Attenuation of radar signal in melting hail at C band

Attenuation in precipitation poses a serious challenge for accurate measurements of precipitation and hail detection at C band. The correction for attenuation / differential attenuation based on the measurements of differential phase is quite efficient and straightforward in the areas of the storm which do not contain large raindrops or mixed-phase hydrometeors like melting hail. Numerous polarimetric radar observations at C band indicate that large wet hydrometeors may produce anomalously high attenuation / differential attenuation which are difficult to correct accurately.

The purpose of this study is to quantify attenuation effects in mixed-phase hydrometeors and provide recommendations for their robust correction. Several hailstorms in Canada and Oklahoma for which polarimetric C-band data have been collected are examined. Simultaneous measurements in Oklahoma with almost collocated C-band OU-PRIME and S-band KOUN polarimetric radars provide a unique opportunity to directly estimate the impact of attenuation on radar reflectivity Z and differential reflectivity Z_DR in heavy rain and melting hail and validate various techniques for attenuation correction at C band.

The most promising attenuation correction scheme separates relative contributions of “hotspots” (i.e., the areas of melting hail and large raindrops originating from melting hail) and the rest of the storm to the path-integrated total and differential attenuation. Observational estimates of the attenuation parameters are found consistent with theoretical predictions from the microphysical model of melting hail described in the companion paper by Ryzhkov and presented at the same conference.