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

最近完成的国家WSR-88D多普勒雷达网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迄今尚未成为重点研究的主题，那就是通过分析被放样的碎片区域内的偏振变量来探测龙卷风的能力，这些变量统称为龙卷风碎片特征。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)是有限的，部分原因是在数量上没有很好地了解龙卷风碎片的散布特征。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到龙卷风碎片。该项目包括四项主要任务和相关任务，这反过来又将使几个科学问题的研究成为可能。研究人员计划通过使用理论、模拟和实验室类型的电波暗室测量来对常见龙卷风碎片类型的雷达截面(RCS)进行编目，从而开始他们的调查。样本对象将包括直枝和小树枝的分布，没有明显粗糙和弯曲效应的独立树叶，小木片，水流星和灰尘。然后，将使用RCS数据库和3D风场(通过先前龙卷风规模的数值模拟工作产生的)对极化雷达数据进行数值模拟。投资促进局还计划从快速扫描X波段偏振测量移动雷达和附近的固定网络雷达收集更多新的高分辨率观测数据，并结合龙卷风后的详细破坏调查对这些数据进行评估。这些任务随后将推动开发一套信号处理算法，以改进龙卷风碎片特征的检测和有意义的表征，目的是区分碎片类型、大小和浓度。主要的科学目标是：1)调查龙卷风中负ZDR的两个主要假设，Mie散射和共同散射排列，以及2)检查与龙卷风碎片相关的物理过程，如放样、离心和装载，以及它们与龙卷风和超级单体动力学的关系。该项目的广泛影响强烈地映射到任务机构提高公共安全的努力，因为这项工作将通过改进龙卷风检测和更好地实时估计后续损害的严重程度来潜在地帮助业务气象界。电波暗室的开发将促进未来专注于天线设计和性能的研究，这既包括受赠大学的研究人员，也包括隶属于国家天气中心的共同所在地的组织。研究生和本科生将直接参加研究活动和跨学科工程和气象学课程。

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.