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A tornadic debris signature (TDS), often colloquially referred to as a debris ball, is an area of high
Debris balls can be a result of
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A tornadic debris signature (TDS), often colloquially referred to as a debris ball, is an area of high reflectivity
The reflectance of the surface of a material is its effectiveness in reflecting radiant energy. It is the fraction of incident electromagnetic power that is reflected at the boundary. Reflectance is a component of the response of the electronic ...
on weather radar
Weather radar, also called weather surveillance radar (WSR) and Doppler weather radar, is a type of radar used to locate precipitation, calculate its motion, and estimate its type (rain, snow, hail etc.). Modern weather radars are mostly puls ...
caused by debris
Debris (, ) is rubble, wreckage, ruins, litter and discarded garbage/refuse/trash, scattered remains of something destroyed, or, as in geology, large rock fragments left by a melting glacier, etc. Depending on context, ''debris'' can refer to ...
lofting into the air, usually associated with a tornado
A tornado is a violently rotating column of air that is in contact with both the surface of the Earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. It is often referred to as a twister, whirlwind or cyclone, altho ...
. A TDS may also be indicated by dual-polarization radar
Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, w ...
products, designated as a polarimetric tornado debris signature (PTDS). Polarimetric radar can discern meteorological and nonmeteorological hydrometeor
In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...
s and 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.
Background
Debris balls can be a result of anthropogenic
Anthropogenic ("human" + "generating") is an adjective that may refer to:
* Anthropogeny, the study of the origins of humanity
Counterintuitively, anthropogenic may also refer to things that have been generated by humans, as follows:
* Human im ...
or biomass
Biomass is plant-based material used as a fuel for heat or electricity production. It can be in the form of wood, wood residues, energy crops, agricultural residues, and waste from industry, farms, and households. Some people use the terms bi ...
debris 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 strong wind
Wind is the natural movement of air or other gases relative to a planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heating of land surfaces and lasting a few hou ...
s required to damage structures and loft debris into the air, debris balls are normally the result of EF3 or stronger tornadoes on the Enhanced Fujita Scale
The Enhanced Fujita scale (abbreviated as EF-Scale) rates tornado intensity based on the severity of the damage they cause. It is used in some countries, including the United States, Canada, China, and Mongolia.
The Enhanced Fujita scale repla ...
. 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. 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. A debris ball on radar images can verify tornadoes 70–80% of the time.
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 the 2011 Super Outbreak
The 2011 Super Outbreak was the largest, costliest, and one of the deadliest tornado outbreaks ever recorded, taking place in the Southern, Midwestern, and Northeastern United States from April 25–28, 2011, leaving catastrophic destruction ...
suggested that horizontal reflectivity from debris balls ranged from 51 to 72 dBZ during those outbreaks. Reflectivity values also decreased with increasing height. Due to the irregular and variable size, shapes, and dielectric constants of debris particles, debris balls typically produce a correlation coefficient
A correlation coefficient is a numerical measure of some type of correlation, meaning a statistical relationship between two variables. The variables may be two columns of a given data set of observations, often called a sample, or two components ...
(''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, the tornado vortex signature
A tornadic vortex signature, abbreviated TVS, is a Pulse-Doppler radar weather radar detected rotation algorithm that indicates the likely presence of a strong mesocyclone that is in some stage of tornadogenesis. It may give meteorologists the abil ...
(TVS) or tornado detection algorithm (TDA).
See also
*Convective storm detection
Convective storm detection is the meteorological observation, and short-term prediction, of deep moist convection (DMC). DMC describes atmospheric conditions producing single or clusters of large vertical extension clouds ranging from cumulus co ...
* Mesocyclone
A mesocyclone is a meso-gamma mesoscale (or storm scale) region of rotation (vortex), typically around in diameter, most often noticed on radar within thunderstorms. In the northern hemisphere it is usually located in the right rear flank (back ...
References
External links
Dual-Polarization Radar Training for NWS Partners
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module by the NWS
Warning Decision Training Branch
The Warning Decision Training Division (WDTD), known as the Warning Decision Training Branch until April 1, 2015, is one of three training organizations in the NWS Training Division which also includes the Forecast Decision Training Branch and the ...
(WDTB)
*
* {{cite journal , last= Bodine , first= David J. , author2= R. D. Palmer , author3= G. Zhang , title= Dual-Wavelength Polarimetric Radar Analyses of Tornadic Debris Signatures , journal= J. Appl. Meteorol. Climatol. , volume= 53 , issue= 2 , pages= 242–61 , date= 2014 , doi= 10.1175/JAMC-D-13-0189.1 , bibcode = 2014JApMC..53..242B , doi-access= free
Radar meteorology
Severe weather and convection
Tornado