Attenuation Correction for Melting Ice at C-Band and Verification from S-Band Profiler Radar Measurements

In this study, simultaneous observations from the C-Band ARMOR Radar and the NOAA Physical Science Laboratory (PSL) S-Band Profiler are used to measure attenuation in melting hail. A convective precipitation event that occurred in the Huntsville region in Alabama on December 11, 2021, is considered as a case study. The S-Band profiler radar is located at the PSL ground instrumentation site at Courtland, about 50 km west of the ARMOR radar. During the event, a squall line was observed along with heavy rain, melting hail, and graupel at multiple locations. Melting hail caused attenuation of the radar signal at C-Band wavelength resulting in decreased observed reflectivity (Z) and negative differential reflectivity (Zdr). First, rain attenuation correction based on differential phase measurements was performed on the C-Band observations. Upon comparison of vertical profiles of reflectivity to profiler observations, it was determined that rain attenuation correction alone is insufficient in accounting for the enhanced attenuation caused by melting ice hydrometeors. Consequently, profiles of Z, Zdr and co-polar correlation coefficient were examined for signatures of melting ice. This was further cross validated with hydrometeor classification algorithm. Attenuation correction coefficient for melting ice is computed separately following a methodology proposed by Arias and Chandrasekar. Next, a piecewise attenuation correction algorithm is implemented to correct regions of rain and melting ice separately. Verification of the attenuation correction method was performed by simultaneous comparisons of vertical profiles of reflectivity from the C-Band and S-Band profiler radar. Overall, this methodology addresses the underestimation of Z and Zdr measurements at C-Band caused by melting ice attenuation.