Understanding Polarimetric Radar Tornadic Debris Signatures Using Modeling, Simulations, and Field Measurements

最近完成的对国家WSR-88D多普勒雷达网络的双极化升级为天气观测提供了各种各样的新能力。一个值得注意的改进领域尚未成为重点研究的主题，即通过分析漂浮碎片区域内的极化变量来探测龙卷风的能力，统称为龙卷风碎片特征（TDS）。虽然已经获得了这些观测数据，但用户对这些新数据的信心（以及由此产生的影响）有限，部分原因是在定量意义上还没有很好地了解龙卷风碎片的散射特征。这个多管齐下的项目将利用观测、模拟和建模来进一步了解气象雷达如何观测龙卷风碎片。该项目体现了四个主要重点和相关任务，这反过来又使几个科学问题的研究成为可能。研究人员计划利用理论、模拟和实验室型消声室测量，对常见龙卷风碎片类型的雷达横截面（RCS）进行编目，以此开始他们的研究。样本对象将包括直枝和细枝的分布，没有明显粗糙度和弯曲效果的独立叶子，小块木头，水成物和灰尘。然后将使用RCS数据库和三维风场对极化雷达数据进行数值模拟（通过先前的龙卷风尺度数值模拟工作产生）。pi还计划从快速扫描x波段偏振（RaXpol）移动雷达和附近的固定网络雷达收集额外的新的高分辨率观测数据，并结合详细的龙卷风损害调查对这些数据进行评估。这些任务随后将推动一套信号处理算法的发展，以改进龙卷风碎片特征的检测和有意义的表征，目标是区分碎片的类型、大小和浓度。主要的科学目标是：1)研究龙卷风负ZDR的两个主要假设，即Mie散射和共同散射对齐；2)研究与龙卷风碎片相关的物理过程，如悬浮、离心和装载，以及它们与龙卷风和超级单体动力学的关系。该项目将对任务机构提高公共安全的努力产生更广泛的影响，因为这项工作将通过改进龙卷风探测和更好地实时估计随之而来的破坏严重程度的能力，潜在地帮助气象部门开展业务。消声室的开发将促进未来对天线设计和性能的研究，这些研究将由受资助大学的研究人员和国家气象中心的共同所在地的组织进行。研究生和本科生将直接参与研究活动和跨学科的工程和气象课程。

The recently completed dual-polarimetric upgrade of the national WSR-88D Doppler radar network has provided a wide variety of new capabilities for weather observations. One notable area of improvement that has as-yet not been the subject of focused research is the ability to detect tornadoes through analysis of polarimetric variables within zones of lofted debris, collectively known as the Tornadic Debris Signature (TDS). While these observations are already being accessed, user confidence in (and hence impact of) these new data is limited in part because the scattering characteristics of tornadic debris are not well understood in a quantitative sense. This multi-pronged project will make use of observations, simulations and modeling to further knowledge on how tornadic debris is observed by weather radars. The project embodies four primary thrusts and associated tasks, which will in-turn enable the study of several scientific questions. The researchers plan to begin their investigation by cataloging radar cross-section (RCS) for common tornadic debris types using theory, simulations and laboratory-type anechoic chamber measurements. Sample objects will include distributions of straight and small twigs, free-standing leaves absent significant roughness and bending effects, small pieces of wood, hydrometeors, and dust. Numerical simulations of polarimetric radar data using the RCS database and 3D wind fields (as generated via prior tornado-scale numerical modeling efforts) will then be conducted. The PIs also plan to collect additional new high-resolution observational data from the Rapid scanning X-band polarimetric (RaXpol) mobile radar and nearby fixed-based network radars, and to evaluate these data in tandem with detailed post-tornado damage surveys. These tasks will subsequently drive development of a suite of signal processing algorithms to improve detection and meaningful characterization tornadic debris signatures with the goal of distinguishing debris type, size, and concentration. The main scientific objectives are to: 1) Investigate the two main hypotheses for negative ZDR in tornadoes, Mie scattering and common scatter alignment, and 2) Examine the physical processes associated with tornadic debris, such as lofting, centrifuging and loading, and their relationship to tornado and supercell dynamics.Broader impacts of this project map strongly on mission agency efforts to increase public safety, as this work will potentially assist the operational meteorological community through improved tornado detection and ability to better estimate severity of ensuing damage in real-time. Development of an anechoic chamber will facilitate future research focusing on antenna design and performance, both by investigators at the grantee university and co-located organizations who are part of the National Weather Center. Graduate and undergraduate students will be directly included in the research activities and the interdisciplinary engineering and meteorology curriculum.