【作者】 朱先德；

【导师】 王启；

【作者基本信息】 中国海洋大学 ， 气象学， 2010， 博士

【摘要】 本文对1997年13号台风Winnie、2001年8号台风Toraji和2004年7号台风Mindulle三个登陆再入海的变性台风的热力特征、动力结构和再发展机制进行了多方面的剖析。通过观测资料和数值模拟研究发现,这三个个例在背景场、热力和动力学结构上既存在着很多共同点,同时也具有很多差异。本文试图总结出不同路径条件下变性台风彼此之间的异同,对变性台风有更深刻的认识,给出此类台风变性加强的物理概念模型,为登陆台风的预报提供相应的依据,起到消灾、减灾的作用。1997年台风Winnie是一个典型的变性加强个例,在变性初期,由于地面摩擦等作用,强度上开始减弱。随着Winnie北上并与中纬度西风槽相互作用,台风外围与中纬度锋面相互融合,西侧冷空气卷入台风内部,与台风中心东侧暖气团形成强烈的对比,导致了热力结构上呈现不对称分布,低层为“半冷半暖”热力特征(西冷东暖)。随着冷空气的持续注入,在台风低层环流内出现包围台风中心的环状锋生,形成了与冷暖锋相对应的倾斜分布特征,西侧具有冷锋特征,北侧具有暖锋特征,台风演变为锋面气旋。在冷空气包围台风中心的过程中,使得斜压位能向动能转换,同时,中心东侧的暖气团被迫抬升,台风内垂直涡度增强,台风低层环流发展。变性气旋与槽前高空急流耦合,高空正的强湿位涡(MPV)下传,与台风低层环流衔接,下传的正位涡使得冷空气增强,相当位温线更加密集,斜压性增强,由湿位涡守恒原理可知,必然会导致气块在垂直方向的拉伸,促使斜压性降低,相对涡度进而得到发展、增强,在低层锋区诱生出气旋性环流。台风的变性,使得热力和动力结构演变为倾斜的非对称分布,其暖心结构首先从台风中心西侧低层遭到破坏,负的温度距平随高度向西倾斜。中高层的暖心加强过程中演变为随东侧倾斜的暖区,且位置由原来200hPa下降到400hPa附近,整个大气层呈现较强的斜压性。台风达到最强后,其低层会逐步被冷空气填塞,对流层中上层为暖中心,斜压系统锢囚。动力特征上,最大风速半径外扩到3个经纬度左右,而相对涡度偏离于台风的中心,最大涡度发生在气旋中心的西侧,且随高度向西倾斜,在对流层高层与西风槽形成的正涡度中心衔接。从能量角度来看,区域平均动能和涡动动能的最强增幅位于对流层低层850-600hPa之间,与冷空气最强位置相对应。可见,Winnie的变性加强过程为中纬度锋面侵入到台风内部,冷空气逐渐包围台风中心,再加上高空能量的下传,与台风残涡相互作用,一个温带气旋在锋面上激发发展起来的过程。2001年台风Toraji在登陆之后经历了衰减、变性加强和快速衰减。在变性加强阶段,除了受到高空槽前西南气流的影响,台风东侧存在一低空急流,在低空急流前方山东半岛的上空一闭合的低空低压系统,此处为一个强烈的辐合区,当台风残涡北移并于该低压系统结合时,两个属性相同的系统叠加,台风获得发展,随着台风再次入海并向低空急流辐合区靠近,再加上海面摩擦的降低,Toraji在移动到山东时再次发展到最强。此后,高空槽向南加深,从西风槽脱离出来而形成切断低压,牵制了台风的持续北上,同时变性气旋难以获得更多的高空能量,冷空气逐步填塞气旋低层,最后锢囚而消亡。由于高空槽前西南气流和副高的作用,中心东侧的环流大于西侧环流,并且最大风速中心位置偏高,位于对流层中层。敏感性试验显示,凝结潜热释放在台风变性加强过程中起到重要的作用,无潜热释放时,台风因为缺乏热量的交换,登陆气旋迅速衰减,很快消亡。2004年台风Mindulle经历了三次登陆过程,在浙江登陆并再入海过程,发生变性加强。其变性加强过程主要受到高空槽及槽前西南气流的影响,台风中心东西两侧环流得到增强,随着台风的发展,南风环流最大值中心由对流层中层下移至对流层低层。区域平均动能和涡动动能显示,两者大值区主要集中在400hPa以下,其加强过程主要位于对流层700hPa,900hPa以下近地面层的增幅在三个台风个例中是最大的,这主要是海面摩擦系数较小的原因。三个个例的对比表明,台风的变性加强与中纬度西风槽相关联,高空槽携带的正涡度平流及高空辐散作用都对台风的发展起到积极作用。而高空正湿位涡的下传,在低层锋区诱生出气旋性环流,同时加强了冷空气侵入,促使斜压位能释放转化为动能,台风残涡获得新生而加强。在此过程中,台风是否与高空急流发生耦合,是否存在低空急流以及地面摩擦的减弱,都影响着台风能否加强,以及加强的强度。更多还原

【Abstract】 In this thesis, the thermal and dynamical structures and re-intensification mechanisms of three extratropical transition typhoon cases with different tracks, such as typhoon Winnie occurred in August 1997, typhoon Toraji and Mindulle occurred in 2001 and 2004 respectively, are investigated by using different available observational data and the results of simulation by PSU/UCAR mesoscale model-MM5. The results show that there are some common characters in synoptic situation, thermodynamics and dynamics structures between these three typhoons, but there also exist some differences among them. This paper aims to conclude the similarities and differences of extratropical transition typhoons in different tracks and further to give the conceptual model about this type of typhoon. This work is helpful to the forecast of typhoon tracks and can be used to reduce typhoon damages.Typhoon Winnie in 1997 is a typical extratropical transition intensification case. At beginning of extratropical transition, the intensification becomes weak because of the surface friction and other factors. But along with its transition up to the north and the interaction with mid-latitude westerly trough, the edge of Winnie and mid-latitude front become to combination, the cold air in the westside can be involved to the inside of Winnie and forms a very sharp contrast with the eastside warm air in the typhoon, this lead the thermodynamics structure to a imbalance distribution, the lower layer appears to a half cold and half warm situation (cold in west and warm east). Along with the continual injection of the cold air, a ring-like frontogenesis appears in the typhoon lower circulation and forms a inclined distribution which is relative to the cold-warm front, the west and the north has cold and warm front characters respectively, the typhoon become to a frontal cyclone. In the process that the cold air surrounds the typhoon center, which makes the baroclinic potential energies transform to kinetic energies. Meanwhile, the warm air is forced to rise and the vertical vorticity enforces, so the low-level circulation of typhoon grows. When cyclone couples with the upper level jet, the strong moist potential voticity(MPV) transmission from upper level strenthens the cold air, which results that equivalent potential temperature is more intensive and baroclinic enhances. From the conservation of MPV we know that in order to reduce the baroclinic, air mass must be stretched in vertical direction, and then relative vorticity develops, cyclonic circulation is induced on low-level frontal zone. In the process of extratropical transition, the thermal and dynamic structure evolve into asymmetric distribution, and negative temperature anomalies westward tilt with height in low-level of typhoon. The warm heart of upper-level falls from 200hPa to 400hPa and strengthens in the process. Meanwhile, the relative vorticity deviates from the center of the typhoon and locates at the west of the cyclone. The radius of maximum wind speed extends to three latitude. From the energy perspective, the strongest growth of regional average kinetic energy and eddy kinetic energy locates at 850-600hPa in the lower troposphere, which corresponds to the cold air. Results show that Winnie’s re-intensification is associated with the meso-scale frontogenesis process in its circulation. A kind of frontogenesis zone in ring form, which wraps up the typhoon center, is found in the lower layer of typhoon remnant circulation. The intensification of the remnant of typhoon Winnie looks like the process of an extratropical cyclone developing in the surface frontal zone.Typhoon Toraji in 2001 goes through decaying, extratropical transition intensification and then decaying rapidly after landfalling. At the stage of extratropical transition intensification, besides the influence of southwesterly ahead of the upper trough, there is a low-level jet stream to the east of typhoon leading to a closed low-level low system above Shandong peninsula in front of the jet stream, where there is an intensive convergence zone. When residual eddies move northward and combine with the low pressure system, typhoon develops due to the combination of two homogeneous systems. Along with typhoon moving onto sea surface and approaching the low-level jet stream convergence zone, and the friction decreasing, the intensity of Toraji reaches peak when it moves to Shandong. Thereafter upper trough deepens southward, departs from westerly trough and becomes cut-off low. This system restrains typhoon moving northward and makes the cyclone get upper level energy hardly. Therefore, cold air fills in the low level of cyclone, which is occluded and vanishes. Due to the effect of southwesterly ahead of the upper trough and subtropical high, circulation on the east side of center is larger than that on the west side, while the maximum wind speed appears too high and locates at the middle-level of troposphere. Sensitivity experiment shows that latent heat release plays an important role in extratropical transition and re-intensification process of typhoon:If there is no latent heat release, typhoon will decay rapidly after landfalling due to the lack of heat exchange.Typhoon Mindulle experiences three landing process in 2004. The circulation both sides of the typhoon center strengthens with the development of the typhoon. the maximum of southerly circulation moves from middle troposphere to lower troposphere. The evolution of regional average kinetic energy and eddy kinetic energy show that, the strengthening process are mainly located in the troposphere underside 700hPa, and the growth is largest in the three typhoon cases below 900hPa because of low coefficient of friction.The research shows that, the extratropical transition and re-intensification of typhoon associates with Westerly trough when the typhoon enters mid-latitude zone. The positive vorticity advection and divergence of upper trough are all play a positive role in re-intensification. Meanwhile, the positive moisture potential vorticity anomaly downward transported from the upper troposphere induces cyclonic circulation in the lower front area and increased cold air which promotes the release of baroclinic potential energy into kinetic energy, and remnant vortex of typhoon develops. In ET process, whether the typhoon couples with the upper level jet, and whether the existence of low-level jet and the weakening of the friction surface, all affect the typhoon could strengthen, and enhance strength.更多还原