Analysis and Observations of Particle Size Distribution in Supercell Thunderstorms

超级单体类型的雷暴体现了一种复杂的长时间旋转上升气流和强烈下降气流的排列，众所周知，它是产生最强烈龙卷风的原因。然而，对于以破坏性龙卷风涡旋的形式导致风暴尺度旋转的实际焦点和向下延伸的机制，仍然存在相当大的不确定性。一些工作假说将这一过程与风暴最低处下沉气流的强度、热力学稳定性(温度)和空间构型联系在一起，而这些下沉气流的强度、热力学稳定性(温度)和空间构型又取决于蒸发冷却的速度，而蒸发冷却速度又受到下落的水流星(主要是雨和冰雹)的类型和大小分布的影响。目前还没有对超级单体雷暴下这些微物理降水特征的范围进行严格的调查。这个项目的总体目标是：i)在2010年春季的第二次龙卷风旋转起源核查实验(VORTEX2；在美国中部实施的称为“龙卷风巷”的实地计划)期间，在超级单体雷暴之下安装多个移动碟仪(测量降水粒子的特征尺寸和下落速度的仪器)，ii)对现有和新获得的碟仪观测进行全面分析，以确定龙卷风与非龙卷风超级单体雷暴的微物理特征，以及iii)将这些结果与同期的高分辨率极化多普勒雷达观测联系起来。碟度计和偏振多普勒雷达都可以探测(或在雷达的情况下，推断)落下的水流星的尺寸分布。虽然初步分析已经提供了一些关于水流星分布及其对超级单体风暴特征演变的影响的见解，但使用适当的高分辨率测量对一些案例进行的全面分析还没有进行，并将在这项工作的过程中实现。智力上的好处：这个项目将增加我们对超级单体雷暴内微物理过程的了解，并可能导致对危及生命的恶劣天气的短期预报和警告的改进。由于VORTEX2拥有有史以来最多的极化多普勒雷达来监测超级单体雷暴的整个生命周期，所以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，这在很大程度上是由于对微物理过程的描述不充分，也缺乏测量。在VORTEX2中移动部署磁盘仪将提供迄今为止收集到的关于超级单体雷暴中的磁盘仪和雷达观测和分析的最全面的数据集。更广泛的影响：恶劣天气的短期预报和警告的改进与微物理过程的表现和理解密切相关，这项工作将大大扩展这一过程。结果将与建模社区共享，并与其他现有的VORTEX2数据集集成。成果还将通过在会议、研讨会和讲习班上的陈述以及相关专业期刊上的出版物来传播。其他更广泛的影响将来自研究生直接参与实地数据集的收集和分析，以及通过加强本科生和研究生的课堂教育。

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.