162 Tornadic Debris Signatures in Tropical Cyclones

Thursday, 10 November 2016
Broadway Rooms (Hilton Portland )
Roger Edwards, SPC, Norman, OK; and J. C. Picca
Manuscript (1.8 MB)

In terms of embedded severe local storms (i.e., tornadoes, large hail and damaging thunderstorm winds), tornadoes are the main hazard in tropical cyclones (TCs).  Radar detection of supercellular TC tornadoes historically has been handicapped by their typically small size, short duration, and the shallowness of their parent mesocyclones.  The upgrade to dual-polarization capabilities in the WSR-88D network has improved that circumstance.  Because of the shallow nature of TC supercells, and because that environment supports a predominance of warm-rain processes and relatively homogeneous drop-size distributions through much of the cell depth, copolar cross-correlation coefficient (ρHV) fields generally yield uniform high-end values within low to middle levels of TC supercells.  In addition to illustrating this, we show that when even weakly rated tornadoes (as is common with TCs) loft debris into those fields of large ρHV, their low- ρHV plumes, also known as tornado-detection signatures (TDSs), often are quite well-defined.  We show that ρHV values commonly fall below 0.75, often <0.5, in contrast to the noisier and more nebulous presentations of nontropical tornadoes of equal or greater damage rating.   

We also examine TC supercells and marginal supercells from 2009–2015 bearing TDSs, along with echo tops, peak rotational velocity at 0.5° beam elevation, and their relationship with tornado duration and damage rating for the majority of cases where a tornado was reported.  Recorded Storm Data tornado timelines are compared with those of observed TDSs, and relationships of TDS strength to both tornado duration and rating are analyzed.  We discuss ramifications for warning operations and focusing damage surveys.

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