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Abstract Polarimetric radar data from the WSR-88D network are used to examine the evolution of various polarimetric precursor signatures to tornado dissipation within a sample of 36 supercell storms. These signatures include an increase in bulk hook echo median raindrop size, a decrease in midlevel differential radar reflectivity factor (ZDR) column area, a decrease in the magnitude of theZDRarc, an increase in the area of low-level large hail, and a decrease in the orientation angle of the vector separating low-levelZDRand specific differential phase (KDP) maxima. Only supercells that produced “long-duration” tornadoes (with at least four consecutive volumes of WSR-88D data) are investigated, so that signatures can be sufficiently tracked in time, and novel algorithms are used to isolate each storm-scale process. During the time leading up to tornado dissipation, we find that hook echo median drop size (D0) and medianZDRremain relatively constant, but hook echo medianKDPand estimated number concentration (NT) increase. TheZDRarc maximum magnitude andZDR–KDPseparation orientation angles are observed to decrease in most dissipation cases. Neither the area of large hail nor theZDRcolumn area exhibit strong signals leading up to tornado dissipation. Finally, combinations of storm-scale behaviors and TVS behaviors occur most frequently just prior to tornado dissipation, but also are common 15–20 min prior to dissipation. The results from this study provide evidence that nowcasting tornado dissipation using dual-polarization radar may be possible when combined with TVS monitoring, subject to important caveats.
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Polarimetric and Electrical Structure of the 19 May 2013 Edmond–Carney, Oklahoma, Tornadic Supercell
Abstract We demonstrate the utility of transient polarimetric signatures (ZDRandKDPcolumns, a proxy for surges in a thunderstorm updraft) to explain variability in lightning flash rates in a tornadic supercell. Observational data from a WSR-88D and the Oklahoma lightning mapping array are used to map the temporal variance of polarimetric signatures and VHF sources from lightning channels. It is shown, via three-dimensional and cross-sectional analyses, that the storm was of inverted polarity resulting from anomalous electrification. Statistical analysis confirms that mean flash area in theZDRcolumn region was 10 times smaller than elsewhere in the storm. On an average, 5 times more flash initiations occurred withinZDRcolumn regions, thereby supporting existing theory of an inverse relationship between flash initiation rates and lightning channel extent. Segmentation and object identification algorithms are applied to gridded radar data to calculate metrics such as height, width, and volume ofZDRandKDPcolumns. Variability in lightning flash rates is best explained by the fluctuations inZDRcolumn volume with a Spearman’s rank correlation coefficient value of 0.72. The highest flash rates occur in conjunction with the deepestZDRcolumns (up to 5 km above environmental melting level) and largest volumes ofZDRcolumns extending up to the −20°C level (3 km above the melting level). Reduced flash rates toward the end of the analysis are indicative of weaker updrafts manifested as lowZDRcolumn volumes at and above the −10°C level. These findings are consistent with recent studies linking lightning to the interplay between storm dynamics, kinematics, thermodynamics, and precipitation microphysics.
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- Award ID(s):
- 1741003
- PAR ID:
- 10513568
- Publisher / Repository:
- American Meteorological Society
- Date Published:
- Journal Name:
- Monthly Weather Review
- Volume:
- 149
- Issue:
- 7
- ISSN:
- 0027-0644
- Format(s):
- Medium: X Size: p. 2049-2078
- Size(s):
- p. 2049-2078
- Sponsoring Org:
- National Science Foundation
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