Mesoscale Studies of Convection, Tornadogenesis, and Fronts

对流、龙卷发生和锋面的中尺度研究

• 批准号: 9801720
• 负责人: Roger Wakimoto
• 金额: $ 49.34万
• 依托单位: University of California-Los Angeles
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1998
• 资助国家: 美国
• 起止时间: 1998-11-15 至 2002-10-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9801720&HistoricalAwards=false
• 关键词: Mesoscale; Studies; Convection; Tornadogenesis; Fronts

9801720Wakimoto The Principal Investigator will pursue three research topics associated with severe local storms and mesoscale frontal structures: 1) tornadoes and tornadogenesis, 2) structure of bow-echo squall lines and squall-line initiation, and 3) mesoscale documentation of warm and cold frontal boundaries. There have been major advances in understanding of mid-level mesocyclones within supercell storms based on numerical simulations and observational studies. However, knowl-edge concerning the genesis and dynamics of tornadoes has not progressed as rapidly. This can be, in part, attributed to the difficulty of collecting high resolution data in the vicinity of these intense vortices. Using unique data-sets collected during the Verification of Origins of Rotation in Thunderstorm Experiment, the Principal Investigator will pursue three outstanding questions that remain the focus of a considerable amount of research on tornadoes and tornadogenesis: I) What are the processes that lead to supercell tornadogenesis? 2) What is the relationship between the mesocyclone and the tornado? 3) Do supercell tornadoes descend from cloud base or build upward from the boundary layer?An analysis of an intense supercell storm which did not spawn a tornado is currently underway. Preliminary results suggest that a well-defined low-level mesocyclone developed on several occasions but did not lead to the initiation of a tornado. Twenty-five passes of an airborne Doppler radar by the supercell are currently being synthesized. A hypothesis to be tested is that vortex breakdown within the mesocyclone led to the development of an weak tornado. Two separate studies focusing on squall lines are currently underway. First, a comprehensive data set on the structure of a bow echo is in the early stages of analysis. The bow echo is a radar signature that is often associated with downbursts and derechos. The present case provides an opportunity to examine the entire evolution of this echo from a linear structure to a bow-shaped. A second study examines the initiation of an intense squall line as a result of the merger between a strong cold front and the dryline. Although the latter event is known to be a common initiation mechanism for the development of squall lines, there does not appear to be a study that has provided detailed measurements of this process.During the winter of 1997, an international field experiment called FASTEX (Fronts and Atlantic Storm Track Experiment) was organized to study oceanic cyclogenesis. The primary data platforms were several research aircraft which released dropwindsondes, recorded in situ measure-ments at flight level, and collected high-resolution radar reflectivity and Doppler velocity informa-tion using on-board radars. Preliminary radar syntheses have revealed unprecedented kinematic structure of cold and warm fronts. Examination of the along-frontal structure and an assessment of frontogenesis using a combination of the Doppler wind field combined with numerous dropsondes deployed at high altitudes are proposed using the FASTEX data set.Successful completion of this research will add substantially to knowledge of severe local convective storms and to the mesoscale aspects of winter-time frontal structures.***

9801720Wakimoto 首席研究员将开展与严重局地风暴和中尺度锋面结构相关的三个研究课题：1）龙卷风和龙卷风形成，2）弓回波飑线结构和飑线启动，以及3）暖锋和冷锋的中尺度记录边界。 基于数值模拟和观测研究，对超级单体风暴中的中级中气旋的理解取得了重大进展。 然而，关于龙卷风的起源和动力学的知识并没有进展得那么快。 这在一定程度上可以归因于在这些强烈涡流附近收集高分辨率数据的困难。 首席研究员将使用在雷暴实验中旋转起源验证过程中收集的独特数据集来解决三个悬而未决的问题，这些问题仍然是大量龙卷风和龙卷风发生研究的焦点：I) 导致超级单体的过程是什么龙卷风发生？ 2）中气旋和龙卷风之间有什么关系？ 3) 超级单体龙卷风是从云底下降还是从边界层向上形成？目前正在对未产生龙卷风的强烈超级单体风暴进行分析。 初步结果表明，明确的低级中气旋曾多次形成，但并未导致龙卷风的形成。 目前正在合成超级单元对机载多普勒雷达的二十五次通过。 需要检验的假设是中气旋内的涡流破裂导致了弱龙卷风的发展。 目前正在进行两项针对飑线的独立研究。 首先，关于弓形回波结构的综合数据集正处于分析的早期阶段。弓形回波是一种雷达特征，通常与下击暴流和反雷回波相关。本案例提供了一个机会来研究这种回声从线性结构到弓形结构的整个演变过程。 第二项研究探讨了由于强冷锋和干线合并而引发的强烈飑线。尽管已知后一事件是飑线发展的常见启动机制，但似乎没有一项研究提供了该过程的详细测量。 1997 年冬季，一项名为 FASTEX（锋线）的国际现场实验和大西洋风暴轨迹实验）的组织目的是研究海洋气旋发生。 主要数据平台是几架研究飞机，它们释放落风探空仪，记录飞行高度的现场测量结果，并使用机载雷达收集高分辨率雷达反射率和多普勒速度信息。初步雷达合成揭示了冷锋和暖锋前所未有的运动结构。建议使用 FASTEX 数据集，结合多普勒风场与部署在高空的大量下投式探空仪来检查沿锋面结构并评估锋生。这项研究的成功完成将大大增加对强局地对流的了解风暴和冬季锋面结构的中尺度方面。***