A Comparison of Dual-Polarization Radar Signatures of Large Melting Hail at S- and C-band

Hail identification tools and procedures have evolved over the last few decades, starting with single-polarization radar (e.g., implementing height of a threshold reflectivity or vertically integrated liquid) to the modern use of dual-polarization (DP) radars. DP radar allows not only the estimate of relative size and number concentration of hydrometeors but also provides information on the particle shape, which helps distinguish hail from other types of hydrometeors such as rain. Most DP radar hail identification studies utilize S-band systems, while studies relying on C-band systems are fewer in number and typically have small sample sizes. This study sets out to make a comparison of hail producing storms located in Northern Alabama between the UAH Advanced Radar for Meteorological and Operational Research (ARMOR) (C-band) and the NOAA Weather Surveillance Radar – 1988 Doppler WSR-88D (S-band) in Hytop, AL (KHTX), which was upgraded to DP capability in early 2012. Forty-four storms that produced large hail (diameter ³ 1 inch) and were well observed in the vertical by both ARMOR and KHTX from 2012 to 2014 were selected for study. From this large sample, a database of vertical profiles of the DP variables horizontal reflectivity (Z_H), differential reflectivity (Z_dr), and correlation coefficient (ρ _hv) was gathered and compared statistically to characterize the DP radar signatures of large melting hail at S- and C-band. The vertical profile of each DP variable in melting hail follows a similar pattern between both radar bands; however, Z_dr and ρ _hv have significantly different magnitudes below the melting layer where Z_dr is larger and ρ _hv is lower at C-band relative to S-band, which is consistent with the effect of resonance at C-band due to the likely presence of large raindrops and small melting hail in the radar resolution volume along with the confirmed large hail. These results generally confirm earlier studies that relied upon a much smaller number of storms and should therefore be considered when designing DP radar hail identification algorithms.