Mesoscale Studies of Convection, Tornadogenesis, and Fronts

9801720 Wakimoto首席研究员将从事与严重的本地风暴和中尺度锋面结构相关的三个研究课题：1）龙卷风和龙卷风发生，2）弓形回波飑线和飑线启动的结构，以及3）暖锋面和冷锋边界的中尺度文件。 基于数值模拟和观测研究，对超级单体风暴中中层中气旋的认识取得了重大进展。 然而，关于龙卷风的成因和动力学的知识并没有迅速发展。 这可以部分归因于在这些强涡流附近收集高分辨率数据的困难。 利用在雷暴实验中旋转起源验证期间收集的独特数据集，首席研究员将继续研究三个突出的问题，这些问题仍然是相当多的龙卷风和龙卷风发生研究的焦点：I）导致超级单体龙卷风发生的过程是什么？2)中气旋与龙卷风有什么关系？3)超级单体龙卷风是从云底下降还是从边界层向上形成？目前正在分析一场没有产生龙卷风的强烈超级单体风暴。 初步结果表明，一个定义明确的低层中气旋发展了几次，但没有导致龙卷风的开始。 目前正在合成超级单体机载多普勒雷达的25次经过。 一个有待检验的假设是，中气旋内的涡旋破裂导致了弱龙卷风的发展。 目前正在进行两项单独的研究，重点是飑线。 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derechos有关。目前的情况下，提供了一个机会，检查整个演变的回声从线性结构的弓形。 第二项研究探讨了一个强烈的飑线之间的合并，一个强大的冷锋和干线的结果开始。虽然后一个事件是已知的一个共同的启动机制的发展，飑线，似乎没有一项研究，提供了详细的测量这一过程，在1997年冬季，一个国际现场实验称为FASTEX（锋和大西洋风暴轨迹实验）组织研究海洋气旋。 主要的数据平台是几架研究飞机，它们释放下投式风测仪，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。初步的雷达合成显示了前所未有的冷锋和暖锋的运动结构。建议利用FASTEX资料集结合多普勒风场和部署在高空的许多投下式探空仪来检查沿锋面结构和评估锋生。这项研究的成功完成将大大增加对强局地对流风暴的认识和对冬季锋面结构的中尺度方面的认识。

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.***