Debris balls can be a result of
anthropogenic or
biomass 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
winds 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. 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. 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 suggested that horizontal reflectivity from debris balls ranged from 51 to 72
dBZ during those outbreaks. Reflectivity values also decreased with increasing height. An algorithm, called
Polarimetric 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 US
National Weather Service weather radar outputs. ==See also==