Bow Echoes and Mesoscale Gravity Waves - The Role of Microphysical Processes

长寿命的中尺度对流系统（mcs）产生了美国中部暖季降雨的很大一部分，并经常产生严重的直线风和龙卷风。2003年春末夏初在美国中部进行的弓形回波和中尺度对流涡实验（BAMEX）研究了弓形回波、强风暴、龙卷风和中尺度涡的形成过程，这些过程通常是MCS环流的一部分。本研究的总体目标是对MCS内产生的下沉气流的时空尺度、气源、动力和热力学强迫提供定量的理解，并将下沉气流环流与MCS中强烈的地面风和中尺度重力波（飑线发生在深稳定层之上）联系起来。该研究包括对机载双多普勒和四多普勒雷达的分析，使用激光光学阵列探头在MCS尾部层状区域收集的微物理数据，在整个MCS系统中采集的下投探空数据，以及WSR-88D多普勒雷达数据，以及使用天气研究和预报模型进行数值模拟研究。具体目标包括：1)利用BAMEX分析表征暖季MCS尾层区微物理结构，进一步了解微物理过程在MCS演化中的作用；2)确定强地面风在多大程度上是对流后缘附近强烈蒸发冷却产生的下暴环流的表现，或在多大程度上是后方入流射流内的高动量空气斜降至地表的表现；3)利用数值模拟研究来了解中尺度和对流下降气流以及上升和下降的后方流入射流的形成、结构和演化的动力学和微物理贡献；4)完成正在进行的中尺度重力波产生的理想化数值模拟研究，以验证在高空飑线环境中产生中尺度重力波的过程与MCSs中产生尾流低的过程在动力上相似的假设。这项研究的知识价值来自于它将提供关于恶劣天气现象的新认识，包括弓形回波、下爆和中尺度重力波。该研究旨在为这些现象中云微物理过程与风暴动力学之间的相互作用建立新的联系和清晰的认识。BAMEX的新方法和独特测量将为中尺度对流系统提供基本的新科学认识。这项研究可能会带来新的发现，因为在过去被调查的过程很少被观察到，而在BAMEX的mcs中进行的专门观察确实是独一无二的。这项研究的广泛影响是实质性的。对地面强风产生的观测分析和建模将有助于改进业务天气预报和临近预报技术、预警提前时间和对恶劣天气系统的了解。对mcs相关的基础物理学的理解将从这项研究中获得，这可能会导致对mcs相关的高影响天气、弓回波和强风暴的预测得到改进，对美国天气研究计划的目标做出重大贡献。伊利诺伊大学至少有四名研究生将在即将进行的研究中发挥重要作用。此外，BAMEX数据将被纳入《中尺度气象学》、《雷达气象学》、《降水物理》等课程，以及《恶劣和异常天气》等调查课程，以及普通教育教材《恶劣和危险天气》第2版。调查结果将通过会议和专题讨论会传达给研究界和业务界。

Long-lived mesoscale convective systems (MCSs) generate a significant fraction of the warm season rainfall in the central United States and frequently produce severe straight-line winds and tornadoes. The Bow Echo and Mesoscale Convective Vortex Experiment (BAMEX), conducted over the central United States in the late spring and early summer of 2003, investigated the processes leading to the formation of bow echoes, severe windstorms, tornadoes, and mesoscale vortices that are often part of MCS circulations. The overarching goal of this research is to provide a quantitative understanding of the temporal and spatial scales, source air, and dynamic and thermodynamic forcing for downdrafts generated within MCSs and to relate the downdraft circulations to severe surface winds in the case of the MCS and mesoscale gravity waves in the case where squall lines occur above a deep stable layer. The research involves analysis of airborne dual and quad Doppler radar, microphysical data collected in the trailing stratiform region of MCSs using laser optical array probes, dropsonde data taken throughout MCS systems, and WSR-88D Doppler radar data, as well as numerical modeling studies using the Weather Research and Forecasting model.Specific objectives include: 1) characterize the microphysical structure of the trailing stratiform region of warm season MCSs using BAMEX analyses to further understanding of the roles of microphysical processes in MCS evolution; 2) determine the degree to which severe surface winds are a manifestation of downburst circulations generated by intense evaporative cooling near the trailing edge of convection, or a manifestation of high momentum air within the rear inflow jet descending slantwise to the earth's surface; 3) use numerical modeling studies to understand the dynamical vs. microphysical contributions to the formation, structure and evolution of mesoscale and convective downdrafts and elevated and descending rear inflow jets; and 4) complete ongoing idealized numerical modeling studies of mesoscale gravity wave generation to test the hypothesis that the processes that create mesoscale gravity waves in elevated squall line environments are dynamically similar to processes creating wake lows in MCSs.The intellectual merit of this research derives from the new understanding it will provide concerning severe weather phenomena including bow echoes, downbursts, and mesoscale gravity waves. The research is designed to develop a new link and clear understanding of the interaction between cloud microphysical processes and storm dynamics in these phenomena. The novel approaches and unique measurements from BAMEX will provide basic new scientific understanding of mesoscale convective systems. The research likely will lead to new discoveries, since the processes to be investigated have been poorly observed in the past and the specialized observations taken in MCSs in BAMEX are truly unique.The broader impacts of this research are substantial. Observational analyses and modeling of the generation of strong surface winds will contribute to improvements in operational weather forecasting and nowcasting techniques, warning lead times, and understanding of severe weather systems. The understanding of the fundamental physics associated with MCSs that will result from this research may lead to improved prediction of the high-impact weather associated with MCSs, bow echoes and severe windstorms, contributing substantially to the goals of the U.S. Weather Research Program. At least four graduate students at the University of Illinois will have a significant role in the research to be performed. Furthermore, BAMEX data will be incorporated into courses including Mesoscale Meteorology, Radar Meteorology, and Precipitation Physics, survey courses such as Severe and Unusual Weather, and the 2nd edition of a general education textbook Severe and Hazardous Weather. Findings will be communicated to the research and operational communities through meetings and symposia.