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

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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.