies. Analyses reveal that the cold air, which appeared in the north edge of Winnie circulation, resulted from the precipitation drag and cooling effect of latent heat absorption associated with the intense precipitation there. The cooling only happened below 3 km and the greatest cooling was below 1 km. With the cold air and its advection by the circulation of Winnie, a front was formed in the lower troposphere. The front above is related not only to the cooling in the lower level but also to the warming effect of latent heat release in the middle-upper levels. The different temperature variation in the vertical caused the temperature gradient over Winnie and resulted in the baroclinicity.     

热带对流活动对热带内外地区环流季内遥相关变化的作用

基于ＥＣＭＷＦ客观分析资料，本文采用诊断分析的方法研究了１９８３／１９８４和１９８６／１９８７两年冬季季内３０—６０ｄ低频域中热带对流与热带外环流以及低频扰动动能频散之间的关系。结果表明，热带对流强度上的差异可以造成热带内外地区季内遥相关波列以及低频波能频散上的差别。热带对流作用可以是联系热带内外地区季内遥相关作用的一个重要的衔接因子。     

热带气旋“利奇马”(1909)暖心演变分析及变性过程探讨

利用NCEP GDAS/FNL再分析数据,根据TFP(Thermal Front Parameter)参数和锋生函数,对1909号热带气旋“利奇马”生命史中各主要阶段暖心特征和变性过程进行了诊断分析。结果表明:“利奇马”强度为热带风暴时,其暖心结构较为松散,500 hPa以上和600 hPa以下分别存在一个最强中心,在强度减弱阶段上下层暖心均偏离气旋中心;当其强度升至强热带风暴及以上级别时,低层暖心消失,高层暖心显著增强,结构变得紧凑,气旋中心上空暖区呈棒槌状分布。高层暖心强度与“利奇马”强度呈正相关,当“利奇马”维持超强台风时,其暖心可达10~14℃。“利奇马”与中纬度西风槽接触后,冷空气开始自对流层中低层进入其环流,低层冷空气入侵的程度比中层更明显;低层暖心被冷空气侵蚀而消失,高层暖心则逐渐减弱,结构亦变得松散。TFP参数和锋生函数计算结果表明受冷空气影响,“利奇马”斜压性逐渐增强,其中心西北侧形成一支暖锋,逐渐变性为温带气旋,但冷锋未见发展。变性过程中“利奇马”高层暖心强度虽减弱但仍然维持,但低层暖区被冷空气完全填塞,导致其变性后较快消亡。     

NUMERICAL SIMULATION OF SSTA IMPACTS UPON THE INTERDECADAL VARIATION OF THE CROSS-EQUATORIAL FLOWS IN EASTERN HEMISPHERE

Impacts of regional sea surface temperature(SST)anomalies on the interdecadal variation of the cross-equatorial flows(CEFs)in Eastern Hemisphere are studied using numerical simulations with a global atmospheric circulation model(NCAR CAM3)driven with 1950-2000 monthly SSTs in different marine areas(the globe,extratropics,tropics,tropical Indian Ocean-Pacific,and tropical Pacific)and ERA-40reanalysis data.Results show that all simulations,except the one driven with extratropical SSTs,can simulate the interdecadal strengthening of CEFs around Somali,120oE,and 150oE that occurred in the midand late-1970s.Among those simulated CEFs,the interdecadal variability in Somali and its interdecadal relationship with the East Asian summer monsoon are in better agreement with the observations,suggesting that changes in the SSTs of tropical oceans,especially the tropical Pacific,play a crucial role in the interdecadal variability of CEFs in Somali.The interdecadal change of CEFs in Somali is highly associated with the interdecadal variation of tropical Pacific SST.As the interdecadal warmer(colder)SST happens in the tropical Pacific,a"sandwich"pattern of SST anomalies,i.e."+,-,+"("-,+,-"),will occur in the eastern tropical Pacific from north to south with a pair of anomalous anticyclone(cyclone)at the lower troposphere;the pair links to another pair of anomalous cyclone(anticyclone)in the tropical Indian Ocean through an atmospheric bridge,and thus strengthens(weakens)the CEFs in Somali.     

Influence of the tropical cyclone Omar on the weather in Europe

A case of the Atlantic tropical cyclone influence on the weather of Europe is considered. It is demonstrated on the basis of computations of the numerical mesoscale ETA model that one of the reasons of the positive air temperature anomaly in fall 2008 was the tropical cyclone Omar. The detailed analysis was carried out of the computation results of the movement and evolution of the tropical cyclone Omar and of the atmospheric structures surrounding it. The energy characteristics, the explicit and latent heat fluxes, and the precipitation in the tropical cyclone were computed. The computations revealed that starting since the certain moment, the tropical storm Omar actively interacted with the polar front which shifted to the low latitudes and with the extratropical disturbance of synoptic scale which originated on this front. It was obtained that this interaction resulted in the transfer of the huge tropical cyclone energy to the extratropical pole-front cyclone and in the intensification of the latter one. It is demonstrated that the air which circulated in the tropical cyclone and possessed high the thermohygrometric characteristics entered the warm sector of extratropical cyclone and was carried out to Europe.     

夏季江淮气旋的Ertel位涡诊断分析

本文应用Ertel位势涡度的理论,分析了两例夏季江准气旋活动的等熵面位涡图和位涡垂直廓线,讨论了这类系统发生发展的一种可能机制以及它们与典型温带气旋的区别,从而得出了夏季江淮气旋活动的一个概念模式:从高原一带东移的对流层中层弱的扰动在有利条件下引起江淮地区较强降水,中层潜热释放导致气旋性环流向下延伸,最终可在地面静止锋上形成波动。当副热带锋区北侧平流层下部空气沿等熵面南下时,气旋波可能发展成为典型的温带气旋。     

Mechanism Study of Tropical Cyclone Impact on East Asian Subtropical Upper-Level Jet: a Numerical Case Investigation

In the case study of this paper, sensitivity experiments are carried out using the mesoscale non-hydrostatic Weather Research and Forecasting (WRF) model to investigate the impact of tropical cyclone (TC) Soudelor (2003) on the East Asian subtropical upper-level jet (EASJ) before TC Soudelor transformed into an extratropical cyclone. The physical mechanism for changes in the EASJ intensity and position caused by TC Soudelor is explored. Results indicate that TC Soudelor would warm the air in the middle and upper troposphere over the Japan Sea and the adjacent areas through stimulating northward propagating teleconnection pattern as well as releasing large amounts of latent heat, which led to increase (decrease) the meridional air temperature gradient to the south (north) below the EASJ axis. As a result, the geopotential height abnormally increased in the upper troposphere, resulting in an anomalous anticyclonic circulation belt along the EASJ axis. Correspondingly, the westerly winds to the north (south) of the EASJ axis intensified (weakened) and the EASJ axis shifted northward by one degree. The case study also suggests that before the extratropical cyclone transition of TC Soudelor, the TC activities had exerted significant impacts on the EASJ through thermodynamic processes.     

热带气旋研究和业务预报进展—第九届世界气象组织热带气旋国际研讨会（IWTC-9）综述

2018年12月3—7日在美国夏威夷召开的第九届世界气象组织热带气旋国际研讨会对国际热带气旋研究和预报预警业务的近期进展进行了充分回顾,并对未来的发展方向进行了系统研讨。过去4年（2015—2018年）,在热带波动和对流对热带气旋生成的影响、复杂环境影响热带气旋路径转向的机理、对流和风垂直切变对热带气旋强度变化的作用机制、双眼墙形成和替换机理、热带气旋变性过程对环境条件的响应、热带气旋气候变化特征、热带气旋多平台观测技术等诸多方面的研究取得了显著进展。同时,在热带气旋生成概率预报、全球模式中热带气旋强度预报改进、热带气旋活动次季节业务预测技术发展以及热带气旋预报不确定性理论等方面也取得积极进展。在综述此次会议的相关议题后,简要讨论中国热带气旋研究和业务发展方向。      

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。     

A CLIMATOLOGY OF EXTRATROPICAL TRANSITION OF TROPICAL CYCLONES IN THE WESTERN NORTH PACIFIC

Based on best-track data and JRA-25 reanalysis, a climatology of western North Pacific extratropical transition (ET) of tropical cyclone (TC) is presented in this paper. It was found that 35% (318 out of 912) of all TCs underwent ET during 1979–2008. The warm-season (June through September) ETs account for 64% of all ET events with the most occurrence in September. The area 120°E–150°E and 20°N–40°N is the most favorable region for ET onsets in western North Pacific. The TCs experience ET at latitudes 30°N–40°N and have the greatest intensity in contrast to other latitude bands. The distribution of ET onset locations shows obviously meridional migration in different seasons. A cyclone phase space (CPS) method was used to analyze the TC evolution during ET. Except for some cases of abnormal ET at relatively high latitudes, typical phase evolution paths—along which TC firstly showed thermal asymmetry and an upper-level cold core and then lost its low-level warm core—can be used to describe the main features of ET processes in western North Pacific. Some seasonal variations of ET evolution paths in CPS were also found at low latitudes south of 15°N, which suggests different ET onset mechanisms there. Further composite analysis concluded that warm-season ETs have generally two types of evolutions, but only one type in cold season (October through next May). The first type of warm-season ETs has less baroclinicity due to long distance between the TC and upper-level mid-latitude system. However, significant interactions between a mid-latitude upper -level trough and TC, of either approaching or being absorbed into the trough, and TC’s relations with downstream and upstream upper-level jets, are the fingerprints for both a second type of warm-season ETs and almost all the cold-season ETs. For each type of ETs, detailed structural characteristics as well as precipitation distribution are illustrated by latitude.     

Large scale features and energetics of the hybrid subtropical low ‘Duck’ over the Tasman Sea

New aspects of the genesis and partial tropical transition of a rare hybrid subtropical cyclone on the eastern Australian coast are presented. The ‘Duck’ (March 2001) attracted more recent attention due to its underlying genesis mechanisms being remarkably similar to the first South Atlantic hurricane (March 2004). Here we put this cyclone in climate perspective, showing that it belongs to a class within the 1 % lowest frequency percentile in the Southern Hemisphere as a function of its thermal evolution. A large scale analysis reveals a combined influence from an existing tropical cyclone and a persistent mid-latitude block. A Lagrangian tracer showed that the upper level air parcels arriving at the cyclone’s center had been modified by the blocking. Lorenz energetics is used to identify connections with both tropical and extratropical processes, and reveal how these create the large scale environment conducive to the development of the vortex. The results reveal that the blocking exerted the most important influence, with a strong peak in barotropic generation of kinetic energy over a large area traversed by the air parcels just before genesis. A secondary peak also coincided with the first time the cyclone developed an upper level warm core, but with insufficient amplitude to allow for a full tropical transition. The applications of this technique are numerous and promising, particularly on the use of global climate models to infer changes in environmental parameters associated with severe storms.     

0216号台风降水及其影响降水机制的数值模拟试验

文中用MM5模式对 0 2 16号台风 (森拉克 )降水进行了数值模拟 ,取得了较好的效果。模拟得到的台风降水中心强度和位置以及降水的分布与实况基本相符。文中还对影响热带气旋降水的机制进行数值模拟试验。结果表明 :冷空气入侵热带气旋外围可以大幅度增加热带气旋外围及倒槽的降水 ,但入侵到热带气旋中心附近的冷空气使热带气旋强度减弱 ,造成中心附近降水明显减少 ,但其外围与倒槽的降水明显加大 ;地形作用使迎风坡及降水中心增加雨量 ,背风坡雨量减少 ,从而使降水分布更不对称、更不均匀 ;大陆及其近海的湿度场对热带气旋降水有较大的影响。     

9617号热带风暴Tom变性过程数值模拟分析

利用中尺度模式MM5对西北太平洋9617号热带风暴Tom转变温带气旋的变性过程进行了模拟.通过对其变性过程的模拟分析发现:热带风暴Tom与西风槽相互作用,风暴东侧低层暖湿气流与槽前正涡度平流发生耦合有利于气旋发展;槽前暖平流与槽后冷平流使风暴形成具有西冷东暖的热力分布结构,诱使风暴向斜压转变;高空急流入口处右侧的气旋式切变及出口处右侧的反气旋式切变有利于风暴右侧气流上升和左侧气流下沉运动,有利于风暴由正压向斜压性转变;来自风暴西北侧的干冷空气自700hPa附近向风暴中心侵入,使风暴中心暖柱体发生自低层向高层的西北一东南向的倾斜,其暖性特征遭到破坏;由于干冷空气的侵入,低层700hPa分为南北两个暖中心,北侧暖中心北侧出现了明显的暖锋锋生,西南侧另一个暖心附近有冷锋锋生迹象;平流层高值PV异常下传有利于变性后的热带风暴的再次加强.     

高空槽对9711号台风变性加强影响的数值研究

9711号台风Winnie是一个在中国大陆长久维持(2—3 d)并产生强降水的热带气旋(TC),在其深入内陆过程中变性加强为一个温带气旋。用MM5V3对不同强度高空槽影响下Winnie的变性加强过程进行了数值研究。结果表明:(1)Winnie变性加强过程表现为强锋面侵入台风内部、冷空气包裹台风中心、一个温带气旋在近地层锋面上强烈发展的过程;(2)Winnie在陆上的变性加强与西风带高空槽的强度密切相关。TC与不同强度高空槽相互作用过程中,较深槽携带较强冷平流、正涡度平流以及较强的槽前高空辐散,从而有利于TC的维持和变性发展。数值试验中,高空槽越强,Winnie变性加强越明显,温带气旋的发展越快;(3)模拟结果的位涡分析表明,Winnie的温带变性发展与对流层高层正位涡下传、低层锋区和TC低压环流三者之间的相互作用有关。