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

长寿命中尺度对流系统(MCSs)产生了美国中部暖季降雨量的很大一部分，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旋试验(BAMEX)研究了导致弓形回波、强风暴、龙卷风和中尺度涡旋形成的过程，这些过程通常是MCS环流的一部分。这项研究的主要目的是提供对MCSs内产生的下沉气流的时间和空间尺度、源空气、动力和热力学强迫的定量了解，并将下沉气流环流与MCS情况下的强烈地面风和发生在深层稳定层上方的中尺度重力波联系起来。研究内容包括：1)利用BAMEX分析暖季MCS拖尾层状区的微物理结构，包括机载双、四多普勒雷达资料、激光阵列探测仪收集的MCS拖尾层状区的微物理资料、整个MCS系统中的滴落探空仪资料和WSR-88D多普勒雷达资料，以及利用天气研究和预报模式进行数值模拟研究。2)确定强地面风在多大程度上是对流尾缘附近的强烈蒸发冷却产生的下击暴流环流的表现，或者是后方入射急流中的高动量空气倾斜下降到地表的表现；3)利用数值模拟研究了解动力与微物理对中尺度对流下沉气流和上升和下降的后方入射急流的形成、结构和演变的贡献；和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，以检验这样的假设，即在高空锋线环境中产生中尺度重力波的过程与在MCS中产生尾迹低的过程动态相似。这项研究的智力价值来自于它将对包括弓形回波、下击暴流和中尺度重力波在内的恶劣天气现象提供新的理解。这项研究旨在为这些现象中云微物理过程和风暴动力学之间的相互作用建立一个新的联系和清晰的理解。BAMEX的新方法和独特的测量将提供对中尺度对流系统的基本的新的科学理解。这项研究可能会带来新的发现，因为过去对要调查的过程的观察很少，而且在BAMEX的MCS中进行的专门观察确实是独一无二的。这项研究的更广泛的影响是巨大的。对强地面风产生的观测分析和模拟将有助于改进业务天气预报和近距离预报技术、预警提前时间和对恶劣天气系统的了解。这项研究将导致对与MCSs相关的基本物理的理解，这可能会改进与MCSs、弓形回波和严重风暴相关的高影响天气的预测，从而为美国天气研究计划的目标做出重大贡献。至少有四名伊利诺伊大学的研究生将在即将进行的研究中发挥重要作用。此外，BAMEX数据将被纳入课程，包括中尺度气象学、雷达气象学和降水物理，调查课程，如严重和异常天气，以及通识教材第二版的严重和危险天气。研究结果将通过会议和座谈会传达给研究和运营界。

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.