Polarimetric characteristics of tornadic and nontornadic supercell thunderstorms

Polarimetric radar offers remarkable insight into the microphysics of convective storms that may be used to elucidate processes associated with tornadogenesis. Several supercell thunderstorms have been observed by the research polarimetric WSR-88D radar in Norman, Oklahoma (KOUN). This study analyzes data from throughout the lifetime of four tornadic storms (8 May 2003, 10 May 2003, 30 May 2004, 10 Nov 2004) and three nontornadic storms (19 May 2003, 26 May 2004, 13 Sept 2005).

A number of repetitive polarimetric signatures are found in each of these storms. The forward-flank downdraft (FFD) area is characterized by a typical signature of hail and a shallow region of very high Z_DR on the southern edge of the FFD. The Z_DR and K_DP columns and midlevel “hooks” of enhanced Z_DR and depressed ρ_HV are usually observed in the vicinity of the main rotating updraft and in the rear-flank downdraft (RFD). Tornado touchdown is marked by a well-pronounced polarimetric debris signature.

Similar polarimetric features in supercell thunderstorms have been reported in other studies conducted in different geographic locations and thus are indicative of fundamental processes intrinsic to the supercell storms. Hypotheses on the origins as well as microphysical and dynamical interpretations of these signatures are presented. Additionally, implications about storm morphology for operational applications are suggested.