【作者】 许向春；

【导师】 于玉斌； 王式功；

【作者基本信息】 兰州大学 ， 气象学， 2009， 硕士

【摘要】 登陆是热带气旋生命史的一个重要转折点。热带气旋登陆过程受到浅海区大陆架和海岸地形等的影响,结构发生突变,从而使与结构相关的强度、运动和风雨分布发生相应变化。目前对台风登陆过程结构演变规律认识不足是台风登陆以后风雨预报失误的一个关键原因。热带气旋是造成海南岛气象灾害最多且最严重的热带天气系统,是海南省防御和抗击自然灾害中最主要的防御对象和防御难点,热带气旋经过海南岛过程的研究对海南省防灾减灾具有重要的现实意义。另外,热带气旋经过岛屿及深入内陆的过程结构变化差异也是值得关注的科学问题。本文首先利用中国气象局整编的《台风年鉴》和《热带气旋年鉴》,分析热带气旋经过海南岛过程中其路径、强度、移速以及对流云系所发生的变化,揭示了一些普遍的演变特征,如热带气旋经过海南岛的平均时间为10小时,热带气旋造成海南岛大风呈东部、南部沿海大而西部内陆小的特征,两种典型的登陆热带气旋降水分布型是:东西多南北少型和南强北弱型。西行路径经过海南岛的热带气旋强对流云系由环流中心向西南偏移,北行路径经过海南岛的热带气旋强对流云系由环流中心南侧向北侧偏移。选取强台风“达维”经过海南岛过程作为典型个例,对其大尺度物理量场的演变进行诊断分析,进而利用中尺度数值模式模拟该热带气旋的过岛过程,分析该过程中其内核结构演变特征。设计地形敏感性试验,分析热带气旋经过海南岛过程中各物理量场对海南岛山脉地形的响应,得出以下主要研究结果:(1)结构对称的强台风经过海南岛时表现为对称结构先破坏到再复原的过程。其中,登陆过程中,边界层靠近陆地一侧风速减小,靠近海洋一侧风速增大,形成风场不对称结构,眼区结构由于低层摩擦加大、入流增强而破坏,环流中心附近的上升气流发生倾斜,次级环流结构破坏;登陆后由陆地到再入海过程中,破坏的不对称结构逐渐复原,低层风场趋于对称,倾斜的上升气流趋于垂直,眼区结构在入海后重新建立。(2)与登陆大陆热带气旋物理量场演变的最大差别是,强台风经过海南岛的过程中,水汽不被切断,反而由于陆地摩擦加大、辐合增强而导致水汽通量辐合增加,水汽垂直输送加强,中低层对流活动在登陆过程经历短暂的衰减,登陆后到再入海过程重新加强。在岛上移动过程中,眼壁上的对流单体易在海南岛南部海岸及山区加强为中尺度雨团。离岛入海后,外螺旋雨带上的对流单体易加强合并为中尺度雨带。(3)强台风登陆海南岛过程以及登陆初期,其内核区的切向风与径向风、凝结加热率同时减小;在岛上移动的后期到再入海过程,其切向风与径向风增大,中低层凝结加热率加大。(4)西行强台风经过海南岛的过程中,形成南强北弱型降水分布的可能机制是:低层中尺度扰动气旋和高层中尺度辐散场在强降水区形成,垂直风切变下风方向左侧的有利于对流发展的区域与降水区对应,以及地形的辐合抬升的共同影响。更多还原

【Abstract】 Land-falling is an important turning point in the life history of a tropical cyclone. Landfall process which subjected to shallow continental shelf and coastal topography may change the TC structure, thus the structure-related intensity, track and precipitation changes. It is a key factor for the wind and precipitation forecast failure after TC landfall that the evolving structure change during the landfall process is lack of understanding.Tropical cyclone is the most severe tropical weather systems caused meteorological disasters in Hainan Island, and it is the most important defense objects and defensive difficulties in Hainan Province. A study on tropical cyclones over the Hainan Island process (TCOHIP) has an important practical significance in disaster prevention and mitigation. In addition, it is also concerned in scientific issue that the structural feature of tropical cyclones when it through a small island differs from land-falling inland.In this paper, the change of track, intensity and moving speed, as well as the convective rain-bands are analyzed when TCOHIP occurs, using the ((Typhoon Yearbook)) and ((Tropical Cyclones Yearbook)) data which are supplied by the China Meteorological Administration (CMA). It has demonstrated that the TCOHIP has some distinctive characteristics, such as the average time is 10 hours in the island activities, Hainan Island wind which caused by tropical cyclones shows the eastern and southern coast stronger, while the western inland weaker, resulting in two kinds of typical rainfall distribution patterns, that is the west and the east strong while the south and the north weak type and the north weak and south strong type. TO a westwards TC, the deep convective rain-bands moves from the center to the southwest quadran of the TC circulation through TCOHIP. To a northwards TC, it moves from the centre to the northern quadrant.Take strong typhoon Damrey (0518) as an example, as it has a typical TCOHIP stage concerned in this paper, its physical field changes in large-scale are diagnosed, and the meso-scale numerical model is applied to simulate the tropical cyclone landfall process, furthermore, terrain sensitivity experiments are designed to analyze the TCOHIP. The results indicate:(1) The symmetric structure shows damage to recovery when a symmetric strong typhoon through a TCOHIP. To the land-falling process, the wind speed near the land side of the boundary layer decreases, while near the ocean side increases, thus results in asymmetric wind field, the eye area and inner eye-wall destruct for the inflow wind. The upward current tilts to the land side, the secondary circulation destroyed. To the TC moving to the sea process, the asymmetric structure recovering, wind field tends to symmetry, the tilting upward current toward vertical, the eye-wall re-established in the sea.(2) Contrasting to land-falling China’s mainland, the biggest difference is the water vapor will not be cut off when TCOHIP occurs, thus may cause water vapor flux convergence increases due to the impact of land surface friction, results in the vertical water vapor transport enhances, the convective activities in lower troposphere exhibits a short-term decay process during land-falling, but it will be re-strengthened after landing, as well as into the sea. When the strong typhoon moves on the island, eye wall convection intensifies into meso-scale rain cluster easily on Hainan Island’s southern coast and mountain region, when it leaving Islands and into the sea, the spiral rain belt convective cells easily develop into meso-scale rain bands.(3) When a strong typhoon landfalls Hainan Island, the tangential wind, the radial wind and condensation heating rate decrease in the inner-core zone. When it leaves Hainan Island and moves into the sea, the tangential wind and the radial wind increase, and the condensation heating rate of the lower-middle troposphere increases as well.(4) A possible mechanism of the north weak and south strong precipitation type may include low-level cyclonic disturbances and high-level meso-scale divergence formatted in the rain area, the down shear left region which favorites to the development of convection has good consistency with the precipitation areas, and the uplift and convergence which caused by topography in central and southern Hainan Island contribute to convection intensitification.更多还原