发生在中国大陆的台风变性加强过程分析

通过对登陆台风Winnie(1997)的演变过程分析，发现登陆后的台风经历三个阶段：衰减阶段、变性阶段、重新加强阶段。其变性过程类似于Sekioka等人提出的复合型，变性后逐渐演变为Shapiro—Keyser气旋模型。通过对物理量的诊断分析发现，对流层中高层冷空气的下沉入侵以及对流层低层的暖平流是热带气旋变性的原因。冷空气的入侵使具有暖心结构的热带气旋演变为斜压结构的温带气旋。变性后气旋得到了重新发展，低层维持的较明显暖平流以及与高空急流相对应的散度区和高空涡度平流是导致气旋重新发展的重要物理因子。     

COMPARATIVE ANALYSIS OF THE INTENSIFYING AND WEAKENING LANDFALL TROPICAL CYCLONES DURING EXTRATROPICAL TRANSITION OVER CHINA

Based on the Tropical Cyclone(TC) Yearbooks data and JRA-25 reanalysis data from the Japan Meteorological Agency(JMA) during 1979-2008, dynamic composite analysis and computation of kinetic energy budget are used to study the intensifying and weakening TCs during Extratropical Transition over China. The TCI shows strong upper-level divergence, strengthened low-level convergence and significantly enhanced upward motion under the influence of strong upper-level troughs and high-level jets. The TCI is correspondingly intensified after Extratropical Transition(ET); TCW exhibits strong upper-level divergence, subdued low-level convergence and slightly enhanced upward motion under the influence of weak upper-level troughs and high-level jets. It then weakens after ET. The increase(decrease) of the generation of kinetic energy by divergence wind in TCI(TCW) at low level is one of the major reasons for TCI’s intensification(TCW’s weakening) after transformation. The generation of kinetic energy by divergence wind is closely related to the development of a low-level baroclinic frontal zone. The growth of the generation of kinetic energy by rotational wind in TCI at upper level is favorable for TCI’s maintenance, which is affected by strong upper-level troughs. The dissipation of the generation of kinetic energy by rotational wind in TCW at upper level is unfavorable for TCW’s maintenance, which is affected by weak upper-level troughs.     

北上变性热带气旋对辽东半岛降水的影响

9711(Winnie)和0509(Matsa)是两个登陆北上影响辽东半岛的变性台风,Matsa直接登陆辽东半岛,但降水量仅为穿过渤海间接影响辽东半岛的Winnie的一半.分析其变性过程与辽东半岛热带气旋降水的关系发现,Winnie和Matsa的降水差异与其北上期间与西风带系统的相互作用密切相关.Winnie变性北上期间被中纬度西风槽"捕获",发生耦合,高层正湿位涡扰动下传,西风带冷空气与热带气旋暖湿气流相互作用,有利于对流云团的生成、发展,在半岛地区产生大暴雨的降水雨带由多个β中尺度云团组成.Matsa在北上变性过程中,只是靠近高空槽底,没有发生耦合,高层正湿位涡扰动不强,没有与低层环流相互作用,冷空气偏南偏弱,变性过程中半岛地区只有1个β中尺度云团生成,降水量较小.     

IMPACTS OF TWO TROPICAL CYCLONES EXPERIENCING EXTRATROPICAL TRANSITION DURING NORTHWARD PROGRESSION ON THE RAINFALL OF LIAODONG PENINSULA

Both of Typhoon Winnie (9711) and Matsa (0509) underwent an extratropical transition (ET) process when they moved northward after landfall and affected Liaodong Peninsula. However, Matsa produced half as much rainfall as Winnie, although it struck Liaodong Peninsula directly while Winnie passed through the Bohai Sea. The relations between the ET processes and the precipitation over Liaodong Peninsula are examined. The result shows that the precipitation difference between Winnie and Matsa was closely related to the interactions between the westerly systems and typhoons during their ET processes. Winnie was captured by the upper westerly trough and then coupled with it when moving to the mid-latitudes, and the positive anomaly of moist potential vorticity (MPV) was transported downward from the upper troposphere over the remnant circulation of the tropical cyclone (TC). It was favorable to the interaction between tropical warm and wet air and westerly cold air, causing convective cloud clusters to form and develop. The rain belt composed of several meso-β cloud clusters over the Liaodong Peninsula, resulting in heavy rainfall. On the other hand, Matsa did not couple with any upper trough during its ET process and the positive anomaly of MPV in the upper troposphere and its downward transfer were weak. Only one meso-β cloud cluster occurred in Matsa’s rain belt during its ET process that tended to lessen rainfall over Liaodong Peninsula.     

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.     

DIAGNOSIS OF THE DEVELOPMENTAL MECHANISM OF THE EXTRATROPICAL TRANSITION OF A TROPICAL CYCLONE USING POTENTIAL VORTICITY INVERSION OF FRONTOGENESIS

This paper diagnoses and analyses the developmental mechanism of a process of extratropical transition of a tropical cyclone which occurred over West Pacific Ocean based on a diagnosis method of potential vorticity inversion of frontogenesis.The study diagnoses quantitatively the role and effect of dynamic influence of westerly cold troughs,middle-latitude baroclinic frontal zones,cyclone cycles and unbalanced wind fields during the different stages of the extratropical transition of a tropical cyclone,and also discusses the interaction between them and the developmental mechanism.The results show that there are different developmental mechanisms during each stage of the extratropical transition and the processes are also unbalanced.     

1949-2007年登陆我国变性热带气旋的特征统计及合成分析

利用1949-2007年热带气旋年鉴等资料,统计分析登陆中国并在我国或附近变性的热带气旋的特征,着重分析不同区域及路径的变性气旋特征.分析结果得出,登陆我国的热带气旋很多,但在我国及附近沿海变性的却较少,大多数热带气旋变性后不发展或迅速衰减,只有约17％的变性热带气旋继续发展.热带气旋变性大多发生在114°E以东,移动...     

APPLICATION OF AN OBJECTIVE DISCRIMINATING METHOD IN THE EVOLUTION OF TROPICAL CYCLONE "HAIMA" DURING EXTRATROPICAL TRANSITION

An objective method for discriminating the process of extratropical transition (ET) in tropical cyclones is introduced. With this method, the gridpoint output data of NWP are used to calculate three parameters: storm-relative thickness symmetry (B), low-level (-VLT) and upper-level thermal wind (-VUT). This objective method is easy to calculate and convenient for operational use. To verify the method, this paper uses the NCEP reanalysis data to identify the evolution of ET for "Haima", a tropical storm (0421) that affected the eastern part of China in 2004. The result shows that the three parameters defined with the objective method are good indicators of the ET process.     

“相空间”方法判断西北太平洋热带气旋变性适用性研究

大部分热带气旋进入中纬度地区都会发生向温带气旋的转变。这一变性过程会造成强降水和大风，并且移速增快，因此给中纬度地区造成很大的灾害。西北太平洋地区热带气旋变性是一个与中纬度系统相互作用的复杂过程，判断其变性与否是一个关键性问题。详细介绍了判定TC变性的“相空间”方法，该方法包含了三个参数：对流层低层热力对称性参数、高层热成风参数、低层热成风参数。使用“相空间”方法对2000—2007年间西北太平洋地区TC的变性过程进行统计分析，以验证此种方法在西北太平洋地区的适用效果。结果表明，“相空间”方法对判定西北太平洋地区TC有一定指示作用，但该方法作为业务应用还存在一定问题。     

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.     

一次变性台风再增强过程的敏感性试验

采用位涡反演技术与数值模拟相结合的方法,通过初值敏感性试验和物理量场的诊断分析,对台风变性后再度增强的影响因子和物理机制进行了深入的分析和研究。结果表明:台风低压由变性减弱转为发展增强主要是由于台风低压环流与西风带斜压锋区之间的相互作用所造成的,随着高空冷涡低槽的加深南下和台风低压的继续北上,两个系统之间的距离逐渐减小,西风带高空槽与台风低压之间相互作用的正反馈机制逐步成为台风变性后强烈加深发展的主要原因。     

A STATISTICAL ANALYSIS ON THE DIFFERENT FEATURES OF TC EXTRATROPICAL TRANSITION OVER LAND AND OCEAN

The extratropical transitions(ETs)of tropical cyclones(TCs)over China and the ocean east to 150°E are investigated by the use of best-track data and JRA-25 reanalysis spanning 1979-2008.The ET events occurring north of 25°N and in the warm season(from May to October)are extracted from the reanalysis to emphasize the interaction between TC and midlatitude circulation.Statistical analysis shows that 18.5%of the warm-season TCs go through land ETs north of 25°N in the western North Pacific.And 20.5%of the ET events occur over the ocean east of 150°E.Most(62.2%)ET TCs over China gradually die out after ET,but more(70.7%)ocean ET cases have post-ET reintensification.The evolutions in cyclone phase space and the composite fields for land and ocean ETs,as well as the ET cases with and without post-ET reintensification,are further analyzed.It is found that most TCs with ET over China and those without post-ET reintensification evolve along the typical ET phase path as follows:emergence of thermal asymmetry→losing upper-level warm core→losing lower-level cold core→evolving as extratropical cyclone.The TCs undergoing ETs over ocean and those with post-ET reintensification form a high-level cold core before the ET onset.The TCs with land ET have long distance between the landing TC and a high-level trough.That makes the TC maintain more tropical features and isolates the TC flow from the upstream and downstream jets of the midlatitude trough.The structure of circulation leads to weak development of baroclinicity in land ET.On the contrary,shorter distance between ocean TC and high-level trough makes the high-level trough absorb the TC absolutely.Under that baroclinicity-favorable environment,strong cold advection makes the TC lose its high-level warm core before ET onset.The composite fields confirm that the TC with ocean ET has stronger baroclinic features.Generally,the TC at land ET onset is located to the south of the ridge of the subtropical high,which tends to prevent the TCs from interacting with midlatitude circulation.But for the ocean ET,the situation is just the opposite.Similar analyses are also carried out for the TCs with and without post-ET reintensification over both land and ocean east of 150°E.The results further prove that the TC with stronger baroclinic characteristics,especially in the circumstance favorable to its interaction with high-level midlatitude systems,has more opportunity to reintensify as an extratropical cyclone after ET.     

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.     

台风Faxai(1403)低纬变性的结构演变特征分析

利用气旋相空间法(cyclone phase space,CPS)对1403号台风Faxai变性前后的环境场及结构演变特征进行分析。结果表明:相空间法能够很好地指示低纬变性台风Faxai的变性起止时间。此次过程是由减弱的台风环流与TC西北侧的短波槽结合发展产生,分析台风Faxai的结构演变特征可知,变性阶段TC低层厚度场由均匀对称分布转为非均匀分布,增大了环境斜压性,变性后B值最大达30 m,为弱的斜压非对称结构。Faxai东侧的偏南风暖湿气流与偏北风气流相交汇,使得经向位温梯度增加从而在TC东北象限形成一带状锋区,锋区正好位于南北两大风圈之间的位置。整个变性阶段Faxai西侧几乎无明显冷锋锋生,只在环流东北侧有一定程度的暖锋锋生,这与典型的锋面气旋的发展过程有所不同。变性前,TC呈现对称分布的暖核结构;变性阶段,冷空气从热带低压西侧对流层中低层下沉入侵,TC呈现左侧冷、右侧暖的非对称斜压结构,中层增温可能与槽后强的下沉气流有关。对锋生函数各分量分析发现,散度场主导了气旋周围的标量锋生,倾斜项的贡献次之,涡度场是引起旋转锋生的主要因素,其余两项可忽略不计。     

COMPARISONS OF THE CHARACTERISTICS OF TROPICAL CYCLONES EXPERIENCING EXTRATROPICAL TRANSITION IN THE WESTERN NORTH PACIFIC BASED ON DIFFERENT DATASETS

The differences in the climatology of extratropical transition(ET) of western North Pacific tropical cyclones(TCs) were investigated in this study using the TCs best-track datasets of China Meteorological Administration(CMA),Japan Meteorological Agency(JMA) and the Joint Typhoon Warning Center(JTWC). The results show that the ET identification, ET completion time, and post-ET duration reported in the JTWC dataset are greatly different from those in CMA and JMA datasets during 2004-2010. However, the key differences between the CMA and JMA datasets from 1951 to 2010 are the ET identification and the post-ET duration, because of inconsistent objective ET criteria used in the centers. Further analysis indicates that annual ET percentage of CMA was lower than that of JMA, and exhibited an interannual decreasing trend, while that of JMA was an unchanged trend. The western North Pacific ET events occurred mainly during the period June to November. The latitude of ET occurrence shifted northward from February to August,followed by a southward shift. Most of ET events were observed between 35°N and 45°N. From a regional perspective,TCs tended to undergo ET in Japan and the ocean east to it. It is found that TCs which experienced the ET process at higher latitudes were generally more intense at the ET completion time. TCs completing the ET overland or offshore were weaker than those finishing the ET over the ocean. Most of the TCs weakened 24 h before the completion of ET.In contrast, 21%(27%) of the TCs showed an intensification process based on the CMA(JMA) dataset during the post-ET period. The results presented in this study indicate that consistent ET determination criteria are needed to reduce the uncertainty involved in ET identification among the centers.     

两广地区热带气旋极端降水特征及成因初探

基于1960—2014年中国广东、广西地区（简称两广地区）184个台站的逐日降水资料、热带气旋（TC）最佳路径集以及ERA-Interim、ERA-40再分析资料,利用TC降水天气图客观识别法、TC路径相似面积指数、动态合成法,从TC过程最大日降水的角度,分析了两广地区TC极端降水的时空特征, 并针对主要特征进行成因诊断。结果表明:50年来,两广地区TC过程的最大日降水≥50、100 mm的频数分别呈-0.66和-0.44次/(10年)的下降趋势,而最大日降水≥250 mm频数则表现出0.16次/(10年)的上升趋势;TC最大日降水频数和强度的大值区主要分布在沿海,并由沿海向内陆递减;大值区相对集中于粤东沿海（东部分区）、珠江三角洲西侧沿海（中部分区）和雷州半岛至广西沿海（西部分区）三个分区,且西部分区在TC最大日降水的平均强度及各级别频次上均为三分区之最大。对比分析发现,造成西部分区极端降水的TC路径规律性较强,主要为TC西行路径,且其登陆点集中在西部分区;对TC极端降水成因分析表明,TC移动速度慢和南海夏季风强度增强均有利于极端降水产生。      

台风Chanchu(0601)变性过程中的强度变化及环境场分析

利用非静力中尺度WRF模式模拟的台风Chanchu(0601)的输出资料,探讨了Chanchu减弱变性过程的强度及结构变化。分析结果表明:在台风Chanchu北移过程中,高层的暖心被破坏,强度快速减弱,眼壁对流发展高度降低,眼壁对流由对称结构演变为非对称,内核对流减弱。此减弱变性过程与惯性稳定度减小、垂直风切变增强、低层锋生等环境要素有关。惯性稳定度与台风强度变化一致,随着惯性稳定度降低,最大切向风减弱并不断外扩,Rossby变形半径增大从而潜热释放不集中难以维持台风强度,台风减弱;同时,内核区的高层暖心更易径向频散,从而高层暖心难以维持;环境的垂直风切变增强使台风的斜压性增强,台风垂直结构的倾斜度增大,对流发展高度降低;低层冷空气侵入台风中心趋于填塞,也利于台风强度减弱;台风登陆以后冷暖空气对比导致的锋生使得不稳定能量释放从而重新加强了Chanchu环流内的中低层对流活动,但较台风最强时刻而言对流强度减弱。总体减少的对流和降低的对流高度,导致潜热能释放减小,其向心输送也减少,不足以维持强暖心结构,最终使得台风减弱并变性。      

全国热带气旋降水量的初步气候分析

利用1949—2009年热带气旋降水资料分析了全国热带气旋降水的时空分布特征。结果表明,全国各地区热带气旋降水的空间分布很不均匀,大致呈现东南—西北向的梯度分布,东南沿海地区降水量最大,西北内陆地区最小。另外,地形对降水的空间分布也有影响,例如东南沿海和山脉迎风坡的地形作用尤为显著。此外,比较不同年份的热带气旋降水的空间分布特征,有很多相似之处,如随经纬度的变化趋势,降水最大中心位置等。热带气旋降水具有比较明显的年代变化和显著的年际震荡。年代变化表现为20世纪50—60年代为大幅增加的过程,60—80年代降水总量基本维持,80年代后期降水呈现明显的震荡趋势。     

Winnie(1997)和Bilis(2000)变性过程的湿位涡分析

9711号台风Winnie和0010号台风Bills均在中国大陆发生变性,但前者变性后再度加强,而后者变性后减弱消亡。从湿位涡理论出发,对比分析两者的变性过程,结果表明：作为变性台风,Winnie和Bilis均在北上过程中与中纬度西风槽发生作用,但前者与高空槽发生耦合,后者仅接近高空槽底部,没有发生耦合;Winnie变性加强过程表现为一个温带气旋在低层锋区上的强烈发展过程,主要与高层正位涡扰动下传、低层锋区及热带气旋低压环流之间的相互作用有关。Pm湿斜压项增长引起的倾斜涡度发展是登陆热带气旋变性加强的主要因子。在Bills变性过程中,高层无明显的正位涡扰动下传,热带气旋低压环流内无锋区面出现,大气斜压性弱且变化不明显。     

登陆台风变性发展与消亡的对比分析

本文对0421(海马)和0311(环高)台风登陆后不同的演变过程进行了对比分析。分析表明,虽然两次台风登陆的时间和路径都很相似,但是由于环境场的形势的不同,特别是北方冷空气情况的不同,一个变性发展成为温带气旋,给江苏地区带来了大面积的降水,另一个直接减弱消失,仅在登陆点附近产生了一些降水。通过讨论锋生函数各项的性质和计算其主要项的分布特征,对变性过程进行了研究,发现台风变性初期其锋生函数中变形项起主要作用。锋生结果造成强烈的辐合上升运动,引起台风暴雨的增幅。