Polarimetric Tornadic Debris Signature Variability and Debris Fallout Signatures

Abstract

Values of polarimetric radar variables may vary substantially between and through tornadic debris signature (TDS) events. Tornadoes with higher intensity ratings are associated with higher average and extreme values of reflectivity factor at horizontal polarization ZHH and lower values of copolar cross-correlation coefficient ρhv. Although values of these variables often fluctuate through reported tornado life cycles, ZHH repeatably decreases and ρhv repeatably increases across the volume scan immediately following reported tornado demise. Land cover has a relatively small effect on values of the polarimetric variables within TDSs, although near-radar urban TDSs may exhibit relatively high ZHH values. TDS areal extent is typically larger aloft than near the surface, although this trend may reverse in the most intense tornadoes. Maximum altitude to which a TDS is visible is more strongly a function of tornado intensity than of land cover or ambient shear and instability. Debris often disappears once lofted but may also be observed to spread out downstream with the storm-relative flow or to fall out along the parent storm’s northwest flank in a debris fallout signature (DFS). DFS characteristics, although variable, most commonly include ZHH values of 30–35 dBZ, ρhv values of 0.60–0.80, and values of differential reflectivity ZDR that are repeatably near 0 dB.

A skill assessment of techniques for real-time diagnosis and short-term prediction of tornado intensity using the WSR-88D

“…Even though both weak and strong/violent tornadoes and TDS/no TDS pairs were sampled evenly, the TDS cases clearly represented a larger percentage of EF2+ cases. Similar results were found by Van Den Broeke (2015). Sixteen of the damage points were associated with convection produced by a squall-line/quasi-linear convective system (QLCS) per the definition by Trapp et al (2005), while the rest were various forms of supercell or hybrid convection containing a persistent independent mesocyclone (Doswell and Burgess 1993;Smith et al 2012).…”

“…The IBW system differentiates tornado events by weak and strong/violent events. This guidance is built off of decades of science, but focuses on recent work quantifying the relationship between tornado damage intensity and subjectively analyzed WSR-88D volumetric products-specifically V rot (Kingfield and LaDue 2015;Smith et al 2015) and TDS height (Entremont and Lamb 2015;Van Den Broeke and Jauernic 2014). This study, evaluating 432 surveyed damage points from 84 different tornadoes, finds that the guidance is skillful.…”

“…They found that a correlation did exist between TDS characteristicsspecifically height and volume-and EF-scale damage. Entremont and Lamb (2015) and Van Den Broeke and Jauernic (2014) quantified this relationship, specifically the height of the TDS versus EF-scale. Stronger tornadoes showed a tendency to produce TDSs that extended higher into the storm.…”

“…For instance, V rot values of 20.57-28.29 m s -1 (40-55 kt) lie within the overlap between weak and strong tornadoes. TDSs higher than 3048 m (10 000 ft) AGL were identified as likely to be associated with a strong tornado, while values of 2438-3048 m (8000-10 000 ft) AGL were considered to lie within the overlap region between strong and weak tornadoes (Van Den Broeke and Jauernic 2014;Entremont and Lamb 2015). This study will evaluate the skill of this guidance.…”

A Preliminary Evaluation of MESO-SAILS Tornadic Debris Signature Detection and its Use in the Iowa Region

“…Research by Van Den Broeke and Jauernic (2014) and Van Den Broeke (2015) catalogued TDS instances and their patterns nationwide using the criteria mentioned above. Using Dual-pol Radar data, Van Den Broeke and Jauernic (2014) found that 16% of the 1284 tornado cases they examined had TDS's associated with them.…”