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Tornado debris signature

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Image showing two radar images. On the left is a base reflectivity radar image, which displays precipitation. On the right is a storm relative velocity radar image, which shows direction and intensity of wind speeds.
On the left, a typical debris ball shown as an area of high reflectivity on the end of thehook echoof the parentsupercellof the2011 Joplin tornadoco-located with a velocity couplet on the right

Atornadic debris signature(TDS), often colloquially referred to as adebris ball,[1]is an area of highreflectivityonweather radarcaused bydebrislofting into the air, usually associated with atornado.[1][2]A TDS may also be indicated by dual-polarizationradarproducts, designated as apolarimetric tornado debris signature(PTDS). Polarimetric radar can discern meteorological and nonmeteorologicalhydrometeorsand the co-location of a PTDS with the enhanced reflectivity of a debris ball are used by meteorologists as confirmation that a tornado is occurring.[3]

Background

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Comparison of four radar products: reflectivity, Z, top left; velocity, SRM, top right; and polarimetric products, differential reflectivity, ZDR,on bottom left; correlation coefficient, CC, on bottom right, used to identify TDSs

Debris balls can be a result ofanthropogenicorbiomassdebris and are more likely to occur if a tornado crosses a "target-rich" environment such as a forest or populated area. A TDS is most likely to be observed when a tornado is closer to a radar site and the farther away from the radar that a TDS is observed the more likely that the tornado is stronger. As a result of the strongwindsrequired to damage structures and loft debris into the air, debris balls are normally the result of EF3 or stronger tornadoes on theEnhanced Fujita Scale.Weaker tornadoes may also not cause debris balls due to their mostly short-lived nature and thus any debris may not be sampled by radar.[4]However, not all tornadoes meeting such strength requirements exhibit debris balls, depending on their vicinity to sources of debris and distance from the radar site.[1]A debris ball on radar images can verify tornadoes 70–80% of the time.[5]

PTDS output from a tornado in Tennessee.
PTDS output from a tornado in Tennessee.

Debris balls are seen on radar reflectivity images as a small, roundish area of high reflectivity values. Research conducted on debris balls that were noted during the2011 Super Outbreaksuggested that horizontal reflectivity from debris balls ranged from 51 to 72dBZduring those outbreaks. Reflectivity values also decreased with increasing height.[1]Due to the irregular and variable size, shapes, and dielectric constants of debris particles, debris balls typically produce acorrelation coefficient(ρhv) less than 0.80. Differential reflectivity (ZDR) values associated with debris balls are typically near or below 0 dB due to the random, tumbling nature of tornadic debris. Debris balls are almost always associated with a strong velocity couplet and the corresponding algorithm based detection, thetornado vortex signature(TVS) or tornado detection algorithm (TDA).[6]

An algorithm, calledPolarimetric Tornado Debris Signature(PTDS), was developed by researchers by combining polarimetric data with reflectivity and velocity data, showing areas with a probability of detection greater than 80%. It is used on the USNational Weather Serviceweather radar outputs.[7]

See also

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References

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  1. ^abcdBunkers, Matthew J.; Baxter, Martin A. (August 23, 2011)."Radar Tornadic Debris Signatures on 27 April 2011"(PDF).National Weather Service.Retrieved31 December2012.
  2. ^"Severe Weather & Flooding Event of March 3, 2012; Lowndes-Lanier Co. EF3 Tornado".Tallahassee, Florida:National Weather Service.Retrieved31 December2012.
  3. ^"Tornadic Debris Signature from Dual Polarization Radar".NWS Birmingham, AL. October 3, 2012.Retrieved2014-05-12.
  4. ^Ryzhkov, Alexander V.; Schuur, Terry J.; Burgess, Donald W.; Heinselman, Pamela L.; Giangrande, Scott E.;Zrnic, Dusan S.(2005)."The Joint Polarization Experiment: Polarimetric Rainfall Measurements and Hydrometeor Classification"(PDF).Bull. Am. Meteorol. Soc.86(6): 809–24 [821].Bibcode:2005BAMS...86..809R.doi:10.1175/BAMS-86-6-809.Retrieved31 December2012.
  5. ^Weinberg, Marc (March 19, 2012)."Learning About Weather Radar... The Debris Ball".WDRB.Retrieved31 December2012.
  6. ^Schlatter, Paul."Dual-Pol Radar Applications: Tornadic Debris Signatures".National Oceanic and Atmospheric Administration.Retrieved31 December2012.
  7. ^Jeffrey C. Snyder; Alexander V. Ryzhkov (September 2015)."Automated Detection of Polarimetric Tornadic Debris Signatures Using a Hydrometeor Classification Algorithm".Journal of Applied Meteorology and Climatology.54(9): 1861–1870.Bibcode:2015JApMC..54.1861S.doi:10.1175/JAMC-D-15-0138.1.ISSN1558-8424.RetrievedFebruary 26,2024.
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