Incorporating Dual-Polarization Signatures into the Tornado Warning Process: ZDR/KDP Separation Signals, ZDR Arc Considerations, and Initial Results of Hook Echo Investigations

Previous field studies investigated the possibility of utilizing certain dual-polarization radar fields (Z_DR and K_DP) to help discriminate between tornadic and non-tornadic storms. The main strategy was to infer trends in storm-scale shear by evaluating the character of preferential drop size sorting. Later research demonstrated, via idealized numerical simulations, that hydrometeor size sorting is not fundamental to wind shear, but rather to the storm-relative flow itself. However, it was also noted that particularly in supercell environments, storm-relative flow (using the degree of drop size sorting as a proxy) and lower tropospheric storm-relative helicity (SRH) are likely well correlated. As such, in supercell environments, it is hypothesized that patterns of Z_DR and K_DP can identify important trends in storm-relative flow and SRH, thereby helping to diagnose a storm’s tornadic potential.

In an attempt to leverage study results and test hypotheses outlined above, a number of tornadic and non-tornadic supercell cases were evaluated. While previous field studies were conducted in specific geographical regions of the United States, this study has looked at a broad array of cases east of the Rocky Mountains, in an effort to find a unified, geographically independent approach to using dual-polarization radar fields for better discrimination between tornadic and non-tornadic storms in the warning decision-making process. Applicable findings center on the separation characteristics between Z_DR and K_DP areal maxima in the forward flank, as well as Z/Z_DR relationships in the Z_DR arc region.

A new initiative on dual-polarization signatures in the hook echo regions of supercells will also be introduced, with initial results presented. These include identifying probable drop size distributions by looking at Z_DR and CC in various sectors of the hook echo. The characters and patterns of such drop size distributions will be used to infer information about possible descending heavy precipitation cores (which may increase the likelihood of generating additional vortex lines), as well as the thermodynamic/buoyancy characteristics of rear-flank downdrafts.