【作者】 梁科；

【导师】 梁建茵； 万齐林；

【作者基本信息】 中国气象科学研究院 ， 气象学， 2007， 硕士

【摘要】 暴雨是华南汛期晕要的天气系统,研究暴雨发生发展的多尺度相互作用和结构等,可以揭示华南暴雨的动力机制和物理机理,提高对华南暴雨的认识和预报能力。文章利用NCEP再分析资料、常规观测资料、云图资料和逐时降水资料等,通过物理诊断方法、尺度分离、数值模拟等方法,对0506华南致灾暴雨过程中的各种尺度的影响系统的相互作用和大气环流结构等进行了研究。2005年6月华南出现了一次强降水过程,其持续时间长,影响范围广,造成了珠江流域的洪灾,研究此次降水的影响系统将对华南暴雨的科研与预报工作有重要意义。本文针对过程的降水特征、环流变化、锋面结构等作了实况分析;使用滤波方法对风场进行了尺度分离;并利用模拟结果,对锋面的要素变化做简要讨论,重点研究了低层风场日变化与实际云团变化和降水发展的关系;通过对比试验分析了季风及水汽在降水过程中产生的作用。通过这些工作研究造成降水的各尺度的主要影响系统,认识它们之间的相互作用关系,得出以下的主要结论:1)分析实况资料,发现降水具有特殊分布、锋面结构具有异常性,并提出本次过程的天气系统的配置模型。本次过程出现两条丰要雨带,降水具有明显的日变化性质,且在一些时段,雨带出现北抬现象。过程由多个尺度的系统影响,在有利的季风环流、行星尺度背景的条件下,静止锋在华南地区维持,中尺度系统不断发展移动并直接造成华南地区的持续强降水。本次过程的锋面结构与典型梅雨锋锋面结构有相似之处,但也存在有许多不同,丰要表现为近地层锋面不明,砂,冷窄气以中层入侵为主,锋面不接地。该过程的天气系统的配置模型是,过程由多个尺度的系统影响,在活跃的西南夏季风、有利的中高纬行星尺度大气环流背景的条件下,准静止锋在华南地区维持和摆动,中尺度系统不断在华南地区发展移动并直接造成华南地区的持续强降水。行星尺度天气系统的变动,是引发整个降水过程结束的重要原因。2)对风场进行尺度分离并分析得到的各尺度系统发现,不同的雨区,影响系统的尺度不同:风场的天气尺度系统在低层表现为切变线,它的移动位置与雨带相同,并且北抬时间与锋面雨带北抬时间一致,尺度约为3000km左右;波长为1000km波动主要表现为低涡,它们沿着切变线的位置东移,与锋面雨带中的强对流雨团有关;波长为400km左右的波动的维持和发展,与锋前暖区对流降水对应,对19-21日广东暖区降水起着关键的作用。3)数值模拟结果表明,过程中华南地区气流的同变化,与一般的海陆风变化有差异,这也是本次暖区降水的日变化有别于华南一般出现的夜雨现象的l丰要原因。华南地区的近地层风场的日变化,反映了由于日夜温度分布不均匀引起的气流的变化。由丁辐射等原因,降水期间地面温度差异与晴空时的海陆热力分布有很大不同,因此引起近地层风的日变化与一般海陆风的风向不同。在平均风场的背景下,近地层风出现明显日变化,造成近地层风场的局地性辐合,触发了锋前不稳定的暖区内强降水的产生及日变化。4)通过季风强度对比试验和水汽输送强度对比试验,发现季风的强度对降水的落区有影响,水汽则对垂直运动和降水有正反馈作用。季风的强度影响了辐合场的位置,为降水提供了充分的动力条件,还输送了源源不断的暖湿气流,补充降水需要的大部分水汽。综合以上各点,各尺度天气系统的相互作用,是整个雨带形成且维持在华南的主要原因,因此,提出关于各尺度系统对降水的共同作用如下:行星尺度的季风北进到华南,副高在华南以南地区维持,西风带上低槽东移速度减慢,加上高层南业高压的盘踞,华南地区形成了有利于天气系统发展的背景。在这一背景下,干空气从中层南下,与强大暖空气相对,形成低层切变线,并造成锋面附近的上升运动。由于切变线的存在,低层风场极易产生低涡,低涡沿着切变线东移,是锋面上对流强降水的直接因素。雨带的北抬,是由于切变线的北抬以及低涡沿着切变线东北移动而造成的。由于温度的日变化,导致低层风场出现日变化。日变化叠加在平均风场上,形成中尺度波动,在处于位势不稳定的锋前暖区,触发强对流上升运动,造成暖区暴雨。以往的华南暴雨研究工作中,局限于研究单个尺度系统或孤立地研究不同尺度系统,缺乏深入研究引起华南暴雨的不同尺度系统之间的相互作用及相互关系。本文通过数值模拟以及尺度分离等新方法,系统地开展影响华南暴雨的多尺度系统的相互作用和相互关系的研究。该工作能够较好的补充了以往研究中的不足,为今后华南暴雨的研究提供新思路和研究方向。更重要的是,本文的一些新方法和新结论如降水分布的特殊性、影响雨团系统的尺度多样性、低层风场日变化对降水日变化的引导作用等,对探索华南暴雨的动力机制和物理机理有重要的科学意义。更多还原

【Abstract】 The rainstorm is an important synoptic system during flood season at South of China, the research of the interactions and their structures of multiple scale systems can post the dynamical and physical mechanism which triggers and maintains the rainstorm, and improve the understanding and forecasting of the rainstorm at South of China. Using NCEP reanalysis data, routine observation, cloud images and hourly precipitation observation, this paper investigates the multi-scale interactions and their structures of the rainstorm on June 2005 at South of China by analyzing, scale separation and numerical simulation.The rainstorm on June 2005 over southern China is an intensive rainfall which maintained a long time, influenced extensive area and caused the flood of Zhujiang River. The investigation of this rainstorm has significant meaning on the research, forecast and disaster mitigation of rainstorm over South of China.First, this paper analyzes the rainfall characteristic, the change of circulation and the structure of front using observation data. Then, this paper separates and analyzes different scale component of the wind of NCEP reanalysis data by filter. Finally, the paper briefly discusses the change of the element in the front, and focuses on the relationship among the daily change of the low-level wind, the change of cloud and the development of the rainfall. The contrastive experiments of the strength of the monsoon and the transportation of vapor show that the monsoon and vapor play a key role during the process to maintain and strengthen the rainfall. This paper investigates multi-scale major influent systems and their interaction which caused the rainstorm, and draws the following major conclusion:1) The analysis of the observation shows the especial distribution characteristic of the rainfall, the abnormity of the front structure, and proposes a conceptual model of the configuration of the systems in the process. The especial characteristic of the rainfall is that the rainfall has two major zones, possesses apparent diurnal variation and the zones would move northward. The abnormity of the front structure shows that the structure is similar to the structure of the Meiyu front, but possesses many differences: the front near ground is not apparent, and the cold air invades from middle level primarily. The configuration of the systems is that the process was impact by many different scale systems, in the favorable monsoon and planetary-scale circumstance, the stationary front maintained at South of China and the meso-scale system continually evolved and resulted in the long time heavy rainfall.2) The analysis of the different scale systems derived from the scale separation of the wind by filter finds that the scale of the impact system on the different rainfall zone is distinct. In synoptic scale, the low-level wind is shear wind and its spatial and temporal moving is consistent with that of rainfall. In meso scale, the low vortex is the wave whose scale is about 1000km, and moves along the line of wind shear and connects with the strong convective precipitation in the front. In small scale, the maintain and development of the wave whose scale is about 400km are corresponding to the convective precipitation in the warm region ahead the front and have significant impact on the rainfall in warm region.3) The numerical simulation indicates the difference between diurnal variation of the flow at South of China and the diurnal change of the circulation of the sea-land wind is the primary reason of the difference between the diurnal variation of the rainfall during this process and that of the nightly rainfall. The diurnal variation of the low-level wind at South of China reflects the change of the flow due to the diurnal uneven distribution of the temperature. The variation caused the local convergence in the near ground wind, which trigger the generation of strong rainfall in the instable warn region ahead the front.4) The contrastive experiments of the strength of the monsoon and the transportation of vapor show that the strength of the monsoon impacts on the location of the rainfall, and the strength of the water vapor posts positive feedback on the vertical movement and rainfall. The strength of the monsoon has impact on the location of the convergence which is the sufficient dynamical condition for rainfall, and transports lasted warm wet water vapor to supply the water vapor needed by rainfall.In summary, the interaction of different scale systems is the key reason for the whole rainfall zone generated and maintained at South of China. The South Asia high in high-level and prevention of the eastern moving of the trough in zonal wind by the arrival of the monsoon and the abnormal western and southern location of the subtropical anticyclone form the favorable background for the development of different scale systems. Under this circumstance, the cold air move to south from middle-level and joint the strong warm wet water vapor from south, then form the shear in low-level and generate the ascend movement near the front. Due to the shear in low-level, the low vortex will arise from the shear wind and move eastern alone the line of the wind shear. This is the direct factor induce the convective strong precipitation in the front. The moving northern of the rainfall zone is the contribution of the moving northern of the shear line and the moving eastern of the low vortex along the shear line. Due to the diurnal variation of the temperature, the diurnal variation of the low-level wind merges into the mean wind to form the meso-scale systems which triggers the strong convection and heavy rainfall in the warm region ahead the front where the potential instability accumulated.The research on the rainstorm at South of China in the past was limited by investigating single scale system or investigating isolated the different scale systems, and lacked of systematic research on the interaction and interrelationship among different scale systems which caused the rainstorm at South of China. By numerical simulation and scale separation, this paper systematically investigates the interaction and interrelationship among different scale systems which caused the rainstorm. This work makes a considerable supplement to the deficiency of the research in the past, and gives a guideline to the further research. The most important point is the new methods and the new conclusion such as the especial characteristic of the rainfall, the diversity of the scale of the influent systems, and the diurnal variations of the low-level wind to the diurnal variation of the precipitation have significant scientific meaning to the exploration for the dynamical and physical mechanism of the rainstorm at South of China.更多还原