Polarimetric Radar Observations of Tornadic Debris Signatures

Polarimetric radar data collected during three significant tornado events in central Oklahoma (May 3, 1999 – observed by the polarimetric NSSL Cimarron radar, and May 8 and 10, 2003 – observed by the polarimetric KOUN WSR-88D radar) provides confirmation of unique and repeatable polarimetric signatures associated with tornadic debris. Although both differential reflectivity (ZDR) and correlation coefficient (Rhohv) are useful for the debris signature and should be used together to maximize signature detection probability, Rhohv appears to have the better signature discriminating power because its highly anomalous values are in the debris region. ZDR values near 0.0 can occur with precipitation particles, allowing for some ambiguity between debris and normally occurring precipitation. On the other hand, Rhohv values are confined to a smaller range for precipitation particles (usually > 0.9), meaning that debris values (~ 0.7 down to below 0.5) are more unique. A coarse look at other supercells indicates that the signature is not associated with non-tornadic storms.

This study suggests that it will be possible to use a future network of polarimetric WSR-88D radars to confirm tornado warnings and pinpoint current tornado location. Additional data collection and research is required to determine whether polarimetric radar data can be used to detect tornadic debris at distant ranges or to identify polarimetric signatures that might be associated with possible microphysical precursors to tornadogenesis.