AGS-PRF: Impacts of Microphysics and Cold Pool Thermodynamics on Supercell Tornadogenesis: Comparisons of Numerical Simulations with VORTEX2 Observations

猛烈而短暂的龙卷风仍然是大气科学中最具挑战性的研究课题之一。龙卷风的形成、维持、增强和衰减机制都是人们仍然知之甚少的特征。这些问题都是最近在2009年和2010年春季在美国大平原进行的VORTEX2（以下简称V2）实地活动的主要动机。在整个项目期间，获得了许多龙卷风和非龙卷风超级单体的前所未有的数据，其中包括丰富的移动雷达数据、高密度的原位地面观测和近距离探测。在这个项目的背景下，对被调查风暴冷池中地表温度和湿度的现场观测，以及水滴大小分布（DSDs）的disdrometer观测与极化雷达数据相结合，是主要的兴趣。过去十年的研究表明，龙卷风的形成、强度和寿命受到相关风暴冷池的热力学性质的强烈影响。特别是，当冷池中的地表温度和水分不足（相对于一个合适的未受干扰的近风暴环境）相对较小时，龙卷风更有可能形成、持续和加强。本研究旨在通过理想化的数值模拟方法来探讨这种经验相关性的因果机制。这项工作将利用V2现场项目中的几个不同案例来帮助初始化和验证模型模拟。因此，它将对由V2情况生成的相当大的参数空间进行采样。智力优势：本研究将通过以下途径为超级单体冷池与龙卷风活动之间的关系提供新的见解：1)利用复杂的微物理参数化软件包了解冷池热力学对水加载、蒸发和融化等微物理过程的敏感性，以及V2提供的案例谱上的方差；2)评估冷池热力学性质的变化对龙卷风的影响，并提高对这种联系的物理认识；3)通过与差测仪和极化雷达数据的对比验证微物理参数化。更广泛的影响：这项研究的结果有望提高我们对超级单体风暴特征的理解能力，这些特征最有可能产生重大龙卷风，因此它将对每年受到龙卷风威胁或影响的数百万美国公民的生活产生直接影响。微物理过程的模型表示与V2提供的丰富的极化雷达和分差仪数据集之间的比较将有助于确定改进这些参数化的途径，从而对强对流降水和相关的洪水和冰雹损害风险的预测具有直接意义。

The violent and ephemeral tornado remains one of the most challenging subjects of study in the atmospheric sciences. Tornadogenesis, maintenance, intensification and decay mechanisms are all characteristics that are still poorly understood. Each of these issues were primary motivations for the recent VORTEX2 (hereafter, V2) field campaign that took place during the Spring of 2009 and 2010 in the Great Plains of the United States. Unprecedented data on many tornadic and nontornadic supercells were acquired over the length of the project, which included rich mobile radar data, high density in situ surface observations, and proximity soundings. Within the context of this project, the surface in situ observations of surface temperature and moisture in the cold pools of the surveyed storms, as well as disdrometer observations of dropsize distributions (DSDs) coupled with polarimetric radar data, are of primary interest.Research over the past decade has indicated a clear empirical signal for tornadogenesis, intensity, and longevity to be strongly influenced by the thermodynamic properties of the associated storm cold pool. In particular, tornadoes are more likely to form, persist, and intensify, when the surface temperature and moisture deficits (relative to a suitable undisturbed near-storm environment) in the cold pool are relatively small. This research aims to investigate the causative mechanisms for this empirical correlation through an idealized numerical modeling approach. The work will leverage several diverse cases from the V2 field program to aid in initialization and verification of the model simulations. As such, it will sample a fairly large parameter space that was spanned by the V2 cases. Intellectual Merit:The research is expected to provide new insights into the relationship between supercell cold pools and tornado activity through the following means:1) Understanding the sensitivity of cold pool thermodynamics to the microphysical processes of water loading, evaporation, and melting utilizing sophisticated microphysics parameterization packages, and the variance across the spectrum of cases provided by V2;2) Assessing the impact of variation in the thermodynamic properties of the cold pools on tornadoes, and improving physical understanding of this connection;3) Verifying microphysical parameterizations through comparison with disdrometer and polarimetric radar data.Broader Impacts:The results of this research are expected to improve our ability to understand supercell storm characteristics that are most likely to produce significant tornadoes, and thus it will have a direct impact on the lives of the millions of U.S. citizens threatened or affected by tornadoes each year. The comparison between model representations of microphysical processes and the rich polarimetric radar and disdrometer datasets available from the V2 will help identify avenues for improvement of these parameterizations and thus have direct implications for forecasts of precipitation from severe convection and the associated risks of flooding and hail damage.