Estimating hail size using polarimetric radar

A preliminary study of the use of polarimetric variables for estimating hail size examines three hail-producing events observed by the National Severe Storms Laboratory's polarimetric-prototype radar (KOUN) in Norman, Oklahoma during 2004. The analysis includes 45 hail reports with hail sizes ranging from 0.75 in to 4.25 in. Horizontal and vertical structures of reflectivity at horizontal polarization (Z_H), differential reflectivity (Z_DR), and correlation coefficient (ρ_HV) associated with these reports are analyzed using Interactive Data Language (IDL) programs. A comparison of Z_H, Z_DR and ρ_HV signatures allows for the hail to be categorized into two groups: hail diameters less than 1.75 in and hail diameters 1.75 in or higher. Vertical profiles of these variables show that hail 1.75 in or higher is characterized by deeper columns of low ZDR and ρHV and a more significant decrease in ƒâHV below the melting layer than smaller hail sizes. A discriminant analysis of Z_H, Z_DR and ρ_HV at the lowest elevation reveals that ρ_HV discriminates best between the two categories.

To explore the validity of these findings, the dataset is expanded to include all 2003 and 2004 storms observed by KOUN with hail reported by Storm Data. This study includes only hail reports meeting validation criteria. Results of the expanded study will be reported in the extended abstract.