Analysis and Observations of Particle Size Distribution in Supercell Thunderstorms

超级单体型雷暴，包含了长时间旋转的上升气流和强烈的下降气流的复杂排列，被认为是产生最强烈龙卷风的原因。然而，在风暴尺度旋转以破坏性龙卷风涡旋形式的实际焦点和向下延伸的机制方面，存在相当大的不确定性。一些工作假设将这一过程与这些风暴最底层的下降气流的强度、热力学稳定性（温度）和空间结构联系起来，而这些下降气流又依赖于受下降的水成物（主要是雨和冰雹）的类型和大小分布影响的蒸发冷却速率。目前还没有严谨的尝试来研究超级单体雷暴下这些微物理降水特征的范围。该项目的总体目标是i)在第二次龙卷风旋转起源验证实验（VORTEX2）期间在超级单体雷暴下部署多个移动disdrometer（测量降水颗粒特征大小和下降速度的仪器）；（一项在美国中部被称为“龙卷风走廊”的野外项目），ii)对现有和新获得的disdrometer观测数据进行全面分析，以确定与非龙卷风超级单体雷暴相比，龙卷风超级单体雷暴的微物理特征，iii)将这些结果与同期高分辨率极化多普勒雷达观测结果联系起来。分差仪和极化多普勒雷达都可以探测（或在雷达的情况下，推断）下降的水成物的大小分布。虽然初步的分析已经提供了一些关于水成物分布及其对超级单体风暴特征演变的影响的见解，但使用位置良好的高分辨率测量对许多案例进行全面分析尚未进行，并将在此工作过程中实现。智力价值：该项目将增加我们对超级单体雷暴内部微物理过程的了解，并可能改进对危及生命的恶劣天气的短期预报和预警。由于VORTEX2拥有数量最多的极化多普勒雷达，可以监测超级细胞雷暴的整个生命周期，因此这个实验是解决这些科学问题的理想实验室。目前，缺乏预测和理解微物理过程的技能主要是由于微物理过程的不充分代表和缺乏测量。在VORTEX2上移动部署的晴雨表将提供迄今为止收集到的最全面的晴雨表和雷达观测数据集，并对超级单体雷暴进行分析。更广泛的影响：恶劣天气短期预报和预警的改进与微物理过程的表现和理解密切相关，这将通过本工作大大扩展。结果将与建模社区共享，并与其他现有的VORTEX2数据集集成。研究结果还将通过在会议、研讨会和讲习班上的发言以及在有关专业期刊上的出版物来传播。研究生直接参与实地数据集的收集和分析，以及加强本科生和研究生的课堂教育，将产生更广泛的影响。

Supercell-type thunderstorms, which embody a complex arrangement of long-lasting rotating updrafts and intense downdrafts, are known to be responsible for generating most intense tornadoes. However, considerable uncertainty exists regarding mechanisms culminating in the actual focus and downward extension of stormscale rotation in the form of a damaging tornadic vortex. Some working hypotheses link this process to the strength, thermodynamic stability (temperature) and spatial configuration of downdrafts in the lowest reaches of these storms, which are in-turn dependent on rates of evaporative cooling influenced by the type and size distributions of falling hydrometeors (chiefly rain and hail.) Rigorous attempts have not yet been made to investigate the range of these microphysical precipitation characteristics beneath supercell thunderstorms. The overarching goal of this project is to i) deploy multiple mobile disdrometers (instruments that measure the characteristic sizes and fallspeeds of precipitation particles) beneath supercell thunderstorms during the second Verification of the Origins of Rotation in Tornadoes EXperiment (VORTEX2; a field program conducted over the central United States known as "tornado alley") in Spring 2010, ii) conduct a comprehensive analysis of both existing and newly-obtained disdrometer observations to determine microphysical characteristics in tornadic compared to nontornadic supercell thunderstorms, and iii) relate these results to contemporaneous high-resolution polarimetric Doppler radar observations. Both disdrometers and polarimetric Doppler radar can detect (or in the case of radar, infer) the size distributions of falling hydrometeors. While preliminary analyses have provided some insights about hydrometeor distributions and their impacts on evolution of supercell storm features, a comprehensive analysis of a number of cases using well-placed high-resolution measurements has yet to be conducted and will be achieved in the course of this work.Intellectual Merit: This project will augment our knowledge about microphysical processes within supercell thunderstorms and may lead to improved short-term forecasts and warnings of life-threatening severe weather. Since VORTEX2 hosts the largest number of polarimetric Doppler radars to ever monitor the full lifecycle of supercell thunderstorms, this experiment is an ideal laboratory to address these scientific questions. At present, the lack of skill in forecasting and understanding microphysical processes is largely due to both the inadequate representation of microphysical processes and the lack of measurements. This mobile deployment of disdrometers in VORTEX2 will provide by far the most comprehensive dataset of disdrometer and radar observations and analysis in supercell thunderstorms ever collected. Broader Impact: The improvement of short-term forecasts and warnings of severe weather is strongly linked to the representation and understanding of the microphysical processes, which will be substantially extended by this work. Results will be shared with the modeling community and integrated with other, existing VORTEX2 data sets. Results will also be disseminated through presentations at conferences, seminars, and workshops as well as through publications in relevant professional journals. Additional Broader Impacts will come through direct involvement of graduate students in collection and analysis of field datasets, as well as through enhanced classroom education at both undergraduate and graduate levels.