Developing a Tornado Debris Signature Algorithm

Tornadic debris contains a diverse range of shapes, sizes, and orientations of meteorological and non-meteorological scatterers. When debris are lofted into the beam of a polarimetric radar, a tornadic debris signature (TDS) is usually identified by a decrease in co-polar cross correlation coefficient (ρHV), a decrease in differential reflectivity (ZDR) to around zero, and an increase in horizontal reflectivity (ZH). An observation of a TDS can provide a warning forecaster with confirmation of a damaging tornado, especially in events where ground truth may not be available such as when the tornado is rain-wrapped or occurring at nighttime. An effort at NSSL to manually track and analyze different characteristics of TDSs along tornado tracks is presented.  The reason for the manual tracking is previous research showed that manual versus automated identification resulted in different parameter distributions, and low-level elevation scans on the WSR-88D separate the surveillance and Doppler scans, which can lead to disparate locations of the polarimetric signature and Doppler velocity couplet.  The distributions of polarimetric parameters and azimuthal shear, TDS height, and other TDS characteristics will be compared to tornado strength, environment, and radar range.  Choices for algorithm set up and inputs and applications of the algorithm within a CONUS-wide climatology will also be discussed.